Zhonghe Jiang

A single electrode room-temperature atmospheric pressure plasma plume generated between a high-voltage electrode and the surrounding room air is reported. The plasma plume has a peak current of about 360mA. This is highest current carried by a room-temperature plasma plume ever reported. The rotational and vibrational temperature of the plasma plume is about 300 and 2950K, respectively. Emission spectra show that excited species, such as O, OH, N2+, etc., are present in the plasma plume.

The roles of various plasma agents in the inactivation of bacteria have recently been investigated. However, up to now, the effect of the charged particles on the inactivation of bacteria is not well understood. In this paper, an atmospheric pressure plasma jet device, which generates a cold plasma plume carrying a peak current of 300 mA, is used to investigate the role of the charged particles in the inactivation process. It is found that the charged particles play a minor role in the inactivation process when He/N2(3%) is used as working gas. On the other hand, when He/O2(3%) is used, the charged particles are expected to play an important role in the inactivation of bacteria. Further analysis shows that the negative ions O2− might be the charged particles that are playing the role. Besides, it is found that the active species, including O, O3, and metastable state O2∗, can play a crucial role in the inactivation of the bacteria. However, the excited He∗, N2 C Π3u, and N2+ B Σ2u+ have no significant direct effect on the inactivation of bacteria. It is also concluded that heat and UV play no or minor role in the inactivation process.

In this letter, a room temperature atmospheric pressure plasma jet device is reported. The high voltage electrode of the device is covered by a quartz tube with one end closed. The device, which is driven by a kilohertz ac power supply, is capable of generating a plasma plume up to 11cm long in the surrounding room air. The rotational and vibrational temperatures of the plasma plume are 300 and 2300K, respectively. A simple electrical model shows that, when the plasma plume is contacted with a human, the voltage drop on the human is less than 66V for applied voltage of 5kV (rms).

Abstract Recent J-TEXT research has highlighted the significance of the role that non-axisymmetric magnetic perturbations, so called three-dimensional (3D) magnetic perturbation (MP) fields, play in a fundamentally 2D concept, i.e. tokamaks. This paper presents the J-TEXT results achieved over the last two years, especially on the impacts of 3D MP fields on magnetohydrodynamic instabilities, plasma disruptions and plasma turbulence transport. On J-TEXT, the resonant MP (RMP) system, capable of providing either a static or a high frequency (up to 8 kHz) rotating RMP field, has been upgraded by adding a new set of 12 in-vessel saddle coils. The shattered pellet injection system was built in J-TEXT in the spring of 2018. The new capabilities advance J-TEXT to be at the forefront of international magnetic fusion facilities, allowing flexible study of 3D effects and disruption mitigation in a tokamak. The fast rotating RMP field has been successfully applied for avoidance of mode locking and the prevention of plasma disruption. A new control strategy, which applies pulsed RMP to the tearing mode only during the accelerating phase region, was proved by nonlinear numerical modelling to be efficient in accelerating mode rotation and even completely suppresses the mode. Remarkably, the rotating tearing mode was completely suppressed by the electrode biasing. The impacts of 3D magnetic topology on the turbulence has been investigated on J-TEXT. It is found that the fluctuations of electron density, electron temperature and plasma potential can be significantly modulated by the island structure, and a larger fluctuation level appears at the X-point of islands. The suppression of runaway electrons during disruptions is essential to the operation of ITER, and it has been reached by utilizing the 3D magnetic perturbations on J-TEXT. This may provide an alternative mechanism of runaway suppression for large-scale tokamaks and ITER.

Rather than using noble gas, room air is used as the working gas for an atmospheric pressure room-temperature plasma. The plasma is driven by submicrosecond pulsed directed current voltages. Several current spikes appear periodically for each voltage pulse. The first current spike has a peak value of more than 1.5 A with a pulse width of about 10 ns. Emission spectra show that besides excited OH, O, N2(C–B), and N2+(B–X) emission, excited NO, N2(B–A), H, and even N emission are also observed in the plasma, which indicates that the plasma may be more reactive than that generated by other plasma jet devices. Utilizing the room-temperature plasma, preliminary inactivation experiments show that Enterococcus faecalis can be killed with a treatment time of only several seconds.

The effects of various discharge parameters and ambient gas on the length of He atmospheric plasma jet plumes expanding into the open air are studied. It is found that the voltage and width of the discharge-sustaining pulses exert significantly stronger effects on the plume length than the pulse frequency, gas flow rate, and nozzle diameter. This result is explained through detailed analysis of the I-V characteristics of the primary and secondary discharges which reveals the major role of the integrated total charges of the primary discharge in the plasma dynamics. The length of the jet plume can be significantly increased by guiding the propagating plume into a glass tube attached to the nozzle. This increase is attributed to elimination of the diffusion of surrounding air into the plasma plume, an absence which facilitates the propagation of the ionization front. These results are important for establishing a good level of understanding of the expansion dynamics and for enabling a high degree of control of atmospheric pressure plasmas in biomedical, materials synthesis and processing, environmental and other existing and emerging industrial applications.

The “plasma bullet” behavior of atmospheric pressure plasma plumes has recently attracted significant interest. In this paper, a specially designed plasma jet device is used to study this phenomenon. It is found that a helium primary plasma can propagate through the wall of a dielectric tube and keep propagating inside the dielectric tube (secondary plasma). High-speed photographs show that the primary plasma disappears before the secondary plasma starts to propagate. Both plumes propagate at a hypersonic speed. Detailed studies on the dynamics of the plasma plumes show that the local electric field induced by the charges on the surface of the dielectric tube plays an important role in the ignition of the secondary plasma. This indicates that the propagation of the plasma plumes may be attributed to the local electric field induced by the charges in the bulletlike plasma volume.

The J-TEXT tokamak has been operated for ten years since its first plasma obtained at the end of 2007. The diagnostics development and main modulation systems, i.e. resonant magnetic perturbation (RMP) systems and massive gas injection (MGI) systems, will be introduced in this paper. Supported by these efforts, J-TEXT has contributed to research on several topics, especially on RMP physics and disruption mitigation. Both experimental and theoretical research show that RMP could lock, suppress or excite the tearing modes, depending on the RMP amplitude, frequency difference between RMP and rational surface rotation, and initial stabilities. The plasma rotation, particle transport and operation region are influenced by the RMP. Utilizing the MGI valves, disruptions have been mitigated with pure He, pure Ne, and a mixture of He and Ar (9:1). A significant runaway current plateau could be generated with moderate amounts of Ar injection. The RMP has been shown to suppress the generation of runaway current during disruptions.

Abstract In the last two years, three major technical improvements have been made on J-TEXT in supporting of the expanded operation regions and diagnostic capabilities. (1) The successful commission of the 105 GHz/500 kW/1 s electron cyclotron resonance heating (ECRH) system increasing the core electron temperature from 0.9 keV up to around 1.5 keV. (2) The poloidal divertor configuration with an X -point in the high-field side has been achieved. In particular, the 400 kW electron cyclotron wave has also been successfully injected into the diverted plasma. (3) A 256-channel electron cyclotron emission imaging diagnostic system and two sets of four-channel Doppler backscattering diagnostics have been successfully developed on J-TEXT, allowing detailed measurement of the electron temperature and density fluctuations for turbulence and MHD research. The locked mode (LM), especially the 2/1 LM, is one of the biggest threats to the plasma operation. Both the thresholds of 2/1 and 3/1 LM are observed to vary non-monotonically on electron density. The electrode biasing was applied successfully to unlock the LM from either a rotating or static resonant magnetic perturbation (RMP) field. In the presence of 2/1 LM, three kinds of standing wave (SW) structures have been observed to share a similar connection to the island structure, i.e. the nodes of the SWs locate around the O - or X -points of the 2/1 island. The control and mitigation of disruption is essential to the safe operation of ITER, and it has been systematically studied by applying a RMP field, massive gas injection (MGI) and shattered pellet injection on J-TEXT. When the RMP-induced 2/1 LM is larger than a critical width, the MGI shutdown process can be significantly influenced. If the phase difference between the O -point of LM and the MGI valve is +90° (or −90°), the penetration depth and the assimilation of impurities can be enhanced (or suppressed) during the pre-thermal quench (TQ) phase and result in a faster (or slower) TQ. A secondary MGI can also suppress the runaway electron (RE) generation, if the additional high-Z impurity gas arrives at the plasma edge before TQ. When the secondary MGI has been applied after the formation of the RE current plateau, the RE current can be dissipated, and the dissipation rate increases with the injected impurity quantity but saturates with a maximum of 28 MA s −1 . The non-local transport is experimentally observed in the ion transport channel. The electron thermal diffusivity significantly increases with the ECRH power. Theoretical work shows that significant intrinsic current can be driven by electromagnetic turbulence, and the robust formation mechanism of the E × B staircase is identified from the Hasegawa–Wakatani system.

Abstract On the J-TEXT tokamak, the dynamics of edge magnetic topology during the opening of the edge magnetic islands induced by the external resonant magnetic perturbation (RMP) are investigated. The edge island chain is pushed outward by increasing plasma toroidal current to intersect the poloidally and toroidally localized divertor plate, forming an open magnetic island in the scrape-off layer (SOL). The location of the strike points on the divertor plate predicted by the HINT code is in agreement with the experimental observations. The influence of the magnetic topology on edge plasma profiles has also been investigated using Langmuir probes. The properties of edge T_e, n_e, P_e and E_r profiles are studied as function of three magnetic structures in q_a-dependence experiments and two magnetic structures in RMP configuration-dependence experiments. Some common features are observed. Inside the edge closed and SOL remnant islands, flat P_e but non-flat T_e and n_e profiles are detected. When transitioning from the edge closed island to the partially open island with remnant island, the local flat P_e profile is shifted outward accompanied by a narrower flattened P_e region. The steep slopes of T_e, n_e and P_e are measured in the SOL regions characterized by a long connection length L_c, and the longer L_c, the steeper slopes. E_r exhibits a negative well inside the remnant island with infinite L_c and in the SOL regions where L_c significantly exceeds than the electron mean free path λ_e, but develops a positive value in the SOL regions where L_c is relatively short.

It has recently been demonstrated that pulsed direct-current (dc) voltages show better performance in generating diffuse plasmas under various conditions. However, it still remains unclear whether the pulsewidth or the rising and falling times of the voltage pulse play the essential role in the improvement of the performance of the dielectric barrier discharges (DBDs). In this paper, we focus on the effect of pulsewidth. Pulsed dc voltages with pulsewidth varying from 0.2 mus to about 1 ms are used to drive the DBDs. High-speed photographs show that diffuse Ar plasmas can be generated by pulsed dc voltages with pulsewidths covering the entire investigated range. It is found that the pulsewidths of the applied voltages affect the discharge current durations significantly when the pulsewidth is shorter than 600 ns or the break between the two consecutive pulses is shorter than 600 ns.

The propagation of an electromagnetic wave in an atmospheric pressure plasma (APP) layer is described numerically with an integral-differential wave equation. When the wave passes through the APP layer, the amplitude and phase of the transmission wave electric field are obviously modulated by the electron density and the collision frequency between the electrons and neutrals in the APP. The dependences of the wave behaviors, such as the phase shift, the coefficient of the transmission, reflection and absorption, on these APP layer characteristics are presented. Appleton’s equation is derived from the Wentzel–Kramers–Brillouin solution of the integral-differential wave equation and is compared with the numerical solution.

Disruptions have the possibility of causing severe wall damage to large tokamaks like ITER. The mitigation of disruption damage is essential to the safe operation of a large-scale tokamak. The shattered pellet injection (SPI) technique, which is regarded as the primary injection method for ITER, presents several advantages relative to massive gas injection, including more rapid particle delivery, higher total particle assimilation, and more centrally peaked particle deposition. A dedicated argon SPI system that focuses on disruption mitigation and runaway current dissipation has been designed for the Joint Texas Experimental Tokamak (J-TEXT). A refrigerator is used to form a single argon pellet at around 64 K. The pellet will be shaped with a 5 mm diameter and a 1.5-10 mm length. Helium gas at room temperature will be used as a propellant gas for pellet acceleration. The pellet can be injected with a speed of 150-300 m/s. The time interval between injection cycles is about 8 min. The pellet will be shattered at the edge of the plasma and then injected into the core of plasma. The first experiments of SPI fast shutdown and runaway current dissipation have been performed.

Dynamics of atmospheric-pressure plasma plumes have recently attracted significant attentions. However, the nature of the ldquoplasma bulletrdquo behavior is still not clearly understood. The plasma bullets have some feature of a cathode-directed streamer. However, there are several notable differences between the streamerlike plasma plumes and the cathode-directed streamers. One of the differences is the repeatability (reproducible in time and space) of the two types of the discharges. All reports on the plasma bullet behavior suggested that the plasma bullets are very repeatable. This feature is different with that of the cathode-directed streamers, which are typically unrepeatable due to the stochastic nature of their initiation. In this paper, a simple plasma jet device is used to study the plasma bullet behavior. It is found that, when the applied voltage is 8 kV or lower, the plasma bullets are not repeatable. On the other hand, when the applied voltage is 9 kV or higher, they are very repeatable. This characteristic is similar with that of the cathode-directed streamer discharge.

Cold plasmas have recently received great attention. In this paper, optical and electrical diagnostics are carried out on a reliable and user-friendly plasma plume. A simple electrical model is used to simulate the electrical characteristics of the device. The plasma is represented by a resistor connected in parallel with a capacitor, an inductor, and another resistor, which are connected in series. The simulated current-voltage waveforms have very good agreement with experimental measurements. Besides, the emission spectra of the plasma are also studied. It shows that, when Ar is used as working gas, there is strong OH (hydroxyl radical) emission and the emission intensities of the N2 emission bands are more than three times higher than that of He. On the contrary, when He is used as working gas, the emission intensities of N2+ band are much stronger. Detail analyses on these observations are presented.

The properties of electromagnetic waves in atmospheric pressure plasmas are investigated with the Lorentz model. The effects of the electromagnetic wave frequency, plasma density, and the electron-neutral collision frequency on the attenuation of electromagnetic waves are discussed. The numerical results indicate that the wave attenuation is stronger at the region of the longer wavelength and at the higher plasma density.

Most state-of-the-art bipedal robots are designed to be anthropomorphic and therefore possess legs with knees. Whilst this facilitates more human-like locomotion, there are implementation issues that make walking with straight or near-straight legs difficult. Most bipedal robots have to move with a constant bend in the legs to avoid singularities at the knee joints, and to keep the centre of mass at a constant height for control purposes. Furthermore, having a knee on the leg increases the design complexity as well as the weight of the leg, hindering the robot's performance in agile behaviours such as running and jumping. We present SLIDER, an ultra-lightweight, low-cost bipedal walking robot with a novel knee-less leg design. This non-anthropomorphic straight-legged design reduces the weight of the legs significantly whilst keeping the same functionality as anthropomorphic legs. Simulation results show that SLIDER's low-inertia legs contribute to less vertical motion in the center of mass (CoM) than anthropomorphic robots during walking, indicating that SLIDER's model is closer to the widely used Inverted Pendulum (IP) model. Finally, stable walking on flat terrain is demonstrated both in simulation and in the physical world, and feedback control is implemented to address challenges with the physical robot.

The mitigation of disruption damage is essential to the safe operation of a large-scale tokamak. In order to achieve the safe operation of ITER, the shattered pellet injection (SPI) has been considered as a primary measure of disruption mitigation. A dedicated argon SPI system, focusing on disruption mitigation has been designed for the J-TEXT tokamak. In the J-TEXT SPI system, a pure argon pellet can be formed in the freezing tube, then separated from the tube and accelerated by a punch mechanism. The pellet can be injected with a speed of 150–300 m s−1. The performance of disruption mitigation by Ar SPI has been compared with Ar massive gas injection (MGI). The cooling process observed from the ECE indicates that the SPI has deeper deposition, with the cold front that can reach the q = 1 rational surface in case of SPI, but stops at the q = 2 profile in MGI. The increase of core plasma density during a fast shutdown is higher than that with Ar MGI, which proves a deeper penetration of SPI. In disruption, the magnetohydrodynamic (MHD) activities, measured at the Mirnov coils, have similar behavior in both MGI and SPI shots. The m/n = 2/1 mode dominates the MHD activities from the penetration to the end of the thermal quench (TQ). Subsequently, in the current quench (CQ) phase, the m/n = 3/1 mode grows to become the dominant mode. The radiation power is much stronger in the SPI shot. The radiation asymmetry is compared in the two plasma disruption mitigation methods. Changing the pellet velocity can effectively adjust the TQ process and CQ rate, which can achieve a higher impurity assimilation rate when the pellet velocity increases in a certain range.

Abstract Experiments conducted on the J-TEXT tokamak have provided the first evidence that the Beta-induced Alfvén Eigenmode (BAE) is localized inside the isolated helical flux tube of its edge m / n = 3/1 magnetic island. The observations show that the BAE forms a standing wave inside the magnetic island, with its nodes located at the X- and O-points of the magnetic island. When the island is cut open by contact with the limiter plates, the BAE is found to remain inside the remnant closed island in the Scrape-Off Layer, but its amplitude decreases as the width of the remnant island becomes smaller.

Operational demands drive operators, machines, and objects to undertake time-space transfers and execute tasks to optimize system objectives in various engineering, manufacturing, and service scenarios such as prefabricated construction, roadbed construction, open-pit mining, pipe casting, steel processing, IT maintenance, airport shuttle service, and community virus elimination service. Establishing a unified concept model framework for the operations routing and scheduling problem by generalizing the characteristics of the problems portrayed by research in various fields, not only integrates research in multiple fields and connects the methods, but also provides a systematic and in-depth portrayal of the elemental structure of the problem. This unification enhances understanding of related research and forms a synergy in the field. This paper explores the establishment of a unified modeling framework for the problem, using a concept system based on elemental analysis, a graphing system based on time-space network, a problem taxonomy and a notation system. The elements in the problem, including the operators, operation machines, operation objects, operation time-space, and operation relations, are analyzed. A unified graphing system is designed for each element and scenario to organize in a time-space network diagram, including a time-space transfer diagram, a space relation diagram, and an operation relation diagram. Based on the type, quantity, function, and structure of each element, a taxonomy and a four-domain notation system for the problem are established. The unified modeling framework is then applied to describe eight typical scenarios, demonstrating its wide applicability.

Abstract The J-TEXT capability is enhanced compared to two years ago with several upgrades of its diagnostics and the increase of electron cyclotron resonance heating (ECRH) power to 1 MW. With the application of electron cyclotron wave (ECW), the ECW assisted plasma startup is achieved; the tearing mode is suppressed; the toroidal injection of 300 kW ECW drives around 24 kA current; fast electrons are generated with toroidal injected ECW and the runaway current conversion efficiency increases with ECRH power. The mode coupling between 2/1 and 3/1 modes are extensively studied. The coupled 2/1 and 3/1 modes usually lead to major disruption. Their coupling can be either suppressed or avoided by external resonant magnetic perturbation (RMP) fields and hence avoids the major disruption. It is also found that the 2/1 threshold of external field is significantly reduced by a pre-excited 3/1 mode, which can be either a locked island or an external kink mode. The disruption control is studied by developing prediction methods capable of cross tokamak application and by new mitigation methods, such as the biased electrode or electromagnetic pellet injector. The high-density operation and related disruptions are studied from various aspects. Approaching the density limit, the collapse of the edge shear layer is observed and such collapse can be prevented by applying edge biasing, leading to an increased density limit. The density limit is also observed to increase, if the plasma is operated in the poloidal divertor configuration or the plasma purity is increased by increasing the pre-filled gas pressure or ECRH power during the start-up phase.

A new measurement device, consisting of swirling blades and capsule-shaped throttling elements, is proposed in this study to eliminate typical measurement errors caused by complex flow patterns in gas-liquid flow.The swirling blades are used to transform the complex flow pattern into a forced annular flow.Drawing on the research of existing blockage flow meters and also exploiting the single-phase flow measurement theory, a formula is introduced to measure the phase-separated flow of gas and liquid.The formula requires the pressure ratio, Lockhart-Martinelli number (L-M number), and the gas phase Froude number.The unknown parameters appearing in the formula are fitted through numerical simulation using computational fluid dynamics (CFD), which involves a comprehensive analysis of the flow field inside the device from multiple perspectives, and takes into account the influence of pressure fluctuations.Finally, the measurement model is validated through an experimental error analysis.The results demonstrate that the measurement error can be maintained within ±8% for various flow patterns, including stratified flow, bubble flow, and wave flow.

Parkinson’s disease (PD), the second most common neurodegenerative disorder, is linked to α-synuclein (α-Syn) aggregation. Despite no specific drug being available for its treatment, curcumin, from the spice turmeric, shows promise. However, its application in PD is limited by a lack of understanding of its anti-amyloidogenic mechanisms. In this study, we first reconstructed the liquid–liquid phase separation (LLPS) of α-Syn in vitro under different conditions, which may be an initial step in entraining the pathogenic aggregation. Subsequently, we evaluated the effects of curcumin on the formation of droplets, oligomers, and aggregated fibers during the LLPS of α-synuclein, as well as its impact on the toxicity of aggregated α-synuclein to cultured cells. Importantly, we found that curcumin can inhibit amyloid formation by inhibiting the occurrence of LLPS and the subsequent formation of oligomers of α-Syn in the early stages of aggregation. Finally, the molecular dynamic simulations of interactions between α-Syn decamer fibrils and curcumin showed that van der Waal’s interactions make the largest contribution to the anti-aggregation effect of curcumin. These results may help to clarify the mechanism by which curcumin inhibits the formation of α-Syn aggregates during the development of PD.

This work presents the impact that multiple island chains co-existent across a tokamak plasma profile have on the heat transport and final temperature of that plasma. Numerical studies using the TM1 code show that error fields (EFs) with multiple poloidal components accelerate the core field penetration compared to pure m/ n = 2/1 EF penetration (here m and n are the poloidal and toroidal mode numbers respectively). After field penetration, locked magnetic islands of 2/1, 3/1 and 4/1 flatten the temperature at the corresponding rational surfaces. The co-existence of these islands significantly enhances the plasma heat transport throughout a wide swath of plasma from the core 2/1 rational surface to plasma edge. The electron temperature profile from 2/1 to 4/1 rational surfaces can be nearly flattened even if there is no island overlap, and the temperature inside each island is determined by the boundary temperature at the outboard separatrix of the island. The resulting central decreases by more than 50%, in good agreement with experimental observations and much lower than modeling with only a single 2/1 locked island. Further comparisons of the profile between numerical modeling and DIII-D experiment indicates that the observed reduction in the edge temperature requires edge island overlap and stochasticity. Numerical scans reveal the profile decreases further when large EF amplitudes create larger islands, wider edge stochastic regions and secondary island structures. Scans of the relative phase between EF harmonics reveal that the 3/1 island width is most sensitive to the island phase and the central changes with the 3/1 island width. These results indicate that the coexistence of multiple LMs in tokamak plasmas deteriorate thermal confinement more than the sum of their isolated impacts would and that this may be responsible for the fast thermal quench observed prior to major disruptions.

Abstract In J-TEXT tokamak, fast electron bremsstrahlung diagnostic with 9 chords equipped with multi-channel analyzer enables detailed studies of the generation and transport of fast electrons. The spatial profiles and energy spectrum of the fast electrons have been measured in two ECCD cases with either on-axis or off-axis injection, and the profiles processed by Abel-inversion are consistent with the calculated power deposition locations. Moreover, it is observed that the energy of fast electrons increases rapidly after turning off the ECCD, which may be attributed to the acceleration by the recovered loop voltage at low electron density.

A two-dimensional metal model is established to investigate the stealth mechanisms of radar absorbing material (RAM) and plasma when they cover the model together. Using the finite-difference time-domain (FDTD) method, the interaction of electromagnetic (EM) waves with the model can be studied. In this paper, three covering cases are considered: a. RAM or plasma covering the metal solely; b. RAM and plasma covering the metal, while plasma is placed outside; c. RAM and plasma covering the metal, while RAM is placed outside. The calculated results show that the covering order has a great influence on the absorption of EM waves. Compared to case a, case b has an advantage in the absorption of relatively high-frequency EM waves (HFWs), whereas case c has an advantage in the absorption of relatively low-frequency EM waves (LFWs). Through the optimization of the parameters of both plasma and RAM, it is hopeful to obtain a broad absorption band by RAM and plasma covering. Near-field attenuation rate and far-field radar cross section (RCS) are employed to compare the different cases.

Abstract Massive gas injection (MGI) experiments have been carried out in many tokamaks to study disruption dynamics and mitigation schemes. Two events often observed in those experiments are the excitation of the m = 2, n = 1 magnetohydrodynamic mode, and the formation of cold bubble structure in the temperature distribution before the thermal quench (TQ). Here m is the poloidal mode number, n the toroidal mode number. The physics mechanisms underlying those phenomena, however, have not been entirely clear. In this work, our recent NIMROD simulations of the MGI process in a tokamak have reproduced the main features of both events, which has allowed us to examine and establish the causal relation between them. In these simulations, the 3/1 and 2/1 islands are found to form successively after the arrival of impurity ion cold front at the corresponding q = 3 and q = 2 rational surfaces. At the interface between impurity and plasma, a local thin current sheet forms due to an enhanced local pressure gradient and moves inward following the gas cold front, this may contribute to the formation of a dominant 2/1 mode. Following the growth of the 2/1 tearing mode, the impurity penetration into the core region inside the q = 2 surface gives rise to the formation of the cold bubble temperature structure and initiates the final TQ. A subdominant 1/1 mode developed earlier near the q = 1 surface alone does not cause such a cold bubble formation, however, the exact manner of the preceding impurity penetration depends on the nature of the 1/1 mode: kink-tearing or quasi-interchange.

In contrast to other atmospheric pressure plasma jets, two perpendicular jet-like plasmas generated in ambient air by a special designed plasma device are reported. High-speed photographs taken by an ICCD camera with exposure time of 2 ns show that the horizontal part of the plasma is actually ignited by the vertical part of the plasma. Both the vertical and horizontal parts of the plasma are in fact a small bullet like volume of plasma traveling along different directions at high velocities. The horizontal plasma volume velocity is about half of the vertical plasma volume velocity at the same instant.

The propagation behavior of atmospheric-pressure plasma plumes has recently attracted lots of attention. In this paper, five different methods are used to measure the propagation velocity of an atmospheric-pressure plasma plume. The first method, named the ¿current method,¿ obtains the propagation velocity of the plasma plume by measuring the currents carried by the plasma plume at different positions. The second method, named the ¿voltage method,¿ obtains the plume propagation velocity by measuring the plasma plume voltage potential at different positions along the plasma jet with a voltage divider. The third method, called the ¿charge method,¿ which significantly interferes with the plume propagation, estimates the plume propagation velocity by measuring the charges deposited on the surface of a quartz tube. The fourth method, which is the noninterference method, obtains the plume propagation velocity by capturing the dynamics of the plasma plume with an intensified charge-coupled device camera. Finally, the fifth method estimates the plume propagation velocity based on the temporal optical-emission intensity measurement of the selected species by using a spectrometer. The advantage and disadvantage of each method are discussed. The experimental results show that plasma plume velocities obtained from the five methods have reasonable agreement with each other. They are all in the range of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> m/s.

The progress of experimental research over the last two years on the J-TEXT tokamak is reviewed and reported in this paper, including: investigations of resonant magnetic perturbations (RMPs) on the J-TEXT operation region show that moderate amplitude of applied RMPs either increases the density limit from less than 0.7nG to 0.85nG (nG is the Greenwald density, ) or lowers edge safety factor qa from 2.15 to nearly 2.0; observations of influence of RMPs with a large m/n = 3/1 dominant component (where m and n are the toroidal and poloidal mode numbers respectively) on electron density indicate electron density first increases (decreases) inside (around/outside) of the 3/1 rational surface, and it is increased globally later together with enhanced edge recycling; investigations of the effect of RMPs on the behavior of runaway electrons/current show that application of RMPs with m/n = 2/1 dominant component during disruptions can reduce runaway production. Furthermore, its application before the disruption can reduce both the amplitude and the length of runaway current; experimental results in the high-density disruption plasmas confirm that local current shrinkage during a multifaceted asymmetric radiation from the edge can directly terminate the discharge; measurements by a multi-channel Doppler reflectometer show that the quasi-coherent modes in the electron diamagnetic direction occur in the J-TEXT ohmic confinement regime in a large plasma region (r/a ~ 0.3–0.8) with frequency of 30–140 kHz.

The generation of runaway electrons during disruptions poses a serious threat for the operation of ITER. The efficiency of the injection of large amounts of impurities by massive gas injection or shattered pellet injection to achieve runaway suppression might be compromised due to low gas mixture efficiency and the high Rosenbluth density for runaway suppression. The transport of runaway electrons is dominated by magnetic perturbations. The magnetic perturbations have the advantage of expelling the runaway seeds before they reach high energy. Robust runaway suppression has been reached on J-TEXT with mode locking by the application of m/n = 2/1 resonant magnetic perturbations before the thermal quench. The mode locking implemented large magnetic islands inside the plasma which acted as an explosive bomb during disruptions and led to stronger stochasticity in the whole plasma cross section. The NIMROD simulation indicates that this strong stochasticity expels the runaway seeds and results in runaway free disruptions on J-TEXT. This might provide an alternative runaway suppression technique during disruptions for large-scale tokamaks.

The injection of a large amount of impurities is one of the possible ways of mitigating disruption in large-scale tokamaks. The deposition of impurities at the center of the plasma is the key to the radiation of plasma energy and suppression of runaway. The interaction of the gas jet with the rational surfaces has been studied by scanning the plasma current. The experimental results show that the injection of a massive amount of argon can cool the plasma from the edge to the core region, and the cooling process is accompanied by different magnetohydrodynamic (MHD) modes when the gas jet reaches the corresponding rational surfaces. It is observed that with different edge safety factors and electron density, gas injection can induce different poloidal modes at first. Then, the poloidal mode traverses to lower m (where m is the poloidal mode number) MHD activities until a 2/1 mode is initiated and a thermal quench is started. The experimental results show that the penetration of a gas jet across the rational surfaces is faster in the plasmas with pre-existing large 2/1 tearing modes, which indicates that the 2/1 mode plays an important role in the penetration process. Disruptions triggered by supersonic molecular beam injection display a slower cooling process compared with massive gas injection, which can be divided into four stages. The dominant poloidal mode transition from m = 3 to m = 2 is associated with electron temperature recovery.

The avoidance and suppression of runaway electron (RE) generation during disruptions is of great importance for the safe operation of tokamaks. Massive gas injection is used to suppress the generation of REs, but the poor gas mixing efficiency and extremely high density required to suppress RE generation make the full RE suppression unreliable. The magnetic perturbations provide an alternative RE suppression during disruptions. The use of mode penetration induced by resonant magnetic perturbations (RMPs) to suppress RE generation has been investigated on the J-TEXT tokamak. For a sufficiently long mode penetration duration, robust runaway suppression has been reached during the disruptions. The m/n = 2/1 mode RMP with high amplitude excites large magnetic islands inside the plasma and leads to the large-scale destruction of magnetic surfaces during disruptions, which results in RE loss and runaway-free disruptions. The critical island width required for runaway suppression is estimated to be larger than 0.16 as the minor radius. This value might be slightly underestimated because of the misalignment between the electron cyclotron emission diagnostic and the island O-point. NIMROD simulations are used to investigate the effect of magnetic islands on RE generation during disruption, showing that the large magnetic islands have the ability to enhance RE seed loss during disruptions. RMP can excite large magnetic islands in the target plasma without tearing mode and might be a way to prevent RE generation during disruptions.

Simulations of argon (Ar) massive gas injection (MGI) into J-TEXT plasmas with 2/1 mode magnetic islands (mode penetration) are performed with the 3D magnetohydrodynamic (MHD) code NIMROD. In order to study the effect of the magnetic island phase on the loss of runaway electrons (REs) in disruption, four different phases of the pre-existing 2/1 magnetic island have been implemented. It is found that the RE confinement is drastically affected by the magnetic island phase during the thermal quench (TQ) phase. Simulation results show that the curve of the remaining RE ratio vs relative toroidal phase between the preseeded m/n = 2/1 islands and the MGI valve approximates a sinelike function dependence. The optimized phase difference for runaway suppression is predicted to be toroidal 90° (Δϕ=ϕMGI−ϕn=1). It is verified that the trajectories of low energy REs follow magnetic field lines strictly. A discrepancy in the evolution of the flux surface among different toroidal phases of 2/1 islands has been found, which greatly depends on the magnetic perturbations induced in disruption. A stronger low-order MHD activity might contribute to the accelerated processes of impurity assimilation and the TQ phase in the optimized phase. These simulations suggest that the relative phase between the MGI and 2/1 islands is important for RE suppression in future tokamaks.

Abstract The topology of a magnetic field and transport properties of runaway electrons can be changed by a resonant magnetic perturbation field. The J-TEXT magnetic topology can be effectively altered via static resonant magnetic perturbation (SRMP) and dynamic resonant magnetic perturbation (DRMP). This paper studies the effect of resonant magnetic perturbation (RMP) on the confinement of runaway electrons via simulating their drift orbits in the magnetic perturbation field and calculating the orbit losses for different runaway initial energies and different runaway electrons, initial locations. The model adopted is based on Hamiltonian guiding center equations for runaway electrons, and the J-TEXT magnetic turbulences and RMP are taken into account. The simulation indicates that the loss rate of runaway electrons is sensitive to the radial position of electrons. The loss of energetic runaway beam is dominated by the shrinkage of the confinement region. Outside the shrinkage region of the runaway electrons are lost rapidly. Inside the shrinkage region the runaway beam is confined very well and is less sensitive to the magnetic perturbation. The experimental result on the response of runaway transport to the application RMP indicates that the loss of runaway electrons is dominated by the shrinkage of the confinement region, other than the external magnetic perturbation.

Abstract Runaway currents following disruptions have an important effect on the first wall in current tokamaks and will be more severe in next generation tokamaks. The behavior of runaway currents in massive gas injection (MGI) induced disruptions have been investigated in the J-TEXT tokamak. The cold front induced by the gas jet penetrates helically along field lines, preferentially toward the high field side and stops at a location near the q = 2 surface before the disruption. When the cold front reaches the q = 2 surface it initiates magnetohydrodynamic activities and results in disruption. It is found that the MGI of He or Ne results in runaway free shutdown in a large range of gas injections. Mixture injection of He and Ar (90% He and 10%Ar) consistently results in runaway free shutdown. A moderate amount of Ar injection could produce significant runaway current. The maximum runaway energy in the runaway plateau is estimated using a simplified model which neglects the drag forces and other energy loss mechanisms. The maximum runaway energy increases with decreasing runaway current. Imaging of the runaway beam using a soft x-ray array during the runaway current plateau indicates that the runaway beam is located in the center of the plasma. Resonant magnetic perturbation (RMP) is applied to reduce the runaway current successfully during the disruption phase in a small scale tokamak, J-TEXT. When the runaway current builds up, the application of RMP cannot decouple the runaway beam due to the lower sensitivity of the energetic runaway electrons to the magnetic perturbation.

Disruption remains to be a serious threat to large tokamaks like the International Thermonuclear Experimental Reactor (ITER). The injection speed of disruption mitigation systems (DMS) driven by high pressure gas is limited by the sound speed of the propellant gas. When extrapolating to ITER-like tokamaks, long overall reaction duration and shallow penetration depth due to low injection speed make it stricter for plasma control system to predict the impending disruptions. Some disruptions with a short warning time may be unavoidable. Thus, a fast time response and high injection speed DMS is essential for large scale devices. The electromagnetic pellet-injection (EMPI) system is a novel massive material injection system aiming to provide rapid and effective disruption mitigation. Based on the railgun concept, EMPI can accelerate the payload to over 1000 m/s and shorten the overall reaction time to a few milliseconds. To verify the injection ability and stability of the EMPI, the prototype injector EMPI-1 has been designed and assembled. The preliminary test has been carried out using a 5.9 g armature to propel a dummy pellet and the results suggest that the EMPI configuration has a great potential to be the DMS of the large scale fusion devices.

Abstract Toroidal coupling between m / n = 2/1 and m / n = 3/1 modes frequently occurs in the J-TEXT, where m ( n ) is the poloidal (toroidal) mode number. These coupled modes destabilize each other, leading to confinement degradation and even triggering a major disruption. This paper presents two control strategies for preventing the mode coupling through the application of a proper static resonant magnetic perturbation (RMP) field. Experimental results demonstrate that moderate 2/1 RMP can suppress the small, rotating 2/1 mode thus prevent coupling between the 2/1 and 3/1 modes. The 3/1 static RMP can excite a large 3/1 locked island while leave the small 2/1 mode rotating at 8 kHz. Enlarging the frequency difference between 2/1 and 3/1 modes makes mode coupling more difficult. Both strategies can break the frequency coupling condition between the 2/1 and 3/1 modes, and hence avoid coupling and mutual destabilizing.

C/SiC composites prepared by polymer infiltration and pyrolysis (PIP) are among the most promising materials for application in ultrahigh-temperature conditions. However, the mechanical properties and damage mechanisms of PIP-C/SiC composites at different loading velocities and temperatures have not been systematically studied. In this study, in-plane compression, bending, and in-plane shear experiments were systematically performed at different loading velocities and temperatures in an inert atmosphere. The ultimate strengths of the PIP-C/SiC composite were determined under different conditions, and the failure modes were revealed. In addition, in-situ X-ray microtomography tension experiments were conducted to study the failure mechanism of the PIP-C/SiC composite. The results showed that the ultimate strengths were considerably affected by the temperature and loading velocity, and the failure modes were dependent on experimental types. The fracture location of the PIP-C/SiC composite is affected by the defect. And the direction of crack propagation is toward the existing cracks and voids.

Accurately forecasting patients admitted to the intensive care units (ICUs) after surgery may improve clinical outcomes and guide the allocation of expensive and limited ICU resources. However, studies on predicting postoperative ICU admission in non-cardiac surgery have been limited.To develop and validate a prediction model combining pre- and intraoperative variables to predict ICU admission after non-cardiac surgery.This study is based on data from the Vital Signs DataBase (VitalDB) database. Predictors were selected using the least absolute shrinkage and selection operator regression method and logistic regression to develop a nomogram and an online web calculator. The model was internally verified by 1000-Bootstrap resampling. Performance of model was evaluated using area under the receiver operating characteristic curve (AUC), calibration curve and Brier score. The Youden's index was used to find the optimal nomogram's probability threshold. Clinical utility was assessed by decision curve analysis.This study included 5216 non-cardiac surgery patients; of these, 812 (15.6%) required postoperative ICU admission. Potential predictors included age, ASA classification, surgical department, emergency surgery, preoperative albumin level, preoperative urea nitrogen level, intraoperative crystalloid, intraoperative transfusion, intraoperative catheterization, and surgical time. A nomogram was constructed with an AUC of 0.917 (95% CI: 0.907-0.926) and a Brier score of 0.077. The Bootstrap-adjusted AUC was 0.914; the adjusted Brier score was 0.078. The calibration curve showed good agreement between predicted and actual probabilities; and the decision curve indicated clinical usefulness. Finally, we established an online web calculator for clinical application (https://xuzhikun.shinyapps.io/postopICUadmission1/).We developed and internally validated an easy-to-use nomogram for predicting ICU admission after non-cardiac surgery.

The propagation property of an electromagnetic wave in a thin plasma layer at high pressure is investigated with the finite-difference time-domain method. The effects of the non-uniformity of plasma distribution, and the frequency of incident wave on the propagation property of the electromagnetic wave are discussed. Numerical results indicate that the phase shift and the reflectivity of wave are sensitive to plasma density distribution, and reflectivity is lower at the middle band of frequency for different plasma distributions.

The reflection of an electromagnetic wave in a thin plasma layer attached to a metal plate at high pressure is investigated with the finite-difference time-domain method. The effects of the plasma thickness, the plasma density distribution function, the collision frequency between electrons and neutrals and the frequency of incident wave on the reflection coefficient of the electromagnetic wave are discussed. Numerical results indicate that the reflection coefficient of the wave depends on its frequency, the plasma thickness, the plasma density distribution and the collision frequency. The reflection coefficient is low only at the low band of the calculated frequency for different plasma distribution functions if the plasma layer is very thin, e.g. 10 mm. Plasmas with an excess of 20 mm for a high collision frequency such as 103 GHz are capable of absorbing microwave radiation over a wider frequency range for different plasma distributions.

As nonthermal atmospheric pressure plasmas come to play an important role in diverse applications, reliable and arcing-free low-temperature plasma sources are needed urgently. In this paper, a low-temperature plasma jet device, which generated four plasma plumes simultaneously, is developed. The plasma jet device can be driven by pulsed dc or kilohertz ac power supply. There is no risk of arcing. When the plasma plumes are contacted with a conductive surface, the four plasma plumes merge together and form a uniform plasma layer on the surface of conductive material with an area of about 1cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The gas temperature of the plasma plumes is close to room temperature.

Disruptions have the potential to cause severe damage to large tokamaks like ITER. The mitigation of disruption damage is one of the essential issues for the tokamak. Massive gas injection (MGI) is a technique in which large amounts of a noble gas are injected into the plasma in order to safely radiate the plasma energy evenly over the entire plasma-facing wall. However, the radiated energy during the disruption triggered by massive gas injection is found to be toroidally asymmetric. In order to investigate the spatial and temporal structures of the radiation asymmetry, the radiated power diagnostics for the J-TEXT tokamak have been upgraded. The multi-channel arrays of absolute extreme ultraviolet photodiodes have been upgraded at four different toroidal positions to investigate the radiation asymmetries during massive gas injection. It is found that the toroidal asymmetry is associated with plasma properties and MGI induced MHD activities.

Abstract The suppression of runaways following disruptions is key for the safe operation of ITER. The massive gas injection (MGI) has been developed to mitigate heat loads, electromagnetic forces and runaway electrons (REs) during disruptions. However, MGI may not completely prevent the generation of REs during disruptions on ITER. Resonant magnetic perturbation (RMP) has been applied to suppress runaway generation during disruptions on several machines. It was found that strong RMP results in the enhancement of runaway production instead of runaway suppression on J-TEXT. The runaway current was about 50% pre-disruption plasma current in argon induced reference disruptions. With moderate RMP, the runway current decreased to below 30% pre-disruption plasma current. The runaway current plateaus reach 80% of the pre-disruptive current when strong RMP was applied. Strong RMP may induce large size magnetic islands that could confine more runaway seed during disruptions. This has important implications for runaway suppression on large machines.

The suppression of disruption-generated runaway electrons (REs) by supersonic molecular beam injection (SMBI) has been investigated on the J-TEXT tokamak. Experimental results demonstrate that the hydrogen injected by SMBI during plasma current flattop phase can provoke magnetic perturbations, which increase RE losses rapidly. The effective radial diffusion coefficient of REs due to SMBI is estimated as Dr ≈ 16 m2 s−1. Based on this benefit, the SMBI has been used to explore the suppression of disruption-generated REs. In J-TEXT, RE current is created with rapid argon injection by a massive gas injection valve. It is found that hydrogen SMBI before disruption efficiently suppresses the generation of RE current.

Property of rectangular structure surface wave plasma was reported. Large-area uniform and high density plasma was produced by the optimization of slot antenna and the shape of dielectric plates. Plasma density and electron temperature for different operation conditions were measured by a Langmuir probe. Profile of plasma density along the vertical direction was modeled by a diffusive model, and the simulation result can be used to interpret qualitatively the measurement value very well.

The attenuation of the electromagnetic wave in a thin plasma layer at high pressure is investigated with finite-difference time-domain method. The effects of the plasma thickness, plasma density distribution function, collision frequency between electron and neutrals, and the frequency of incident wave on the attenuation of the electromagnetic wave are discussed. Numerical results indicate that the phase shift is sensitive to plasma distributions, and the attenuation of wave depends on its frequency, the plasma thickness, plasma density distribution, and collision frequency. In the case of a thin plasma layer, the attenuation of wave is strong only at the low band of frequency for the different distribution functions with a certain collision frequency. Plasmas with a certain thickness for high collision frequency are capable of absorbing microwave radiation over a wider frequency range for the different plasma distributions.

A three-dimensional model of a surface-wave plasma (SWP) source is built numerically using the finite-difference time-domain (FDTD) method to investigate the structure of the surface wave propagation along the plasma-dielectric interface and the distributions of electromagnetic fields in the whole system. A good-performance excitation source technique for the waveguide which is pivotal to the simulation is presented. The technique can avoid the dc distortions of magnetic fields caused by the forcing electric wall. An example of simulation is given to confirm the existence of the surface waves. The simulation also shows that the code developed is a useful tool in the computer-aided design of the antenna of the SWP source.

Locked modes (LMs) will be one of the major causes of disruptions in the ITER tokamak. Disruption mitigation systems (DMSs), such as massive gas injection (MGI) or shattered pellet injection (SPI), are expected to be deployed in pre-disruption discharges with large pre-existing locked modes. A series of target plasmas with an m/n = 2/1 locked mode induced by resonant magnetic perturbation (RMP) penetration was terminated by an MGI on the J-TEXT tokamak. The penetration of the injected impurities during the process was diagnosed using a fast frame visible camera and a multi-channel polarimeter-interferometer (POLARIS) in combination. The electron temperature evolution during thermal quench (TQ) is also shown in detail. It is found that both the phase and width of the 2/1 mode have an effect on MGI shutdown dynamics. When the mode is larger than the critical width, the penetration depth and assimilation of impurities can be enhanced during pre-TQ, leading to a faster quenching process if the relative phase between the O-point of the 2/1 mode and the MGI valve is +90°. Conversely, the penetration depth and assimilation of impurities are suppressed, leading to a slower TQ when the relative phase is −90°. The toroidal radiation asymmetry is worse with the locked mode. The results suggest that the 3D effect between the injected impurities and the 2/1 locked mode is important during the disruption mitigation process.

Finite-difference-time-domain arithmetic is applied to simulate the propagation of an electromagnetic (EM) wave in a two-dimensional atmospheric pressure plasma (APP) and a metal layer with strong electron-neutral collisions. The dependences of the EM wave attenuation on the parameters of the APP are provided. The two-dimensional numerical results indicate that when the profile of the electron density is given, the attenuation of an EM wave in APP is strongly affected by (a) the polarization mode (TM mode or TE mode), (b) the incident angle of the EM wave, (c) the EM wave frequency, (d) the width of the plasma layer, and (e) the collision frequency between electrons and neutrals. In this paper, the behaviour of the propagation of an EM wave inside the plasma layer is explained by the principle of wave interference. The relationship between the attenuation property and the above-mentioned parameters is also studied.

The finite-difference-time-domain (FDTD) method is applied to simulate the two-dimensional propagation of electromagnetic TM (S-polarization) mode in atmospheric plasma and in metal layer for strong electron-neutral collisions. Dependence of the wave attenuation on both plasma parameters and incident wave angle are obtained. It is indicated that for a given electron density profile the attenuation depends strongly on the incident angle, the wave frequency, the width of plasma layer, and the collision frequency between electrons and neutrals.

Effects of two compressibility parameters, i.e. the ratio of specific heats and the equilibrium pressure at the interface, on the Rayleigh–Taylor instability (RTI) growth rates are studied under the same initial conditions, which include the mass, pressure profile, and density profile of the two superposed fluids. The results obtained reconcile the stabilizing and destabilizing effects of compressibility reported in the literature. The influences of the ratio of specific heats on the RTI growth rates are not only stabilized but also destabilized. The effects of the equilibrium pressure at the interface on the growth rates are destabilized.

Numerical instability occurs when coupled Maxwell equations and nonlinear two-fluid plasma equations are solved using finite difference method through parallel algorithm. Thus, a perfectly matched layer (PML) boundary condition is set to avoid the instability caused by velocity and density gradients between vacuum and plasma. A splitting method is used to first decompose governing equations to time-dependent nonlinear and linear equations. Then, a proper complex variable is used for the spatial derivative terms of the time-dependent nonlinear equation. Finally, with several auxiliary function equations, the governing equations of the absorbing boundary condition are derived by rewriting the frequency domain PML in the original physical space and time coordinates. Numerical examples in one- and two-dimensional domains show that the PML boundary condition is valid and effective. PML stability depends on the absorbing coefficient and thickness of absorbing layers.

Abstract High-density experiments in the high-field-side mid-plane single-null divertor configuration have been performed for the first time on J-TEXT. The experiments show an increase in the highest central channel line-averaged density from <?CDATA $2.73\,\times \,{10}^{19}\,{{\rm{m}}}^{-3}$?> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>2.73</mml:mn> <mml:mspace width=".25em" /> <mml:mo>×</mml:mo> <mml:mspace width=".25em" /> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>19</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width=".25em" /> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> </mml:math> to <?CDATA $6.49\,\times \,{10}^{19}\,{{\rm{m}}}^{-3}$?> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>6.49</mml:mn> <mml:mspace width=".25em" /> <mml:mo>×</mml:mo> <mml:mspace width=".25em" /> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>19</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width=".25em" /> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> </mml:math> , while the X-point moves away from the target by increasing the divertor coil current. The corresponding Greenwald fraction rises from 0.50 to 0.79. For the impurity transport, the density normalized radiation intensity (absolute extreme ultraviolet and soft x-ray) of the central channel density decreased significantly (&gt;50%) with an increase in the plasma density. To better understand the underlying physics mechanisms, the 3D edge Monte Carlo code coupled with EIRENE (EMC3- EIRENE) has been implemented for the first time on J-TEXT. The simulation results show good agreement with the experimental findings. As the X-point moves away from the target, the divertor power decay length drops and the scrape-off layer impurity screening effect is enhanced.

Abstract In order to measure boundary electrostatic and magnetic fluctuations simultaneously, a combined Langmuir-magnetic probe (CLMP) has been designed and built on joint-Texas experimental tokamak. The probe consists of 8 graphite probe pins and a 3D magnetic probe, driven by a mechanical pneumatic device. By means of simulation, the shielding effect of the graphite sleeve on the magnetic fluctuation signal is explored, and the influence of the eddy current was reduced by cutting the graphite sleeve. In the experiment, it has been verified that the mutual inductance of electromagnetic signals can be ignored, and a 70–90 kHz electromagnetic mode is observed around the last closed magnetic surface. The establishment of CLMP provides data for the exploration of the coupling of electrostatic and magnetic fluctuations.

The suppression of runaway electrons (REs) is influenced by the size of pre-existing 2/1 magnetic islands. Simulations of argon (Ar) massive gas injection into J-TEXT plasmas with pre-existing 2/1 magnetic islands of different width are performed with the 3D magnetohydrodynamic code called NIMROD (Sovinec et al 2004 J. Comput. Phys. 195 355). Results show that the ratio of remaining REs is not monotonically dependent on the width of pre-existing 2/1 magnetic islands. Large enough pre-existing 2/1 magnetic islands can lead to strong magnetic perturbation and strong magnetic surface stochasticity to expel the REs. The critical width for the suppression of REs is to be 0.31 as the minor radius. Under the condition of suitable small pre-existing 2/1 magnetic islands width, with island width ranging from 0.07 to 0.11 times the minor radius, the mitigation of REs is achieved. The duration of magnetic perturbations δB/B(n = 1) (exceeding (4 to 6) × 10−3) is a key for RE loss, and high amplitude of high n modes plays an important role in RE loss.

The Rankine-Hugoniot relations of an axial shock in cylindrical non-neutral plasma with current, electric and magnetic field are presented. These relations are all dependent on the radius of cylindrical plasma, and markedly different from the one-dimensional (i.e., nonradially dependent) case. These two-dimensional Rankine-Hugoniot relations cause at least two important new results. First, the radial profiles of the shock downstream parameters are always different from the upstream profiles due to the magnetic effects. Second, the critical Mach number for the shock existence will depend on the shock carried current (i.e., magnetic field). As an example, a set of shock downstream profiles is provided numerically when the upstream profiles are taken as a kind of typical equilibrium profiles of a Z-pinch-Bennett profiles. By comparing the downstream profiles to the corresponding upstream profiles, the dependents of both the amplitudes and profiles of the downstream parameters on the shock carried current are shown.

The plasma surface wave propagation in a rectangular structured device is simulated using the finite-difference time-domain method. The effect of device parameters on the propagation of plasma surface wave excited by slot antenna array is investigated. The parameters considered include the relative permittivity and thickness of dielectric slab, and the air gap on the top of dielectric slab. Appropriate parameters for the relative permittivity and thickness of dielectric slab are obtained through simulations, and it is found that the existence of air gap would greatly weaken the excitation of surface wave. The simulation results provide a good reference for the design optimization of large-scale rectangular surface-wave plasma source.

This study presents the design and principle of a current-pulsed power supply (CPPS) for the tearing mode (TM) feedback control of the J-TEXT tokamak. CPPS is a new method of stabilizing large magnetic islands and accelerating mode rotation through the use of modulated magnetic perturbation. In this application, continuous magnetic perturbation pulse trains with frequency of 1 kHz to kHz, amplitude of 0.25 G, and duty ratio of 20%–50% are required generating via in-vessel magnetic coils. A modified topology based on buck chopper is raised to satisfy the demands of inductive load. This modified topology is characterized by high frequency, rapid rising and falling edges, and large amplitude of current pulses. Appropriate RCD snubber circuit is applied to protect the Insulated Gate Bipolar Transistor (IGBT) switch device. Equipment with peak current that reaches 1 kA, frequency that ranges from 1 kHz to 3 kHz, and rising and falling time within 100 μs was constructed and applied to physical experiment.

The EFIT program is integrated with the high resolution laser polarimeter interferometer system (POLARIS), the soft X-ray imaging diagnostic system (SXR) and the electron cyclotron emission radiometer (ECE) in the J-TEXT tokamak. Then some internal information about Faraday angle and the position of safety factor q=1 can be obtained as a constraint to EFIT. The modified EFIT code is used to calculate the internal parameters such as flux function, safety factor q, pressure and current density.

Abstract The main works on disruption mitigation including suppression and mitigation of runaway current on the J-TEXT tokamak are summarized in this paper. Two strategies for the mitigation of runaway electron (RE) beams are applied in experiments. The first strategy enables the REs to be completely suppressed by means of supersonic molecular beam injection and resonant magnetic perturbation which can enhance RE loss, magnetic energy transfer which can reduce the electric field, and secondary massive gas injection (MGI) which can increase the collisional damping. For the second strategy, the runaway current is allowed to form but should be dissipated or soft landed within tolerance. It is observed that the runaway current can be significantly dissipated by MGI, and the dissipation rate increases with the injected impurity particle number and eventually stabilizes at 28 MA s −1 . The dissipation rate of the runaway current can be up to 3 MA s −1 by ohmic field. Shattered pellet injection has been chosen as the main disruption mitigation method, which has the capability of injecting material deeper into the plasma for higher density assimilation when compared to MGI. Moreover, simulation works show that the RE seeds in the plasma are strongly influenced under different phases and sizes of 2/1 mode locked islands during thermal quench. The robust runaway suppression and runaway current dissipation provide an important insight on the disruption mitigation for future large tokamaks.

The effects of the ambient pressure Pambient on the bubble characteristics of pulsed discharge in water are investigated. The simulation results show that, when Pambient increases from 1 atm to 100 atm, the bubble radius R decreases from 4 cm to 7 mm, and its pulsation period decreases from 8 ms to 0.2 ms. The results also show that the peak pressure of the first shock wave is independent of Pambient, but the peak pressure of the second shock wave caused by the bubble re-expansion decreases when Pambient increases. On the other hand, the larger the ambient pressure, the larger the peak pressure of the plasma in the bubble, while the plasma temperature is independent of Pambient.

Atmospheric pressure glow discharge was observed in a surface discharge generator. The frequency of ac power supply is more than 9 kHz and the sinusoidal peak-to-peak applied voltage is 9 kV. The electric field intensity in a kind of surface discharge generators is calculated with the boundary element method. Then a two-dimensional fluid model was used to simulate the ion trapping and electron trapping in a surface discharge just before the breakdown. The simulation results are in good agreement with our observation.

Numerical simulations of plasma heating with waves in the ion cyclotron range of frequencies (ICRF) require to iteratively couple a solver for wave propagation in plasmas with a solver of the quasilinear kinetic equation. Among the codes developed for this purpose, the TORIC-SSFPQL package is characterized by its high execution speed. The kinetic code SSFPQL, however, was based on a somewhat simplified physical model, in which some important effects of the toroidal geometry were omitted. We have recently improved this model by taking into account in the zero–banana–width limit the influence of toroidal trapping on the ICRF quasilinear operator. To make the extended model compatible with the representation of the ion distribution functions as a truncated series of Legendre polynomials in the velocity pitch-angle adopted in SSFPQL, a special approach based on the multiprecision arithmetic had to be developed. We describe these new developments, and present first results obtained with the improved model.

摘要 利用洛沦兹模型来研究大气层人造非均匀等离子体的电磁响应特性,讨论了电磁波频率、等离子体密度及电子碰撞频率对电磁波衰减特性的影响.结果表明,电磁波在长波长区域及等离子体密度大时,其能量衰减越快.当等离子体密度高时,电子温度越低,大气层高度越高,电磁波的能量衰减越快. 关键词: 电磁波 / 大气等离子体 / 能量衰减 Abstract Keywords: / / 作者及机构信息 刘明海, 胡希伟, 江中和, 刘克富, 辜承林, 潘垣 1. 华中科技大学电气与电子工程学院,武汉430074 Authors and contacts Liu Ming-Hai, Hu Xi-Wei, Jiang Zhong-He, Liu Ke-Fu, Gu Cheng-Lin, Pan Yuan 1. 华中科技大学电气与电子工程学院,武汉430074 参考文献 施引文献

The finite-difference-time-domain method is applied to simulate the two-dimensional propagation of a p-polarization mode electromagnetic wave in atmospheric plasma and metal layer for strong electron–neutral collisions. It is indicated that for a giving electron density profile, the p-polarization attenuation is very different from the s-polarization attenuation and it depends even strongly on the incident angle. The mechanism of p-polarization attenuation is analysed by the interference of wave and the relationship between the attenuation property and the main parameters is given.

Abstract The propagation of a microwave in an atmospheric pressure plasma (APP) layer is described numerically with an integral–differential wave equation in one dimension (normal incident) case and with the Finite Difference Time Domain (FDTD) method in two dimension (oblique incident) case. When the microwave passes through the APP layer, its amplitude and phase of the wave electric field are obviously modulated by both the electron density and the collisions between the electrons and neutrals. The dependencies of the passed wave behaviors (i.e. the phase shift, the reflectivity, the transmissivity and absorptivity) on the APP layer characteristics (width, electron density, and collision frequency) and microwave characteristics (incident angle and polarization) are presented. The Appleton's Equation can be derived from the Wentzel–Kramers–Brillouin (WKB) solution of the integral–differential wave equation and is compared with the one-dimensional numerical solution.

Fast electron bremsstrahlung (FEB) emission during Ohmic discharge experiments on the Joint Texas Experimental Tokamak (J-TEXT) has been measured by a recently developed vertical multi-channel FEB diagnostic based on CdZnTe detectors. There are 5 sight lines to observe the vertical emission of fast electrons at the high-field side with a spatial resolution of 5 cm. The FEB emission in the energy range of 30-300 keV can be measured. The generation of fast electrons accelerated by loop voltage has been confirmed during the early phase of discharge by analyzing the signals of FEB emission. The runaway electron beam instabilities have been observed with the FEB diagnostic on J-TEXT.

The linear instabilities induced by the electrostatic fields and gradients of equilibrium parameters in a plasma shock front are analyzed for the plasma shock structure. Small perturbations as well as the steady-state shock structure are described by a set of coupled two-fluid and Poisson equations. The dispersion relations are obtained at high frequency in two cases, in which the wave vectors are, respectively, parallel and perpendicular to the shock propagation direction. The imaginary parts of the frequency (growth rates) of the instabilities are dependent on the fields and the gradients.

In the experiments of actively triggering plasma disruption by massive gas injection, the externally applied resonant magnetic perturbation has been used to mitigate the hazard of runaway electron (RE). Motivated by the experiment of multimode coupling to suppress REs on J-TEXT, some typical simulation cases with non-ideal MHD with rotation-open discussion (NIMROD) code are carried out to explore the influential mechanism of different relative phases between m / n = 2/1 and m / n = 3/1 magnetic islands on the confinement of REs. Results show that the RE confinement is drastically affected by the relative phase between 2/1 and 3/1 magnetic islands. When the O point phase of 2/1 and 3/1 magnetic islands is toroidal 330°, REs can be effectively lost. The fitting curve of the remaining ratio of REs vs. the relative toroidal phase is predicted to approximate a sine-like function dependence. Further studies indicate that the phase difference between coexisting 2/1 and 3/1 islands can affect the radial transport of impurities. The loss of runaway electrons is closely related to the deposition effect of impurity. The impurity is easier to spread into the core region with smaller poloidal phase difference between the radial velocity of impurity and the impurity quantity of Ar.

Whether the hydraulic conductivity representative elementary volume (KREV) exists is a fundamental question for understanding the hydraulic behavior of fractured rock masses. The fracture density and size of rocks vary greatly, and are the two most important parameters affecting the existence of a KREV. The International Society for Rock Mechanics (ISRM) presented quantitative descriptions of fracture persistence and density, dividing the persistence into 5 rates and the density into 7 rates, defining 35 basic types of isotropic fractured rock masses with different persistence and densities. Based on ISRM classification suggestions, we construct an additional 40 anisotropic fractured rocks and conduct a systematic investigation of the KREVs of all 75 rock types. The 3D DFNs of the 75 rocks are established with the Monte Carlo method; the water flow in the DFNs is simulated with the finite difference method; the equivalent conductivities of each rock are calculated in 10 domain sizes and 21 different flow directions; and the optimum conductivity ellipsoid and the fitting errors of the equivalent directional conductivity vectors are analyzed to determine the existence and size of the KREVs. A KREV is more likely to exist in rock masses with a high fracture density and persistence. The effect of fracture density and persistence can be comprehensively represented by blockiness, defined as the ratio of the volume of isolated blocks formed by fractures to the total rock volume. A strong correlation is found between the blockiness and the existence of a KREV. A KREV always exists when the blockiness is higher than 0.5%, and its size is between 2 and 18 times the fracture spacing. A KREV may or may not exist in the range of 0.1% < B < 0.5%. When B < 0.1%, a KREV does not exist.

SiCf/SiC composites are potential candidates in the aerospace fields for application as high-temperature structural components. Their mechanical properties and failure behaviors at ultra-high temperatures (above 1473 K) are important to obtain systematically. This work performed the in-plane compressive, bending, and interlaminar shear tests at 1573 K and 1773 K in an inert atmosphere. The results showed dramatically that the in-plane compressive and interlaminar shear strengths increased with the temperature increment from 1573 K to 1773 K. In contrast, a reduction in flexural strength was noticeable. To reveal the failure mechanisms, fracture surface microstructures of these SiCf/SiC samples were characterized. It was found that the fiber surfaces for the samples tested at 1773K were rougher than the samples tested at 1573K. It meant that, with the temperature increasing, the fiber-matrix interfaces enhanced, which resulted in increasing compressive and interlaminar strengths. For the bending tests, serious delamination occurred when the temperature increased to 1773K, which induced the flexural strength reduction. The numerical simulations of bending samples were developed to reveal the mechanism of strength degradation as the temperature elevated.

Effective classification of autonomous vehicle (AV) driving behavior emerges as a critical area for diagnosing AV operation faults, enhancing autonomous driving algorithms, and reducing accident rates. This paper presents the Gramian Angular Field Vision Transformer (GAF-ViT) model, designed to analyze AV driving behavior. The proposed GAF-ViT model consists of three key components: GAF Transformer Module, Channel Attention Module, and Multi-Channel ViT Module. These modules collectively convert representative sequences of multivariate behavior into multi-channel images and employ image recognition techniques for behavior classification. A channel attention mechanism is applied to multi-channel images to discern the impact of various driving behavior features. Experimental evaluation on the Waymo Open Dataset of trajectories demonstrates that the proposed model achieves state-of-the-art performance. Furthermore, an ablation study effectively substantiates the efficacy of individual modules within the model.

Regular inspection of Bridges is a necessary condition for bridge maintenance and safety. Traditional human detection is time-consuming and laborious. Using UAVs instead of manpower not only improves detection efficiency but also saves costs. Usually, underbridge environments are accompanied by poor GNSS signals, making reliable drone positioning under bridge challenging. The visual odometer, the classic drone positioning scheme, often fails in the ever-changing light noise. The ground-air system and structured light assisted localization algorithm designed in this paper can effectively improve the robustness of UAV positioning. We use ground visual beacon to provide positioning reference for UAV and introduce attention mechanism to improve the effect of feature extraction during beacon recognition. In addition, the establishment of structured light protection enhanced the stability of the system under weak light environment. Deep convolutional Neural Networks is used to identify candidate regions containing these markers. This region is projected onto an infrared image for positioning, and structured light ranging is employed for accurate beacon positioning. We also conduct modeling and error analysis to optimize the system's performance in spatial deployment. Real experiments and simulations are conducted under various conditions, demonstrating the system's stable performance in changing lighting environments and GNSS signal absence.

The Go language (Go/Golang) has been attracting increasing attention from the industry over recent years due to its strong concurrency support and ease of deployment. This programming language encourages developers to use channel-based concurrency, which simplifies the development of concurrent programs. Unfortunately, it also introduces new concurrency problems that differ from those caused by the mechanism of shared memory concurrency. However, there are only few works that aim to detect such Go-specific concurrency issues. Even state-of-the-art testing tools will miss critical concurrent bugs that require fine-grained and effective interleaving exploration. This paper presents GoPie, a novel testing approach for detecting Go concurrency bugs through primitive-constrained interleaving exploration. GoPie utilizes execution histories to identify new interleavings instead of relying on exhaustive exploration or random scheduling. To evaluate its performance, we applied GoPie to existing benchmarks and large-scale open-source projects. Results show that GoPie can effectively explore concurrent interleavings and detect significantly more bugs in the benchmark. Furthermore, it uncovered 11 unique previously unknown concurrent bugs, and 9 of which have been confirmed.

Abstract Accurate measurements of the edge plasma equilibrium profiles, including the temperature and density of electrons and ions, are critical to understanding the characteristics of the scrape-off layer (SOL) and divertor plasma transport in magnetically confined fusion research. On the J-TEXT tokamak, a multi-channel retarding field analyzer (RFA) probe has been developed to study edge plasma equilibrium profiles under various poloidal divertor and island divertor configurations. The edge radial profile of the ion-to-electron temperature ratio, τ_{i/e}, has been determined, which gradually decreases as the SOL ion self-collisionality, ν_{SOL}^*, increases. This is widely consistent with what has been observed previously from various tokamak experiments. However, the comparison of experimental results under different configurations shows that in the poloidal divertor configuration, even under the same ν_{SOL}^*, τ_{i/e} in the SOL region becomes smaller as the distance from the X-point to the target plate increases. In the island divertor configuration, τ_{i/e} near the O-point is higher than that near the X-point at the same ν_{SOL}^*, and both are higher than the limiter configuration. These results suggest that the magnetic configuration plays a critical role in the energy distributions between electrons and ions at the plasma boundary.

Disruption-induced runaway electrons greatly reduce the lifespan of the nuclear fusion magnetic confinement device tokamak. At present, passive runaway electron mitigation coils have been modeled on the tokamak device SPARC and preliminary simulation results have been obtained. In this work, we use the three-dimensional nonlinear magnet-o-hydrodynamics (MHD) program NIMROD to study the impact of different mode and phase of the passive field on J-TEXT tokamak in the presence of a massive injection of argon impurity gas. The results indicate that the behavior of runaway electrons is significantly influenced by the passive runaway electron mitigation coils. It also reveals that under the same helicity condition of coil configuration, better results can be captured by operating in low-n mode. Under specific phases of operation, the coils in the 1/1 mode can completely suppress runaway currents.

In order to test the performance of the ion cyclotron range of frequencies (ICRF) antenna of the J-TEXT tokamak, a coupling model between ICRF wave and plasma is established using finite element method. The model is configured with cold plasma dielectric tensor, flat straps and perfectly matched layer (PML) which is used to emulate radiating boundary conditions beyond a critical cutoff layer for the fast wave. 2D and 3D coupling models are constructed to complete a preliminary analysis of the antenna.

The propagating behaviours, i.e. phase shift, transmissivity, reflectivity and absorptivity, of an electromagnetic (EM) wave in a two-dimensional atmospheric pressure plasma layer are described by the numerical solutions of integral-differential Maxwell's equations through a generalized finite-difference-time-domain (FDTD) algorithm. These propagating behaviours are found to be strongly affected by five factors: two EM wave characteristics relevant to the oblique incident and three dimensionless factors. The two EM wave factors are the polarization mode (TM mode or TE mode) and its incident angle. The three dimensionless factors are: the ratio of the maximum electron density to the critical density n0/ncr, the ratio of the plasma layer width to the wave length d/λ, and the ratio of the collision frequency between electrons and neutrals to the incident wave frequency ve0/f.

The effect of air gap on the uniformity of large-scale surface-wave plasma (SWP) in a rectangular chamber device is studied by using three-dimensional numerical analyses based on the finite difference time-domain (FDTD) approximation to Maxwell's equations and plasma fluid model. The spatial distributions of surface wave excited by slot-antenna array and the plasma parameters such as electron density and temperature are presented. For different air gap thicknesses, the results show that the existence of air gap would severely weaken the excitations of the surface wave and thereby the SWP. Thus the air gap should be eliminated completely in the design of the SWP source, which is opposite to the former research results.

Numerical simulation of tearing mode suppression by applying non-resonant magnetic perturbations (non-RMPs) has been carried out in the J-TEXT tokamak based on the NIMROD (Non-Ideal Magnetohydrodynamics with Rotation, Open Discussion) code. In the present work, we investigate the growth of n = 1 and n = 2 (n is the toroidal mode number) magnetohydrodynamics (MHD) instabilities, mainly as tearing modes, in response to different modes and amplitudes of non-RMPs generated by the external helical coils. It is found that the tearing mode can be stabilized by non-RMPs, especially for the non-RMPs with mode m/n = -1/1 (m is the poloidal mode number) and coil current I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MP</sub> = 4kA.

Application of resonant magnetic perturbation (RMP) coils could break the initial axisymmetry and change the magnetic topology in Tokamak systems. To understand the plasma equilibrium response to the RMP fields, three-dimensional (3D) non-linear magnetohydrodynamics (MHD) equilibrium calculations have been carried out using the HINT code for an RMP field-penetration experiment on J-TEXT. The HINT code does not assume perfectly nested flux surfaces, and is able to consider directly the change of magnetic topology due to the RMP field penetrations. Correlations between 3D equilibrium calculations and experimental observations are presented. The magnetic topologies calculated by HINT were compared with the field topologies obtained from a vacuum approximation method. It turns out that the effects of redistribution of plasma pressure and current due to the formation of magnetic islands at various resonant rational surfaces should be considered self-consistently for understanding the change of magnetic structure. Such changes include changes in the shape and size of magnetic islands, and the distribution of stochastic fields around the magnetic islands and at the plasma boundary, which plays an important role for plasma-wall interactions.

The measurement of internal magnetic fluctuation is important for the study of transport in tokamak plasmas. The runaway electron transport induced by the sawtooth crash can be used to obtain the internal magnetic fluctuation. Inversed sawtooth-like activities on hard x-ray (HXR) fluxes following sawtooth activities were observed after the application of electrode biasing on J-TEXT tokamak. The runaway diffusion coefficient Dr is deduced to be about 30 m2/s according to the time delay of HXR flux peaks to the sawtooth crashes. The averaged value of normalized magnetic fluctuation in the discharges with electrode biasing was increased to the order of 1 × 10−4.

In this paper, the toroidal field of a tokamak produced by separate coils has been calculated from the basic electrodynamic theory. As an example, the toroidal magnetic field (R) in TEXT-U tokamak is plotted, and the curve is fitted well to the analysis formula (R) = 0R0/R with a precision of several percents.

Structures of strong shock waves in dense plasmas are investigated via the steady-state Navier–Stokes equations and Poisson equation. The structures from fluid simulation agree with the ones from kinetic simulation. The effects of the transport coefficients on the structures are analysed. The enhancements of the electronic heat conduction and ionic viscosity both will broaden the width of the shock fronts, and decrease the electric fields in the fronts.

Instability of a planar shock front perturbed by a corrugated interface is analyzed, where the perturbation wavelength is along the shock front plane. The presented analysis involves the effects of the features on the shock front, which is different from a general method presented by D'yakov and Kontorovich, where the shock front is taken as an infinitely discontinuity. The growth rate of the instability of the perturbed shock front is obtained and compared with the growth rate of the Rayleigh—Taylor instability (RTI) of an interface, on which the density gradient and the initial conditions are similar to the perturbed shock front. The analysis and comparisons of the growth rate of the instability indicate that the features of the shock front should be considered seriously in the shock interface interactions.

Abstract A heterodyne collective scattering system has been designed and developed to investigate the turbulent transport of core plasma on J-TEXT. A dual-HCN laser which consists of two separately pumped HCN gas lasers at 337 μ m has been developed as the laser source of the scattering system. The intermediate frequency (IF) is ∼1 MHz when there is a 4 μ m cavity length difference and capable to maintain stability more than 5 h without manual operation. Detection channels at three different angles (2 ≤ k ⊥ ≤ 12 cm −1 ) have been installed with Schottky barrier diode mixers of 893 GHz. The sampling frequency of the acquisition system is 6 MHz to observe low-frequency density fluctuations. Initial experimental results have been detected and more results can be expected in future experiments.

Abstract The acceleration of the magnetic island rotation by the modulated resonant magnetic perturbation (MRMP) has been studied in J-TEXT tokamak experiments. After applying the MRMP, the phase difference between the tearing mode (TM) and MRMP, Δ ξ , oscillated near the effective phase difference, Δ ξ eff , which was defined as the time averaged value of Δ ξ . When the Δ ξ eff was closed to the— π /2, the MRMP only contributed an accelerating torque on the TM. As the result, the TM rotation frequency was increased by a few kilohertz for the optimized relative phase by small RMPs of the order of 10 −5 of the toroidal field and the locked mode induced disruption was avoided. It is found that the TM rotation could be increased to a higher frequency by applying a stronger MRMP. There is a negative sinusoidal relationship between TM frequency and Δ ξ eff .

Abstract The three-dimensional (3D) magnetic configuration system in the J-TEXT tokamak has featured in many experimental studies. The system mainly consists of three subsystems: the static resonant magnetic perturbation (SRMP) system, the dynamic resonant magnetic perturbation (DRMP) system and the helical coil system. The SRMP coil system consist of two kinds of coils, i.e. three six-loop coils and two five-loop coils. It can suppress tearing modes with a moderate strength, and may also cause mode locking with larger amplitude. The DRMP coil system consists of 12 single-turn saddle coils (DRMP1) and 12 double-turn saddle coils (DRMP2). Its magnetic field can be rotated at a few kHz, leading to either acceleration or deceleration of the tearing mode velocity and the plasma rotation. The helical coil system consists of two closed coils, and is currently under construction to provide external rotational transform in J-TEXT. The 3D magnetic configuration system can suppress tearing modes, preventing and avoiding the occurrence of major disruption.

Abstract The generation of runaway electrons (REs) during disruptions is a key issue for the safe operation of large tokamaks. For better design, a reliable scenario to suppress RE generation and for the investigation of RE generation during disruptions is highly essential. On J-TEXT, RE generation is strongly dependent on the pre-disruption electron density, toroidal magnetic fields ( B T ) and magnetic perturbations. RE generation can be avoided in discharges with a low B T or a high electron density. For discharges with a high B T , a high electron density threshold is required to suppress RE generation. However, this threshold decreases with the application of resonant magnetic perturbations (RMP) which is applied before the thermal quench. The enhancement of magnetic perturbation increases the RE loss during disruptions, leading to robust runaway suppression in the discharges with a relatively low electron density. The electron density threshold required for RE suppression reduces with the increase of RMP strength and the m / n = 2/1 mode RMP is more efficient than the m / n = 3/1 mode RMP for the reduction of density threshold, where m and n are the poloidal and toroidal mode numbers, respectively. The NIMROD simulation is applied to investigate the transport of REs during disruptions, which indicates that the 2/1 mode RMP can create stronger magnetic perturbations during a disruption, resulting in a high loss ratio of RE seeds. All results provide evidence of the significant effect of RMP mode and amplitude on the electron density threshold for RE generation, which might give an insight into future large reactor tokamak operation with high electron densities.

The effect of externally applied resonant magnetic perturbation (RMP) on carbon impurity behavior is investigated in the J-TEXT tokamak. It is found that the m/n = 3/1 islands have an impurity screening effect, which becomes obvious while the edge magnetic island is generated via RMP field penetration. The impurity screening effect shows a dependence on the RMP phase with the field penetration, which is strongest if the O point of the magnetic island is near the low-field-side (LFS) limiter plate. By combining a methane injection experimental study and STRAHL impurity transport analysis, we found that the variation of the impurity transport dominates the impurity screening effect. The impurity diffusion at the inner plasma region (r/a < 0.8) is enhanced with a significant increase in outward convection velocity at the edge region in the case of the magnetic island's O point near the LFS limiter plate. The impurity transport coefficient varies by a much lower level for the case with the magnetic island's X point near the LFS limiter plate. The interaction of the magnetic island and the LFS limiter plate is thought to contribute to the impurity transport variation with the dependence on the RMP phase. A possible reason is the interaction between the magnetic island and the LFS limiter.

We have tested recent suggestion of anomalous sensitivity in highly excited quantum many-body systems. Two independent measurements of cross sections for the 19 F + 93 Nb strongly dissipative heavy-ion collisions have been performed at incident energies from 102 to 108 MeV in steps of 250 keV. In the two measurements we used different, independently prepared, 93 Nb target foils with nominally the same thickness. The data indicate statistically significant non-reproducibility of the energy oscillating yields in the two measurements. The observed non-reproducibility is consistent with recent theoretical arguments on spontaneous correlation, slow phase randomization and chaos in highly excited complex quantum systems.

In this paper, derived from Maxwell and fluid equations of plasmas, unified nonlinear wave equations are used to describe the parametric decay instability (PDI) in magnetized plasmas, and in view of mode-coupling, we can obtain all the possible PDI channels. By solving the nonlinear equations with a mode-coupling method, we obtain the growth rate of the PDI, of which all of the three waves are ordinary mode (O-mode) or extraordinary mode (X-mode) wave. Under the dipole approximation, an explicit formula of the growth rate of the X-mode and the condition of the equilibrium density scale are obtained. According to the existence conditions of three X-mode waves, this kind of instability might exist in ECRH with the second harmonic X-mode wave.

Electron cyclotron extraordinary-wave decay into two upper hybrid waves in an inhomogeneous magnetized plasma is studied theoretically and numerically. The analytic expressions for the local coupling constant and convective amplification factor of two-plasmon decay (TPD) are obtained. It shows that the TPD threshold intensity is very high (about 15 MW) with the linear density profile in a tokamak plasma. However, within the nonmonotonicity density profile, the power threshold of TPD can significantly be reduced more than one order of magnitude (about 1.2MW). The comparison of the numerical and simulation results of the local coupling constant shows that they agree well with each other.

为满足学术型和应用型研究生以及交叉学科研究生培养的需要，对我校研究生全校公选课“表面物理化学”进行了教学改革和实践。建立了满足研究生分类培养的课程内容体系，基于不同类型研究生的学习需求和本科基础来组织实施教学和考核，教学中注重教学与科研相结合、理论与实践相统一，使课程适应两类研究生和交叉学科研究生人才培养的需要。