A GPU-based general numerical framework for plasma simulations in terms of microscopic kinetic equations with full collision terms

We have proposed a general numerical framework for plasma simulations on graphics processing unit clusters based on microscopic kinetic equations with full collision terms.Our numerical algorithm consistently deals with both long-range(classical forces in the Vlasov term)and short-range(quantum processes in the collision term)interactions.Providing the relevant particle masses,charges and types(classical,fermionic or bosonic),as well as the external forces and the matrix elements(in the collisional integral),the algorithm consistently solves the coupled multi-particle kinetic equations.Currently,the framework is being tested and applied in the field of relativistic heavy-ion collisions;extensions to other plasma systems are straightforward.Our framework is a potential and competitive numerical platform for consistent plasma simulations.

Plasma Simulation of Dielectric-lined Multiwave Cerenkov Generators Producing High Power Millimeter Waves

This paper presents the concept of a Dielectric-lined Multiwave Cerenkov Generator producing high power millimeter waves, which has been investigated with a two and onehalf dimensional electromagnetic relativistic Particle-in-Cell (PIC) plasma simulation code. Themodified device can operate in a lower diode-voltage regime with much higher radiation efficiencyand slight downshift of operation frequency. There exist the optima for the permittivity of thedielectric liner and for the magnitude of the guiding magnetic field. The required intensity of theguiding field is reduced by the introduction of the liner. The enhanced propagation of the electronbeam is studied in the presence of the liner.

A Volume-Weight ing Cloud-in-Cell Model for Particle Simulation of Axially Symmetric Plasmas

A volume-weighting cloud-in-cell (VW-CIC) model is developed to implement the particle-in-cell (PIC) simulation in axially symmetric systems. This model gives a first-order accuracy in the cylindrical system, and it is incorporated into a PIC code. A planar diode with a finite-radius circular emitter is simulated with the code. The simulation results show that the VW-CIC model has a better accuracy and a lower noise than the conventional area-weighting cloud-in-cell (AW-CIC) model, especially on those points near the axis. The two-dimensional (2-D) space-charge-limited current density obtained from VW-CIC model is in better agreement with Lau’s analytical result. This model is more suitable for 2.5-D PIC simulation of axially symmetric plasmas.

Monte Carlo simulation of electron beam air plasma characteristics

A high-energy electron beam generator is used to generate a plasma in atmosphere. Based on a Monte Carlo toolkit named GEANT4, a model including complete physics processes is established to simulate the passage of the electron beam in air. Based on the model, the characteristics of the electron beam air plasma are calculated. The energy distribution of beam electrons （BEs） indicates that high-energy electrons almost reside in the centre region of the beam, but low-energy electrons always live in the fringe area. The energy deposition is calculated in two cases, i.e., with and without secondary electrons （SEs）. Analysis indicates that the energy deposition of SEs accounts for a large part of the total energy deposition. The results of the energy spectrum show that the electrons in the inlet layer of the low-pressure chamber （LPC） are monoenergetic, but the energy spectrum of the electrons in the outlet layer is not pure. The SEs are largely generated at the outlet of the LPC. Moreover, both the energy distribution of BEs and the magnitude of the density of SEs are closely related to the pressure of LPC. Thus, a conclusion is drawn that a low magnitude of LPC pressure is helpful for reducing the energy loss in the LPC and also useful for greatly increasing the secondary electron density in dense air.

Numerical Simulation of the Self-Heating Effect Induced by Electron Beam Plasma in Atmosphere

For exploiting advantages of electron beam air plasma in some unusual applications, a Monte Carlo （MC） model coupled with heat transfer model is established to simulate the characteristics of electron beam air plasma by considering the self-heating effect. Based on the model, the electron beam induced temperature field and the related plasma properties are investigated. The results indicate that a nonuniform temperature field is formed in the electron beam plasma region and the average temperature is of the order of 600 K. Moreover, much larger volume pear-shaped electron beam plasma is produced in hot state rather than in cold state. The beam ranges can, with beam energies of 75 keV and 80 keV, exceed 1.0 m and 1.2 m in air at pressure of 100 torr, respectively. Finally, a well verified formula is obtained for calculating the range of high energy electron beam in atmosphere.

A numerical simulation of the backward Raman amplifying in plasma

This paper describe a numerical simulation method for the interaction between laser pulses and low density plasmas based on hydrodynamic approximation. We investigate Backward Raman Amplifying （BRA） experiments and their variants. The numerical results are in good agreement with experiments.

Magnetohydrodynamics with Implicit Plasma Simulation

We considerwhether implicit simulation techniques can be extended in time and space scales to magnetohydrodynamics without any change but the addition of collisions.Our goal is to couple fluid and kinetic models together for application to multi-scale problems.Within a simulation framework,transition from one model to the other would occur not by a change of algorithm,but by a change of parameters.This would greatly simplify the coupling.Along the way,we have found new ways to impose consistent boundary conditions for the field solver that result in charge and energy conservation,and establish that numerically-generated stochastic heating is the problem to overcome.For an MHD-like problem,collisions are clearly necessary to reduce the stochastic heating.Without collisions,the heating rate is unacceptable.With collisions,the heating rate is significantly reduced.

Features of transport induced by ion-driven trapped-electron modes in tokamak plasmas

As an obstacle in high-performance discharge in future fusion devices,disruptions may do great damages to the reactors through causing strong electromagnetic forces,heat loads and so on.The drift waves in tokamak are illustrated to play essential roles in the confinement performance as well.Depending on the plasma parameters and mode perpendicular wavelength,the mode phase velocity is either in the direction of electron diamagnetic velocity(namely,typical trapped electron mode)or in the direction of ion diamagnetic velocity(namely,the ubiquitous mode).Among them,the ubiquitous mode is directly investigated using gyro-fluid simulation associating with gyro-fluid equations for drift waves in tokamak plasmas.The ubiquitous mode is charactered by the short wavelength and propagates in ion diamagnetic direction.It is suggested that the density gradient is essential for the occurrence of the ubiquitous mode.However,the ubiquitous mode is also influenced by the temperature gradients and other plasma parameters including the magnetic shear and the fraction of trapped electrons.Furthermore,the ubiquitous mode may play essential roles in the turbulent transport.Meanwhile,the relevant parameters are scanned using a great number of electrostatic gyro-fluid simulations.The stability map is taken into consideration with the micro-instabilities contributing to the turbulent transport.The stability valley of the growth rates occurs with the assumption of the normalized temperature gradient equaling to the normalized density gradient.

Dual-Channel Communication of Column Plasma Antenna Excited by a Surface Wave——Actualization and Simulation of Radiation Pattern

Along with the introduction of the concept of dual-channel communication,we utilized the finite-difference time-domain（FDTD） method to simulate and measure the radiation pattern under certain plasma densities and plasma collision frequencies.Results show that under certain settings,the radiation pattern of a plasma antenna resembles that of a metallic antenna.In contrast to a metallic antenna,a plasma antenna possesses other functionalities,such as dynamic reconfiguration and digital controllability.The data from simulation are similar to the measurement results,indicating that column plasma antenna can realize dual-channel communication.This work confirms the viability of realizing dual-channel communication by column plasma antenna,which adds a new but promising method for modern intelligent communication.

Diagnostic of capacitively coupled radio frequency plasma from electrical discharge characteristics：comparison with optical emission spectroscopy and fluid model simulation

The capacitively coupled radio frequency（CCRF）plasma has been widely used in various fields.In some cases,it requires us to estimate the range of key plasma parameters simpler and quicker in order to understand the behavior in plasma.In this paper,a glass vacuum chamber and a pair of plate electrodes were designed and fabricated,using 13.56 MHz radio frequency（RF）discharge technology to ionize the working gas of Ar.This discharge was mathematically described with equivalent circuit model.The discharge voltage and current of the plasma were measured atdifferent pressures and different powers.Based on the capacitively coupled homogeneous discharge model,the equivalent circuit and the analytical formula were established.The plasma density and temperature were calculated by using the equivalent impedance principle and energy balance equation.The experimental results show that when RF discharge power is 50–300 W and pressure is 25–250 Pa,the average electron temperature is about 1.7–2.1 e V and the average electron density is about 0.5？×10^17–3.6？×10^17m^-3.Agreement was found when the results were compared to those given by optical emission spectroscopy and COMSOL simulation.

Numercial Simulation for Plasma Stream of ECR Plasma Source

Using a Monte Carlo method and resonable data in our experiment device, we simulate the plasma stream of ECR plasma source on condition that the plasma is collisionless. We can get the distribution of ion density and the effect of magnetic field on the plasma along the divergent magnetic field. The research is beneficial to plasma processing applications.

Simulation of Plasma Disruptions for HL-2M with the DINA Code

Plasma disruption is often an unavoidable aspect of tokamak operations. It may cause severe damage to in-vessel components such as the vacuum vessel conductors, the first wall and the divertor target plates. Two types of disruption, the hot-plasma vertical displacement event and the major disruption with a cold-plasma vertical displacement event, are simulated by the DINA code for HL-2M. The time evolutions of the plasma current, the halo current, the magnetic axis, the minor radius, the elongation as well as the electromagnetic force and eddy currents on the vacuum vessel during the thermal quench and the current quench are investigated. By comparing the electromagnetic forces before and after the disruption, we find that the disruption causes great damage to the vacuum vessel conductors. In addition, the hot-plasma vertical displacement event is more dangerous than the major disruption with the cold-plasma vertical displacement event.

Simulations of High-Current Plasma Beam by Continuum and Statistical Mechanical Models

The paper builds the high-current plasma beams model under different dimensions (1D, 2D, and 3D) by continuum (magnetohydrodynamics MHD) and statistical (Monte Carlo MC) mechanics under conditions of low pressures (10-3 Pa). After detailed presentation of the model, two methods firstly have been analyzed in terms of plasma beam properties. Then, we compare the simulation results of MHD numerical simulation with MC stochastic particles simulation. Finally, through further analysis, it is demonstrated that integrated hybrid MHD and MC method (IMHDMC) provides an innovative practical tool to capture essential properties of high-current plasma beams.

Simulation of nonlinear behavior in an electron cyclotron resonance plasma

Some nonlinear behavior in electron cyclotron resonance plasma was investigated using a two-dimension hybrid-mode with self-consistent microwave absorption. The saturation,oscillations of plasma parameters (plasma density, potential, electron temperature) versus operating conditions (pressure, power) are discussed. Our simulation results are consistent qualitatively with many experimental measurements.

Electron characteristics and dynamics in sub-millimeter pulsed atmospheric dielectric barrier discharge

The discharge characteristics and mechanism of sub-millimeter pulsed dielectric barrier discharge in atmosphericpressure helium are investigated experimentally and theoretically, demonstrating that when the discharge gap distance is reduced from 1.00 mm to 0.20 mm, the discharge ignition time is reduced to approximately 40 ns and discharge intensity is enhanced in terms of the discharge optical emission intensity and density of the plasma species,(energetic electrons with energy above 8.40 e V). The simulated results show that as the discharge gap distance is further reduced to 0.10 mm,the number of energetic electrons decreases, which is attributable to the contraction of plasma bulk regime and reduction of electron density in the discharge bulk. Conversely, the proportion of energetic electrons to the total electrons in the discharge monotonically increases as the discharge gap distance is reduced from 1.00 mm to 0.10 mm. It is proposed that a gap distance of 0.12 mm is optimal to achieve a high concentration and proportion of energetic electrons in sub-millimeter pulsed atmosphere dielectric barrier discharge.

Backward Raman amplification in plasmas with chirped wideband pump and seed pulses

Chirped wideband pump and seed pulses are usually considered for backward Raman amplification（BRA） in plasmas to achieve an extremely high-power laser pulse. However, current theoretical models only contain either a chirped pump or a chirped seed. In this paper, modified three-wave coupling equations are proposed for the BRA in the plasmas with both chirped wideband pump and seed. The simulation results can more precisely describe the experiments, such as the Princeton University experiment. The optimized chirp and bandwidth are determined based on the simulation to enhance the output intensity and efficiency.

A Simple Model for the Calculation of Plasma Impedance in Atmospheric Radio Frequency Discharges

In atmospheric radio-frequency （rf） discharges, the plasma parameters, such as electron density, sheath thickness and sheath voltage, are not easy to be probed experimentally, while the electrical characteristics, such as impedance, resistance and reactance, are relatively convenient to be measured. In this paper we presented a simple theoretical model derived from the fluid description of generated plasmas without considering the circuit model, to investigate the relationship between the plasma impedance and plasma parameters. By introducing a relaxation frequency, the plasma impedance could be predicted by formulas presented in this study, and the mean electron density and sheath thickness can also be calculated from the measured or simulated impedance and reactance, respectively.

Transport Simulation of ECRH H-Mode Experiments on HL-2A Tokamak

Transport simulation of ECRH H-mode experiments on HL-2A tokamak is carried out using ONETWO code, the GLF23 and PEDESTAL models, along with TORAY code for ECRH. It is found that the initial electron and ion temperature profiles affect L-H transition significantly, and larger initial temperature gradient at the edge plasma benefits the transition. The simulation results show that it is possible to achieve ECRH H-mode with appropriate initial electron and ion temperature profiles under present discharge conditions on HL-2A tokamak. In addition, the pedestal density, electron temperature and pedestal width are predicted, and the evolutions of electron and ion temperature profile are calculated.

Numerical study of the effect of water content on OH production in a pulsed-dc atmospheric pressure helium–air plasma jet

A numerical study of the effect of water content on OH production in a pulsed-dc atmospheric pressure helium-air plasma jet is presented. The generation and loss mechanisms of the OH radicals in a positive half-cycle of the applied voltage are studied and discussed. It is found that the peak OH density increases with water content in air （varying from 0% to 1%） and reaches 6.3 x 10^18 m-3 when the water content is 1%. Besides, as the water content increases from 0.01% to 1%, the space-averaged reaction rate of three-body recombination increases dramatically and is comparable to those of main OH generation reactions.

Simulation of radio-frequency atmospheric pressure glow discharge in γ mode

The existence of two diffe1：ent discharge modes has been verified in an rf （radio-frequency） atmospheric pressure glow discharge （APGD） by Shi [J. Appl. Phys. 97, 023306 （2005）]. In the first mode, referred to as a mode, the discharge current density is relatively low and the bulk plasma electrons acquire the energy due to the sheath expansion. In the second mode, termed γ mode, the discharge current density is relatively high, the secondary electrons emitted by cathodc under ion bombardment in the cathode sheath region play an important role in sustaining the discharge. In this paper, a one-dimensional self-consistent fluid model for rf APGDs is used to simulate the discharge mechanisms in the mode in helium discharge between two parallel metallic planar electrodes. The results show that as the applied voltage increases, the discharge current becomes greater and the plasma density correspondingly increases, consequentially the discharge transits from the a mode into the γ mode. The high collisionality of the APGD plasma results in significant drop of discharge potential across the sheath region, and the electron Joule heating and the electron collisional energy loss reach their maxima in the region. The validity of the simulation is checked with the available experimental and numerical data.