Calculation of Electron Swarm Parameters of SF_6/N_2 in a Uniform Field Using an Improved Monte Carlo Collision Simulation Method

The electron swarm parameters of SF6/N2 are calculated in the present study using an improved Monte Carlo collision simulation method （MCS）. And some improved sampling techniques are also adopted. The simulation results show that the improved simulation method can provide more accurate results.

Analysis of application range of simplified models for field to thermo-field to thermionic emission processes from the cathode

Electron emission plays a dominant role in plasma-cathode interactions and is a key factor in many plasma phenomena and industrial applications.It is necessary to illustrate the various electron emission mechanisms and the corresponding applicable description models to evaluate their impacts on discharge properties.In this study,detailed expressions of the simplified formulas valid for field emission to thermo-field emission to thermionic emission typically used in the numerical simulation are proposed,and the corresponding application ranges are determined in the framework of the Murphy-Good theory,which is commonly regarded as the general model and to be accurate in the full range of conditions of the validity of the theory.Dimensionless parameterization was used to evaluate the emission current density of the Murphy-Good formula,and a deviation factor was defined to obtain the application ranges for different work functions(2.5‒5 eV),cathode temperatures(300‒6000 K),and emitted electric fields(10^(5) to 10^(10) V·m^(-1)).The deviation factor was shown to be a nonmonotonic function of the three parameters.A comparative study of particle number densities in atmospheric gas discharge with a tungsten cathode was performed based on the one-dimensional implicit particle-in-cell(PIC)with the Monte Carlo collision(MCC)method according to the aforementioned application ranges.It was found that small differences in emission current density can lead to variations in the distributions of particle number density due to changes in the collisional environment.This study provides a theoretical basis for selecting emission models for subsequent numerical simulations.

Particle-in-Cell with Monte CarloCollisions Gun Code Simulations of a Surface-Conversion H^(−)Ion Source

We present an extended update on the status of a particle-in-cellwithMonte Carlo collisions(PIC-MCC)gun code developed at LosAlamos for the study of surfaceconverter H−ion sources.The programis fully kinetic.Some of the program’s features include:solution of arbitrary electrostatic and magnetostatic fields in an axisymmetric(r,z)geometry to describe the self-consistent time evolution of a plasma;simulation of a multi-species(e^(−),H^(+),H^(+)_(2),H^(+)_(3),H^(−))plasma discharge from a neutral hydrogen gas and filament-originated seed electrons;full 2-dimensional(r,z)3-velocity(v_(r),v_(z),vφ)dynamics for all species;detailed collision physics between charged particles and neutrals and the ability to represent multiple smooth(not stair-stepped)electrodes of arbitrary shape and voltage whose surfaces may be secondary-particle emitters(H^(−)and e^(−)).The status of this development is discussed in terms of its physics content and current implementation details.

Particle Simulation of Three-Grid ECR Ion Thruster Optics and Erosion Prediction

Ion optics is a critical component of ion thrusters. A two-dimensional axisymmetric model is developed to study the characteristics of three-grid electron cyclotron resonance ion thruster optics. The code is based on a particle-in-cell combined with the Monte Carlo collision method to simulate ion dynamics and charge-exchange processes in the grid region. The simulation results show that the mode can give a reasonable estimate of the physics characteristics of the ion optics. The design of the ion optics satisfies the requirement of preventing electron backstreaming. Charge-exchange ions can cause damage to the grids, especially to the accelerator grid. ＇Barrel＇ erosion can increase the accelerator grid aperture radius at a rate of 1.91~ 10-11 m/s, while the decelerator grid plays an important role in reducing ＇pits-and-grooves＇ erosion.

Ion-focused propagation of a relativistic electron beam in the self-generated plasma in atmosphere

It is known that ion-focused regime(IFR)can effectively suppress expansion of a relativistic electron beam(REB).Using the particle-in-cell Monte Carlo collision(PIC-MCC)method,we numerically investigate the propagation of an REB in neutral gas.The results demonstrate that the beam body is charge neutralization and a stable IFR can be established.As a result,the beam transverse dimensions and longitudinal velocities keep close to the initial parameters.We also calculate the charge and current neutralization factors of the REB.Combined with envelope equations,we obtain the variations of beam envelopes,which agree well with the PIC simulations.However,both the energy loss and instabilities of the REB may lead to a low transport efficiency during long-range propagation.It is proved that decreasing the initial pulse length of the REB can avoid the influence of electron avalanche.Using parts of REB pulses to build a long-distance IFR in advance can improve the beam quality of subsequent pulses.Further,a long-distance IFR may contribute to the implementation of long-range propagation of the REB in space environment.

Numerical simulation of the start-up process of a miniature ion thruster

A particle-in-cell Monte Carlo collision model of a discharge chamber is established to investigate the start-up process of a miniature ion thruster.We present the discharge characteristics at different stages(the initial stage,development stage,and stable stage)according to the trend of the discharge current with time.The discharge current is the sum of the sidewall current and the backplate current.During the start-up process,the sidewall current lags behind the backplate current.The variation and distribution characteristics of the discharge current over time are determined by the electron density distribution and electric potential distribution.

The influence of weak transverse magnetic field on plasma dissipation process in the post-arc phase in a vacuum interrupter

Transverse magnetic field(TMF)contacts and applying external TMF are often adopted for reducing the ablation of the contact surface,but TMF will also affect the breaking performance of the vacuum interrupters.In this work,we investigated the influence of weak TMF on the expansion of the plasma in the post-arc phase with one-dimensional implicit particle-in-cell/Monte Carlo collision model,and we added an external circuit to the model to ensure the correctness of the calculation results.We simulated multiple magnetic field strengths(<30 mT),compared the plasma expansion process with the TMF strengths of 0 mT and 10 mT,and discussed the influence of metal vapor density on the insulation performance recovery of the vacuum interrupter.From the results,applying TMF with strength below 5 mT has little effect on the expansion of the plasma,and the TMF can increase the plasma density which improve the flow capacity of vacuum circuit breakers when the magnetic field above 10 mT,which is because the particles become more difficult to leave the discharge area under the force of the magnetic field.In general,we find that weak external TMF may adversely affect the breaking performance of the vacuum circuit breakers.

Microwave propagation with the gas breakdown

By combining the microwave propagation theory and the gas breakdown theory, the microwave propagation with the gas breakdown is analyzed theoretically. Particle-in-cell/Monte Carlo collision （PIC/MCC） simulations are carried out to verify the theoretical results. Based on this theoretical method, the breakdown phenomenon of the pulse microwave is analyzed. The results show that the product values of the initial electron density and the propagation length are the criterion to distinguish the pulse peak decline breakdown and the pulse width reduction breakdown. Furthermore, the energy transmission is also studied, which shows that the total output energy is approximately independent of the input electric field if the electric field is not extremely large.

Three-dimensional PIC/MCC simulation of electron deposition in JAEA 10 A ion sources

A systematic research on the electron deposition process in the JAEA 10 A ion source is carried out by using a particle-in-cell/Monte Carlo collision simulation, which is based on a full three-dimensional self-developed code. Two parts are studied. One is the space and energy distribution of fast and slow electrons, the other is the vibration excitation collisions between electrons and hydrogen moleculars. The results show that the inhomogeneity of electrons comes from the Y direction drift of the fast electrons （Te ≥25 eV） due to the action of the magnetic fields. This drift also increases the number of vibration excitation collisions in the -Y direction, and results in the increase of Ha in the -Y direction, eventually leading to the -Y drift of H^-. It explains the spatial non-uniformity in the JAEA 10 A ion source.

Monte Carlo Simulations of Elastic Scattering with Applications to DC and High Power Pulsed Magnetron Sputtering for Ti3_(S)iC_(2)

We simulate the particle transport in a thin film deposition process made by PVD(physical vapor deposition)and present several models for projectile and target collisions in order to compute the mean free path and the differential cross section(angular distribution of scattered projectiles)of the scattering process.A detailed description of collision models is of the highest importance in Monte Carlo simulations of high power impulse magnetron sputtering and DC sputtering.We derive an equation for the mean free path for arbitrary interactions(cross sections)that includes the relative velocity between the particles.We apply our results to two major interaction models:hard sphere interaction&screened Coulomb interaction.Both types of interaction separate DC sputtering from HIPIMS.