Modeling of beam ions loss and slowing down with Coulomb collisions in EAST

This paper uses the implicit Monte–Carlo full-orbit-following parallel program ISSDE to calculate the prompt loss and slowing down process of neutral beam injection(NBI)-generated fast ions due to Coulomb collisions in the equilibrium configuration of Experimental Advanced Superconducting Tokamak(EAST).This program is based on the weak equivalence of the Fokker–Planck equation under Rosenbluth Mac Donald Judd(RMJ)potential and Stratonovich stochastic differential equation(SDE).The prompt loss with the LCFS boundary and the first wall(FW)boundary of the two co-current neutral injection beams are studied.Simulation results indicate that the loss behavior of fast ions using the FW boundary is very different from that of the LCFS boundary,especially for fast ions with a large gyration radius.According to our calculations,about 5.11%of fast ions generated by perpendicular injection drift out of the LCFS and then return inside the LCFS to be captured by the magnetic field.The prompt loss ratio of fast ions and the ratio of orbital types depend on the initial distribution of fast ions in the Pζ–Λspace.Under the effect of Coulomb collisions,the pitch-angle scattering and stochastic diffusion happens,which will cause more fast ion loss.For short time scales,among the particles lost due to collisions,the fraction of banana ions reaches 92.31%in the perpendicular beam and 58.65%in the tangential beam when the fraction of banana ions in the tangential beam is 3.4%of the total ions,which means that the effect of Coulomb collisions on banana fast ions is more significant.For long time scales,the additional fast ion loss caused by Coulomb collisions of tangential and perpendicular beams accounted for 16.21%and 25.05%of the total particles,respectively.We have also investigated the slowing down process of NBI fast ions.

Numerical study of low-frequency discharge oscillations in a 5kW Hall thruster

A two-dimensional particle-in-cell plasma model is built in the R-Z plane to investigate the low- frequency plasma oscillations in the discharge channel of a 5 kW LHT-140 Hall thruster. In addition to the elastic, excitation, and ionization collisions between neutral atoms and electrons, the Coulomb collisions between electrons and electrons and between electrons and ions are analyzed. The sheath characteristic distortion is also corrected. Simulation results indicate the capability of the built model to reproduce the low-frequency oscillation with high accuracy. The oscillations of the discharge current and ion density produced by the model are consistent with the existing conclusions. The model predicts a frequency that is consistent with that calculated by the zero-dimensional theoretical model.

Dynamics of the inner electron radiation belt:A review

The Van Allen radiation belts are an extraordinary science discovery in the Earth magnetosphere and consist of two electron belts.The inner Van Allen belt contains electrons of 10s to 100s keV;the outer belt consists mainly of 0.1-10 MeV electrons.Their dynamics have been analyzed for decades.The newly-launched Van Allen Probes provide unprecedented opportunities to investigate the inner belt more thoroughly.Data from this advanced mission have allowed scientists to demonstrate that the inner belt was formed not only through inward transport of outer belt electrons but Cosmic Ray Albedo Neutron Decay(CRAND)has also played an important role.In addition,the inner belt electrons show energy-dependent variations and present“zebra stripe”structures in the energy spectrum.At the same time,scientists have further confirmed that the electrons in the inner radiation belt get lost through coulomb collision and wave-particle interaction.Despite these advances,important questions remain unanswered and require further investigation.The launch of Macao Science Satellite-1 mission,with its low inclination angle and low altitude orbit,will provide advanced radiation belt data for better understanding of the structure and dynamics of the inner electron radiation belt.

New method for oblique impact dynamics research of a flexible beam with large overall motion considering impact friction force

A flexible beam with large overall rotating motion impacting with a rigid slope is studied in this paper. The tangential friction force caused by the oblique impact is analyzed. The tangential motion of the system is divided into a stick state and a slip state. The contact constraint model and Coulomb friction model are used respectively to deal with the two states. Based on this hybrid modeling method, dynamic equations of the system, which include all states（before, during, and after the collision）are obtained. Simulation results of a concrete example are compared with the results obtained from two other models： a nontangential friction model and a modified Coulomb model. Differences in the results from the three models are discussed. The tangential friction force cannot be ignored when an oblique impact occurs. In addition, the results obtained from the model proposed in this paper are more consistent with real movement.

A Gas-Kinetic Scheme for Collisional Vlasov-Poisson Equations in Cylindrical Coordinates

Many configurations in plasma physics are axisymmetric,it will be more convenient to depict them in cylindrical coordinates compared with Cartesian coordinates.In this paper,a gas-kinetic scheme for collisional Vlasov-Poisson equations in cylindrical coordinates is proposed,our algorithm is based on Strang splitting.The equation is divided into two parts,one is the kinetic transport-collision part solved by multiscale gas-kinetic scheme,and the other is the acceleration part solved by a Runge-Kutta solver.The asymptotic preserving property of whole algorithm is proved and it’s applied on the study of charge separation problem in plasma edge and 1D Z-pinch configuration.Numerical results show it can capture the process fromnon-equilibrium to equilibrium state by Coulomb collisions,and numerical accuracy is obtained.

Modeling of Long-Range Intra- and Inter-Species Charged Particle Collisions for PIC Simulations

In this paper we present the modelling of elastic intra-species electron-electron and inter-species electron-ion scattering in a plasma on the basis of the FokkerPlanck collision operator.Taking into account the equivalence of this operator with a stochastic differential equation,we propose a Particle-in-Cell based approach for the numerical solution of the Fokker-Planck collision term.As we will see,the introduced numerical concept allows the simulation of the collisional relaxation process in a fully self-consistent fashion.

Random Batch Particle Methods for the Homogeneous Landau Equation

We consider in this paper randombatch particlemethods for efficiently solving the homogeneous Landau equation in plasma physics.The methods are stochastic variations of the particle methods proposed by Carrillo et al.[J.Comput.Phys.:X 7:100066,2020]using the random batch strategy.The collisions only take place inside the small but randomly selected batches so that the computational cost is reduced to O(N)per time step.Meanwhile,our methods can preserve the conservation of mass,momentum,energy and the decay of entropy.Several numerical examples are performed to validate our methods.

Weibel Instability Growth Rate in Magnetized Plasmas with Quasi-Relativistic Distribution Function

The mechanism of the Weibel instability is investigated for dense magnetized plasmas. As we know, due to the electron velocity distribution, the Coulomb collision effect of electron-ion and the relativistic properties play an important role in such study. In this study an analytical expression for the growth rate and the condition of restricting the Weibel instability are derived for low-frequency limit. These calculations are done for the oscillation frequency dependence on the electron cyclotron frequency. It is shown that, the relativistic properties of the particle lead to increasing the growth rate of the instability. On the other hand the collision effects and background magnetic field try to decrease the growth rate by decreasing the temperature anisotropy and restricting the particles movement.