Particle Simulation Of Plasmas Research Articles

High order Gauss-Seidel schemes for charged particle dynamics

Gauss-Seidel projection methods are designed for achieving desirable long-term computational efficiency and reliability in micromagnetics simulations. While conventional Gauss-Seidel schemes are explicit, easy to use and furnish a better stability as compared to Euler's method, their order of accuracy is only one. This paper proposes an improved Gauss-Seidel methodology for particle simulations of magnetized plasmas. A novel new class of high order schemes are implemented via composition strategies. The new algorithms acquired are not only explicit and symmetric, but also volume-preserving together with their adjoint schemes. They are highly favorable for long-term computations. The new high order schemes are then utilized for simulating charged particle motions under the Lorentz force. Our experiments indicate a remarkable satisfaction of the energy preservation and angular momentum conservation of the numerical methods in multi-scale plasma dynamics computations.

Efficient evaluation of collisional energy transfer terms for plasma particle simulations

Particle-based simulations, such as in particle-in-cell (PIC) codes, are widely used in plasma physics research. The analysis of particle energy transfers, as described by the second moment of the Boltzmann equation, is often necessary within these simulations. We present computationally efficient, analytically derived equations for evaluating collisional energy transfer terms from simulations using discrete particles. The equations are expressed as a sum over the properties of the discrete particles.

Electrostatic environment near lunar vertical hole: 3D plasma particle simulations

The dayside electrostatic environment near the lunar surface is governed by interactions among the solar wind plasma, photoelectrons, and the charged lunar surface, providing topologically complex boundaries to the plasma. Three-dimensional, particle-in-cell simulations are applied to recently discovered vertical holes on the Moon, which have spatial scales of tens of meters and greater depth-to-diameter ratios than typical impact craters. The vertical wall of the hole introduces a new boundary for both photo and solar wind electrons. The current balance condition established at a hole bottom is altered by the limited solar wind electron penetration into the hole due to loss at the wall and photoelectron current path connecting the hole bottom and wall surfaces. The self-consistent modeling not only reproduces intense differential charging between sunlit and shadowed surfaces, but also reveals the potential difference between sunlit surfaces inside and outside the hole, demonstrating the uniqueness of the near-hole electrostatic environment.

Application of the phase space action principle to finite-size particle plasma simulations in the drift-kinetic approximation

We formulate a finite-size particle numerical model of strongly magnetized plasmas in the drift-kinetic approximation. We use the phase space action as an alternative to previous variational formulations based on Low’s Lagrangian or on a Hamiltonian with a non-canonical Poisson bracket. The useful property of this variational principle is that it allows independent transformations of particle coordinates and velocities, i.e., transformations in particle phase space. With such transformations, a finite degree-of-freedom drift-kinetic action is obtained through time-averaging of the finite degree-of-freedom fully-kinetic action. Variation of the drift-kinetic Lagrangian density leads to a self-consistent, macro-particles and fields numerical model. Since the computational particles utilize only guiding center coordinates and velocities, there is a large computational advantage in the time integration part of the algorithm. Numerical comparison between the time-averaged fully-kinetic and drift-kinetic charge and current, deposited on a computational grid, offers insight into the range of validity of the model. Being based on a variational principle, the algorithm respects the energy conserving property of the underlying continuous system. The development in this paper serves to further emphasize the advantages of using variational approaches in plasma particle simulations.

Plasma particle simulations of wake formation behind a spacecraft with thin wire booms

Double‐probe electric field sensors installed on scientific spacecraft are often deployed using wire booms with radii much less than typical Debye lengths of magnetospheric plasmas (millimeters compared to tens of meters). However, in tenuous and cold‐streaming plasmas seen in the polar cap and lobe regions, the wire booms, electrically grounded at the spacecraft, have a high positive potential due to photoelectron emission and can strongly scatter approaching ions. Consequently, an electrostatic wake formed behind the spacecraft is further enhanced by the presence of the wire booms. We reproduce this process for the case of the Cluster satellite by performing plasma particle‐in‐cell (PIC) simulations, which include the effects of both the spacecraft body and the wire booms in a simultaneous manner. The simulations reveal that the effective thickness of the booms for the Cluster Electric Field and Wave (EFW) instrument is magnified from its real diameter (2.2mm) to several meters, when the spacecraft potential is at tens of volts. Such booms enhance the wake electric field magnitude by a factor of 1.5–2 depending on the spacecraft potential and play a principal role in explaining the in situ Cluster EFW data showing sinusoidal spurious electric fields with about 10mV/m amplitude. The boom effects are quantified by comparing PIC simulations with and without wire booms and also by examining the wake formation for various spacecraft potentials.

A grid-based binary model for coulomb collisions in plasmas

Both binary and grid-based Langevin equations models for Coulomb collisions are used in particle simulation of plasmas. We introduce a variant of the conventional binary collision algorithm for performing Coulomb collisions. In this algorithm particles in a configuration space cell are not paired for collisions. Instead, for every test particle in the cell, a unique field particle is defined by randomly sampling a velocity distribution defined on the grid by accumulating moments of the particle distribution function(s). The test and field particle pair then undergoes a collision using the standard methodology for binary collisions. The performance of the new algorithm is illustrated in example computations and compared to a drag-diffusion Langevin equations algorithm. The grid-based algorithms do not conserve momentum and energy, although with good particle statistics the non-conservation is relatively small. Conservation can be restored after collisions using a shift and scaling of the momenta. The comparative merits of the new algorithm are discussed.

Plasma particle simulations on stray photoelectron current flows around a spacecraft

In tenuous space plasmas, photoelectron flows produce complex current paths among multiple conducting elements of spacecraft, which may influence the current–voltage characteristics of double‐probe electric field sensors. We performed full‐particle simulations on this effect by assuming a sensor configuration that is typical of recent designs like those on Cluster, THEMIS, and BepiColombo/MMO; the spherical probe is separated from a conducting boom by biased electrodes known as the ‘stub’ and the ‘guard’. The assumed bias potential scheme corresponds to that planned for BepiColombo/MMO and is different from those used in the other satellites. The analysis focuses on stray photoelectron currents flowing from these electrodes and a spacecraft body. Photoelectrons approaching the probe are commonly repelled by the guard, the potential of which is strongly biased negatively, and are subsequently affected by the probe potential. Consequently, the photoelectron current magnitude increases with increasing probe potential regardless of their origins, when the probe operates between the plasma and floating spacecraft potentials. The result indicates that both photoelectron currents from the spacecraft body and biased electrodes can be minimized by selecting the probe working potential as close as possible to the plasma potential. We also examine the photoelectron current dependence on the presence or absence of the guard electrode operation and confirm a positive effect of reducing the photoelectron current from the spacecraft. However, negative side effects of the guard operation enhance the photoelectron currents from the stub and guard, when the probe operates nearly at the plasma potential.

Multiscale plasma particle simulation toward development of interplanetary flight system

Multiscale plasma particle simulation toward development of interplanetary flight system

P3M simulations of dusty plasmas

In this paper a review of the work on particle simulations of dusty plasmas using a three-dimensional Particle–Particle Particle–Mesh (P3M) code is presented. The code is applied to study the charging process of micrometre size dust grains confined in low temperature plasmas. This code gives a full-scale self-consistent kinetic description of both the background plasma and the charging of the dust particle. Particles (electrons and ions) are treated kinetically (Particle-in-Cell with Monte Carlo Collisions (PIC-MCC)), which allows us to self-consistently resolve the electrostatic sheath in front of the material wall. In order to accurately resolve the plasma particles' motion close to the dust grain, the PIC technique is supplemented with molecular dynamics (MD), employing the Coulomb potential for the interaction with the dust grain. The plasma particle trajectories are accurately followed in the close vicinity of the dust grain and by this finite-size effects for dust grains are included. Dust grain charging due to absorption of plasma particles and ion drag forces arising from momentum transfer of flowing ions to dust grains are studied.

Issues on beam-plasma instability: early simulations focusing on the development of a compact neutron generator

The first issue on compact neutron generator design is the definition of the plasma generation process following the analysis of the physical plasma state. The plasma features and the nuclear reactions of fusion involved in the operation of the generator, deuterium-deuterium or deuterium-tritium, as well as the system which determines the trajectories of the particles and the target, are decisive to predict the neutron yield from the generator. Hence, the plasma behavior analysis under established conditions becomes an important evidence. This analysis may be done by means of plasma simulation models. Particle simulation of plasmas, employed since 1960s, provides a picture of the general plasma characteristics. Plasma physics is determined in most cases by simple equations, i.e. equations of motion of electrons, ions and neutrals atoms including the effect of collisions and self-consistent electric and magnetic fields. Computer simulation of plasmas comprises two general areas based on kinetic and fluid. While fluids simulation proceeds by solving numerically the magnetohydrodynamic (MHD) equations, assuming approximate transport coefficients, kinetic simulation considers more detailed models of plasma involving particle interactions through the electromagnetic fields. This article is focused on the simulation and analysis of injected beam into a steady state and periodic plasma. The applied calculation model, for this simulation purpose, is referring to an electrostatic one dimension code, based on kinetic simulation, which simulates periodic plasmas illustrating various fundamental considerations of plasma simulation and make it useful in simulations of the beam optic system for neutron generators. The main goal of this research is explore the PIC code reviewing the computational and physics theory necessary to build the structure of the elementary principles intending to introduce concepts of plasma physics and the computational theory. Moreover, foundations of plasma analysis for neutron generators will be stated

Emission of Visible Light by Hot Dense Metals

Author(s): More, R.M. | Abstract: We consider the emission of visible light by hot metal surfaces having uniform and non-uniform temperature distributions and by small droplets of liquid metal. The calculations employ a nonlocal transport theory for light emission, using the Kubo formula to relate microscopic current fluctuations to the dielectric function of the material. We describe a related algorithm for calculating radiation emission in particle simulation of hot fusion plasmas.

Improved Open Boundary Model for Plasma Particle Simulations

An open system one-dimensional electrostatic particle code that adopts the new constant current generator model has been developed. Using this new model, we have been able to study various phenomena at large electron drift velocities, where the original model is not applicable. In this new model, the contribution of the ion flux, which is not considered in the original model, is added into the electric current. By examining the code, we find that the result in a case where the electron drift velocity is smaller than the electron thermal velocity is similar to that of a previous study, which showed double layer creation as a result of ion-acoustic instability. We also present the results of simulations of an electron drift velocity comparable to or larger than the electron thermal velocity.

Radiation in particle simulations

Hot dense radiative (HDR) plasmas common to Inertial Confinement Fusion (ICF) and stellar interiors have high temperature (a few hundred eV to tens of keV), high density (tens to hundreds of g/cc) and high pressure (hundreds of megabars to thousands of gigabars). Typically, such plasmas undergo collisional, radiative, atomic and possibly thermonuclear processes. In order to describe HDR plasmas, computational physicists in ICF and astrophysics use atomic-scale microphysical models implemented in various simulation codes. Experimental validation of the models used to describe HDR plasmas are difficult to perform. Direct Numerical Simulation (DNS) of the many-body interactions of plasmas is a promising approach to model validation but, previous work either relies on the collisionless approximation or ignores radiation. We present four methods that attempt a new numerical simulation technique to address a currently unsolved problem: the extension of molecular dynamics to collisional plasmas including emission and absorption of radiation. The first method applies the Lienard–Weichert solution of Maxwell's equations for a classical particle whose motion is assumed to be known. The second method expands the electromagnetic field in normal modes (plane-waves in a box with periodic boundary conditions) and solves the equation for wave amplitudes coupled to the particle motion. The third method is a hybrid molecular dynamics/Monte Carlo (MD/MC) method which calculates radiation emitted or absorbed by electron–ion pairs during close collisions. The fourth method is a generalization of the third method to include small clusters of particles emitting radiation during close encounters: one electron simultaneously hitting two ions, two electrons simultaneously hitting one ion, etc. This approach is inspired by the virial expansion method of equilibrium statistical mechanics. Using a combination of these methods we believe it is possible to do atomic-scale particle simulations of fusion ignition plasmas including the important effects of radiation emission and absorption.

XOOPIC Simulation of Ion Motion and Sheath Behavior Caused by a Sudden Negative Pulse Applied to an Electrode

It is well known that a plasma produces a transient ion-matrix sheath when a sudden negative step bias is applied to a grid-shaped electrode. During this sheath forming process, ions are expected to be rushing to the grid electrode. Due to the grid structure, rushing ions are trapped and oscillate in the negative potential well formed around the grid. As soon as the bias is removed from the grid, ions propagate with a ballistic mode, forming a pseudowave. In this research, we studied the characteristics of the trapped ion motion by using the XOOPIC plasma particle simulation program. The energy distribution of ions and their dependence on the negative pulse shape and grid spacing, together with transient sheath expansion phenomena, were studied. We observed that the voltage rise time of the pulse did not affect the pseudowave properties. On the other hand, the pulse fall time was crucial to the pseudowave characteristics because ions escaping from the sheath were decelerated during the fall time. Grid spacing and the pulse width effects were also considered.

Ultra-fast ionization modeling in laser-plasma interaction

A new ionization model for weighted particle simulation of large density scale plasmas has been developed. It is capable of treating both field and impact ionization. The high-order interpolation scheme we have adopted reduces numerical noises of electromagnetic waves, which ionize the target unphysically. This model has been tested in simulations of high intensity laser interaction with both underdense and overdense targets. With the addition of the treatment of collisions, this new code allows us to perform large-scale simulations of laser matter interaction with atomic physics. This model is a very valuable tool for the design of high-energy density experiments with short pulse lasers.

Energetic neutral atom imaging of comets

We present the first computer simulated images of energetic neutral atoms (ENAs) produced by charge exchange between solar wind protons and cometary neutrals. Proton bulk flow and temperature from MHD simulations are used along with a model of cometary neutral densities. The emission of hydrogen ENAs from the comet is then calculated using cross sections for the charge exchange collisions. The ENA production rate is integrated along lines of sight to produce an image of the fluxes. We find detection of hydrogen ENAs feasible and most favorable at solar zenith angles between 80 and 130 degrees.

The Transition and Adoption to Modern Programming Concepts for Scientific Computing in Fortran

This paper describes our experiences in the early exploration of modern concepts introduced in Fortran90 for large‐scale scientific programming. We review our early work in expressing object‐oriented concepts based on the new Fortran90 constructs – foreign to most programmers at the time – our experimental work in applying them to various applications, the impact on the WG5/J3 standards committees to consider formalizing object‐oriented constructs for later versions of Fortran, and work in exploring how other modern programming techniques such as Design Patterns can and have impacted our software development. Applications will be drawn from plasma particle simulation and finite element adaptive mesh refinement for solid earth crustal deformation modeling.

Plasma particle simulations using a special-purpose computer system for gravitational N-body problems

Plasma particle simulations are performed using GRAPE-6, a special-purpose computer for calculating gravitational N-body systems. GRAPE-6 rapidly calculates the gravitational force between particles using specialized pipeline processors. The peak performance of a unit of GRAPE-6 reaches 985 GFLOPS. We investigated speeding up plasma simulations through the use of GRAPE-6 for the calculation of Coulomb interactions, which have the same form of central force as the gravitational force. As an example of plasma particle simulation using GRAPE-6, we simulated the Buneman instability. As another example of plasma particle simulation, we simulated a Coulomb crystal in a dusty plasma. The formation of a Coulomb crystal was observed under typical laboratory conditions. We found that GRAPE-6 can perform the entire operation of the simulation of a Coulomb crystal with 5 × 103 particles up to 210 times faster than a 1.6-GHz Pentium4 CPU.

Gyrokinetic particle simulation of fusion plasmas: path to petascale computing

Gyrokinetic particle simulation of fusion plasmas for studying turbulent transport on state-of-theart computers has a long history of important scientific discoveries. The primary examples are: (i) the identification of ion temperature gradient (ITG) drift turbulence as the most plausible process responsible for the thermal transport observed in tokamak experiments; (ii) the reduction of such transport due to the presence of zonal flows; (iii) the confinement scaling trends associated with size of the plasma and also with the ionic isotope species. With the availability of terascale computers in recent years, we have also been able to carry out simulations with improved physics fidelity using experimentally relevant parameters. Computationally, we have demonstrated that our lead Particle-in- Cell (PIC) code, the Gyrokinetic Turbulence Code (GTC), is portable, efficient, and scalable on various MPP platforms. Convergence studies with unprecedented phase-space resolution have also been carried out. Since petascale resources are expected to be available in the near future, we have also engaged in developing better physics models and more efficient numerical algorithms to take advantage of this exciting opportunity. For the near term, we are interested in understanding some basic physics issues related to burning plasmas experiments in International Thermonuclear Experimental Reactor (ITER) - a multi-billion dollar device to be constructed over the next decade. Our long range goal is to carry out integrated simulations for ITER plasmas for a wide range of temporal and spatial scales, including high-frequency short-wavelength wave heating, low-frequency meso-scale transport, and low-frequency large scale magnetohydrodynamic (MHD) physics on these computers.

All particle simulations of cathodic arc plasmas

The early stages of the expansion of fully ionized cathode spot cathodic arc plasmas from a localized initial volume are simulated by an all particle molecular dynamics model. The particles are given an initial temperature and interact by Coulomb forces. Although there are limits on the number of particles and the starting density, the model is relevant in describing processes occurring in cells that are the smallest structures of a cathodic arc. Our model predicts that a cell undergoes an explosive expansion leading to a halo of electrons surrounding an ion-rich core. The ion kinetic energies are lower than experimental observation but may be consistent with them after extrapolation to higher initial densities. For mixed charge state plasmas, the ion kinetic energy increases with ion charge state.