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All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Kinetic Simulation of Inhomogeneous Plasma with a Variable Sized Grid System

Space plasmas are usually inhomogeneous and irregular. Particle in cell (PIC) plasma simulations, however, often consider the plasma to be homogeneous and periodic. Here non-periodic PIC simulations with inhomogeneities in the density, temperature and background magnetic field are considered. Boundary conditions and a variable sized grid system are discussed, along with an application to a magnetospheric plasma physics problem in the auroral zone.

Schriver, David↗
NASA NTRS1985

Self-consistent simulation of plasma interactions with secondary-emitting insulators

A cylindrical particle-in-cell (PIC) plasma simulation code applicable to plasma densities encountered in low Earth orbit (LEO) is described. The simulated geometries include that of a plain disk and a disk surrounded by a dielectric. Both configurations are mounted upon a ground plate in contact with a plasma environment. Techniques allowing simulation of dielectric charging using PIC time scales are discussed. Current versus voltage characteristic curves are calculated and the results are compared to experimental data.

Brandon, S. T.↗
NASA NTRS1995

Implementation and Characterization of Three-Dimensional Particle-in-Cell Codes on Multiple-Instruction-Multiple-Data Massively Parallel Supercomputers

A three-dimensional electrostatic particle-in-cell (PIC) plasma simulation code has been developed on coarse-grain distributed-memory massively parallel computers with message passing communications. Our implementation is the generalization to three-dimensions of the general concurrent particle-in-cell (GCPIC) algorithm. In the GCPIC algorithm, the particle computation is divided among the processors using a domain decomposition of the simulation domain. In a three-dimensional simulation, the domain can be partitioned into one-, two-, or three-dimensional subdomains ("slabs," "rods," or "cubes") and we investigate the efficiency of the parallel implementation of the push for all three choices. The present implementation runs on the Intel Touchstone Delta machine at Caltech; a multiple-instruction-multiple-data (MIMD) parallel computer with 512 nodes. We find that the parallel efficiency of the push is very high, with the ratio of communication to computation time in the range 0.3%-10.0%. The highest efficiency (> 99%) occurs for a large, scaled problem with 64(sup 3) particles per processing node (approximately 134 million particles of 512 nodes) which has a push time of about 250 ns per particle per time step. We have also developed expressions for the timing of the code which are a function of both code parameters (number of grid points, particles, etc.) and machine-dependent parameters (effective FLOP rate, and the effective interprocessor bandwidths for the communication of particles and grid points). These expressions can be used to estimate the performance of scaled problems--including those with inhomogeneous plasmas--to other parallel machines once the machine-dependent parameters are known.

Lyster, P. M.↗
NASA NTRS1992

High voltage spheres in an unmagnetized plasma - Fluid and PIC simulations

The basic physics involving the interaction of a high voltage sphere with a LEO-Plasma was investigated via computer experiments. Two approaches were used: the fluid description and the more general particle pushing method. Both techniques displayed qualitatively similar features. Thus, the initial time-dependent response of the plasma predicted by the fluid model, including the initial current surge and sheath formation, the formation of ion and electron density shells about the sphere with a double layer potential structure, and the subsequent propagation of the density shells away from the sphere. The PIC results also displayed an oscillatory character and slightly different time constants for the growth and decay mechanisms involved.

Thiemann, H.↗
NASA NTRS1992

Two dimensional PIC simulations of plasma heating by the dissipation of Alfven waves

Two dimensional plasma particle simulations of the evolution of large amplitude circularly polarized Alfven waves propagating parallel to the magnetic field show that the waves decay via both one- and two- dimensional parametric decay instabilities. For parameters studied, one-dimensional processes dominate the simulations, but two-dimensional decay processes, including the recently predicted filamentation instability are also observed. The daughter waves generated by the parametric decay are primarily damped by the ions, leading to ion heating. The parametric decay processes efficiently convert the ordered fluid ion motion in the Alfven wave into ion thermal energy. These processes may be important for the dissipation of Alfven waves in the solar wind, the corona and other space plasma environments. The computations were performed on the Intel Touchstone parallel supercomputer.

Liewer, P. C.↗
NASA NTRS2010

Hybrid-PIC Computer Simulation of the Plasma and Erosion Processes in Hall Thrusters

HPHall software simulates and tracks the time-dependent evolution of the plasma and erosion processes in the discharge chamber and near-field plume of Hall thrusters. HPHall is an axisymmetric solver that employs a hybrid fluid/particle-in-cell (Hybrid-PIC) numerical approach. HPHall, originally developed by MIT in 1998, was upgraded to HPHall-2 by the Polytechnic University of Madrid in 2006. The Jet Propulsion Laboratory has continued the development of HPHall-2 through upgrades to the physical models employed in the code, and the addition of entirely new ones. Primary among these are the inclusion of a three-region electron mobility model that more accurately depicts the cross-field electron transport, and the development of an erosion sub-model that allows for the tracking of the erosion of the discharge chamber wall. The code is being developed to provide NASA science missions with a predictive tool of Hall thruster performance and lifetime that can be used to validate Hall thrusters for missions.

Hofer, Richard R.↗
NASA NTRS1991

Computer simulation of astrophysical plasmas

The role of sophisticated numerical models and simulations in the field of plasma astrophysics is discussed. The need for an iteration between microphysics and macrophysics in order for astrophysical plasma physics to produce quantitative results that can be related to astronomical data is stressed. A discussion on computational requirements for simulations of astrophysical plasmas contrasts microscopic plasma simulations with macroscopic system models. An overview of particle-in-cell simulations (PICS) is given and two examples of PICS of astrophysical plasma are discussed including particle acceleration by collisionless shocks in relativistic plasmas and magnetic field reconnection in astrophysical plasmas.

Max, Claire E.↗
NASA NTRS1991

Simulation of the nonlinear evolution of electron plasma waves

Electrostatic waves driven by an electron beam in an ambient magnetized plasma were studied using a quasi-1D PIC simulation of electron plasma waves (i.e., Langmuir waves). The results disclose the presence of a process for moving wave energy from frequencies and wavenumbers predicted by linear theory to the Langmuir-like frequencies during saturation of the instability. A decay process for producing backward propagating Langmuir-like waves, along with low-frequency waves, is observed. The simulation results, however, indicate that the backscattering process is not the conventional Langmuir wave decay. Electrostatic waves near multiples of the electron plasma frequency are generated by wave-wave coupling during the nonlinear stage of the simulations, confirming the suggestion of Klimas (1983).

Nishikawa, K.-I.↗
NASA NTRS1993

Studies on equatorial shock formation during plasmaspheric refilling

During the grant period starting August 1, 1992, our major effort has been on examining the presence of equatorially trapped hot plasma on plasmaspheric refilling. We performed one-dimensional PIC simulations of cold plasmas expanding into a hot plasma, consisting of hot anisotropic ions and warm isotropic electrons, trapped in a region of minimum magnetic field. Simulations showed that the electric potential barrier built up by the anisotropy of the hot ion population facilitates in the formation of electrostatic shocks when the cold ion beams begin to come into contact with the hot plasma. The shock formation occurs even when the cold ion beams are highly supersonic with respect to the ion-acoustic speed. This finding is interesting because equatorial shock formation during the early stage of plasmaspheric refilling has been debated over about two decades. In the past ion-ion instability has been invoked as the main mechanism for the coupling between the cold ion beams approaching the equator from the conjugate ionspheres. This coupling occurs when the beams are sufficiently slow; the beam velocity being less than three times the ion-acoustic speed. In the presence of hot plasma, the beams slow down by the potential barrier. The slowing down and the reflection process lead to the formation of the electrostatic shock even for highly supersonic ion beams. The mixing of hot and cold plasma was also studied.

Singh, Nagendra↗
NASA NTRS1991

The circumstellar disks of Beta Pictoris analogs

A survey using data from the International Ultraviolet Explorer (IUE) of previously known B and A shell stars with IRAS detections has resulted in the identification of three stars, HD 93563, Sigma Her, and 51 Oph, which have spectral signatures of infalling circumstellar plasma similar to Beta Pic. Two of these systems have infrared flux distributions indicating the presence of circumstellar dust disks, while the other, HD 93563, has an infrared excess consistent with free-free emission from the plasma envelope. With the identification of three such systems, it is clear that infalling circumstellar plasma is more common than previously anticipated among late-type B shell stars. The absence of dust in one system, HD 93563, suggests that infalling plasma in these stars, and possibly also in Beta Pic itself, may not be due to either erosion of a dust disk or to high cometary bombardment rates, but may instead be linked to stellar activity.

Grady, Carol A.↗
NASA NTRS1994

A two-dimensional particle-in-cell model of a dusty plasma

Dusty plasmas are present in comets, in the ring systems of the outer planets, and in the interstellar medium. A two-dimensional particle-in-cell (PIC) model of a dusty plasma is presented in this paper. The PIC code is best suited for modeling the plasma-dust interaction for large grains, with diameters of the order of a centimeter. We have modeled the charging process for an individual dust grain and the associated potential pattern in the surrounding plasma. We have also considered the case of a large number of grains in a plasma, with intergrain separations of the order of the Debye length, and have shown that the plasma becomes depleted and the charge on a dust grain is reduced, as other workers in this field have predicted (cf. C. K. Goertz, 1989). We examine the electron and ion distribution functions in the vicinity of a charged grain and demonstrate that the ions near a grain have clearly been accelerated by the electrostatic potential.

Young, B.↗
NASA NTRS1991

The flow of plasma in the solar terrestrial environment

The overall goal of our NASA Theory Program is to study the coupling, time delays, and feedback mechanisms between the various regions of the solar-terrestrial system in a self-consistent, quantitative, manner. To accomplish this goal, it will eventually be necessary to have time-dependent macroscopic models of the different regions of the solar-terrestrial system and we are continually working toward this goal. However, our immediate emphasis is on the near-earth plasma environment, including the ionosphere, the plasmasphere, and the polar wind. In this area, we have developed unique global models that allow us to study the coupling between the different regions. These results are highlighted. Another important aspect of our NASA Theory Program concerns the effect that localized structure has on the macroscopic flow in the ionosphere, plasmasphere, thermosphere and polar wind. The localized structure can be created by structured magnetospheric inputs (i.e., structured plasma convection, particle precipitation or Birkeland current patterns) or time variations in these inputs due to storms and substorms. Also, some of the plasma flows that we predict with our macroscopic models may be unstable. Another one of our goals is to examine the stability of our predicted flows. Because time-dependent three-dimensional numerical models of the solar-terrestrial environment generally require extensive computer resources, they are usually based on relatively simple mathematical formulations (i.e., simple MHD or hydrodynamic formulations). Therefore, another long-range goal of our NASA Theory Program is to study the conditions under which various mathematical formulations can be applied to specific solar-terrestrial regions. This may involve a detailed comparison of kinetic, semikinetic, and hydrodynamic predictions for a given polar wind scenario or it may involve the comparison of a small-scale particle-in-cell (PIC) simulation of a plasma expansion event with a similar macroscopic expansion event. The different mathematical formulations have different strengths and weaknesses and a careful comparison of model predictions for similar geophysical situations will provide insight into when the various models can be used with confidence.

Schunk, Robert W.↗
NASA NTRS1990

The flow of plasma in the solar terrestrial environment

The overall goal of our NASA Theory Program was to study the coupling, time delays, and feedback mechanisms between the various regions of the solar-terrestrial system in a self-consistent, quantitative manner. To accomplish this goal, it will eventually be necessary to have time-dependent macroscopic models of the different regions of the solar-terrestrial system and we are continually working toward this goal. However, with the funding from this NASA program, we concentrated on the near-earth plasma environment, including the ionosphere, the plasmasphere, and the polar wind. In this area, we developed unique global models that allowed us to study the coupling between the different regions. These results are highlighted in the next section. Another important aspect of our NASA Theory Program concerned the effect that localized 'structure' had on the macroscopic flow in the ionosphere, plasmasphere, thermosphere, and polar wind. The localized structure can be created by structured magnetospheric inputs (i.e., structured plasma convection, particle precipitation or Birkland current patterns) or time variations in these input due to storms and substorms. Also, some of the plasma flows that we predicted with our macroscopic models could be unstable, and another one of our goals was to examine the stability of our predicted flows. Because time-dependent, three-dimensional numerical models of the solar-terrestrial environment generally require extensive computer resources, they are usually based on relatively simple mathematical formulations (i.e., simple MHD or hydrodynamic formulations). Therefore, another goal of our NASA Theory Program was to study the conditions under which various mathematical formulations can be applied to specific solar-terrestrial regions. This could involve a detailed comparison of kinetic, semi-kinetic, and hydrodynamic predictions for a given polar wind scenario or it could involve the comparison of a small-scale particle-in-cell (PIC) simulation of a plasma expansion event with a similar macroscopic expansion event. The different mathematical formulations have different strengths and weaknesses and a careful comparison of model predictions for similar geophysical situations provides insight into when the various models can be used with confidence.

Schunk, Robert W.↗