Computational Modeling Capabilities for

Neutral Gas Injection

Wayne Scales and Joseph Wang

Space @ Virginia Tech

Center for Space Science and Engineering Research

College of Engineering

Virginia Tech

Blacksburg, Virginia

Objectives

• Develop computational models for artificial plasma cloud creation by neutral gas injection

• Investigate the nonlinear evolution of plasma waves generated by artificial plasma cloud creation that lead to pitch angle scattering of trapped electrons (Ganguli et al., 2007)

• Determine the efficiency of the process in terms of plasma wave energy compared to injected neutral gas kinetic energy

Space @ VT Plasma Simulation Capabilities

• Relevant plasma simulation models available:

– 3-D Electromagnetic Particle-in-Cell (PIC) (full particle)– 3-D Electromagnetic Particle-in-Cell with Monte Carlo Collision (PIC-MCC) (full particle)– 3-D Electromagnetic PIC with Deformable Grids (full particle)

– 3-D Hybrid Electromagnetic PIC (hybrid fluid-particle)– 2-D Hybrid Electromagnetic PIC (hybrid fluid-particle)

– 3-D Electrostatic PIC (full particle/hybrid fluid-particle)– 3-D Electrostatic PIC-MCC (full particle/hybrid fluid-particle)– 3-D Electrostatic Immersed-Finite-Element PIC (IFE-PIC) (full particle/hybrid fluid

particle)– 3-D Electrostatic Hybrid-Grid Immersed-Finite-Element PIC (HG-IFE-PIC) (full

particle/hybrid fluid-particle)

Prior Relevant Experience in Neutral Gas Release/Plasma Cloud Injection in Space

• Modeling of Critical Ionization Velocity (CIV) Experiments

• Modeling of Electron Attachment Chemical Release Experiments

• Modeling of Dust Cloud Releases

• Modeling of Artificial Perpendicular Ion Beam Injections

• Modeling of Micro-Instabilities in Space Plasmas (Heavy Ion/Proton Instability, Ion Cyclotron Instability, Whistler Instability, etc)

Electromagnetic Full Particle PIC and PIC-MCC

• Governing Equations:

• Code Formulation (Wang et al, Computer Physics Comm., 87, 1995):– Finite-difference time-domain solution for EM wave– Particle representation for both ions and electrons (relativistic equation of motion)– Buneman’s rigorous charge conservation scheme for current deposit– Monte-Carlo collision subroutine for charged particle-neutral collision– Implemented on massively parallel supercomputers

Electromagnetic Hybrid PIC

• Governing Equations:

• Code Formulation (Winski and Omidi, 1993):– Ions: macro-particles; Electrons: massless fluid– Maxwell’s equation in the low frequency approximation – Quasi-neutral plasma

Electrons:

Ions:

• 3-D EM Full Particle PIC-MCC Simulations of Critical Ionization Velocity Experiment in Space (Wang et al., JGR, 101A(1), 1996)

Selected Relevant Previous Studies: Release Experiments in Space

• 2-D ES hybrid (PIC-fluid) modeling of plasma turbulence created by dust cloud releases across the geomagnetic field (Scales et al., 2001) resulting from plasma velocity shear instabilities (Ganguli et al., 1992).

electrons

ions

dust

• EM Hybrid PIC Simulations of Electromagnetic Heavy Ion/Proton Instabilities (Wang et al., JGR, 104(A11), 1999)

Selected Relevant Previous Studies: Micro-Instabilities in Space Plasmas

• EM Full Particle PIC Simulations of Whistler Instabilities and Electron Anisotropy Upper Bound (Gary and Wang, JGR, 101(A5), 1996)

Initial Approach:• I: Initial Studies:

– Apply existing hybrid PIC code (zero electron inertia) for preliminary simulations of instabilities generated by the velocity ring distribution– Initial studies on effects of electron model used by hybrid code

• Finite Electron Inertia?• Electron Energy Equation?• Hybrid PIC vs. Full particle PIC?

– Explore the feasibility of applying parallel full particle PIC in this study

• II: Computational Model Modification: – Explore 2 implementation approaches to include finite electron inertia in hybrid codes:

• Lipatov (2001)

• “kinetic” density electron fluid model (Advance electron density and velocities defined at mesh points using a pseudo-particle approach)

• III: Simulation Studies: Consider efficiency of wave generation with the following parameters:

– neutral density– neutral mass

– characteristics of velocity ring distribution