Unified Code for

Nonequilibrium Plasma Systems

 

 

 

Overview

The goal of this project is to develop a new computational code to be used at the Arnold Engineering Development Center (AEDC), Tullahoma, TN, for analysis of plasmas characterized by high ionization fractions and extremely low number densities. Such conditions arise in two particular test facilities operated at AEDC. The Decade Nuclear Weapons Effects (NWE) facility is used to test the effects of strong radiation sources on materials and spacecraft components. The V12 Space Chamber is used to test electric propulsion (EP) thrusters used to control spacecraft. The low-density flow conditions of these facilities result in nonequilibrium plasma systems due to relatively low collision rates. The most important physical phenomena concern molecular collisions and electro-static plasma dynamics in a nonequilibrium environment. In our work, the direct simulation Monte Carlo (DSMC) method will be used to simulate collisions. The plasma dynamics will be simulated using a hybrid approach in which the electrons are modeled as a fluid and the ions are modeled by the Particle-In-Cell (PIC) method using the same particles employed in DSMC. It is the overall goal of this effort to develop an easy-to-use, robust, three-dimensional, unstructured grid, unsteady, DSMC-PIC code. Such a code will greatly facilitate the testing and evaluation capabilities provided by AEDC for the two important technilogy areas tested in the Decade and V12 facilities.

Photo of DECADE

Photo of chamber 12V

Sketch of chamber 12V

 

 

Introduction

The objective of this project is to develop a new computational code to analyze the flows of plasmas characterized by high ionization fractions and extremely low number densities, for application to the Nuclear Weapons Effects (NWE) Decade facility and to the 12V Electric Propulsion (EP) plumes facility located at the Arnold Engineering and Development Center (AEDC). Physically accurate numerical simulations are expected to play a significant role in optimizing the performance of the facilities as well as in playing an integral role in the testing capabilities provided by AEDC.

Typical flow conditions in Decade and 12 V give a Debye length and a mean free path that indicate that the flow is in the quasi-neutral, kinetic flow regime. Traditional continuum-based computational codes are unsuitable for very low density, or rarefied, gas and plasmas. Particle methods, such as the direct simulation Monte Carlo method (DSMC), are becoming mature for modeling rarefied flows of neutral gases, but do not account for charged particle interactions. Particle-in-Cell (PIC) methods account for field interaction effects of charged particles, but do not fully resolve particle energy and momentum transfer effects. Codes combining the capabilities of DSMC and PIC must be utilized to account for all the afore-mentioned effects in NWE and EP testing. This research effort will build upon existing DSMC and PIC techniques to develop a combined PIC/DSMC code directly applicable to AEDC's test facility needs: a general, unsteady, 3D, electro-static nonequilibrium gas and plasma simulation code that is readily usable by engineers at AEDC for analysis of the Decade and 12V facilities.

 

Code Development

We have added many features to code MONACO that expands the capability of the code and improves the interface to users. Such developments includes:

The code has been widely validated and the results agree very well with published data. The validation ranges from one-dimensional to three-dimensional flows, and includes subsonic and supersonic flows.

 

Code Applications

Decade Flow

 

Fig. 1. Indication of nonequilibrium (Kn>0.05)

Fig. 2. Indication of nucleation and condensation

Fig. 3. Density comparison at x=0.072m

Fig. 4. Density comparison at x=0.10m

12V Flow

 

Fig. 5. Ion current density (A/m2)

Fig. 6. Plasma potential (V)

Acknowledgements

This work is funded by Air Force Office of Scientific Research. We are glad to acknowledge the generous collaboration with Dr. Kenneth E. Tatum.

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