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Title: Fully Implict Magneto-hydrodynamics Simulations of Coaxial Plasma Accelerators

Abstract

The resistive Magneto-Hydrodynamic (MHD) model describes the behavior of a strongly ionized plasma in the presence of external electric and magnetic fields. We developed a fully implicit MHD simulation tool to solve the resistive MHD governing equations in the context of a cell-centered finite-volume scheme. The primary objective of this study is to use the fully-implicit algorithm to obtain insights into the plasma acceleration and jet formation processes in Coaxial Plasma accelerators; electromagnetic acceleration devices that utilize self-induced magnetic fields to accelerate thermal plasmas to large velocities. We also carry out plasma-surface simulations in order to study the impact interactions when these high velocity plasma jets impinge on target material surfaces. Scaling studies are carried out to establish some basic functional relationships between the target-stagnation conditions and the current discharged between the coaxial electrodes.

Authors:
 [1];  [1]
  1. Univ. of Texas, Austin, TX (United States)
Publication Date:
Research Org.:
Stanford Univ., CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1363886
Grant/Contract Number:
NA0003347; NA0002011
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
AIAA Aerospace Sciences Meeting
Additional Journal Information:
Journal Volume: 55; Conference: 55th AIAA Aerospace Sciences Meeting, Grapevine, TX (United States), 9-13 Jan 2017; Journal ID: ISSN 1947-7902
Publisher:
American Institute of Aeronautics and Astronautics
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Subramaniam, Vivek, and Raja, Laxminarayan L. Fully Implict Magneto-hydrodynamics Simulations of Coaxial Plasma Accelerators. United States: N. p., 2017. Web. doi:10.2514/6.2017-0843.
Subramaniam, Vivek, & Raja, Laxminarayan L. Fully Implict Magneto-hydrodynamics Simulations of Coaxial Plasma Accelerators. United States. doi:10.2514/6.2017-0843.
Subramaniam, Vivek, and Raja, Laxminarayan L. Thu . "Fully Implict Magneto-hydrodynamics Simulations of Coaxial Plasma Accelerators". United States. doi:10.2514/6.2017-0843. https://www.osti.gov/servlets/purl/1363886.
@article{osti_1363886,
title = {Fully Implict Magneto-hydrodynamics Simulations of Coaxial Plasma Accelerators},
author = {Subramaniam, Vivek and Raja, Laxminarayan L.},
abstractNote = {The resistive Magneto-Hydrodynamic (MHD) model describes the behavior of a strongly ionized plasma in the presence of external electric and magnetic fields. We developed a fully implicit MHD simulation tool to solve the resistive MHD governing equations in the context of a cell-centered finite-volume scheme. The primary objective of this study is to use the fully-implicit algorithm to obtain insights into the plasma acceleration and jet formation processes in Coaxial Plasma accelerators; electromagnetic acceleration devices that utilize self-induced magnetic fields to accelerate thermal plasmas to large velocities. We also carry out plasma-surface simulations in order to study the impact interactions when these high velocity plasma jets impinge on target material surfaces. Scaling studies are carried out to establish some basic functional relationships between the target-stagnation conditions and the current discharged between the coaxial electrodes.},
doi = {10.2514/6.2017-0843},
journal = {AIAA Aerospace Sciences Meeting},
number = ,
volume = 55,
place = {United States},
year = {Thu Jan 05 00:00:00 EST 2017},
month = {Thu Jan 05 00:00:00 EST 2017}
}

Journal Article:
Free Publicly Available Full Text
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  • Experimental studies by Poehlmann et al. [Phys. Plasmas 17(12), 123508 (2010)] on a coaxial electrode magnetohydrodynamic (MHD) plasma accelerator have revealed two modes of operation. A deflagration or stationary mode is observed for lower power settings, while higher input power leads to a detonation or snowplow mode. A numerical modeling study of a coaxial plasma accelerator using the non-ideal MHD equations is presented. The effect of plasma conductivity on the axial distribution of radial current is studied and found to agree well with experiments. Lower conductivities lead to the formation of a high current density, stationary region close to themore » inlet/breech, which is a characteristic of the deflagration mode, while a propagating current sheet like feature is observed at higher conductivities, similar to the detonation mode. Results confirm that plasma resistivity, which determines magnetic field diffusion effects, is fundamentally responsible for the two modes.« less
  • This paper formulates the Tokamak Magneto-Hydrodynamics (TMHD), initially outlined by X. Li and L. E. Zakharov [Plasma Science and Technology 17(2), 97–104 (2015)] for proper simulations of macroscopic plasma dynamics. The simplest set of magneto-hydrodynamics equations, sufficient for disruption modeling and extendable to more refined physics, is explained in detail. First, the TMHD introduces to 3-D simulations the Reference Magnetic Coordinates (RMC), which are aligned with the magnetic field in the best possible way. The numerical implementation of RMC is adaptive grids. Being consistent with the high anisotropy of the tokamak plasma, RMC allow simulations at realistic, very high plasmamore » electric conductivity. Second, the TMHD splits the equation of motion into an equilibrium equation and the plasma advancing equation. This resolves the 4 decade old problem of Courant limitations of the time step in existing, plasma inertia driven numerical codes. The splitting allows disruption simulations on a relatively slow time scale in comparison with the fast time of ideal MHD instabilities. A new, efficient numerical scheme is proposed for TMHD.« less
  • Cited by 5
  • Recent experiments by Loebner et al. [IEEE Trans. Plasma Sci. 44, 1534 (2016)] studied the effect of a hypervelocity jet emanating from a coaxial plasma accelerator incident on target surfaces in an effort to mimic the transient loading created during edge localized mode disruption events in fusion plasmas. In this study, we present a magnetohydrodynamic (MHD) numerical model to simulate plasma jet formation and plasma-surface contact in this coaxial plasma accelerator experiment. The MHD system of equations is spatially discretized using a cell-centered finite volume formulation. The temporal discretization is performed using a fully implicit backward Euler scheme and themore » resultant stiff system of nonlinear equations is solved using the Newton method. The numerical model is employed to obtain some key insights into the physical processes responsible for the generation of extreme stagnation conditions on the target surfaces. Simulations of the plume (without the target plate) are performed to isolate and study phenomena such as the magnetic pinch effect that is responsible for launching pressure pulses into the jet free stream. The simulations also yield insights into the incipient conditions responsible for producing the pinch, such as the formation of conductive channels. The jet-target impact studies indicate the existence of two distinct stages involved in the plasma-surface interaction. A fast transient stage characterized by a thin normal shock transitions into a pseudo-steady stage that exhibits an extended oblique shock structure. A quadratic scaling of the pinch and stagnation conditions with the total current discharged between the electrodes is in qualitative agreement with the results obtained in the experiments. Finally, this also illustrates the dominant contribution of the magnetic pressure term in determining the magnitude of the quantities of interest.« less