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Title: Computational and experimental investigation of plasma deflagration jets and detonation shocks in coaxial plasma accelerators

Abstract

Here, we present a magnetohydrodynamic (MHD) numerical simulation to study the physical mechanisms underlying plasma acceleration in a coaxial plasma gun. Coaxial plasma accelerators are known to exhibit two distinct modes of operation depending on the delay between gas loading and capacitor discharging. Shorter delays lead to a high velocity plasma deflagration jet and longer delays produce detonation shocks. During a single operational cycle that typically consists of two discharge events, the plasma acceleration exhibits a behavior characterized by a mode transition from deflagration to detonation. The first of the discharge events, a deflagration that occurs when the discharge expands into an initially evacuated domain, requires a modification of the standard MHD algorithm to account for rarefied regions of the simulation domain. The conventional approach of using a low background density gas to mimic the vacuum background results in the formation of an artificial shock, inconsistent with the physics of free expansion. To this end, we present a plasma-vacuum interface tracking framework with the objective of predicting a physically consistent free expansion, devoid of the spurious shock obtained with the low background density approach. The interface tracking formulation is integrated within the MHD framework to simulate the plasma deflagration andmore » the second discharge event, a plasma detonation, formed due to its initiation in a background prefilled with gas remnant from the deflagration. The mode transition behavior obtained in the simulations is qualitatively compared to that observed in the experiments using high framing rate Schlieren videography. The deflagration mode is further investigated to understand the jet formation process and the axial velocities obtained are compared against experimentally obtained deflagration plasma front velocities. The simulations are also used to provide insight into the conditions responsible for the generation and sustenance of the magnetic pinch. The pinch width and number density distribution are compared to experimentally obtained data to calibrate the inlet boundary conditions used to set up the plasma acceleration problem.« less

Authors:
ORCiD logo [1];  [2];  [1];  [2]
  1. Univ. of Texas, Austin, TX (United States). Dept. of Aerospace Engineering and Engineering Mechanics
  2. Stanford Univ., CA (United States). Dept. of Mechanical Engineering
Publication Date:
Research Org.:
Stanford Univ., CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1485496
Grant/Contract Number:  
NA0002011
Resource Type:
Accepted Manuscript
Journal Name:
Plasma Sources Science and Technology
Additional Journal Information:
Journal Volume: 27; Journal Issue: 2; Journal ID: ISSN 1361-6595
Publisher:
IOP Publishing
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Subramaniam, Vivek, Underwood, Thomas C., Raja, Laxminarayan L., and Cappelli, Mark A. Computational and experimental investigation of plasma deflagration jets and detonation shocks in coaxial plasma accelerators. United States: N. p., 2018. Web. doi:10.1088/1361-6595/aaabec.
Subramaniam, Vivek, Underwood, Thomas C., Raja, Laxminarayan L., & Cappelli, Mark A. Computational and experimental investigation of plasma deflagration jets and detonation shocks in coaxial plasma accelerators. United States. doi:10.1088/1361-6595/aaabec.
Subramaniam, Vivek, Underwood, Thomas C., Raja, Laxminarayan L., and Cappelli, Mark A. Fri . "Computational and experimental investigation of plasma deflagration jets and detonation shocks in coaxial plasma accelerators". United States. doi:10.1088/1361-6595/aaabec. https://www.osti.gov/servlets/purl/1485496.
@article{osti_1485496,
title = {Computational and experimental investigation of plasma deflagration jets and detonation shocks in coaxial plasma accelerators},
author = {Subramaniam, Vivek and Underwood, Thomas C. and Raja, Laxminarayan L. and Cappelli, Mark A.},
abstractNote = {Here, we present a magnetohydrodynamic (MHD) numerical simulation to study the physical mechanisms underlying plasma acceleration in a coaxial plasma gun. Coaxial plasma accelerators are known to exhibit two distinct modes of operation depending on the delay between gas loading and capacitor discharging. Shorter delays lead to a high velocity plasma deflagration jet and longer delays produce detonation shocks. During a single operational cycle that typically consists of two discharge events, the plasma acceleration exhibits a behavior characterized by a mode transition from deflagration to detonation. The first of the discharge events, a deflagration that occurs when the discharge expands into an initially evacuated domain, requires a modification of the standard MHD algorithm to account for rarefied regions of the simulation domain. The conventional approach of using a low background density gas to mimic the vacuum background results in the formation of an artificial shock, inconsistent with the physics of free expansion. To this end, we present a plasma-vacuum interface tracking framework with the objective of predicting a physically consistent free expansion, devoid of the spurious shock obtained with the low background density approach. The interface tracking formulation is integrated within the MHD framework to simulate the plasma deflagration and the second discharge event, a plasma detonation, formed due to its initiation in a background prefilled with gas remnant from the deflagration. The mode transition behavior obtained in the simulations is qualitatively compared to that observed in the experiments using high framing rate Schlieren videography. The deflagration mode is further investigated to understand the jet formation process and the axial velocities obtained are compared against experimentally obtained deflagration plasma front velocities. The simulations are also used to provide insight into the conditions responsible for the generation and sustenance of the magnetic pinch. The pinch width and number density distribution are compared to experimentally obtained data to calibrate the inlet boundary conditions used to set up the plasma acceleration problem.},
doi = {10.1088/1361-6595/aaabec},
journal = {Plasma Sources Science and Technology},
number = 2,
volume = 27,
place = {United States},
year = {2018},
month = {2}
}

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