Damage Morphologies in Targets Exposed to a New Plasma Deflagration Accelerator for ELM Simulation

Loebner, Keith; Underwood, Thomas; Wang, Benjamin C.; Cappelli, Mark A.

doi:10.1109/tps.2016.2565508

Cited by 15 publications

(4 citation statements)

References 28 publications

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“…The plasma acceleration process over an effective gun length l eff is simulated by specifying the temperature, pressure and velocity of the thermalized plasma as an inflow boundary condition. The plasma temperature is estimated from the experimental measurements of Woodall and Len [14] to be around 1 eV and the pressure is taken to be the choked flow pressure corresponding to a stagnation chamber pressure of 2 atm to match the experimentally regulated gas valve pressures [6][7][8][9][10]. The velocity boundary condition is obtained from the neutral gas front velocity measurements carried out in the SPG facility, determined to be of the order of 1000 m s −1 [15].…”

Section: Boundary Conditionsmentioning

confidence: 99%

“…The hypervelocity plasma jet that emerges from the accelerator exhibits a large number density and a high degree of collimation [7,8] making it attractive for studying plasma material interactions. Recent experiments carried out by Loebner et al on the Stanford plasma gun (SPG) facility [9] examine the material response to the impingement of these jets on target surfaces. The motivation here is to use these plasma jets to mimic the transient loading on the inner walls of nuclear fusion reactors during edge localized mode disruption events.…”

Section: Introductionmentioning

confidence: 99%

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

Subramaniam

Underwood

Raja

et al. 2018

Plasma Sources Sci. Technol.

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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.

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Section: Boundary Conditionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Subramaniam

Underwood

Raja

et al. 2018

Plasma Sources Sci. Technol.

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“…Also referred to in the literature as a magnetoplasmadynamic (MPD) thruster, this device has found a wide variety of applications ranging from space propulsion [3], materials processing [4], fusion experiments [5] to more recently as a laboratory scale platform for studying astrophysical phenomena [6]. The specific application that motivates the current study is the utilization of the accelerator as a high energy density plasma source for studying plasma surface interactions [7][8][9]. Depending on the delay between the gas loading into the device and capacitor discharging, plasma accelerators have been known to exhibit two distinct modes of operation, referred to as 'deflagration' and 'detonation', respectively [10][11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Modeling of thermalization phenomena in coaxial plasma accelerators

Subramaniam¹,

PanneerChelvam²,

Raja³

2018

J. Phys. D: Appl. Phys.

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Coaxial plasma accelerators are electromagnetic acceleration devices that employ a self-induced Lorentz force to produce collimated plasma jets with velocities ~50 km s −1 . The accelerator operation is characterized by the formation of an ionization/thermalization zone near gas inlet of the device that continually processes the incoming neutral gas into a highly ionized thermal plasma. In this paper, we present a 1D non-equilibrium plasma model to resolve the plasma formation and the electron-heavy species thermalization phenomena that take place in the thermalization zone. The non-equilibrium model is based on a self-consistent multi-species continuum description of the plasma with finite-rate chemistry. The thermalization zone is modelled by tracking a 1D gas-bit as it convects down the device with an initial gas pressure of 1 atm. The thermalization process occurs in two stages. The first is a plasma production stage, associated with a rapid increase in the charged species number densities facilitated by cathode surface electron emission and volumetric production processes. The production stage results in the formation of a two-temperature plasma with electron energies of ~2.5 eV in a low temperature background gas of ~300 K. The second, a temperature equilibration stage, is characterized by the energy transfer between the electrons and heavy species. The characteristic length scale for thermalization is found to be comparable to axial length of the accelerator thus putting into question the equilibrium magnetohydrodynamics assumption used in modeling coaxial accelerators.

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“…The device, as shown schematically in Fig. 1, features a coaxial rod configuration which has been used extensively in past studies for a variety of applications [13,14,15,16]. In terms of geometry, the entire accelerator region is 26 cm long, 5 cm in diameter and features a set of stainless steel rod anodes and a single central copper cathode.…”

Section: Plasma Deflagration Acceleratormentioning

confidence: 99%

A plasma deflagration accelerator as a platform for laboratory astrophysics

Underwood

Loebner

Cappelli

2017

High Energy Density Physics

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The replication of astrophysical flows in the laboratory is critical for isolating particular phenomena and dynamics that appear in complex, highly-coupled natural systems. In particular, plasma jets are observed in astrophysical contexts at a variety of scales, typically at high magnetic Reynolds number and driven by internal currents. In this paper, we present detailed measurements of the plasma parameters within deflagration-produced plasma jets, the scaling of these parameters against both machine operating conditions and the corresponding astrophysical phenomena. Using optical and spectroscopic diagnostics, including Schlieren cinematography, we demonstrate the production of current-driven plasma jets of ∼100 km/s and magnetic Reynolds numbers of ∼100, and discuss the dynamics of their acceleration into vacuum. The results of this study will contribute to the reproduction of various types of astrophysical jets in the laboratory and indicate the ability to further probe active research areas such as jet collimation, stability, and interaction.

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Damage Morphologies in Targets Exposed to a New Plasma Deflagration Accelerator for ELM Simulation

Cited by 15 publications

References 28 publications

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

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

Modeling of thermalization phenomena in coaxial plasma accelerators

A plasma deflagration accelerator as a platform for laboratory astrophysics

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