The structure of 3-D collisional magnetized bow shocks in pulsed-power-driven plasma flows

Datta, R.; Russell, D. R.; Tang, Iek; Clayson, Thomas; Suttle, L.; Chittenden, J. P.; Lebedev, S. V.; Hare, Jack

doi:10.1017/s0022377822001118

Cited by 6 publications

(3 citation statements)

References 71 publications

(174 reference statements)

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“…The implications of this finding have already been published in Datta et al. (2022 a , b ) for the use of small inductive probes in a collisional plasma.…”

Section: Resultssupporting

confidence: 52%

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Observation of subcritical shocks in a collisional laboratory plasma: scale dependence near the resistive length

Russell,

Burdiak,

Carroll-Nellenback

et al. 2023

J. Plasma Phys.

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We present a study of subcritical shocks in a highly collisional laboratory plasma with a dynamically significant magnetic field. Shocks were produced by placing cylindrical obstacles into the supermagnetosonic ( $M_{{\rm MS}} \sim 1.9$ ) outflow from an inverse wire array z-pinch at the MAGPIE pulsed power facility ( $n_{e} \sim 8.5 \times 10^{17}\,{\rm cm}^{-3}$ , $v \sim 45\,{\rm km}\,{\rm s}^{-1}$ ). We demonstrate the existence of subcritical shocks in this regime and find that secondary stagnation shocks form in the downstream which we infer from interferometry and optical Thomson scattering measurements are hydrodynamic in nature. The subcritical shock width is found to be approximately equal to the resistive diffusion length and we demonstrate the absence of a jump in hydrodynamic parameters. Temperature measurements by collective optical Thomson scattering showed little temperature change across the subcritical shock ( ${<}10\,\%$ of the ion kinetic energy) which is consistent with a balance between adiabatic and Ohmic heating and radiative cooling. We demonstrate the absence of subcritical shocks when the obstacle diameter is less than the resistive diffusion length due to decoupling of the magnetic field from the plasma. These findings are supported by magnetohydrodynamic simulations using the Gorgon and AstroBEAR codes and discrepancies between the simulations and experiment are discussed.

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“…The implications of this finding have already been published in Datta et al. (2022 a , b ) for the use of small inductive probes in a collisional plasma.…”

Section: Resultssupporting

confidence: 52%

“…This property has recently been used in Datta et al. (2022 a , b ) to infer upstream plasma conditions from ‘B-dot’ probe measurements in which the probe was smaller than but much larger than the collisional m.f.p. of the plasma.…”

Section: Introductionmentioning

confidence: 99%

Observation of subcritical shocks in a collisional laboratory plasma: scale dependence near the resistive length

Russell,

Burdiak,

Carroll-Nellenback

et al. 2023

J. Plasma Phys.

Self Cite

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“…2019; Datta et al. 2022 a , b ). This process is referred to as ablation, and in the MARZ experiments, we choose an initial wire diameter such that the arrays are ‘over-massed’, and the wires act as stationary reservoirs of mass throughout the current pulse (Lebedev et al.…”

Section: Introductionmentioning

confidence: 99%

Simulations of radiatively cooled magnetic reconnection driven by pulsed power

Datta,

Crilly,

Chittenden

et al. 2024

J. Plasma Phys.

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Magnetic reconnection is an important process in astrophysical environments, as it reconfigures magnetic field topology and converts magnetic energy into thermal and kinetic energy. In extreme astrophysical systems, such as black hole coronae and pulsar magnetospheres, radiative cooling modifies the energy partition by radiating away internal energy, which can lead to the radiative collapse of the reconnection layer. In this paper, we perform two- and three-dimensional simulations to model the MARZ (Magnetic Reconnection on Z) experiments, which are designed to access cooling rates in the laboratory necessary to investigate reconnection in a previously unexplored radiatively cooled regime. These simulations are performed in GORGON, an Eulerian two-temperature resistive magnetohydrodynamic code, which models the experimental geometry comprising two exploding wire arrays driven by 20 MA of current on the Z machine (Sandia National Laboratories). Radiative losses are implemented using non-local thermodynamic equilibrium tables computed using the atomic code Spk, and we probe the effects of radiation transport by implementing both a local radiation loss model and $P_{1/3}$ multi-group radiation transport. The load produces highly collisional, super-Alfvénic (Alfvén Mach number $M_A \approx 1.5$ ), supersonic (Sonic Mach number $M_S \approx 4-5$ ) strongly driven plasma flows which generate an elongated reconnection layer (Aspect Ratio $L/\delta \approx 100$ , Lundquist number $S_L \approx 400$ ). The reconnection layer undergoes radiative collapse when the radiative losses exceed the rates of ohmic and compressional heating (cooling rate/hydrodynamic transit rate = $\tau _{\text {cool}}^{-1}/\tau _{H}^{-1}\approx 100$ ); this generates a cold strongly compressed current sheet, leading to an accelerated reconnection rate, consistent with theoretical predictions. Finally, the current sheet is also unstable to the plasmoid instability, but the magnetic islands are extinguished by strong radiative cooling before ejection from the layer.

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Radiative cooling effects on reverse shocks formed by magnetized supersonic plasma flows

Merlini,

Hare,

Burdiak

et al. 2023

Physics of Plasmas

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We study the structure of reverse shocks formed by the collision of supersonic, magnetized plasma flows driven by an inverse (or exploding) wire array with a planar conducting obstacle. We observe that the structure of these reverse shocks varies dramatically with wire material, despite the similar upstream flow velocities and mass densities. For aluminum wire arrays, the shock is sharp and well-defined, consistent with magneto-hydrodynamic theory. In contrast, we do not observe a well-defined shock using tungsten wires, and instead we see a broad region dominated by density fluctuations on a wide range of spatial scales. We diagnose these two very different interactions using interferometry, Thomson scattering, shadowgraphy, and a newly developed imaging refractometer that is sensitive to small deflections of the probing laser corresponding to small-scale density perturbations. We conclude that the differences in shock structure are most likely due to radiative cooling instabilities, which create small-scale density perturbations elongated along magnetic field lines in the tungsten plasma. These instabilities grow more slowly and are smoothed by thermal conduction in the aluminum plasma.

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The structure of 3-D collisional magnetized bow shocks in pulsed-power-driven plasma flows

Cited by 6 publications

References 71 publications

Observation of subcritical shocks in a collisional laboratory plasma: scale dependence near the resistive length

Observation of subcritical shocks in a collisional laboratory plasma: scale dependence near the resistive length

Simulations of radiatively cooled magnetic reconnection driven by pulsed power

Radiative cooling effects on reverse shocks formed by magnetized supersonic plasma flows

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