Time-resolved velocity and ion sound speed measurements from simultaneous bow shock imaging and inductive probe measurements

Journal Article · Sat Oct 01 00:00:00 EDT 2022 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/5.0098823· OSTI ID:1893977

Datta, R.  ^[1]; Russell, D. R.  ^[2]; Tang, I. ^[2]; Clayson, T. ^[2]; Suttle, L. G.  ^[2]; Chittenden, J. P.  ^[2]; Lebedev, S. V.  ^[2]; Hare, J. D.  ^[1]

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1. Plasma Science & Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
2. Blackett Laboratory, Imperial College London, London SW7 2BW, United Kingdom

We present a technique to measure the time-resolved velocity and ion sound speed in magnetized, supersonic high-energy-density plasmas. We place an inductive (“b-dot”) probe in a supersonic pulsed-power-driven plasma flow and measure the magnetic field advected by the plasma. As the magnetic Reynolds number is large ( R _M > 10), the plasma flow advects a magnetic field proportional to the current at the load. This enables us to estimate the flow velocity as a function of time from the delay between the current at the load and the signal at the probe. The supersonic flow also generates a hydrodynamic bow shock around the probe, the structure of which depends on the upstream sonic Mach number. By imaging the shock around the probe with a Mach–Zehnder interferometer, we determine the upstream Mach number from the shock Mach angle, which we then use to determine the ion sound speed from the known upstream velocity. We use the sound speed to infer the value of [Formula: see text], where [Formula: see text] is the average ionization and T _e is the electron temperature. We use this diagnostic to measure the time-resolved velocity and sound speed of a supersonic ( M _S ∼ 8), super-Alfvénic ( M _A ∼ 2) aluminum plasma generated during the ablation stage of an exploding wire array on the Magpie generator (1.4 MA, 250 ns). The velocity and [Formula: see text] measurements agree well with the optical Thompson scattering measurements reported in the literature and with 3D resistive magnetohydrodynamic simulations in GORGON.

• Sponsoring Organization: USDOE
• Grant/Contract Number: PHY2108050; SC0020434; NA0003764; F03-02NA00057; SC-0001063; NA0003868; FG02-91-ER54109
• OSTI ID: 1893977
• Journal Information: Review of Scientific Instruments, Journal Name: Review of Scientific Instruments Vol. 93 Journal Issue: 10; ISSN 0034-6748
• Publisher: American Institute of Physics
• Country of Publication: United States
• Language: English