Measurement of pulsed-power-driven magnetic fields via proton deflectometry

Abstract

Measuring magnetic field and current distribution in Z-pinch plasma systems is crucial to the validation of Z-pinch theory. In this letter, the demonstration of proton deflectometry to pulsed-power-driven loads at the mega-amp scale is presented, which is capable of making more detailed field maps in high-density regions of plasmas. In this method, a laser-driven, broad-spectrum, MeV-energy proton beam is directed through a pulsed-power-driven plasma system, and the resulting deflections are measured to examine configuration of magnetic fields and to infer the currents that support them. The technique was first demonstrated on simple short-circuit loads, and the results are in excellent agreement with numerical simulations providing reliable estimates of the field and current configurations. It was then applied to a more complex—radial foil—plasma load. The measurements show unexpected proton deflections that exhibit the complexity of the plasma load and that with further analysis will reveal details about the current and magnetic field topology in this complex configuration.

Proton deflectometry of a capacitor coil target along two axes

“…Proton deflectometry has been used in single-and dualaxis configurations to diagnose magnetic fields in laserheated plasmas [29,30] and pulsed power discharges [31,32] . Of these different methods, comparing simultaneous dual-axis images has the clear advantage that it allows one to examine E/B-fields under identical conditions from two directions [30] .…”

Measurements of the spatial magnetic field distribution in a z-pinch plasma throughout the stagnation process

“…In general, spectroscopic methods based on the Zeeman effect for the determination of magnetic fields in plasmas, are limited due to their sensitivity to density-or temperature-induced broadenings [4,5]. Alternative approaches to Zeeman spectroscopy are based on Farady rotation [6][7][8][9], B probes [10][11][12][13] or proton beam deflectometry [14][15][16][17][18]. Yet each of the methods has its own difficulties.…”

Study of magnetic fields and current in the Z pinch at stagnation

“…Recently, proton deflectometry was applied to plasma in the wire array. 10 A radial Z pinch was probed by the laser-produced proton beam with energy of 4.4 MeV.…”