Photographic, magnetic, and interferometric measurements of current sheet canting in a pulsed electromagnetic accelerator

The propagation speed and canting angle of current sheets in a pulsed electromagnetic accelerator were measured using three different techniques: highspeed photography, magnetic field probes, and laser interferometry. Current sheet canting may have adverse effects on accelerator performance. The goal of the present work is to provide a database of canting angles under a variety of experimental conditions. Eight different propellants (hydrogen, deuterium, helium, neon, argon, krypton, xenon, and methane) were tested in a rectangular-geometry accelerator, at pressures ranging from 50-400 mTorr. The photographic, magnetic, and interferometric diagnostics were used to infer the spatial configuration of the current sheet by measuring the its optical emission, current density, and electron density, respectively. The three techniques gave qualitative agreement; the magnetic and interferometric measurements gave general quantitative agreement as well. The canting angle was found to depend on the atomic mass of the propellant; lighter atoms were observed to yield less canting (the measured angles ranged from approximately 20° for deuterium to 70° for xenon). Hydrogen, deuterium, and methane were found to exhibit the peculiar, and possibly beneficial, property of having reduced current sheet canting at higher pressures.