Enhanced density in a stabilized high-current plasma beam

Abstract

Abstract Externally generated, axial magnetic fields used to confine high-current plasma beams in compact linear devices are usually 0.5 Tesla or less and can be insufficient to suppress plasma instabilities. Such an issue is addressed in this study by closely winding the current-carrying cable around a small chamber attached to the end of a linear device. The magnetic field generated inside the small chamber during the high-current pulse reached 0.8 Tesla at the peak current of 10.83 kA. Formation of a steady plasma beam through a mixture of argon, hydrogen and helium was photographed by a high-speed camera at the instant of the peak current. The beam width profile starts from over 24.8 mm at the upstream location and becomes thinner with distance down-stream. At the location of laser-interferometer measurement, at the right-most viewing window on the test chamber, the beam width was estimated as 7.4 mm and plasma density was evaluated to be 1.0 × 1022 m−3, an increase of two orders of magnitude compared to a previous study. A simple relationship was derived for the plasma density as a function of beam width. Based on examination of the metal target at the far end, the final beam width was estimated as 50 µm, with the plasma density evaluated to be 4.31 × 1022 m−3, with a calculated ion energy of 4.35 keV, consistent with x-ray spectrum measurements.