Plasma Injection into a Vacuum Magnetic Field

Abstract

Experimental measurements have been made on the axial injection of dense, highly directed plasmas of deuterium, hydrogen, and helium into a cusp magnetic field. Magnetic probe measurements show that during injection a diamagnetic region forms over a radius which varies inversely with the axial field strength for each type plasma. Axial velocities of the dense plasma are measured with a movable loop‐permanent magnet assembly. For deuterium the mean axial velocity was v₀ = 8.7 ± 0.5 × 10⁶ cm/sec, for helium v₀ = 1.08 ± 0.5 × 10⁷ cm/sec and for hydrogen 1.4 ± 0.1 × 10⁷ cm/sec. Optical emission line shapes for helium show a Doppler width equal to 118 ± 11 ev in the peak axial field region during injection. Deuterium emission lines gave both ion kinetic temperature and ion densities after injection which indicate reasonable containment with high β. A simple hydrodynamic model of a supersonic diffuser compares favorably with the experimental observations during injection for both deuterium and helium.