Behavior of a Cold Ion Plasma in a Toroidal Octupole

Abstract

By raising the background hydrogen gas pressure to ∼10−4 Torr and injecting 10-100 kW of 700-9000 MHz microwave power for ∼100 μsec, an afterglow plasma with n ∼ 109−1011 cm−3 and kTi < kTe ∼ 1 eV can be produced in the Wisconsin toroidal octupole. The particle lifetime is ∼3 msec, or somewhat longer than for a hot ion, gun injected plasma, and most (∼80%) of the plasma is lost to the hoops. The electron temperature decays rapidly as a result of inelastic electron-neutral collisions. By changing the magnetic field strength and microwave frequency, the density distribution can be varied, and a variety of fluctuations produced. These fluctuations do not appear to be an important source of plasma loss.