Pulsed Probe Studies on the Diffusion Coefficient of an Afterglow Plasma across a Magnetic Field

The pulsed probe technique is applied to an afterglow plasma to measure the diffusion coefficient across a magnetic field. This technique allows a determination of Langmuir probe curves accurately in a short time interval such as 5 µs. The experiments are performed in the ranges from 0 to 3000 Gauss and 0.05 to 1.0 Torr. The absolute values and the dependence of the diffusion coefficient on the magnetic field strength agree well with the ambipolar diffusion coefficient, but when B/P>10 in helium, irregular oscillations appear in the probe curves, and the plasma decay is much more rapid than would be predicted by a collisional diffusion theory.