Investigations of a wave packet instability

Summary form only given. Probe measurements in the triple plasma device DOLI-1 and in a multidipole soup-pot plasma device have shown, under certain conditions, a wave packet instability near the ion plasma frequency. This instability is similar to the continuous double-plasma instability found by P.J. Barret and R.G. Greaves (1989) and has been shown to be useful as a convenient measure of plasma flow. These wave packets and the mechanism that generates them are not well understood. The existence of the wave packets seems to depend on the presence of a sheath, in the present case the sheath at the grid between the source and target chambers of DOLI-1 and at the wall of the soup-pot. Among other wave packet characteristics, data have been obtained, showing the wave packet amplitude /spl delta/n/n (where n is the local plasma density) vs. both location in the sheath and potential drop across the sheath.