ION SHEATH OSCILLATIONS IN DOUBLE PLASMA MACHINES

The oscillations of the ion sheath around a negatively biased grid in dp machines are studied experimentally and compared with PIC simulatio ns. It is argued that for asymmetric densities in the source and targe t chamber the ion sheath on the low density side becomes unstable to v irtual anode oscillations which act as a driver for the ion bounce osc illations in the sheath. Resonant coupling with the ion plasma frequen cy at the sheath edge of the source plasma is found. Subharmonic coupl ing with potential relaxation oscillations may explain the period doub ling route to chaos found in such systems.