High voltage sheath behavior in a drifting plasma

We describe a simple experiment in which a high voltage substrate is immersed in a streaming, vacuum-arc-produced, titanium plasma. We show that high substrate voltages that are orders of magnitude greater than the electron temperature can be sustained, effectively on a direct current basis, by a well-rounded substrate (no sharp points or edges) immersed in the plasma stream, for the case of a plasma with density not too low (greater than about 10(9) cm(-3)) and with drift velocity that is equal to or greater than the sheath propagation speed, typically of order the ion acoustic speed. This result is significant not only from a basic plasma physics perspective, but also for the technology of carrying out plasma immersion surface processing. (C) 1999 American Institute of Physics. [S0003-6951(99)03517-2].