Some consequences to ion source behavior of high plasma drift velocity

We consider the case of energetic ion beam formation when the ion streaming velocity within the source plasma is substantial, i.e., when the ions have a drift speed (in the positive downstream direction) that is on the order of or greater than the ion acoustic speed in the plasma. Some interesting c onsequences can follow, including the capability of a negatively biased sub strate located in the plasma stream to maintain high bias voltage, and of a n ion source with no extractor or "conventionally poor" extractor providing a kind of plasma immersion ion implantation mode of operation. Here we sum marize the kind of plasma geometry in which this situation can occur, and d escribe some experimental observations we've made of these effects, with re ference to a simple theoretical basis for the mechanism. (C) 2000 American Institute of Physics. [S0034-6748(00)65502-8].