Electron Beam Probing of Plasmas

Abstract

Measurement of static and dynamic electric fields in plasmas presents considerable experimental difficulties, particularly in regions such as sheaths, where the fields vary rapidly in space and common techniques such as the use of probes are not applicable. An extremely powerful approach is to employ an electron beam probe. This technique is a very old one which in recent years has passed through several stages of refinement. The authors review the previous work and describe in detail a system suitable for measuring accurately dc and rf fields up to several hundred Mc in low pressure discharges. The apparatus has been used to make a wide variety of measurements of plasma properties, and the associated techniques that have been developed are presented. These include methods of plasma production and of precision measurement of rf fields in amplitude and phase.