Plasma potential measurements using an emissive probe made of oxide cathode

Abstract

A novel emissive probe consisting of an oxide cathode coating is developed to achieve a low operating temperature and long service life. The properties of the novel emissive probe are investigated in detail, in comparison with a traditional tungsten emissive probe, including the operating temperature, the electron emission capability and the plasma potential measurement. Studies of the operating temperature and electron emission capability show that the tungsten emissive probe usually works at a temperature of 1800 K–2200 K while the oxide cathode emissive probe can function at about 1200 K–1400 K. In addition, plasma potential measurements using the oxide cathode emissive probe with different techniques have been accomplished in microwave electron cyclotron resonance plasmas with different discharge powers. It is found that a reliable plasma potential can be obtained using the improved inflection point method and the hot probe with zero emission limit method, while the floating point method is invalid for the oxide cathode emissive probe.