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 the low operating temperature and long service life of the emissive probe. Compared with the traditional tungsten emissive probe, the properties of the novel emissive probe are investigated in detail, including the operating temperature, the electron emission capability and the plasma potential measurement. Studies of the operating temperature and the electron emission capability show that the tungsten emissive probe usually works at a temperature of 1800-2200 K, while the oxide cathode emissive probe can function at about 1200-1400 K. In addition, the plasma potential measurements using the oxide cathode emissive probe with different techniques have also been accomplished in MW-ECR plasmas with different discharge powers. It is found that the reliable plasma potential can be obtained by using the improved inflection point (IIP) method and the hot probe with zero emission limit (HP-ZEL) method, while the floating point (FP) method is invalid for the oxide cathode emissive probe.