Properties of a large volume glow discharge helium plasma by measuring the broadband microwave phase shift in different pressures

A novel type of large cylindrical glow discharge helium plasma with a 50 cm diameter and a 40 cm thickness is presented, which is powered by dual reticular electrodes under an AC source with frequency 20 kHz. Microwave characteristics are studied using vector network analyzer with two broadband antennae ranging from 2 GHz to 18 GHz to measure the phase shift. The phase shift under varying gas pressure is used to calculate the electron density ne , which varies from 2.36 × 1016 m−3 to 11.2 × 1016 m−3 under different discharge conditions. The measured results provide a method to diagnose helium plasma with large volume, high pressure, and high collision rate, especially for the condition which the probe is not suitable.