Experimental Study on the Hollow Cathode Discharge

Abstract

Hollow cathode discharges (HCDs), especially microhollow cathode discharges (MHCDs), have more and more applications in various fields. In order to investigate the working range of the so called “hollow cathode effect”, the experiments of low-pressure $(20\text{Pa}\leq p\leq 800\text{Pa})$ hollow cathode discharges were carried out between a plane anode and a cathode made of stainless steel with a cylindrical cavity. The diameter $D$ and depth $h$ of the cavity were 2cm and 4cm respectively. Argon was chosen as the working gas. The voltage-current characteristic curves of the hollow cathode discharges under different gas pressure $p$ were obtained. It is found that the lower boundary of working range of the hollow cathode effect in our experiment is $p\cdot D\approx 2p\cdot d_{n}$ where $d_{n}$ is the cathode layer thickness of normal glow discharge. This means that for the optimal operation of HCDs, the cavity in the cathode should be small just enough to house two opposing glow discharges, i.e., $D\approx 2d_{n}$ . The value of $d_{n}$ is important. In order to determine the cathode layer thickness $d_{n}$ in the normal glow discharge, the computational method based on the iteration and the experimental method with a Langmuir probe were used in this paper. The upper boundary of the working range is that $p\cdot D$ is about several Torr.cm, less than 10 Torr.cm in general. Compared with glow discharges between parallel-plane electrodes, current density will increase largely in the hollow cathode discharges when the hollow cathode effect occurs, leading to a great increasing of the operating range of the discharge current. The similarity law of hollow cathode discharges and its physical mechanism between two similar hollow cathode discharge gaps were also studied in this paper.