Experimental and Simulation Study on Cathode Spot Characteristics of Surface Flashover Ion Sources

ABSTRACT The surface flashover ion source is a possible development direction of micro/nano ion source technology. In this paper, a two‐electrode surface flashover ion source was fabricated by deposition of titanium film on a ceramic substrate by magnetron sputtering. The evolution of luminescence image, temperature distribution and erosion characteristics of this ion source during discharge were analyzed by using a high‐speed camera, a multispectral temperature measurement method and a microscope. A simplified simulation model of the initial discharge of this ion source is established by using a two‐dimensional particle‐in‐cell coupled with Direct Simulation Monte Carlo method. The evolution characteristics of plasma distribution, electric field distribution and potential distribution during the discharge process were obtained. It is shown that the electric field at the metal‐ceramic‐vacuum “triple junction” is suppressed during the discharge process, and field‐induced electron emission is formed at the edge of the cathode, which leads to the discharge. In addition, it is revealed that the high density plasma accumulated near the cathode will form a sheath, which enlarges the strong electric field region and makes the cathode spot develop along the cathode surface. This is the reason why the discharge process of this ion source is different from that of the usual surface flashover. These findings provide support for further understanding of the physical mechanism of surface flashover ion sources.