Characteristics of magnetically insulated diode in a multi-shot operation

We have evaluated beam characteristics in a multi-shot operation. The MID utilizes in the experiment is a racetrack. type diode, where flat electrodes of anode and cathode are utilized. On the anode, polyethylene sheet of 1 mm thickness is attached as an ion source. The MID is successively operated without breaking the vacuum. An ion current density (Ji) of 350 A/cm² is observed at the first shot when diode gap is 5 mm. The value decreases with increasing the number of shot and at 7th shot Ji is decreased to be less than 150 A/cm². After 7 shots, the surface of anode is observed and is found to be covered with sticked matter of metallic materials such as Zn, Al, Fe, Cu. These matelials seem to be produced by the ablation of the MID electrode. By eliminating the sticked matter form the surface, Ji is recovered to the initial value. The decrease of Ji is due to that the anode is covered with the sticked matter, which prevent the growth of anode plasma.