Effects of anode material on the evolution of anode plasma and characteristics of intense electron beam diode

Abstract

In this paper, three kinds of materials, graphite, titanium (Ti) and molybdenum (Mo) are respectively used as anodes to figure out the influence factors of anode material on the characteristics of the intense electron beam diode. The results point out that the characteristics of diode are mainly determined by the cathode plasma motion under a 15 mm diode gap, in which the typical electron beam parameters are 280 kV, 3.5 kA. When the diode gap is reduced to 5 mm, the voltage of the electron beam reduces to about 200 kV, and its current increases to more than 8.2 kA. It is found by calculation that the surface temperatures of Ti and Mo anodes are higher than their melting points. The diode plasma luminescence images show that Ti and Mo anodes produce plasmas soon after the bombardment of electron beams. Ti lines and Mo lines are respectively found in the plasma composition of Ti and Mo anode diodes. Surface melting traces are also observed on Ti and Mo anodes by comparing the micromorphologies before and after bombardment of electron beam. These results suggest that the time of anode plasma generation is closely related to anode material. Compared with graphite, metal Ti and Mo anode are more likely to produce large amounts of plasma due to their more significant temperature rise effect. According to the moment that anode plasma begins to generate, the average expansion velocities of cathode and anode plasma are estimated by fitting the improved space-charge limited flow model. This reveals that generation and motion of the anode plasma significantly affect the characteristics of intense electron beam diode.