Development of High-Power-Density Ion Beam System with High-Repetition Pulse Operation

Abstract

A high-power-density ion beam system with high-repetition pulses was successfully developed. In the ITER (International Thermonuclear Experimental Reactor), it is anticipated that an intermittent thermal flux, due to the edge localized mode (ELM), to the plasma facing materials causes severe damage of the mechanical properties. Therefore, it is very important to study the effect of ELM phenomena. We already developed an ion beam system with a power density as high as ∼1 GW/m² around the focal point of the beam. In order to imitate the intermittent high-power-density pulsed flux, we modified the beam operation method and part of the acceleration power supply. A pulsed helium ion beam with the beam width of 2 ms and 4 ms intervals between pulses was successfully extracted. In this case, beam energy, current and power were ∼22 keV, ∼40 A, and ∼0.88 MW, respectively. This high-repetition pulsed helium ion beam with high power density (∼300 MW/m² ) was irradiated to a tungsten material. It was found that this repetitive short-pulse irradiation caused less surface damage compared with long-pulse irradiation, even when the total amount of irradiation fluence (1.5× 10²² particles/m²) was the same for each condition. This would provide important data for the design of ITER diverter.