Development of high power ion sources for fusion (invited)

Abstract

Recent progress and development activities regarding high power ion sources for fusion researches are reviewed. High power positive ion sources, which have progressed in the 1980s, played important roles in fusion research. Most of the ion sources developed for major neutral beam injection (NBI) systems are a large area magnetic multipole type with tungsten cathode, and produce tens of amperes of positive hydrogen/deuterium/tritium ion beams at the energy around 100 keV. The NBI systems based on these ion sources delivered tens of MW neutral beams to the plasmas, and contributed to produce high temperature plasmas in the break-even condition in the tokamak type fusion devices. Meanwhile, R and D of high current negative ion sources were carried out for a high energy NBI system to be utilized not only for plasma heating, but also for the steady state operation and stable plasma control in the fusion burning plasmas. In the 1990s, rapid progress of high current negative ion sources has been made. Particularly, a cesiated magnetic filter source with high plasma confinement has, for the first time, produced a multi-ampere negative ion beam stably in the conditions required for the negative-ion-based NBI systems, namely high negative ion current density, low operating pressure, low extracted electron current, and good beamlet optics. Based on this progress, a 500 keV 10 MW NBI system has been developed for JT-60U at the Japan Atomic Energy Research Institute, and construction of a 180 keV 15 MW NBI system is carried on at the National Institute for Fusion Science in Japan. The same type of negative ion source is applied to the design of a 1 MeV NBI system for the International Thermonuclear Experimental Reactor (ITER).