ISX-B neutral beam injector experiment on a prototype beam line

Abstract

Two PLT‐injector‐type duoPIGatron sources, modified further by shaping the beam‐forming apertures, have been tested and experimented on a protype beam line similar to the ISX‐B neutral beam injection system. The accelerator column modification has resulted in an increase of the beam power transmission efficiency from that of the straight‐bore aperture by 50%. Maximum neutral beam powers achieved on a 28‐cm‐diam target simulating the ISX‐B plasma, located 4.1 m downstream from the source, are ?910 kW of H⁰ at an accelerator power of 42 kV and 61 A and ?1020 kW of D⁰ at 43 kV and 55 A. Measurements have been made to investigate the following: the effects on beam optics of aperture shape, aspect ratio, and different ions (H⁺ or D⁺); the distribution of beam power deposition along the beam line; ion species compositions; and background pressure behavior due to scrape‐off beam particles. The injectors have been shown to be characterized by an optimum perveance of 6×10⁻⁶ AV^−3/2 for an effective extraction area of 142 cm² (1799 apertures), which is approximately invariant over the beam energies tried (viz., 25‐45 keV).