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

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).