A plasma target for neutralization of the negative ion beam

Abstract

The results of the experimental study of build-up and confinement of low-temperature plasma target for neutralization of high energy negative ion beam are presented in the paper. The cylindrical vacuum chamber of the plasma target is 1.2 m long and 0.2 m in diameter. The axisymmetric multicusp magnetic field is formed at the periphery of the target chamber by using an array of the permanent NdFeB magnets, which are placed closely on the thin chamber walls. The target chamber is ended by the two diaphragms with 0.1m diameter apertures for the negative ion beam passing through. For reduction of the plasma losses through the ends, the inverse magnetic field are formed in the apertures. The plasma is produced in the target by ionization of the working gas by electrons, which emitted by six plane LaB6 cathodes, which are placed uniformly over azimuth at the center of the plasma target. The discharge duration is set to 1 s. In short pulses at 300 kW power, the hydrogen plasma with density ni ≈ 2.5 · 1013 cm-3 is produced. Spatial profiles of the plasma parameters in the target were measured.