Neutral beam line ion beam raster scanning with a dipole magnet

Abstract

An ion beam raster scanning method utilizing a wide gap dipole magnet has been developed at the Oak Ridge National Laboratory that can reduce the time-averaged amplitude of the ion beam power density on the ion beam dump by factors of 3 to 6. Time-varying in-phase and out-of-phase modulation current components are used in the dipole magnet coils in order to generate a time-varying magnetic field shape and magnitude whose magnetostatic central surface position oscillates between the two magnet iron poles. This time-varying three-dimensional (3-D) magnetic field shape deflects the ion beam onto an ion dump and can be programmed to produce a raster scan pattern that depends on the coil current modulation pattern. The 3-D magnetic field produced by an iron yoke system has been computed for different coil current ratios using a finite-element integral method. Ion orbit equations do not need to include the small space-charge forces present in the beam used for these purposes. The time-averaged amplitude of beam dump power densities should be lowered by a factor of 6 by sharing the beam impact pattern over a larger area with a short raster scan period compared to the ion dump thermal time constant.