Compact, maintainable 80-keV neutral beam module

A compact, maintainable 80-kev arc chamber, extractor module for a neutral beam system immersed in a vacuum of <10-2 torr, incorporating a nested 60-kev gradient shield located midway between the high voltage ion source and surrounding grounded frame. The shield reduces breakdown or arcing path length without increasing the voltage gradient, tends to keep electric fields normal to conducting surfaces rather than skewed and reduces the peak electric field around irregularities on the 80-kev electrodes. The arc chamber or ion source is mounted separately from the extractor or ion accelerator to reduce misalignment of the accelerator and to permit separate maintenance to be performed on these systems. The separate mounting of the ion source provides for maintaining same without removing the ion accelerator