Hydrogen negative ion beam acceleration in a multiaperture five-stage electrostatic accelerator

To develop a high power negative ion source/accelerator for 1 MeV class neutral beam injector, hydrogen negative ion beam acceleration has been studied using a five-stage, multiaperture electrostatic accelerator. After conditioning each accelerator stage, the negative ions are accelerated to 1 MeV successfully with a drain current of 25 mA for 1 s. Cs was introduced into the ion source to produce higher current density. The highenst acceleration current density of 15 mA/cm2 was successfully accelerated up to an energy of 700 keV for 1 s, keeping the optimum perveance. The total acceleration current of 200 mA was extracted from nine central apertures 14 mm diameter each. A preliminary measurement of the heat load in the accelerator showed that the direct interception of the beam for the first grid and the third grid was negligibly small. The highest heat load was 4.5% of the input power at the second grid.