Development of the Long Pulse Negative Ion Source for ITER

Abstract

A model of the ion source designed for the neutral beam injectors of the International Thermonuclear Experimental Reactor (ITER), the KAMABOKO III ion source, is being tested on the MANTIS test stand at the DRFC Cadarache in collaboration with JAERI, Japan, who designed and supplied the ion source. The ion source is attached to a 3 grid 30 keV accelerator (also supplied by JAERI) and the accelerated negative ion current is determined from the energy deposited on a calorimeter located 1.6 m from the source.During experiments on MANTIS three adverse effects of long pulse operation were found:• The negative ion current to the calorimeter is ≈50% of that obtained from short pulse operation• Increasing the plasma grid (PG) temperature results in ⩽40% enhancement in negative ion yield, substantially below that reported for short pulse operation, ⩾100%.• The caesium “consumption” is up to 1500 times that expected.Results presented here indicate that each of these is, at least partially, explained by thermal effe...