Performance Enhancement of Negative Ion Sources for the JT-60U Tokamak

摘要

The negative ion based neutral beam system now operating for plasma heating andcurrent drive on the large JT-60U tokamak marked the first application of negative ion source technology to the production of high current, high voltage beams for conversion to neutral atomic beams. This pioneering system has demonstrated the technical feasibility of negative ion based neutral beams for future fusion devices. Because this was a very large advance in the state of the art with respect to all system parameters, the principal physical processes governing the performance of the ion source and accelerator were somewhat different than had been the case with earlier much smaller negative ion sources. We have explored the physical mechanisms limiting the power and pulse length capability of these large sources, and have implemented ameliorating changes to reduce power loading on the accelerator grids and increase the transmitted power fraction.