Development of negative ion based NBI system for JT-60U

Development for enhancing the beam characteristics in the N-NBI system for JT-60U has been continued since 1996. In order to increase beam power and duration time, a few countermeasures for improvement of source plasma non-uniformity have been tried. The first is changing are current limiting resistors for changing are current distribution, the second is regulating filament temperature for altering an: discharge mode, the third is optimizing a magnetic barrier in an: chamber, and the fourth is blocking the beam acceleration at a strongly non-uniform source plasma area by masking both upper and lower edge of plasma grid AU of these countermeasures have been confirmed to be effective.