Design of a 500 KEV negative-ion-based NBI system for JT-60U

Abstract The design of a negative-ion-based NBI system for JT-60U rated to inject neutral beams of 500 keV, 10 MW for 10 seconds is described. The neutral beam is injected tangentially from a beamline with two ion sources. The ion source is a cesium-seeded multicusp volume source. The acceleration current per source is 22 A with deuterium at a current density of 13 mA/cm2. The operating pressure of the plasma generator is less than 0.3 Pa. A three-stage multi-aperture electrostatic acceleration system is adopted as the accelerator. Residual ions are deflected horizontally by the combined magnetic fields produced by the deflecting coils and the stray field from the tokamak. The deflecting magnetic field is swept with a frequency of 2 Hz. An acceleration power supply of 490 kV, 64 A is inverter type power supply. The freauency of the inverters is 150 Hz. The system will be completed in 1996. The system will be the first negative-ion-based NBI system in the world.