Development of a High-Current Hydrogen-Negative Ion Source for LHD-NBI System

概要

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We have developed a high-current hydrogen-negative ion source for a negative-ion-based NBI system in Large Helical Device(LHD). The ion source is a cesium-seeded volume-production source equipped with an external magnetic filter. An arc chamber is rectangular, the dimensions of which are 35cm×145cm in cross section and 21cm in depth. A three-grid single-stage accelerator is divided into five sections longitudinally, each of which has 154(14×11)apertures in an area of 25cm×25cm. The ion source was tested in the negative-ion-based NBI teststand, and 25A of the negative ion beam is incident on a beam dump positioned at 13m downstream with an energy of 104keV for 1sec. Multi-beamlets of 770 are focused on a focal point of 13m downstream with an averaged divergence angle of 10 mrad by a geometrical arrangement of five sections of grid and an aperture displacement technique of the grounded grid. A uniform beam in the vertical direction over 125cm was obtained through uniform plasma production in the arc chamber by balancing individual arc currents flowing through each filament. Long-pulse beam production was realized, and 1.3MW of the negative ion beam was incident on the beam dump for 10sec, and the temperature rise of the cooling water for the extraction and the grounded grids was almost saturated. These results satisfy the primary specification of the LHD-NBI system.
社団法人プラズマ・核融合学会の論文
1998-12-25