Suppression of accelerated electrons in a high-current large negative ion source
- National Institute for Fusion Science, Nagoya 464-01 (Japan)
Accelerated electrons, which would lead to high thermal load of grids, have been suppressed in a high-current large hydrogen negative ion source. An extraction grid, with apertures shaped as the secondary electrons generated on the grid aperture surface would be shielded against the acceleration electric field, works well to prevent the secondary electrons from leaking to the acceleration gap, compared with a straight aperture extraction grid. Although the strong magnetic field at the extraction grid also lowers the electron leakage downstream, the aperture shaping of the extraction grid is more effective for the suppression of the accelerated electrons. The acceleration efficiency, defined by the ratio of the negative-ion current to the acceleration drain current, is improved to around 85{percent}. There remains the accelerated electrons generated in the negative ion neutralization by collision with the residual neutral molecules during the acceleration. The direct interception of the accelerated negative ions with the downstream grid is small. The reduction of the operational gas pressure is quite important to achieve further improvement of the acceleration efficiency. {copyright} {ital 1997 American Institute of Physics.}
- OSTI ID:
- 496910
- Journal Information:
- Review of Scientific Instruments, Vol. 68, Issue 5; Other Information: PBD: May 1997
- Country of Publication:
- United States
- Language:
- English
Similar Records
Long-pulse operation of a cesium-seeded high-current large negative ion source
Beam acceleration test in negative-ion based NBI system for JT-60U