@techreport{oai:nifs-repository.repo.nii.ac.jp:00010275,
 author = {"Takeiri,  Y. and Oka,  Y. and Osakabe,  M. and Tsumori,  K. and Kaneko,  O. and Takanashi,  T. and Asano,  E. and Kawamoto,  T. and Akiyama,  R. and Kuroda,  T."},
 month = {Dec},
 note = {"Accelerated electrons, which would lead to high thermal load of grids, have been suppressed in a high-current large hydrogen negative ion source. An aperture of the extraction grid is shaped as the secondary electrons generated on the grid aperture surface would be shielded against the acceleration electric field. The shaped aperture extraction grid 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 %. 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 the further improvement of the acceleration efficiency."},
 title = {Suppression of Accelerated Electrons in a High-current Large Negative Ion Source},
 year = {1996}
}