Acceleration experiments for an intense H- ion beam

A. Ando, Y. Takeiri, O. Kaneko, Y. Oka, K. Tsumori, E. Asano, T. Kawamoto, R. Akiyama, T. Kuroda

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4 Citations (Scopus)

Abstract

Intense H- beams have been extracted from a large multicusp plasma source operated with cesium seeding. The H- beams were accelerated up to 100 keV by a single-stage or a two-stage electrode system. Spatial profiles of the beams are measured calorimetrically and the beam divergence angle is obtained from half of the e-folding width. A minimum beam divergence angle of 5 mrads is achieved at a H- current density of 30 mA/cm2 with a beam energy of 100 keV. The ratio of acceleration current to H- current increases abruptly when a H- current saturates in the space charge limited region. This enhancement is mainly due to secondary electrons caused by the intersection of H- beams with an extraction grid. When the operating gas pressure decreases, the ratio of the acceleration current to the H- current decreases. This is related to a stripping loss of H- ions in the electrodes. A beam divergence angle reaches a minimum when a ratio of Vacc to Vext is set at an optimum value of 1.6 in the single-stage acceleration. This ratio is almost the same as that in the double-stage acceleration, where the optimum ratio of Eaccl/Eext is 1.5. In the optimum E accl/Eext ratio the divergence angle is not affected by Vacc2. The divergence angle can be reduced by changing V acc2 even if the ratio of Eaccl/Eext is not optimized. The beam steering effect by permanent magnets buried in an extraction grid is observed in nine beamlets experiments. A simple calculation of a single particle trajectory gives a good approximation of the beam deflection angle.

Original languageEnglish
Pages (from-to)5412-5418
Number of pages7
JournalReview of Scientific Instruments
Volume66
Issue number12
DOIs
Publication statusPublished - 1995 Dec 1

ASJC Scopus subject areas

  • Instrumentation

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