To prevent an electron on the downstream side from entering an acceleration space even when an impression voltage by a deceleration electrode is lowered for preventing problematic generation of a new electron in the acceleration space due to collision of the ion on the downstream side to the deceleration electrode.

This beam accelerator 19 for an ion mass separator constructed of a conductor 6b in an exit part 3 of a curved ion deflection casing 5 and the deceleration electrode 15 and the acceleration electrode 16 arranged sequentially on the downstream side of the conductor 6b is provided with the acceleration space 17 with a required longitudinal width A arranged in the front and back parts of the ion beam bending direction. By means of the beam accelerator 19 for the ion mass separator, an ion beam with a desired mass among the curved ion beams is accelerated in the acceleration space 17 to be taken out to the downstream side. A positive ion retardation electrode 20, to which positive voltage is impressed, is arranged between the deceleration electrode 15 and the acceleration electrode 16.

COPYRIGHT: (C)2006,JPO&NCIPI