A Source of He++ Ions for a Van De Graaff Accelerator

An ion source for the production of well-collimated beams of doubly charged helium ions has been constructed, tested, and put into operation. It consists of an einzel lens to maintain a well-focussed beam and a crossed field analyzer that permits only one component of the beam to leave the source assembly. Beam currents of 1 to 2 microamperes of analyzed (He4)++ or (He3)++ ions are obtainable from the source assembly for acceleration in a Van de Graaff generator. Up to 0.25 microamperes of (He4)++ beam has been obtained at the entrance to the beam tubes after acceleration in a Van de Graaff generator and after momentum analysis, but this figure is subject to improvement. The source can also be used with H+, D+, and He+ ions. By applying an RF voltage to the deflector plates, it has been found possible to pulse the singly ionized beams. A pulsed beam of 1/2 μa of (He3)+ ions with a pulse width of 7 ns has been obtained. The design and installation of the source is described.