Source of helium ions twice ionized

An intense beam of α (He⁺⁺) particles has been obtained for use in an electrostatic accelerator, by a method of exchanging charges. A focussed He⁺ beam, supplied by a Philips-type ion source, is accelerated by a small Van de Graaff, in a tube with a pressure of 3.10^-4 mmHg, up to an energy ranging from 200 to 500 keV. This beam then passes through a gaseous layer whose pressure can be varied substantially from 10^-3 to 1 mm Hg. The He⁺ ions undergo shocks with the atoms of the gaseous layer. There is a sequence of captures and losses of electrons that result in an equilibrium between He, He⁺ and He⁺⁺, a function of the energy of the incident particles and the density of the gaseous layer. Reprint of a paper published in 'Comptes Rendus des Seances de l'Academie des Sciences', t. 238, sitting of Apr 12, 1954, p. 1578-1580.