Production of “Fast” and “Exotic” Negative Ions in He II

The “fast” negative ion provides, in principle, the basis for a determination of the Landau critical velocity for roton creation in HeII under its SVP; but precise measurements will require a more reliable ion source than those reported hitherto. It is known that a glow discharge above the liquid surface is necessary, but not sufficient, for the production of large fluxes of “fast” or “exotic” ions. Several new electrode geometries have been tested with HeII at 1.03K with variable results which are discussed. We report the new observation that the discharge must be white (rather than the more usual violet) for “fast” or “exotic” ions to be generated.