On Recombination Losses in the Electron Cooling of Highly Charged Ions

Abstract

In this contribution we investigate the loss of a stored beam of Ar15+ ions through dielectronic recombination (DR) with copropagating, equal velocity electrons (e.g., in an electron cooler). We find that the Ar15+ 1s22s ion can undergo dielectronic recombination through a set of doubly excited states 1s22p10l in Ar14+ that lies just above the ionization limit. Recombination occurs when the DR resonance profile overlaps the electron velocity profile as viewed from the reference frame of an ion. The recombination rate coefficient is found for the case of a flattened electron distribution interacting with a one-dimensional ion beam. Losses generally depend upon the electron density and temperature, the initial and final ion temperatures, the cooling rate, and very sensitively on the energies of the participating auto-ionizing states. We find, however, for the model adopted, that the losses depend only weakly on the ion temperature. Using typical values for electron and ion temperatures and the present theoretical atomic data, we find that DR losses of a continuously cooled Ar15+ ion beam are negligible, giving a beam storage half-life which is much longer than those due to electron capture from the rest gas and radiative recombination from the electron beam. In a worst case, where the energy of the maximum DR cross section was chosen to coincide with the maximum of the electron energy distribution, the conclusion based on the original data is still valid.