HEAVY-ION-BEAM-INDUCED LASER SCHEME IN HYDROGENLIKE HE+

A recombination laser scheme on the lambda = 164 nm n = 3 -2 transitio n in H-like He+ ions is studied. Doubly ionized helium is produced in a 300-mbar He gastarget using a pulsed 110-MeV S-32(8+) heavy-ion bea m. The cross section for this ionization process is 9.2x10(-17) cm(2). Since the flux of existing heavy-ion accelerators is limited, plasmas generated directly by heavy-ion beams reach only an electron density n(e) on the order of 10(12) cm(-3). In order to study three body recom bination of He2+ ions with free electrons, electron densities n, of at least 10(14) cm(-3) and electron temperatures T-e well below 0.1 eV a re necessary. In this study the required electron density is produced by means of a special gas discharge. Time evolution of the plasma para meters n(e) and T-e in the plasma target prior to the arrival of the h eavy-ion beam pulse is described by a numerical model. Light intensity on the 164-nm n=3-2 transition following heavy-ion beam excitation is measured using time resolved optical spectroscopy. Light intensity on this spectral line and its dependence from electron density and tempe rature in the plasma is interpreted using a system of coupled rate equ ations modeling the He+ system. [S1063-651X(98)08211-7].