PRODUCTION AND TRAPPING OF HYDROGENLIKE AND BARE URANIUM IONS IN AN ELECTRON-BEAM ION-TRAP

An equilibrium population of approximately 500 hydrogenlike U91+ ions and ten fully stripped U92+ ions has been produced and trapped in an e lectron beam ion trap at 198-keV electron energy. The equilibrium ioni zation balance, determined from the intensities of radiative recombina tion x rays, gives values of 1.55 +/- 0.27 and 2.82 +/- 0.35 b for the electron impact ionization cross sections of hydrogenlike and heliuml ike uranium, respectively. These values are somewhat larger than relat ivistic distorted wave calculations, and much smaller than previous va lues inferred from stripping of accelerator beams.