“…Of particular interest are those results obtained for projectiles in high charge states at high velocity, v. In the discussion below, regimes of validity are delineated for each of the mechanisms, and ratios of double-to-single ionization cross sections are presented and compared with theoretical predictions. Double ionization of helium by charged particles has been the subject of numerous experimental and theoretical investigations for nearly three decades [Mittleman 1966, Byron and Joachain 1966, Horsdal-Pedersen and Larson 1979, McGuire 1982, Knudsen et al 1984, Andersen et al 1986, 1987, Reading and Ford 1987a, Reading and Ford 1987b, Giese and Horsdal 1988, Kamber et al 1988, Reading et al 1989, Herber et al 1990]. Much ofthe interest in double ionization by charged particles stems from its fundamental nature [Mittleman 1966, Byron and Joachain 1966, McGuire 1982 and its relationship to double ionization by photons [HorsdalPedersen and Larsen 1979, Samson 1990, Levin et al 1991] (see Sec.…”