Projectile electron loss and capture in MeV/u collisions of U28+ with H2, N2 and Ar

Electron capture and loss cross sections for U28+. colliding with Hi(2), N-2 and Ar were measured at 3.5 and 6.5 MeV/u. These data were used to benchmark-n-body calculations using the classical trajectory Monte Carlo method. The n-body calculations include electrons on both nuclear centres and all electron-electron and electron-nuclear interactions between each centre. For the U28+ ion, 36 electrons were incorporated in the calculations (4s(2)4p(6)4d (10)4f (14)5s(2)5p(2)). while for the H-2, N-2, and Ar targets all electrons were used except those for the K-shell of Ar, leading to 39-, 45- and 54-body calculations, respectively. Projectile electron loss was predicted for U28+ at energies from 2 to 150 MeV/u. Only for the H-target did the projectile electron loss cross section decrease approximately as E-1. The heavier targets exhibited slower energy dependences, contrary to the E-1 prediction of one-electron theories. Moreover. the collisional interactions are quite strong with an average of 1.64 and 2.88 electrons removed from the U28+, ion at 10 MeV/u in each collision with N and Ar. respectively. These data and calculations were used to assess the vacuum requirements for the SIS-100 synchrotron ring under construction at GSI-Darmstadt. For the residual gases expected to be in the ring. the U28+ lifetime was found to be essentially constant as a function of projectile enema. leading to very stringent vacuum requirements.