Stripping in Foils and Gases

Equilibrium charge state distributions have been measured in many laboratories for both solids and gases with ions of a very large number of elements, and the range of ion velocities has been extended as new accellerators have become available. Many different charge changing cross sections contribute to any given equilibrium distribution so that direct measurement is preferable to computer predictions in cases where cross-section data are not known. Engineering difficulties due to short foil life under bombardment, especially at low energies, cause the choice of strippers in accelerators to be uncertain. Recent work on nonequilibrium charge distributions from small angle scattering in gas targets suggests that the intensity penalties incurred with gas stripping will be accept, able for a wide variety of applications. For large tandem accelerators, the use of gas strippers may depend upon the current-carrying capacity of the negative ion accelerator tube.