Selected Charge States Research Articles

Charge Transfer and Ionization Cross Sections for Collisions of Tiq, Crq+, Feq+ and Niq+ Ions with Atomic Hydrogen

Using the classical Monte Carlo method and a Thomas-Fermi type pseudo-potential for the incompletely stripped ion, total electron capture and ionization cross sections have been calculated for the collisions of Tiq+, Crq+, Feq+ and Niq+ ions with hydrogen atoms for a large number of selected charge states in the energy range from 10 to 103keV/amu. The charge transfer cross sections for q > 6 confirm the scaling σcx/q vs. E/q0.5 in the entire energy range.

High- velocity ionic projectiles interacting with metals: Models and measurements of secondary-electron yields from gold and aluminum targets struck by 13.5–31.5 MeV 7Li and 9–63 MeV 12C

This study examines the fate of high-velocity, high- z ionic projectiles that impact metal targets, with the resulting secondary-electron yields being of particular interest. Three models are constructed for the evolution of the electron clouds of the projectiles as they pass through the first few tens of Å of target material, and the secondary-electron yields predicted from these models are then compared with yields measured at a Van de Graaff facility for 7Li and 12C ions of selected charge states and energies striking thick targets of gold and oxidized aluminum. These measurements provide a first look at the secondaries produced by impacts of z > 1 projectiles travelling with velocities above the Bohr speed (2.18 × 10 8 cm/s), thus allowing tests of the kinetic theory for secondary-electron emission to be made in a new regime. When the secondary-electron yields are high, it is found that measured yields are less than those predicted by theory, most probably because (1) the number of scatterable electrons along the pojectiles's path through the target material is limited (electron-depletion effects) and (2) the probability that scattered target electrons can reach the target's surface is lessened owing to large electrostatic potentials that are set up in the charge trail behind the projectile. It is found that secondary-electron yields for high- z ions are influenced by the attachment and stripping of electrons in the very shallow secondary-electron-escape layers (tens of Å).

Suggestion for a charge-state “enforcer” for heavy ion accelerators

The design of a new type of device, a charge-state “enforcer”, is described. This device, using an intense magnetic field with some static or rf electric field deflection, causes the stripping of a beam of heavy ions into a single selected charge state with nearly 100% efficiency. The requirements and limitations of the device are discussed.

Three-lens heavy ion beam transport system for terminals of two-stage (tandem) electrostatic accelerators

A beam transport system for heavy ions in a terminal of an electrostatic accelerator is described. The system consists of three electrostatic quadropole lenses and four apertures in series. The first two lenses act as the charge selector and the third lens acts as a matching lens for the high energy tube. Most of the unwanted charge states are filtered down to a background level at least one order of magnitude below the selected charge state level. With ±60 kV supplies the system can be used for ions with energy-to-charge ratio of 2.5 MeV per electronic charge. Whenever less filtering is tolerated, its use may be extended up to about 4 MeV per electronic charge.