Production of High-Q Ions by Laser Bombardment Method

The expanding plasma produced when an intense pulse of laser radiation is focused in vacuum onto a solid target has been used as a source of highly stripped ions for collision cross-section measurements. Usable fluxes of carbon nuclei at energies of a few hundred eV/charge have been obtained by irradiation of graphite with pulses of CO2 laser radiation at a focused power density of 3 × 1010 W/cm2. Bombardment of aluminum and iron targets at comparable power levels have yielded ions of maximum charges of 9 and 16 respectively. A time-of-flight apparatus has been constructed to utilize the laser source for measurement of electron capture cross sections for highly stripped ions in gases at energies in the few hundred eV/charge range. Apertures collimate an ion beam from the plasma blowoff, and an electrostatic analyzer selects ions from the expanding plasma which have the same energy per charge. The beam is directed through a gas target cell, charge analyzed once more by deceleration, and detected by a channel plate electron multiplier used in a current amplification mode. Electron capture cross sections have been measured for C+q ions, q = 3, 4, 5 in H2 at energies ranging from 150-1160 eV/charge. Preliminary data have been obtained for carbon ions in atomic hydrogen, and similar measurements are planned for O+q and Fe+q ions.