High-energy ions from a CO2 laser-produced plasma

Abstract

A time-of-flight ion collector was used to measure the energy of ions from the plasma produced by a high-power CO2 laser pulse focused on a flat polyethylene target. At laser irradiances exceeding 5×1012 W/cm2 at the target, high-energy ion current spikes appeared in addition to the ion current from an expanding thermalized plasma. The measured arrival time of these spikes was consistent with the assumption that ions of different charge and mass were accelerated by a high potential during the laser pulse which was produced by a steep pressure gradient at the plasma surface. The accelerating potential (equal to the measured energy of a singly charged ion) was proportional to the laser irradiance at the target to the 2/3 power. At an irradiance of 2×1014 W/cm2, the H+ ion energy was 140 keV. About 90% of the total ion energy appeared as high-energy ions.

High energy heavy ion jets emerging from laser plasma generated by long pulse laser beams from the NHELIX laser system at GSI

“…At higher laser intensities this may well be attributed to relativistic self focusing~Hora, 1975;Ehler, 1975!, and the effect of relativistic self-focusing or of its suppression is of utmost importance for plasma block generation, which is currently discussed also for a new fusion scheme in current literaturẽ Osman et al, 2004;Hora, 2004Wilks, 2005;Badziak et al, 2005!. The exact cause of the observed plasma jets is not known for this experiment.…”

Charge losses in expanding plasma created by an XeCl laser

“…Observing the data at 8 cm a lower ratio of the measured and predicted charge is reached. This decrease can be explained by the effect of the angular distribution of ion emission: the ion emission decreased with the increasing angle, , related to the target normal as 7 …”

Two-component structure in the angular emission of a laser-produced Ta plasma

“…Generally, in this range the ion spectra can be consistently interpreted if atomic interactions, namely ionization and threebody recombination, are assumed to be the essential processes dominating the expansion dynamics (Goforth and Hammerling 1976, Caruso et a1 1983, Kunz and Mulser 1982, Kunz 1986, Stevefelt and Collins 1991. When the laser intensity is enhanced to above about 1011 W cm-* additional structures have been observed in the ion energy distributions (Ehler 1975, Rohr ef ai 1989, Mann and Rohr 1992. These structures, sometimes called thermal and fast ion groups, have been correlated with the different electron temperatures that have been shown to exist in the focal region (Eidmann 1975, Stenz et a1 1977.…”