K. Nishigori

Measurement of stopping power of 240 MeV argon ions in partially ionized helium discharge plasma

An energy loss of 240 MeV argon ions in a Z -pinch helium plasma has been for the first time observed throughout the entire pinching process. Standard Stark broadening analysis gives an electron density ranging from 4 to 6 × 10 17 cm −3 during the pinch. To deduce stopping power from the energy loss, the target thickness of the helium plasma has been evaluated assuming the mean charge of helium based on thermal equilibrium. The observed electron density and the mean charge of helium give a target thickness of 30 ± 3 μg cm −2 from 1 μs to 1.8 μs after the discharge ignition. The measured stopping power exceeds a tabulated value for cold helium gas by a factor of 2 to 3 around the time of the first pinch. The experimental stopping power is compared with theoretical values calculated using an equation of stopping power for a partially ionized plasma.

Energy loss of 6 MeV/u iron ions in partially ionized helium plasma

Energy loss of heavy ions in partially ionized helium plasma has been measured for ⁵⁶Fe ions of 6 MeV/u energy as a function of incident charge state. The charge states of iron ions were varied between 21 and 25. Electron density of the plasma formed by Z-pinch discharge ranged from 1×10¹⁸ to 4×10¹⁸ cm⁻³. Enhanced stopping in plasma has been observed compared to cold helium gas. The measured stopping power has been analyzed with an equation for partially ionized plasma.

Energy loss and effective charge of low-energy oxygen ions in partially ionized plasma

This article reports on the interaction between slow ions and a partially ionized plasma. Temporal evolutions of energy loss and charge distribution of 2.4 MeV oxygen beams in the laser-induced polyethylene plasma were measured. The charge distribution showed strong stripping ability in the early phase of the plasma. Stopping power deduced from the experimental energy loss was 1.9 times larger than that for the solid. The effective charge of the projectile ion was estimated from the yields of 4+ and 6+ states. The peak value of the effective charge was 1.4 times larger than that of the solid. The stopping power equation given by Sigmund was extended for the partially ionized plasma and it could reproduce the measured energy loss.

Beam-plasma interaction experiments between low-energy heavy ions and laser plasmas

Interaction of /spl ap/0.2 MeV/u oxygen ions with plasmas has been studied using laser plasma targets. We have observed high charge stripping at an early rise time of CO/sub 2/ laser and enhanced energy loss in LiH plasma.

Development and diagnostics of revised ion beam analyzer, ion or laser produced plasmas and X-ray pre-ionizer for gas lasers

A CCD element was tested as an end plate of a Thomson parabola analyzer. This element was directly irradiated by ion beams to produce electric signals associated with the beams. With a pin-hole camera, we also tried to measure the divergence angle of ion beams. Coated thin layers of ion source materials on a quartz plate were back-lighted by an e-beam pumped KrF laser, and the produced plasmas were observed to supply advanced source plasmas for pulsed ion diodes. We built a cryogenic target which was cooled by liquid nitrogen, and the ice-covered target was irradiated by proton beams to measure the concerned ablation processes. Fundamental characteristics of an X-ray source with wire-initiated discharge plasmas for pre-ionization of gas mixtures of our former discharge-pumped KrF laser in place of UV pre-ionization were also investigated.