Spectral measurements have been made of charged fusion products produced in deuterium ϩ helium-3 filled targets irradiated by the OMEGA laser system ͓T. R. Boehly et al., Opt. Commun. 133, 495 ͑1997͔͒. Comparing the energy shifts of four particle types has allowed two distinct physical processes to be probed: Electrostatic acceleration in the low-density corona and energy loss in the high-density target. When the fusion burn occurred during the laser pulse, particle energy shifts were dominated by acceleration effects. Using a simple model for the accelerating field region, the time history of the target electrostatic potential was found and shown to decay to zero soon after laser irradiation was complete. When the fusion burn occurred after the pulse, particle energy shifts were dominated by energy losses in the target, allowing fundamental charged-particle stopping-power predictions to be tested. The results provide the first experimental verification of the general form of stopping power theories over a wide velocity range.
The unique combination of a high-energy Nd:glass laser system and the intense heavy-ion beam at Gesellschaft für Schwerionenforschung (GSI) allowed for the first time the measurement of the stopping power of heavy ions in plasmas at the level of one percent solidstate density and temperatures of about 60 eV. Energy loss measurements of swift heavy ions (5-6 MeV/u) in a carbon plasma revealed a stopping power exceeding theoretical predictions which was not observed in earlier experiments at lower plasma densities. This discrepancy can be resolved assuming higher effective charge states of the projectiles resulting in a consistent picture for the measured parameter range.
Fast protons տ1 MeV have been observed on the 60-beam, 30 kJ OMEGA laser ͓T. R. Boehly et al., Opt. Commun. 133, 495 ͑1997͔͒ at an intensity IӍ10 15 W/cm 2 and a wavelength ϭ0.35 m. These energies are more than 5 times greater than those observed on previous, single-beam experiments at the same I 2. The total energy in the proton spectrum above 0.2 MeV is ϳ0.1% of the laser energy. Some of the proton spectra display intense, regular lines which may be related to ion acoustic perturbations in the expanding plasma.
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