Abstract Details
Isochoric heating of reduced-mass targets by laser driven relativistic electrons
Author: Sophie D. Baton
Requested Type: Oral Only
Submitted: 2009-04-21 10:01:53
Co-authors: P.Audebert, M. Koenig, F. Perez, M. Chahid, C. Rousseaux, L. Gremillet, E. Lefebvre, J. Rassuchine, T. Cowan, S. Bastiani-Ceccotti, P. Renaudin, F. Dorchies, M. Harmand, E. Brambrink, M. Geissel, O.Peyrusse, S. Jacquemot
Contact Info:
LULI, Ecole Polytechnique
Route de Saclay
Palaiseau, Paris 91128
France
Abstract Text:
Recent works have shown the possibility to heat isochorically mass limited targets by using the electron refluxing. We report here on experiments performed at the 100 TW LULI sub-picosecond laser facility. The pulse was approximately 300fs and delivered an energy of ~20J within a ~10 µm FWHM spot size, yielding an intensity of ~2x10^19 W/cm2 at 1.057 µm. Two series of experiments have been conducted to study fast electron transport in multilayer targets by using X-ray diagnostics (K-shell imaging and spectroscopy). In the first series we irradiated thin solid targets of various atomic number Z. A fast streak camera was coupled to a conical Bragg crystal providing spectra in the 1600 eV range with high temporal and spectral resolution. A second conical Bragg crystal was used to collect time-integrated spectra on a larger spectral range. The analysis shows that the hot electrons play an important role on the spectral feature of the tamped layer target. For the second series, reduced mass targets have been used ; they were composed of 0.2V/5Cu/5Al µm and varied from 300 to 50 µm in diameter. They were irradiated by the laser pulse at 1.057 µm and 0.53 µm. In the last case, the intensity is reduced to ~10^19 W/cm2 due to the conversion efficiency. Emission from the rear side was observed using Kα spectroscopy and imaging diagnostics. Spectra including the Al-Kα, Al He-like, and Cu-Kα emissions show changes as a function of total mass. It is clearly observed that when the mass is reduced, the heating is increased. The data obtained from all diagnostics (Kα spectroscopy, Kα imagers on the rear side and the transverse side) show a different behavior depending on the incident wavelength. The highest temperatures, of the order of 100 eV, have been reached when irradiating the smallest targets with a frequency doubled pulse despite the reduced laser energy. Collisional PIC simulations confirm the detrimental influence of the preformed plasma on the bulk target heating.
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