X-ray spectra from laser targets in experiments on the SOKOL-P facility
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X-ray Spectra from Laser Targets in Experiments on the SOKOL-P Facility A. V. Potapov, E. A. Loboda, V. A. Pronin, V. Yu. Politov, L. V. Antonova, A. V. Lipin, A. G. Kakshin, and O. V. Chefonov Zababakhin All-Russia Research Institute of Technical Physics, Russian Federal Nuclear Center, Snezhinsk, Chelyabinsk oblast, 456770 Russia Received November 8, 2005; in final form, April 3, 2006
Abstract—X-ray spectra from targets irradiated by picosecond laser pulses with intensities of 3 × 1017– 1018 W/cm2 have been studied experimentally on the SOKOL-P facility. Both massive metal targets and multilayer targets with a buried emitting layer have been examined. The measurement results are interpreted by using numerical simulations and theoretical analysis. Experimental data on the X-ray continuum in the photon energy range of 0.8–6 keV and the line spectra of hydrogen- and helium-like aluminum ions are found to agree satisfactorily with numerical results. PACS numbers: 52.38.Ph, 52.70.La DOI: 10.1134/S1063780X07010011
This spectral range contains both the continuum of thermal electrons and the resonance lines of H- and Helike aluminum ions. The measurements were aimed primarily at determining the temperature of the target material irradiated by an intense picosecond laser pulse and estimating the penetration depth of the thermal wave during the X-ray pulse. It should be noted that, at intensities of ~1018 W/cm2, the depth to which the target is heated depends on both the classical Spitzer heat conductivity and the spectrum of the electrons accelerated in a strong laser field [4]. These electrons can also influence the intensity of hard X-ray (HXR) emission.
1. INTRODUCTION Rapid progress in high-power laser technology has made it possible to produce picosecond and subpicosecond pulses with intensities of 1017–1018 W/cm2 and higher. When such an intense laser pulse interacts with a target, the surface layer of the target transforms into a high-temperature plasma with a density close to the solid-state density [1]. The plasma so produced remains nearly uniform for several picoseconds, until gas-dynamic processes come into play. Such a plasma is of great interest from the standpoint of studying equilibrium path lengths of photons in different spectral ranges. The relevant experimental information can be obtained by measuring X-ray emission from the plasma. Such measurements are necessary for calibrating physical and mathematical models used to calculate photon path lengths, because the results predicted by different models can differ severalfold [2]. In the present paper, the first results from experimental studies of X-ray spectra from targets irradiated by picosecond laser pulses on the SOKOL-P facility [3] are reported. Two types of target were investigated: massive metal plates and thin multilayer targets with a buried emitting layer (multilayer targets were used to suppress the expansion of the emitting plasma by the outer-layer material). As a plasma-producing material of the massive plates and the buried lay
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