Abstract
We present experimental results at intensities relevant to Shock Ignition obtained at the sub-ns Prague Asterix Laser System in 2012. We studied shock waves produced by laser-matter interaction in presence of a pre-plasma. We used a first beam at 1ω (1315 nm) at 7 x 1013 W/cm2 to create a pre-plasma on the front side of the target and a second at 3ω (438 nm) at ∼ 1016 W/cm2 to create the shock wave. Multilayer targets composed of 25 (or 40 µm) of plastic (doped with Cl), 5 µm of Cu (for Kα diagnostics) and 20 µm of Al for shock measurement were used. We used X-ray spectroscopy of Cl to evaluate the plasma temperature, Kα imaging and spectroscopy to evaluate spatial and spectral properties of the fast electrons and a streak camera for shock breakout measurements. Parametric instabilities (Stimulated Raman Scattering, Stimulated Brillouin Scattering and Two Plasmon Decay) were studied by collecting the back scattered light and analysing its spectrum. Back scattered energy was measured with calorimeters. To evaluate the maximum pressure reached in our experiment we performed hydro simulations with CHIC and DUED codes. The maximum shock pressure generated in our experiment at the front side of the target during laser-interaction is 90 Mbar. The conversion efficiency into hot electrons was estimated to be of the order of ∼ 0.1% and their mean energy in the order ∼50 keV.
Highlights
Shock Ignition is a novel approach to ICF proposed in 2007 [1]
The experiments were performed at the Prague Asterix Laser System
The maximum pressure produced by the laser on the target front during interaction was inferred by reproducing the shock breakout time on target rear side
Summary
Shock Ignition is a novel approach to ICF proposed in 2007 [1]. In this approach, the compression phase and the ignition phase are separated. Two different laser pulses are used: the first one in the ns regime to compress the target and the second one in ps regime and more intense to launch a strong convergent shock to achieve the ignition conditions. The first one at 7×1013 W/cm and 1315 nm to create an extended plasma corona in front of the target, and the second one at ∼ 1016 W/cm and 438 nm to lunch strong shock. We changed the delay between the beams from 0 up to 1200 ps to observe the influence of the plasma corona on the shock wave
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