Studies of ablated plasma and shocks produced in a planar target by a sub-nanosecond laser pulse of intensity relevant to shock ignition

Abstract

The effect of laser intensity on characteristics of the plasma ablated from a low-Z (CH) planar target irradiated by a 250 ps, 0.438 µm laser pulse with the intensity of up to 1016 W/cm2 as well as on parameters of the laser-driven shock generated in the target for various scale-lengths of preformed plasma was investigated at the kilojoule Prague Asterix Laser System (PALS) laser facility. Characteristics of the plasma were measured with the use of 3-frame interferometry, ion diagnostics, an X-ray spectrometer, and Kα imaging. Parameters of the shock generated in a Cl doped CH target by the intense 3ω laser pulse were inferred by numerical hydrodynamic simulations from the measurements of craters produced by the shock in the massive Cu target behind the CH layer. It was found that the pressure of the shock generated in the plastic layer is relatively weakly influenced by the preplasma (the pressure drop due to the preplasma presence is ~10–20%) and at the pulse intensity of ~1016 W/cm2 the maximum pressure reaches ~80–90 Mbar. However, an increase in pressure of the shock with the laser intensity is slower than predicted by theory for a planar shock and the maximum pressure achieved in the experiment is by a factor of ~2 lower than predicted by the theory. Both at the preplasma absence and presence, the laser-to-hot electrons energy conversion efficiency is small, ~1% or below, and the influence of hot electrons on the generated shock is expected to be weak.

Measurements of parametric instabilities at laser intensities relevant to strong shock generation

“…The overall description of the diagnostics used and an overview of the experimental results obtained, including the measured pressure of the shock wave, are reported elsewhere. [38][39][40][41][42] Here, we focus on the laser plasma interaction and in particular, on the Stimulated Raman Scattering and Two Plasmon Decay instabilities. Despite our density scalelength ($100 lm) and the electron temperature ($1.5-2 keV) being lower than those envisaged in a real SI scenario, the data reported here provide a comprehensive study of the growth of parametric instabilities at a laser intensity relevant for SI where very little experimental data exist and where, as discussed above, a strong nonlinearity and interplay between different processes are expected to play a dominant role.…”

Production of sub-gigabar pressures by a hyper-velocity impact in the collider using laser-induced cavity pressure acceleration

“…In that case, the verification was made by the comparison of parameters of craters produced in a massive Al target by the impact of Al projectiles of various masses calculated using the code with the ones obtained from measurements performed at the PALS laser facility, and a very good qualitative and quantitative agreement between the numerical and experimental results was found (Badziak et al, 2015a). The code was also used to simulate the shock generation in a CH/Cu target by the direct target irradiation by the PALS laser beam and fairly good agreement (within ~ 30 %) between the results of the PALE simulations and the results of measurements was obtained as well (Koester et al, 2013;Badziak et al, 2015b). Positive results of these verifications allow us to believe that numerical results obtained in this paper are correct not only qualitatively but also quantitatively within a factor ~ 1.5 or smaller.…”

Burst-mode 500 ps fiber laser ablation in 304 stainless steel

“…Sub-nanosecond laser (SNL) ablation is an alternative approach, considering its low cost, compact configuration, as well as having a pulse duration shorter than the material thermal relaxation time [16,17]. However, the single sub-nanosecond pulse is still inadequate to get a high ablation efficiency.…”