Preliminary results from the LMJ-PETAL experiment on hot electrons characterization in the context of shock ignition

Abstract

In the Shock Ignition scheme, the spike pulse intensity is well above the threshold of parametric instabilities, which produce a considerable amount of hot electrons that could be beneficial or detrimental to the ignition. To study their impact, an experiment has been carried out on the LMJ-PETAL facility with a goal to generate a strong shock inside a plastic layer under plasma conditions relevant to full-scale shock ignition targets. To evaluate the effect of hot electrons on the shock characteristics, laser temporal smoothing was either switched on or off, which in turns varies the quantity of hot electrons being generated. In this paper, we present preliminary results obtained during the experiment dedicated to the hot electron characterization. We present also calculations for the second part of the experiment, scheduled in 2020 and focused on the shock characterization.

Observation and modelling of stimulated Raman scattering driven by an optically smoothed laser beam in experimental conditions relevant for shock ignition

“…In typical exploding foil experiments, in fact, SRS is driven at later times of interaction, when the plasma scalelength has become sufficiently large, and is convectively amplified at densities well below the quarter critical density, close to the Landau damping cutoff determined by the plasma temperature (k epw λ D ≈ 0.3) [11,12] . Very few experiments [13,22,23] , however, explored LPI at laser intensities close to 10 16 W/cm 2 together with plasma density scalelength higher than 200 μm, as envisaged in the SI scheme, where the non-linear character of SRS is expected to be strong. These works show that SRS is driven at very low densities, well below the Landau cutoff limit k epw λ D > 0.3, where Landau damping is expected to severely reduce the instability growth rate.…”

Bremsstrahlung cannon design for shock ignition relevant regime

“…More details on the experimental setup and results from further diagnostics can be found elsewhere 20 . The data points were fitted with a three-temperature X-ray photon distribution:…”

“…Here we focus on the bremsstrahlung measurements. The discussion of the results from fluorescence emission can be found elsewhere 20 .…”

Observation and modelling of Stimulated Raman Scattering driven by an optically smoothed laser beam in experimental conditions relevant for Shock Ignition

“…In typical exploding-foil experiments, in fact, SRS is driven at later times of interaction, when the plasma scalelength has become sufficiently large, and is convectively amplified at densities well below the quarter critical density, close to the Landau damping cutoff determined by the plasma temperature (k epw λ D ≈ 0.3). Very few experiments [13][14][15], however, explored LPI at laser intensities close to 10 16 W/cm 2 together with plasma density scalelength higher than 200 µm, as envisaged in the SI scheme, where the non-linear character of SRS is expected to be strong. These works show that SRS is driven at very low densities, well below the Landau cutoff limit k epw λ D > 0.3, where Landau damping is expected to severely reduce the instability growth rate.…”