Laser plasma instabilities and hot electron generation from multi-kilojoule shock ignition relevant high-intensity IR and UV lasers

As an alternative ignition scheme, shock ignition uses a strong convergent shock driven by a high-intensity laser (\textasciitilde 10$^{\mathrm{16}}$ W/cm$^{\mathrm{2}})$ on a pre-compressed fuel to achieve ignition. Moderately energetic hot electrons (\textless 100 keV) generated from the laser plasma instabilities (LPI) can strengthen the ignition shock by depositing energy at the compressed outer shell increasing ablation pressure. In our previous experiments on OMEGA-EP, 90 keV collimated hot electrons were observed from a 100 ps, 2.5 kJ IR laser interacting with SI long scale length hot plasmas ($L_{\mathrm{n}}$ \textasciitilde 200 $-$ 500 \textmu m, $T_{\mathrm{e\thinspace \thinspace }}$\textgreater 1 keV, produced by low-intensity UV beams). To further characterize hot electron generation and investigate the related LPIs, we have extended the experiments with high-intensity, multi-kJ IR and UV lasers (both at normal incidence, up to 2\texttimes 10$^{\mathrm{16}}$ W/cm$^{\mathrm{2}})$. Two IR beams in co-propagation extend the pulse duration to 200 ps, closer to required ignition pulse duration. The scattered light is spectrally resolved to identify the LPI. Angular filter refractometer images from 4$\omega $ probe show the details of the laser propagation and interaction. The divergence, energy, and temperature of the hot electrons are diagnosed by measuring the bremsstrahlung and Cu K$\alpha $ emission. Details of the experimental results will be presented.