Coupled hydrodynamic model for laser-plasma interaction and hot electron generation

Abstract

We present a formulation of the model of laser-plasma interaction (LPI) at hydrodynamical scales that couples the plasma dynamics with linear and nonlinear LPI processes, including the creation and propagation of high-energy electrons excited by parametric instabilities and collective effects. This formulation accounts for laser beam refraction and diffraction, energy absorption due to collisional and resonant processes, and hot electron generation due to the stimulated Raman scattering, two-plasmon decay, and resonant absorption processes. Hot electron (HE) transport and absorption are described within the multigroup angular scattering approximation, adapted for transversally Gaussian electron beams. This multiscale inline LPI-HE model is used to interpret several shock ignition experiments, highlighting the importance of target preheating by HEs and the shortcomings of standard geometrical optics when modeling the propagation and absorption of intense laser pulses. It is found that HEs from parametric instabilities significantly increase the shock pressure and velocity in the target, while decreasing its strength and the overall ablation pressure.

Interplay of Laser-Plasma Interactions and Inertial Fusion Hydrodynamics

“…CBET calculations either postprocess plasma conditions from a hydro simulation with no CBET [6,12], or are directly implemented "inline" in simulations that describe lasers with ray-tracing [13,14] or paraxial complex geometric optics [15]. SRS is usually treated by removing the escaping light from the incident laser, though recent work has included SRS-produced superthermal electrons in direct-drive hydrodynamic modeling [16].…”

The role of hot electrons in the dynamics of a laser-driven strong converging shock

“…The model assures the energy conservation at each time step. First comparisons of the PCGO model with experiments conducted on the PALS Laser Facility in a planar geometry show quite good agreement for both the hot-electron fraction and temperature [19] and the scaling with the laser intensity [20]. It was demonstrated that hot electrons generated by RAB and SRS processes have a relatively low energy, deposit their energy downstream of the shock front, and increase the shock pressure and shock velocity.…”

“…The present 2-D version of PCGO describes the beamlet diraction in only one transverse direction. The laser collisional absorption is complemented with the resonant absorption (RAB) at the ray's turning point, the TPD instability at the n c /4, and the SRS instability, which was localized near the zone where the plasma density was 20% of the critical density [19]. The TPD and SRS processes are activated locally as soon as the corresponding threshold conditions are fullled.…”

“…The previous parameters of the PCGO model were chosen based on a comparison with experiments in the planar geometry [19]. The hot-electron beamlets propagate in the meridional plane with a xed transverse width.…”

“…The PCGO model provides access to the laser intensity in any location in plasma and is well suited to account for nonlinear processes in plasma. The model accounts for the resonant absorption (RAB), stimulated Raman scattering (SRS), and two-plasmon decay (TPD) [19]. Each of these processes is a source of energetic electrons, which are characterized by a temperature, density, direction and angular divergence.…”