Implementation of Short-Time-Scale Laser Deposition Physics in Radiation-Hydrodynamics code HELIOS-CR*

HELIOS-CR is a 1-D radiation-magnetohydrodynamics code that is used to simulate the dynamic evolution of plasmas created in high energy density physics (HEDP) experiments. The energy sources include lasers, radiation sources, electric currents (in cylindrical geometry), and particle beams. The laser deposition model in the code utilizes ray tracing algorithms for different 1D geometries. The refraction is computed using a geometrical optics model with a plasma refractive index being governed by local values of electron density. Following the conventional approach, the laser energy is deposited in the plasma using an inverse Bremsstrahlung model when the electron density is less that the critical density. Although the deposition models have been extensively tested for simulations that include longer nanosecond-scale laser pulses, they may not be adequate for the ultra-short pulses. We will discuss development of a new model for the laser energy deposition suitable for sub-picosecond laser pulses. In this approach, Maxwell's equations will be solved explicitly to obtain the radiation field and will account for laser-matter interaction in the presence of steep density gradients. We will also discuss the need to re-evaluate the models for the thermal fluxes and electron–ion relaxation in the plasmas with extreme temperature gradients,