Application of a steady-state laser-plasma instability model to a planar target experiment on the OMEGA laser facility*

To maximise progress in ICF, we need to be able to accurately model an implosion, which will enable better designs and improve the analysis of experiments. Implosion dynamics are typically modelled using radiation hydrodynamics codes, yet most of these codes do not include descriptions of the wave physics needed to characterise laser-plasma instabilities (LPI) and instead use multipliers to account for these processes. To include descriptions of LPI, we are creating a computationally fast model for the following LPI processes: (i) stimulated Raman scattering, (ii) stimulated Brillouin scattering and (iii) two plasmon decay. These models are designed to run in-line with laser ray-tracing routines as part of a hydrodynamics simulation for the evaluation of energy losses to LPI driven scattering of laser light and generation of hot electrons. 

The physics descriptions must enable computational speed; consequently our approach uses steady-state approximations where instabilities have saturated between each time step of the hydrodynamic calculation. This enables the use of analytic, linear theory to describe these saturated levels for LPI as well as descriptions of nonlinear pump depletion and the Langmuir decay instability to provide a more complete physical picture of the LPI processes. 

Here I will present promising early results applying this model to a planar target experiment carried out on the OMEGA laser facility and discuss tweaks necessary to replicate the experimental results.