Effect of small normalized magnetic fields on rescatter of SRS in the kinetic regime

We have previously shown [1] how small magnetic fields can significantly modify the evolution of backward stimulated Raman scattering (SRS) in the kinetic regime ($k\lambda_{De} \approx 0.20 - 0.35$ for backscattered plasma wave) due to the enhanced dissipation of nonlinear electron plasma waves propagating perpendicular to magnetic fields. We present results of OSIRIS simulations of SRS in the kinetic regime for unmagnetized and magnetized plasmas at densities low enough ($n_e/n_c \lessapprox 11\%$) such that rescatter (where the daughter wave backscatters) is possible. We show that when rescatter occurs, the magnetic field can increase the overall reflectivity by mitigating the initial backscatter event and hence the subsequent rescatter. We present 1D and 2D simulations for a variety of parameters to illustrate this effect. 

We also present preliminary results modeling SRS using the Quasi-3D algorithm in OSIRIS. Such simulations are reasonable if the laser spot size is round and they include three dimensional geometric effects including side loss and transverse laser and plasma wave evolution. Carrying out such parameter scans using full 3D is impracticable even on the top high performance computing systems available today.