Theory and OSIRIS Particle-in-cell Simulations of Stimulated Raman Scattering in unmagnetized and magnetized Plasmas*

We use the particle-in-cell code OSIRIS to study stimulated Raman scattering (SRS) in magnetized and unmagnetized plasmas in a wide range of parameter space. We have previously shown how small magnetic fields can significantly modify the evolution of backward stimulated Raman scattering (SRS) in the kinetic regime ($k\lambda_{De} \approx 0.32$ for backscattered plasma wave) due to the enhanced dissipation of nonlinear electron plasma waves propagating perpendicular to magnetic fields. Driven by the collaboration between UCLA and UCSD, the range of validity of these results is extended, showing that they are valid in a wide range of parameter space, $k\lambda_{De} \approx 0.19 - 0.32$. Furthermore, we have identified a number of areas rich in complex, largely unstudied physics. This includes regimes in which magnetic fields appear to lead to enhanced SRS, which we believe to be related to rescatter appearing to reduce the amount of backscatter and diminished non-linear frequency shift in magnetized plasmas. This also includes frequently observed evidence of competition between forward and backward SRS and backscatter in strongly coupled regimes where $k\lambda_{De} \approx 1$. These observations offer promising opportunities for new avenues of research and future experime