Experimental observation of the effect of an external magnetic field on Backward Stimulated Raman Scattering (SRS)*

SRS plays a detrimental role in inertial confinement fusion (ICF) due to pump depletion and preheat of the fuel by suprathermal electrons generated by electron plasma waves (EPW). However, recent numerical work [1] has shown that SRS in the kinetic regime (kλ_D ~ 0.3 where k is the EPW wavenumber and λ_D is the Debye length and at a density) can be mitigated by a moderate external magnetic field. With the availability of the MIFEDS coil to pre-magnetize the plasma at OMEGA-EP, investigation of the effect of magnetic field on SRS is now possible. We present recent results of a new platform designed to investigate the mitigation of SRS by an external magnetic field at OMEGA-EP. The Sub-Aperture Backward Scatter (SABS) diagnostic was fielded to time resolve reflected light from backward-SRS (BSRS). Interestingly, we observed a mitigation of the BSRS by an external B-field in the kinetic regime (kλ_D ~ 0.3) and at a density n_e ~ 10% n_cr (n_cr is the critical density). At lower density (n_e < 8% n_cr), the magnetic field induces an enhancement of the SRS. 

 

Reference:

[1] B. J. Winjum, et al. Phys. Rev. E 98, 043208 (2018)