The effect of nonlocal electron heat transport on filamentation and laser plasma instabilities in a laser speckle.*

We present pF3D simulations of a Gaussian laser speckle in a plasma which include the effects of nonlocal electron heat transport, inverse bremsstrahlung absorption and laser ponderomotive force. We find that the thermal pressure enhancement in the speckle due to nonlocal electron heat transport lowers the filamentation threshold for high Z* materials (e.g. Au, AuB, and Ta₂O₅) under ICF conditions (ne/nc ~ 0.1, Te ~ 5 keV). However, the single speckle filamentation threshold in Au is still approximately a factor of two higher than the intensity of the brightest speckles encountered on the NIF during peak power.

 

Below the speckle filamentation threshold, we find that self-focusing leads to a significant decrease in the speckle f# and an increase in intensity at the speckle waist. For our chosen plasma conditions, the intensity enhancement with nonlocal electron heat transport is approximately a factor of two in Au for a speckle intensity of 5E15 W/cm².

 

Finally, we compare Stimulated Brillouin Scattering (SBS) in a laser speckle with Spitzer-Härm versus nonlocal electron heat transport. We find that the intensity enhancement with nonlocal electron heat transport substantially increases the instability growth rate, which has implications for ICF modeling.