Performance impacts on direct drive ICF due to beam width

In direct drive ICF, beams incident on a spherical target impose a variety of incidence angles across the illumination surface which may be characterized by the beam radius (r_b) to target radius (r_t). Previous studies [1] examine the effects of the r_b/r_t ratio on implosion velocity, scattered light fraction, and neutron yield in the r_b/r_t ~ 1 regime. In this presentation, the impact of the beam radius to target radius on the ablation pressure and the mass ablation rate due to incidence angle spread is explored using radiation hydrodynamic simulations. An analytic expression is derived for the average incidence angle of a beam as a function of the r_b/r_t ratio. Comparisons of the ablation pressure, mass ablation rate, and scattered light fraction are made with respect to this average incidence angle parameter. Analysis of the effects of beam width may indicate benefits of using narrower beams such as in the Revolver design [2].

[1] D. Froula, et al. Phy. Rev. Lett. 108 125003 (2012)

[2] K. Molvig, et al. Phy. Rev. Lett. 116, 255003 (2016)