Laser-Direct-Drive Cryogenic Implosion Performance on OMEGA Versus Target and Laser-Spot Radius

Advances in statistical modeling of laser-direct-drive (LDD) implosions have led to record fusion yields on the OMEGA laser.[1,2] Experiments on the NIF have shown Si dopant and wavelength detuning can mitigate hot-electron preheat and cross-beam energy transfer (CBET).[3,4] Applying these concepts to ignition-scale LDD requires an understanding of performance as a function of physical size (using scale factor S = R_t/R_W, the ratio of target radius to a fiducial OMEGA target radius) and the beam-to-target radius (defined as R = R_b/R_t). We show the measured fusion yield Y and areal density ρR increase with capsule size as S^5.0±0.2 and S^1.6±0.2, respectively, in excess of simple 1-D expectations (Y~S^4.3, and ρR~S^1.0). Neutron production also increases with beam to target radius as R^3.5±0.5, with benefits that saturate at R~1. Both results imply that target and relative beam size mitigate sources of degradation and improve confinement. DRACO simulations including nonlocal transport and CBET[5] show these trends are expected when laser imperfections (e.g., speckles, port geometry) are a primary source of perturbations in 2/3-D. To test this hypothesis, we have also performed implosions with improved stability, and find higher yields and areal densities. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856.

 

[1] V. Gopalaswamy et al., Nature 565, 581 (2019).

[2] A. Lees, Bull. Am. Phys. Soc. 65, TI01.00005 (2020).

[3] A. A. Solodov et al., Phys. Plasmas 27, 052706 (2020).

[4] J. A. Marozas et al., Phys. Rev. Lett. 120, 085001 (2018).

[5] P. B. Radha et al., Phys. Plasmas 12, 032702 (2005).