Design of a long pulse, low adiabat drive in a low gas-fill hohlraum

We have revisited an earlier low adiabat design that employs a (non-crystalline) CH ablator¹ (allowing higher compression for a given laser energy at the cost of ~2x longer laser pulses) in a low-density gas-filled hohlraum to effect more benign plasma conditions. Recent experiments² using a subscale CH target suggest that the dynamics of wall plasma ablation using low picket and low long trough pulses differ from typical HDC pulses. Specifically, the ablated wall plasma slows down during the trough delaying its intrusion onto the path of the inner beams. This effect when combined with the use of cross-beam-energy-transfer (CBET) is effective at controlling the low-order drive mode l=2. Additionally, these experiments introduce time-staggering of the two outer cone beams powers of the NIF laser system. Measurements of the inflight capsule symmetry show that this technique is successful at limiting the low-mode l=4 swings. In this paper, we will present simulations of these experiments showing that our model predicts the observed data reasonably well and explore possible directions to scale up to an ignition design.



¹Clark et al. PoP 21, 112705 (2014), Casey et al. PRL 115, 105001 (2015); Milovich et al. PoP 22, 122702 (2015)

² Izumi et al. this section