Observation of mitigated surface feature growth in laser direct drive

Domes are a prominent non-uniformity in laser-fusion targets. We present results from of thru-foil radiography of 3D printed domes on foil targets which suggest a mitigation of growth that can be qualitatively recovered with modest (~5 eV) preheat. Non-thermal electrons due to high-intensity driven plasma waves, laser-imprint, and radiation preheat from back-lighter have been dismissed based on additional experiments. Rather, we observed a significant change, consistent with reduced preheating, with introduction of a picket in advance of the laser drive. Previously, it has been shown in focused experiments at OMEGA that resonance absorption, i.e. direct excitation of plasma waves by incident light, is active precisely over the picket duration [1]. We find, using calculated density scale lengths as inputs to analytical expressions for fraction of resonant absorbed light [2], that this is a plausible source of the preheating and its dependence on early laser drive. Data is anticipated from a test of an even lower picket drive that this theory suggests will more strongly modify the resonant absorption preheat. [1] Igumenshchev I. V. et al., Phys. Plasmas 14 (2007) 092701. [2] Michel P., Introduction to Laser-Plasma Interactions, Graduate Texts in Physics (Springer Cham, 2023).