Abstract
Higher implosion efficiency is of great significance in direct-drive fusion research. We demonstrated the critical role played by the intensity gradient of the main drive laser pulse in improving efficiency of direct-drive implosions, using a double-gradient nanosecond pulse. Compared with a square pulse, the burn-through depth was increased by over 200%, and the shell velocity was increased by times with an optimized double-gradient pulse. As the result, the implosion efficiency was enhanced by six times. It was found that by limiting the intensity gradient of the main drive pulse to no more than , heat flux inhibition by nonlocal electron thermal transport effects could be eliminated, and ultimately an efficient mass ablation process was achieved. These results have relevance for pulse designs in ignition-scale direct-drive implosions.
- Received 20 December 2021
- Revised 24 March 2022
- Accepted 12 May 2022
DOI:https://doi.org/10.1103/PhysRevE.105.L053203
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