Laser Imprint Workshop

22–24 May 2019 at LLE, University of Rochester

One of the attractive features for direct-drive ICF is that it can be more efficient for laser-energy coupling to an imploding target. There are challenges, however, for this ICF approach to work. For example, because of its spatial and temporal coherence, a focused laser beam can have interference patterns that cause a spatially nonuniform distribution of intensity on the target. It has long been recognized that such laser-intensity nonuniformity is a major issue for the laser direct drive fusion approach. Laser nonuniformity can transfer ("imprint"") perturbations through the ablation process to shock density/pressure at the ablation surface, which can become the seed for the Rayleigh–Taylor (RT) instability growth during the subsequent target implosion. Experimental evidence and simulation studies have suggested that laser imprint is a major source for degrading low-adiabat (α = 2 ~ 3) and high-convergence target implosions. Research on the impact of laser imprint is ongoing. Understanding and mitigating laser-imprinting is essential for the success of direct-drive fusion.

Workshop Goals

This 3 day meeting at the Laboratory of Laser Energetics (LLE) at the University of Rochester will cover various aspects of the physics of laser imprint and mitigation strategies. Through combined review talks and group discussions, we seek better physics understanding of: (1) How laser imprint is established including the startup of plasma formation; (2) How do material properties affect the initial plasma formation; and (3) how laser intensity non-uniformities are transferred into modulations in pressure and shock velocity.

Furthermore, the workshop will examine laser and target strategies to mitigate laser imprint effects for direct drive ICF: High-Z coating, hybrid target design, foam layer targets, broadband laser sources, optimizing ablators with high ablation velocity, and utilizing material strength properties. An output of the workshop will be an inclusive review paper of the present state of knowledge of imprint and the research pathway to improve our understanding and mitigation strategies for laser imprint.

Specific goals include:

  • Review the experimental results and theoretical understanding for each mitigation strategy
  • Define the experimental/theoretical needs for demonstrating viable strategies of mitigating laser imprint
  • Identify target fabrication issues, with an ultimate goal of fabricating cryogenic capsules that mitigate laser imprint
  • Develop the timeline for a multi-year research program for imprint mitigation
  • Publication of a review paper on the state of research and knowledge of imprint

Registration

Please email Wolfgang Theobald (wthe@lle.rochester.edu) and Suxing Hu (shu@lle.rochester.edu) to register for the workshop. The deadlines are: 15 March 2019 for non-U.S. citizens, and 30 March 2019 for U. S. citizens.

Foreign National Attendance

All visits of foreign nationals must be approved through the U.S. Department of Energy Foreign Visit and Assignment System. As such, we will need to have all attendees verify their citizenship at the time of registration. Foreign Nationals must be processed through the system no later than 15 March 2019. Foreign nationals should email Jean Steve (jste@lle.rochester.edu) regarding the approval to enter LLE.