Investigating the Joint Feature in Double Shell Targets

The Double Shells campaign at Los Alamos National Laboratory seeks to reach ignition using a nested capsule design, where the outer shell is accelerated and collides with a high-Z inner shell, which then compressed a liquid DT fuel. By necessity, the outer shell is comprised of two hemispheres that are fitted around the inner shell. The joint feature of the outer shell is a region of instability and radiation leakage, which can reduce the yield output by a factor of 10⁴ if not mitigated for gaps between ~1-7 um. The current design uses a gold coating (up to 500 nm) that prevents the joint feature from growing [Stark, D.J. et al. PoP 2021]. 2D simulations show that this can increase the anticipated yield by a factor of 100. A series of shots using hydrogrowth radiography (HGR) at the National Ignition Facility (NIF) are planned to test our models’ predictions of the joint feature. The first shot (September 2025) will test our current joint feature without any coating, giving us a baseline comparison to our predictions. The second shot (November 2025) will test a 300-nm gold coating for comparison. Results from the first shot will be presented, with potential preliminary results from the second shot included.