Studying Mix Mechanisms in a Regime Transitioning From Hydro-Like to Kinetic Using Shock-Driven Separated Reactant Experiments at OMEGA
Benjamin Reichelt, Massachusetts Institute of Technology
Capsule-gas mix in Inertial Confinement Fusion (ICF) implosions is an important yield degradation mechanism, as bremsstrahlung losses scale with charge squared and thus small amounts of mixed material can significantly alter hot-spot-energy losses. Previous work on mix has largely been focused on hydrodynamic mechanisms due to instability growth and the propagation of turbulent eddies down to the diffusive length scale. However, recent cryo campaigns at the OMEGA laser facility have moved to lower areal density and higher implosion velocities, leading to longer diffusive length scales and more hydrodynamic stability. This has caused non-hydrodynamic mix mechanisms to play a more prominent role in the capsule dynamics. This work presents results from a separated reactant experiment campaign at OMEGA, in which plastic capsules with a buried deuterated layer are filled with 3He gas. In these experiments, the shell thickness was varied to alter the Knudsen number of the fusion reactants, facilitating studies of the mix mechanism in a more kinetic regime than previously done. Charged-particle and neutron data provide information about capsule mix, augmented by X-ray data that constrains charged-particle stopping and capsule-shell trajectory. Comparison to hydrodynamic and kinetic simulations using the codes xRAGE and iFP, developed by Los Alamos National Laboratory, provide a detailed picture about the mix mechanisms at play. Systematic differences are observed in the data from the separated-reactant and control experiments, including nuclear reaction histories with trends opposite of those seen in previous more hydrodynamic experiments, indicating mix governed by diffusive and nonlocal mix mechanisms.
This work was supported, in part, by the U.S. Department of Energy NNSA MIT Center-of Excellence under Contract No. DE-NA0003868 and by the National Laser Users Facility under Contract No. DE-NA0003938. B. Reichelt is supported by NNSA SSGF DE-NA0003960.
Authors: Benjamin Reichelt1, Maria Gatu Johnson1, Patrick Adrian1, Tucker Evans1, Justin Kunimune1, Timothy Johnson1, Chikang Li1, Neel Kabadi2, Nicholas Pelepchan2, Vladamir Glebov2, Timothy Filkins2, Chad Forrest3, William Taitano3, Steven Anderson3, Luis Chacon3, Brian Haines3
1Plasma Science and Fusion Center, Massachusetts Institute of Technology, USA
2Laboratory for Laser Energetics, University of Rochester, USA
3Los Alamos National Laboratory, USA
Abstract Author(s): (see above entries)