A collaborative research team from Los Alamos National Laboratory (LANL) and Lawrence Livermore National Laboratory (LLNL) has implemented its Thinned Hohlraum Optimization for Radflow (THOR) window diagnostic tool in its latest ignition experiment at the National Ignition Facility (NIF). The team conducted an experiment that generated a yield of 2.4 +- 0.09 MJ of energy and created a self-sustaining feedback loop called a “burning plasma.” The THOR window system leverages a modified version of LLNL’s ignition platform to produce extreme x-ray output. Scientists plan to use these x-rays to blast test materials to study how radiation flows through them or how much x-ray energy gets absorbed. The Thinned Hohlraum Optimization for Radflow (THOR) target, featuring the windows around the hohlraum’s equator. Courtesy of Los Alamos National Laboratory. “This experiment marks a critical step in validating high-fidelity simulations and in demonstrating that ignition-scale performance can be achieved even with the THOR platform modifications,” said Ryan Lester, THOR campaign lead. In a NIF fusion experiment, lasers are fired into a gold-coated cylinder called a hohlraum, which is just a few millimeters long and wide. The hohlraum holds a tiny capsule of deuterium and tritium — the fuel for fusion. The lasers hit the inner walls of the hohlraum creating a uniform bath of x-rays that drives the symmetrical implosion of the inner capsule, resulting in fusion ignition. THOR experiments differ by using a new LANL-designed hohlarum, based on the LLNL ignition design, but incorporating windows to allow some of the high-flux x-rays to escape. The x-rays provide a source to test how materials interact with high temperatures and radiation levels. The challenge in this design was ensuring that adding windows to the hohlraum did not result in significant energy or implosion symmetry loss that would prevent fusion ignition from happening. “Igniting capsule implosions are incredibly sensitive and any energy loss or perturbation can easily prevent ignition, which would eliminate the generation of the x-ray fluxes we want to use as a source,” said LANL physicist Brian Haines. Haines, who helped design the experiment and made significant contributions to x-RAGE — LANL’s pivotal computer code used to enable the modeling of hohlraums and capsule implosions — outlined next steps. He said now that the team has achieved ignition with a THOR design, the team members must explore if the windows can be made more transparent and to design experiments that will attach to the THOR windows.
