X-ray spectroscopy and Inertial Confinement Fusion

S. P. Regan, Laboratory for Laser Energetics, U. of Rochester

Hopeman 224

The spherical concentric layers of an inertial confinement fusion (ICF) target consist of a central region of a near-equimolar deuterium and tritium (DT) vapor surrounded by a cryogenic DT-fuel layer and a plastic ablator.  High-power lasers like the OMEGA laser system at the University of Rochester and the National Ignition Facility at the Lawrence Livermore National Laboratory are used to study ICF plasmas.  The outer surface of the ablator is uniformly irradiated directly with overlapping laser beams for laser direct drive or with x rays for laser indirect drive.  The resulting ablation process causes the target to accelerate and implode. As the DT-fuel layer decelerates, the initial DT vapor and the fuel mass thermally ablated from the inner surface of the ice layer are compressed and form a central hot spot, in which fusion reactions occur.  ICF relies on the 3.5-MeV DT-fusion alpha particles depositing their energy in the hot spot, causing the hot spot temperature to rise sharply and a thermonuclear burn wave to propagate out through the surrounding nearly degenerate, cold, dense DT fuel, producing significantly more energy than was used to heat and compress the fuel.  This talk will show how x-ray spectroscopy of high-Z tracer elements in an ICF target is used to study the four phases of the implosion---shock transit, acceleration, deceleration, and stagnation---with tailor-made x-ray spectrometers.  Diagnosing the Richtmyer–Meshkov and Rayleigh–Taylor hydrodynamic instabilities will be highlighted. This material is based upon work supported by the Department Of Energy National Nuclear Security Administration under Award Number DE‑NA0001944.