Studies for the Laser Preheating Stage of Magnetized Liner Inertial Fusion

Abstract

Magnetized Liner Inertial Fusion (MagLIF) is an approach to inertial confinement fusion being studied experimentally on the Z pulsed-power facility at Sandia National Laboratories (SNL). In MagLIF, a preheating laser enters a cylindrical target after passing through a laser entrance hole (LEH) window. The laser then heats the pressurized target fuel and sends shock waves through the fuel, towards the fuel-confining cylindrical metal shell (or "liner"). The shock waves are then transmitted into (and travel through) the liner wall.

To scale MagLIF to higher fusion yield and ultimately reach ignition, the laser energy coupled to the fuel must be maximized. Additionally, the laser must not ablate target materials that could mix into and contaminate the fuel. Energy coupling and mix mitigation can be improved with a method of removing the LEH window called "Laser Gate." Presented in this dissertation is a successful proof-of-concept of the Laser Gate method for removing the LEH window. In our experimental tests, the LEH window was removed from the target and cleared from the laser path. The measured window opening time (from fast framing camera images) agrees well with estimates from a simple window opening model.

Another important factor in preventing mix of target material into the fuel is the target walls. As the shock waves move through the walls, the walls first compress and then expand. There can also be material ejected from the liner that mixes into the fuel and degrades the fusion yield. An experimental campaign was conducted on the Omega EP laser facility to study this wall movement and to compare the experimental results with numerical simulations. The key takeaways from these experiments include the observation of an axial dependence of wall movement radially away from the axis, and density profiles that allude to potential mix of target material into the fuel.

Overall, the experimental results help to validate and compare HYDRA simulations and predictions. This is crucial because efforts at SNL to scale MagLIF to larger yields are ongoing, and this scaling work relies heavily on simulation capabilities. The discrepancies observed between the experimental wall movement and the simulated wall movement indicate that there are areas where the models, simulations, and measurements could be improved. These and other findings are presented and discussed throughout this dissertation.