Demonstration of High-Energy, Low-Mix Laser Preheat for MagLIF*

The Magnetized Liner Inertial Fusion (MagLIF) platform on the Z Facility has demonstrated thermonuclear fusion yields by imploding a cylindrical liner filled with D₂ fuel that is preheated with a 0.53 μm, multi-kJ laser and pre-magnetized with an axial B_z = 10-30 T magnetic field. The challenge of fuel preheat is to efficiently deposit >1 kJ of energy into the underdense (n_e/n_c < 0.1) fuel over a ~10 mm target length without introducing deleterious mix. To achieve this goal, we have developed new diagnostic capabilities to measure laser-energy deposition and contaminants introduced during fuel preheat. In addition, we also developed more efficient laser heating protocols using numerical simulations and offline (separate to the Z chamber) laser experiments.

The offline experiments measure backscatter from laser—plasma instabilities (LPI) and constrain energy deposition via a multi-frame shadowgraphy diagnostic that observes the blast-wave produced in the gas. Laser heating protocols are then tested in integrated MagLIF experiments that quantify the preheat-induced mix by using mid-Z coatings applied to various surfaces of the target. This talk will summarize the significant progress that has been made in developing new diagnostics and new MagLIF preheat protocols over the past 2 years. Our results show that >1 kJ of preheat energy can be coupled to the fuel without introducing contaminants and without significant LPI backscatter by applying DPP smoothing and pulse shaping the beam with a low-energy (20 J), early pre-pulse. These efforts have culminated in the highest neutron yield (1.1e13±20%) recorded to date in a MagLIF experiment.