Assessing Stagnation Conditions and Identifying Trends in Magnetized Liner Inertial Fusion

Magnetized Liner Inertial Fusion (MagLIF) is a magneto-inertial fusion concept, which is presently being studied on the Z Pulsed Power Facility. The concept utilizes an axial magnetic field and laser heating to produce fusion-relevant conditions at stagnation despite a peak magnetically driven implosion velocity of less than 100 km/s. Initial experiments demonstrated the viability of the concept but left open questions about the amount of laser energy coupled to the fuel and the role that mix played in the stagnation conditions. In this paper, simple methodologies for estimating the laser energy coupled to the fuel and determining the stagnation pressure and mix are presented. These tools enabled comparisons across many experiments to establish performance trends, as well as allow comparisons with 2-D magnetohydrodynamics simulations. The initial experiments were affected by low laser energy coupling (0.2-0.6 kJ), which resulted in reduced neutron yields (1-2 x 1012). In addition, all early experiments utilized mid-Z (aluminum) fuel-facing components. Mixing from these components had a significant impact on stagnation and increased with laser energy. Lower neutron yields (1-3 x 10(11)) were measured with higher laser coupling (0.8-1.2 kJ), which significantly deviated from the predicted scaling. When all fuel-facing components were made from a low-Z material (beryllium), neutron production increased (3.2 x 10(12)) and scaled as expected with laser energy; experimental yields were approximately 40% of simulated yields. In addition, roughly I-4 yield scaling was observed in experiments, where the load current was varied from 16-18 MA. These results represent the first step in experimental demonstration of stagnation performance scaling with input parameters in MagLIF.