R. R. Paguio

With the achievement of thermonuclear ignition, there is interest to increase the performance of inertial-confinement-fusion (ICF) systems to reach high fusion yields and high-energy gain for energy-production purposes. One approach to achieve this is magnetic-direct-drive (MDD) ICF, where magnetic fields are used to compress ICF targets to thermonuclear conditions. To study the scaling of MDD ICF to high yields, we performed experiments on the 20-MA, 100-ns Z machine to study the invariant behavior of the magneto-Rayleigh-Taylor instability when changing the magnetic-field drive. Similarity-scaled aluminum cylindrical shells with preseeded axial perturbations were imploded at two different maximum currents: 14.7 and 19.2 MA. Consistent with dynamical similarity within experimental uncertainties, the magneto-Rayleigh-Taylor growth history measured via x-ray radiography exhibits agreement at the 16% level or better for late-time growth factors of 10x to 50x. However, the early instability development is not dynamically similar due to Ohmic-heating effects, which are not conserved by the proposed scaling prescriptions. This Letter exemplifies the application of similarity scaling to rigorously investigate the scaling of MDD ICF to high yields.

Magnetized liner inertial fusion (MagLIF) experiments have demonstrated fusion-relevant ion temperatures up to 3.1 keV and thermonuclear production of up to 1.1 × 1013 deuterium–deuterium neutrons. This performance was enabled through platform development that provided increases in applied magnetic field, coupled preheat energy, and drive current. Advanced coil designs with internal reinforcement enabled an increase from 10 to 20 T. An improved laser pulse shape, beam smoothing, and thinner laser entrance foils increased preheat energy coupling from less than 1 to 2.3 kJ. A redesign of the final transmission line and load region increased peak load current from 16 to 20 MA. The wider range of input parameters was leveraged to study target performance trends with preheat energy, applied magnetic field, and peak load current. Ion temperature and neutron yield generally followed trends in two-dimensional clean Lasnex calculations. Stagnation performance improved with peak load current when other input parameters were also increased such that convergence was maintained. This dataset suggests that reducing convergence to less than 30 would improve predictability of target performance. Lasnex was used to identify a simulation-optimized scaling path, which suggests 10+ kJ of fusion yield is possible on the Z facility with achievable input parameters. This path also indicates >10 MJ could be generated through volume burn on a future facility with a path to high yield (>200 MJ) using cryogenic dense fuel layers. The newly developed MagLIF platform enables exploration of both this simulation optimized scaling path and a recently developed similarity-scaling path.

We report on a series of Magnetized Liner Inertial Fusion (MagLIF) experiments conducted on the Z pulsed power facility that utilized high aspect ratio (ratio of outer radius to wall thickness) liners with dielectric coatings and low-mix laser preheat configurations. The liners consisted of an aspect ratio of 10.6 beryllium tube coated with 75 μm of epoxy on the outside that have been shown to maintain a better implosion stability than uncoated beryllium and have demonstrated consistent stagnation performances in previous experiments [Ampleford et al., Phys. Plasmas 31, 022703 (2024)]. Two-dimensional HYDRA simulations were used to design three different “co-injection” laser configurations, whereby a second laser is used to provide an early prepulse before the main pulse, to reduce LEH foil mix while increasing the fuel density and coupled energy. The laser preheat energy for each configuration was constrained using dedicated laser experiments before being applied to the integrated MagLIF experiments on Z. The DD neutron yield for experiments using co-injection preheat configurations is found to increase with the specific preheat energy in line with simulations. The highest neutron yield achieved in this study of 1.1 × 1013 matches the highest reported in a MagLIF experiment to date and is a factor 3.5 times higher than similar experiments using preheat with no phase plate smoothing. We attempt to assess the effects of mix and morphology to explain the improved performance; however, neither factor is found to be conclusive within the uncertainty of the measurements.

X-ray imaging indicates magnetized liner inertial fusion (MagLIF) stagnation columns have a complicated quasi-helical structure with significant variations in x-ray brightness along the column. In this work, we describe MagLIF experiments aimed at controlling these stagnation structures by varying the initial liner geometry and composition. First, by varying the initial aspect ratio of the liner, we demonstrate a change in the stagnation structures that is consistent with helical magneto Rayleigh–Taylor (MRT) instabilities feedthrough from the outer-to-inner surfaces of the liner. Second, to minimize the seed for such instabilities, we incorporate a dielectric coating on the outer surface of the beryllium liner, which has previously been shown to reduce the growth of the electrothermal instability, a likely seed for MRT growth. Using this coating, we achieve a stagnation column with significantly reduced helical structure and axial variation in x-ray brightness. We discuss how this coating changes the evolution of structures through stagnation along with the spatial uniformity of neutron production. Finally, we show that these more uniform stagnations also result in improved reproducibility in stagnation temperatures and primary DD neutron yield.

A class of dynamic material property (DMP) experiments on the Sandia National Laboratories pulse power Z-Machine requires planar samples to be held in a panel assembly. A custom press device to fabricate the assemblies has the ability to assemble one sample, window, or stack at a time, resulting in a 1-week lead time for a typical three-pocket panel assembly. Fabrication of targets with more than three pockets can take longer. In late 2015, General Atomics conceptualized a new multi-press device to enable several samples, windows, or stacks to be assembled simultaneously, and a prototype was designed, procured, and outfitted in 6 months. Since June 2016, this multi-press design has successfully assembled 60 planar DMP targets. The development considerations for this new device and the resulting benefits for the fabrication of targets are discussed.