Jeffrey R. Fein

In magnetized liner inertial fusion (MagLIF), a magnetized sample of gaseous deuterium fuel is “preheated” and subsequently compressed. Preheat is required to allow for the compression to follow a higher adiabat, thus achieving much higher end-temperatures than starting with cold fuel. This temperature enhancement is critical for achieving fusion conditions. To deposit preheat into the target with a high-energy laser, a film-covered laser-entrance hole (LEH) is required, which can confine the deuterium gas while allowing laser energy to reach the fuel. However, this thin-film window absorbs laser energy and can mix with the fuel, which degrades the fusion yield. Cryogenically cooling the deuterium fuel allows the thickness of the LEH window to be significantly reduced. Simultaneously, the implementation of a larger-diameter laser beam waist in the interaction volume allows for a reduction of the laser intensity. By reducing the overall mass of the heated window material and lowering the intensity on target, the average fraction of laser energy that is deposited in the fuel improves from 65% to 83%, without overshooting the useful depth of a MagLIF target. Informed by previous campaigns, the laser pulse length and spot profile were chosen to reduce the intensity below the threshold for losses from stimulated Brillouin scattering. Although the initial expectation was that the dominating contribution to a preheat increase should be the reduced material in the entrance window, it was found that reducing residual laser-plasma-instabilities is even more important for maximizing laser deposition despite the relatively low intensities. The increase in laser-fuel coupling presented here has contributed to the highest performing MagLIF experiments to date.

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.

We report two magnetized liner inertial fusion (MagLIF) experiments that produced record thermonuclear D–D neutron yields of 2.11×1013 and 2.33×1013. These yields are about a factor of two higher than previous MagLIF results. The experiments achieved ion temperatures of 3.0 and 3.3 keV and stagnation pressures of 1.6 and 1.3 Gbar. The inferred Lawson parameters were χ=0.2 and 0.1, which are the largest reported for MagLIF. The performance increase used a high-aspect-ratio beryllium liner with a dielectric coating and modest increases in preheat energy (∼2.2 kJ), peak current (18.5 MA), and axial magnetic field (15 T). Three-dimensional HYDRA simulations are consistent with the measured liner dynamics and fusion outputs. These results indicate a pathway to higher-yield MagLIF designs using coated, high-aspect-ratio liners and improved input parameters. Simulations further suggest that adding an ice fuel layer could increase yield by up to a factor of 2.5 by reducing liner convergence, instability feedthrough, and mix.

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.