Zap Energy is developing the sheared-flow-stabilized Z pinch concept for fusion energy applications. Z pinches offer many advantages as a fusion platform, including intrinsically high beta, absence of external coils, and simple geometry particularly well-suited to tackling the engineering challenges for commercialization. Despite these advantages, the Z pinch path to fusion has not been explored with as much vigor as MCF and ICF concepts, in part, because the classic Z pinch is MHD unstable to m=0 ‘sausage’ and m=1 ‘kink’ modes. These fast instabilities destroy plasma confinement on Alfvenic timescales, hindering prospects for thermonuclear gain. Sheared-flow stabilization offers a path to overcoming these instabilities to produce an MHD-stable column of flowing Z pinch plasma that can reach thermonuclear conditions through adiabatic compression. Energy confinement is defined by the flow-through time of about 10 μs, making it possible to produce thermonuclear gain.

Tracing their lineage to early experiments at the University of Washington, the FuZE and FuZE-Q devices currently operating at Zap Energy consist of a coaxial plasma accelerator, where flowing plasma is generated, coupled to an assembly region, where Z pinches are formed. Recently, record pinch currents, > 600 kA, electron temperature > 2 keV, ion temperature > 2.5 keV and DD neutron yield > 2e8/pulse have been achieved. In parallel with experiments, we perform full device MHD simulations. These simulations produce synthetic diagnostic signals that show remarkable agreement with experimental measurements and reveal complex details of the pinch formation and neutron generation processes. The goal of the combined experimental/modeling program is to reach plasma parameters consistent with scientific breakeven Q=1 conditions. The status of this effort and its future outlook will be presented.

Magneto-inertial fusion (MIF) concepts, such as the Magnetized Liner Inertial Fusion (MagLIF) platform, constitute a promising and scalable technological path to reach high fusion yields (>100 MJ) and gains (G>100) in the laboratory. However, scaling MagLIF is not entirely straightforward: the space of experimental input parameters defining a MagLIF load is highly multi-dimensional, and the implosions themselves are complex events involving many physical processes. In this talk, we present a simplified analytical model that identifies the main physical processes at play during a MagLIF implosion [1]. Using non-dimensional analysis, we determine the most important dimensionless parameters characterizing MagLIF implosions and provide estimates of such parameters. We show that MagLIF targets can be “incompletely” similarity scaled, meaning that the experimental input parameters of MagLIF can be varied such that many (but not all) of the dimensionless quantities are conserved. Based on similarity scaling, we can explore the parameter space of MagLIF targets and estimate the performance of scaled targets. We test the similarity scaling theory against simulations for two different scaling “vectors”: current scaling [2] and rise-time scaling [3]. Good agreement is obtained.

* SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

[1] D. E. Ruiz, P. F. Schmit, D. A. Yager-Elorriaga, C. A. Jennings, and K. Beckwith, Phys. Plasmas 30, 032707 (2023).

[2] D. E. Ruiz, P. F. Schmit, D. A. Yager-Elorriaga, et al., Phys. Plasmas 30, 032708 (2023).

[3] D. E. Ruiz, P. F. Schmit, M. R. Weis, K. J. Peterson, and M. K. Matzen, Phys. Plasmas 30, 032709 (2023).

The Magnetized Liner Inertial Fusion (MagLIF) platform, at Sandia National Laboratories, requires the successful compression and confinement of pre-heated and pre-magnetized fusion fuel. Over recent years, the experimental platform has been substantially improved by increasing electrical current delivery to the target (reduced power feed losses) and increased laser energy coupled to the fuel (reduced backscatter and laser entrance foil losses) alongside more constraining measurements of these inputs [1,2]. Using the LLNL code HYDRA, this talk will review post-shot 3D modeling of a number of these experiments with a focus on the impact of MHD instabilities on fusion output and experimental observables. For a fixed set of perturbations and over a range of inputs (current and laser preheat), these simulations typically overpredict neutron yields by a factor of 2 but show agreement with Tion inferred from neutron time-of-flight diagnostics. Additionally, the experimental pressure and convergence ratio inferred using a Bayesian analysis are significantly higher than the burn averaged values calculated from simulations. Although it should be noted, the Bayesian inferences also calculate a significant mix fraction not included in the simulations. Resolving these discrepancies is a focus of ongoing work, but these simulations suggest improvements to stability offer a deceptively simple path to higher yield and motivate future research directions.

[1] Gomez et al., Phys. Rev. Lett. 125, 155002 (2020).

[2] Harvey-Thompson et al., RSI, under review.

SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. This work was performed under the auspices of the U.S. Department of Energy by LLNL under Contract DE-AC52-07NA27344.

Metal liners rapidly imploded by a fast rising (<100ns) current to compress a magnetized, preheated fuel offer the potential to efficiently reach fusion conditions [S.A. Slutz et al. Phys. Plasmas 17, 056303 (2010)]. Liner implosion research on Z in support of the MagLIF scheme has typically focused on acceleration instabilities during the implosion phase. However, the growth of inner surface instabilities during deceleration as the liner stagnates on compressed fuel on axis have the potential to be very detrimental to performance. During the deceleration stage azimuthally asymmetric, short wavelength "flute" modes grow aggressively and can penetrate the fuel volume, mixing in liner material and degrading fuel confinement. We discuss the implications of these instabilities on MagLIF performance and how their effect may vary as experiment input parameters change. We then discuss a series of Z experiments that have been proposed to purposefully introduce azimuthally asymmetric structures into MagLIF relevant experiments to study their impact on stagnation performance and assess simulation predictions of these processes.

* SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.