Advances in Thermonuclear Fusion Yield Produced in Sheared-Flow-Stabilized Z Pinches*

The sheared-flow-stabilized (SFS) Z-pinch fusion concept, developed at the University of Washington with LLNL collaborators, is now on a path to commercialization at Zap Energy [Levitt et al., Phys. Plasmas 30, 9 (2023)]. Recent experiments corroborate predicted thermonuclear fusion reaction rates, as the discharge current is scaled toward higher gain performance.  Two SFS Z-pinch platforms, FuZE and FuZE-Q, are leveraged for parallel operations with different power supplies and configuration optimization strategies.  Experimental campaigns are underway to increase the triple product, pinch stability duration, and DD fusion neutron production. These efforts aim to scale the pinch current, plasma density, and plasma temperature to reach scientific breakeven.

In this presentation, we report recent results from both experimental platforms, demonstrating operation with thermonuclear plasmas.  Electron temperatures in excess of 2 keV are measured with Thomson scattering [Levitt et al., Phys. Rev. Lett. 132, 15 (2024)], placing a lower bound on ion temperature, which is also independently inferred from impurity radiation spectra to be greater than 2.5 keV.  Simultaneous Thomson electron density measurements result in pinch pressure profiles [Goyon et al., in review 2024] in agreement with predictions by analytical and computational models [Meier et al., Phys. Plasmas 28, 9 (2021)].  These devices produce DD neutron yields that scale strongly with plasma current (Yn~I^11) [ Levitt et al., Phys. Plasmas 30, 9 (2023)] up to 10^10, consistent with adiabatic scaling of a SFS Z pinch [Shumlak, J. Appl. Phys. 127, 20 (2020)], and with 2D MHD modeling results. Measurements of neutron spatial isotropy place stringent limits on the possible contribution of beam-target fusion events and suggest that roughly 90% of the observed yield originates from thermalized deuterium plasma.  These recent advances in performance constitute a factor of 10^5 improvement in fusion yield since 2021.