Sheared-Flow-Stabilized Z Pinch as a Compact Fusion Device

The Z-pinch equilibrium radially confines plasma pressure with an axial current. High densities and temperatures should result through plasma compression from increasing the current. However, virulent pressure-driven instabilities quickly destroy the equilibrium and impede the path to a viable fusion device for the traditional Z pinch. Introducing a sheared axial flow to the plasma was theorized to stabilize the Z pinch. Closely coupled with computational studies, Z-pinch experiments at the University of Washington tested the theory of sheared-flow stabilization. Measurements of the plasma equilibrium and stability confirmed that in the presence of a sufficiently large flow-shear, gross Z-pinch instabilities were mitigated, and radial force balance was achieved. Z-pinch plasmas were held stable for durations much longer than predicted for a static plasma, i.e. stable for thousands of instability growth times. Experimental results were combined with adiabatic scaling relations and detailed single-fluid, multi-fluid, and kinetic computational studies to explore the limits of possible plasma properties that may be achieved in a sheared-flow-stabilized (SFS) Z pinch. The improved understanding of stabilization provided a means of increasing plasma parameters, e.g.
$\mathrm{n}_{\mathrm{e}} > 1\mathrm{e}17\ /\text{cc}$
and
$\mathrm{T}_{\mathrm{i}} > 1$
keV. The collaborative FuZE (Fusion Z-pinch Experiment) project between UW and LLNL scaled the SFS Z pinch to fusion conditions. Results have demonstrated that fusion reactions are sustained along a 50-cm long Z-pinch deuterium plasma. Steady neutron production
¹
was observed for durations up to 8 microseconds during which the plasma was stable, and the current was sufficiently high to compress the plasma to fusion conditions. The neutron production was demonstrated to be consistent with a thermonuclear fusion process. Increasing the pinch current has demonstrated a corresponding increase in neutron yield. The dependence of yield on current will be presented and compared to theoretical scaling relations and numerical simulations. Experimental observations generally agree with theoretical and computational predictions, indicating that sheared flows can stabilize and sustain a Z-pinch equilibrium and offering a potential path to achieve even higher performing plasmas.