Historical research guide · 0855 · 2023
The Sheared-Flow-Stabilized Z-Pinch Approach to Fusion Energy
Uri Shumlak · Brian A. Nelson · Ben J. Levitt
In one minute
Uri Shumlak and his Zap Energy colleagues brought a status report to the 2023 IEEE plasma science conference on the simplest fusion machine anyone is building. A Z pinch is a column of gas with a very large current driven straight down it: the current’s own magnetic field squeezes and heats the column, so there are no external magnets and no separate heating system to build. The approach was set aside in the 1960s because the column kinks and destroys itself within microseconds. Shumlak’s group, first at the University of Washington with Livermore collaborators and now commercially at Zap Energy, revived it by giving the plasma a velocity shear — the gas moves at different speeds at different radii, and that shear smooths the kink away before it can grow. Their Fusion Z-pinch Experiment reached pinch currents above 600 kA, electron and ion temperatures above 2 and 2.5 keV, and more than 200 million fusion neutrons in a single pulse. The successor machine, FuZE-Q, is operating and aimed at scientific breakeven.
Connection
Chapter 12 follows fusion as the energy substrate the rest of the programme rests on, and this is its compact end: no external magnet set, no auxiliary heating, a device small and cheap enough to iterate on in months rather than decades. Chapter 9 gets the plasmoid argument in its most testable form — a plasma column that organises, confines and compresses itself, with neutron measurements that show the reactions are thermal rather than an artefact of a fast particle beam.
From the source
The sheared-flow-stabilized Z-pinch concept was developed at the University of Washington with Lawrence Livermore National Laboratory collaborators, and is now on a path to commercialization at Zap Energy Inc. Recent experiments corroborate expected thermonuclear fusion reaction rates as the discharge current is scaled towards compact reactor conditions.ICOPS 2023 abstract, opening sentences; conference paper, page 1
The Fusion Z-pinch Experiment, FuZE, employs high power-handling electrodes, flexible gas injection, and independently switched capacitor bank modules, so that the discharge current and the gas distribution can be tailored to establish both the stabilizing sheared flow and the pinch current itself. Stability is a property of how the plasma is driven, not of an external magnet cage.ICOPS 2023 abstract, second paragraph; conference paper, page 1
Record performance reported to the conference: pinch currents greater than 600 kA, electron temperature greater than 2 keV, ion temperature greater than 2.5 keV, and neutron yield greater than 2 times 10 to the eighth per pulse.ICOPS 2023 abstract, results sentence; conference paper, page 1
The independent check that the neutrons are real fusion and not a fast-beam artefact: measuring how evenly the neutron energy is spread across directions bounds the energy of any deuteron beam in FuZE to 7.4 keV, with a statistical uncertainty of 5.6 and a systematic uncertainty of 3.7 keV, at average plasma currents of 370 kA and yields of 4 times 10 to the seventh neutrons per discharge. The majority of the neutron production is isotropic, consistent with thermonuclear origin.Ryan and colleagues, Nuclear Fusion, doi 10.1088/1741-4326/ada8bf, abstract and results
The machine can now be simulated end to end. Whole-device resistive magnetohydrodynamic modelling of FuZE reproduces pinch densities of about 10 to the twenty-second per cubic metre and a deuterium-deuterium neutron rate of 10 to the seventh per microsecond sustained for about two microseconds, matching measured peak currents and voltages within ten per cent and total yield within about thirty per cent — a predictive capability for designing the next device rather than only explaining the last one.Datta, Meier and Shumlak, Nuclear Fusion, doi 10.1088/1741-4326/ad3fcb, abstract
The named next measurement, and the parallel engineering: FuZE-Q, the next-generation device, is operational, and the effort is to scale pinch current, plasma density and plasma temperature to reach scientific breakeven. Alongside it Zap Energy develops the power-plant technologies — high-average-power repetitive pulsed power, high-duty-cycle cathodes, and liquid metal wall systems.ICOPS 2023 abstract, closing sentences; conference paper, page 1
The way in
https://doi.org/10.1109/ICOPS45740.2023.10481340How to cite it
Uri Shumlak, Brian A. Nelson, Ben J. Levitt (2023) The Sheared-Flow-Stabilized Z-Pinch Approach to Fusion Energy doi:10.1109/ICOPS45740.2023.10481340