Zap Energy is an american company headquartered in Seattle, which is aiming to commercialise a shear-flow stabilized Z-Pinch.
The company grew out of research conducted on shear-flow stabilisation lead by Uri Shumlak at the University of Washington.
Having confirmed sustained D-D thermonuclear neutron production from FuZE (Fusion Z-pinch experiment) at 200kA (Zhang et al., 2019), with tested plasma currents up to 500kA, they now are in the process of testing their next generation prototype, FuZE-Q, which is expected to reach scientific breakeven at 650kA.
- Confinement:
- Shear-flow stabilized Z-Pinch
- Fuel cycle:
- Neutronic deuterium-tritium (DT). LiPb blanket breeding (BR≈1.1).
- Compression:
- Plasma current induced, β=1
- Magnets:
- N/A
- Energy Extraction:
- LiPb to steam cycle.
The Z-Pinch
The Z-pinch is a form of magnetic compression induced in a conductor by the flow of current. Such a flow produces a magnetic field around the axis of travel, resulting in a Lorentz crushing force in the radial direction. This effect can be seen in practice occuring in lighning rods when struck.
The Z-pinch is applied to fusion by substituting the metal conductor for a plasma, which is crushed by the discharge of a large capacitor bank in order to bring the fuel to fusion conditions. This approach was one of the earliest promising avenues, however attempts suffered from instabilities that resulted in insuffient containment times for fusion. Various methods of stabilization such as placing the pinch within an axial magnetic field (Shumlak, 2020) have been tried, however with mixed results.
Shear Flow Stabilization
The key innovation at Zap Energy is the introduction of a sheared flow to the plasma, which acts to restrain the plasma during the compresssion pulse, greatly delaying the onset of instabilities.
If you’re ever watched Nemo (come on, who hasn’t), the scene with the East Australian Current presents a fun analogy. Replace the ocean current with the central high velocity plasma flow, and the turtles with ionised deuterium and tritium, and you have have yourself a a shear-flow stabilized plasma!
For more about this, Zap have some excellent graphics on their website demonstrating the sheared flow.
Plant Engineering
Achieving fusion is all well and good, but the true end goal is to build an economic power plant, not just to prove the physics.
To this end a Z-pinch has a number of significant advantages over other frontrunners such as tokamaks and laser inertial confinement.
- The system requires no superconductors or magnets of any kind, reducing cost.
- Without the presense of strong magnetic fields, the use of liquid metal coolants is greatly simplified due to the lack of magneto-hydrodynamic forces.
- A high Beta* results in a very small plasma volume compared to tokamaks, reducing reactor size and complexity.
- In contrast to laser inertial confinement systems, there is no requirement for sensitive high precision optics in the vicinity of the fusion reaction.
- Electrical energy is used directly to initiate the fusion reaction, rather than through inefficient intermediate conversions to laser or RF energy.
*Beta refers to the ratio of plasma pressure to magnetic pressure. In effect it is the ‘leverage’ that the magnetic field can exert on the plasma, and is a useful indicator of plasma density.
Background Resources
https://www.zapenergy.com/news/first-plasmas-fuzeq-series-c
Shumlak, U., Golingo, R. P., Nelson, B. A., Bowers, C. A., Doty, S. A., Forbes, E. G., Hughes, M. C., Kim, B., Knecht, S. D., Lambert, K. K., Lowrie, W., Ross, M. P., & Weed, J. R. (2014). High energy density Z-pinch plasmas using flow stabilization. 76–79. https://doi.org/10.1063/1.4904781
Engineering Paradigms for Sheared-Flow-Stabilized Z-Pinch Fusion Energy. (n.d.). Retrieved August 30, 2023, from https://www.tandfonline.com/doi/epdf/10.1080/15361055.2023.2209131?needAccess=true&role=button
Shumlak, U., Meier, E. T., & Levitt, B. J. (2023). Fusion Gain and Triple Product for the Sheared-Flow-Stabilized Z Pinch. Fusion Science and Technology, 0(0), 1–16. https://doi.org/10.1080/15361055.2023.2198049
Shumlak, U. (2020). Z-pinch fusion. Journal of Applied Physics, 127(20), 200901. https://doi.org/10.1063/5.0004228
Forbes, E. G., Shumlak, U., McLean, H. S., Nelson, B. A., Claveau, E. L., Golingo, R. P., Higginson, D. P., Mitrani, J. M., Stepanov, A. D., Tummel, K. K., Weber, T. R., & Zhang, Y. (2019). Progress Toward a Compact Fusion Reactor Using the Sheared-Flow-Stabilized Z-Pinch. Fusion Science and Technology, 75(7), Article LLNL-JRNL-811187. https://doi.org/10.1080/15361055.2019.1622971
Shumlak, U., Chadney, J., Golingo, R. P., Den Hartog, D. J., Hughes, M. C., Knecht, S. D., Lowrie, W., Lukin, V. S., Nelson, B. A., Oberto, R. J., Rohrbach, J. L., Ross, M. P., & Vogman, G. V. (2012). The Sheared-Flow Stabilized Z-Pinch. Fusion Science and Technology, 61(1T), 119–124. https://doi.org/10.13182/FST12-A13407
Zhang, Y., Shumlak, U., Nelson, B. A., Golingo, R. P., Weber, T. R., Stepanov, A. D., Claveau, E. L., Forbes, E. G., Draper, Z. T., Mitrani, J. M., McLean, H. S., Tummel, K. K., Higginson, D. P., & Cooper, C. M. (2019). Sustained Neutron Production from a Sheared-Flow Stabilized $Z$ Pinch. Physical Review Letters, 122(13), 135001. https://doi.org/10.1103/PhysRevLett.122.135001
Presentations
Other References
James, A. P. B. (n.d.). English: A photograph of a section of the crushed lightning rod first described by J.A. Pollock and S. Barraclough, 1905, Proc. R. Soc. New South Wales 39, 131. They correctly described the crushing mechanism as a result of the interaction of the large current flowing in the conductor with its own magnetic field. Historical collection of the School of Physics, University of Sydney, Australia. Retrieved August 30, 2023, from https://commons.wikimedia.org/wiki/File:Crushed_rod_pollock_barraclough.jpg
H.J. De Blank. Mhd instabilities in tokamaks. Fusion Science and Technology, vol. 53, 2008
