Potentially Smallest Fusion Device Using Improved Z-Pinch Fusion

ARPA-E-funded alternative z-pinch fusion which is being developed by Zap Energy.

Zap Energy is the most compact solution to Fusion Energy and does not use complex and costly magnetic coils. They surpassed ARPA-E Alpha Milestones in August 2018. Their reactor is consistently producing neutrons and they received $6.8 million ARPA-E OPEN funding.

* The new Z-pinch has the simplest geometry of any magnetic confinement configuration. It is a cylindrical plasma column.

The U.S. Department of Energy announced $98 million in funding for 40 new projects in 2018.

Talk Polywell has had discussions of this work.

Arxiv- Sustained neutron production from a sheared-flow stabilized Z-pinch (2018,2019)

The sheared-flow stabilized (SFS) Z-pinch has demonstrated long-lived plasmas with fusion-relevant parameters. This Letter presents the first experimental results demonstrating sustained, quasi-steady-state neutron production from the Fusion Z-pinch Experiment (FuZE), operated with a mixture of 20% deuterium/80% hydrogen by volume. Neutron emissions lasting approximately 5 µs are reproducibly observed with pinch currents of approximately 200 kA during an approximately 16 µs period of plasma quiescence. The average neutron yield is estimated to be (1.25±0.45)×100,000 neutrons/pulse and scales with the square of the deuterium concentration. Coincident with the neutron signal, plasma temperatures of 1 − 2 keV.

Employing the SFS Z-pinch concept, FuZE has achieved equilibrium-stabilized plasma with fusion-relevant parameters of 10^17 cm−3 number density, 1 − 2 keV temperature, 0.3 cm pinch radius, and long-lived quiescent periods of approximately 16 µs on a scale that facilitates diagnostic measurements. The demonstration of sustained neutron production lasting approximately 5 µs, thousands of the theoretical m = 1 mode growth time, the absence of m = 0 and m = 1 instabilities during neutron production, and the observation of neutron yield scaling indicate consistency with a thermonuclear fusion process. The measured neutron yields are approximately 100000 neutrons/pulse, consistent with theoretical expectations for the measured plasma parameters and within the statistical expectations of a steady-state line neutron source.

SOURCES- Lawrence Livermore National Labs, ARPA-E, Washington University, Arxiv
Written By Brian Wang. Nextbigfuture.com

Electrode Technology Development for the Sheared-Flow Stabilized Z-Pinch Fusion Reactor
Zap Energy Inc. | Seattle, WA | $6,767,334

Zap Energy will advance the fusion performance of the sheared-flow stabilized (SFS) Z-pinch fusion concept. SFS Z-pinch drives electrical current through a plasma to create magnetic fields that compress and heat the plasma toward fusion conditions. Under this project, the team will raise the electrical current, reduce physics risks relating to plasma stability and confinement, and develop the electrode technology and plasma-initiation techniques necessary to enable the next steps toward a functional SFS Z-pinch fusion power plant. This could provide nearly limitless, on-demand, emission-free energy with negligible fuel costs.

19 thoughts on “Potentially Smallest Fusion Device Using Improved Z-Pinch Fusion”

  1. This seems no different than the Columbus-1 linear pinch device from 1951. Just a smaller version employing geometry calculated from Lawsons Criterion.

  2. Interesting. Wonder what exactly they are doing.
    Worth noting that reactor designs like Helion’s Fusion Engine can produce their own He3 and according to Helion could also be used to produce commercial scale He3 at competitive price. In any case, there potentially are options.

  3. Their design has a path to advanced fuels such as D+He3 and PB11. That said, it is probably a good idea to go with D+T first. Also worth mentioning that with small, linear reactor designs like this one, D+T has much less engineering issues than you would have with a Tokamak. Replacing the reactor core would be really easy and if mass produced, they would be very cheap.
    As for electrodes, I think that problem is solvable, given enough funding. Most issues LPP has had are because of a lack of funding. The Sheared Flow Stabilized Z- Pinch also seems more plausible, at least to me.

  4. I believe some numbers are using exhaust velocity instead of seconds, but I am not sure. The numbers I know for D+He3 assumed an Isp of 357,000 seconds and 330 kN of thrust.
    The big unknown is the power supply. If that can be compact/light weight enough to provide the current, it could be possible to have a T/W over 1.
    I believe that some of the (very high) Isp could be traded for more thrust by having cooling channels in the walls of the reactor that would heat hydrogen and exhaust that out the back. Assuming 1000 C temperature, the engine could still have a very high average(!) Isp in the 10s of thousands and much more thrust. I believe that with a couple of engines like that, you might be able to take a ship, the mass of Dragon 2 with an elongated trunk all the way to the moon as an SSTO at a continuous 1.1g acceleration. Then turn around half way, brake and land. Then launch again and do the same for the way back, all without refueling. ~4 hour trip time (one way) and it won’t even need a heat shield due to completely propulsive deceleration and landing.
    Problem is He3 availability. One could probably use dedicated reactors of the same typ to produce the He3 from D+D reactions. No need for moon mining, though with engines like that, even mining the moon could become economically viable.
    That said, it would probably start out as a space drive only with slightly lower parameters. The problem is the electrode materials, which would have to withstand 5 MA input current.

  5. Some articles mention 10 million Isp and 1 MN of thrust.

    Were that the numbers you worked with?

    Would love to see more mission profiles… like a trip to Jupiter or Saturn, using this ZPinch Fusion propulsion on a modified SpaceX Starship 🙂

  6. Well. Let’s just pay attention what the team below in the link is up to. If the resulting product is (much) cheaper than mining He3 on the Moon (which is pure lunacy given the scale of the mining operation required), or the high priced terrestrially available He3 reserves, companies might actually start to get interested in designing reactors for the very expensive stuff: https://prometeon.it/production-of-helium-3-new/

  7. Tokamaks actually started out using the same containment mechanism as the Z pinch machine, an axial current, and got kink instabilities. They tried preventing that with an external magnetic field, and found that increasing it, and relying less on the pinch, helped stabilize things.

    But I’m pretty sure even current Tokamaks are getting part of their containment, and a lot of the heating, from a Z pinch style axial current. That’s part of the reason they’re only pulsed devices, the current has to be produced inductively, and you can only ramp a magnet for so long. While the linear Z pinch machine could, in principle, run continuously.

    My point, though, is that they’ve long used flow shear to help stabilize tokamaks. Not surprised it works in Z pinch machines, too.

    The really nice thing about Z pinch machines, as alluded to in the OP, is that you can experiment with them without needing something the size of ITER.

  8. Depends on the choice of fuel. With D+He3, the pinch has to be a lot longer than with D+T, but you safe yourself some problems with shielding and radioactive exhaust.
    There are tricks to increase the thrust at the cost of Isp, which would be in the hundreds of thousands with this. Based on the somewhat limited information available so far, I calculated that one could build an SSTO based on a Dragon 2 with an oversized “trunk” that could take off from earth, go half way to the moon, decelerate propulsively, land and then fly back to earth and then land propulsively there. Trip time would be just a few hours.
    Big unknown is the mass of the pulsed power supply. If that is off by too much, it would not work as an SSTO, but would still make an excellent space drive. Trips to Mars could be measured in days for the _average_ distance between Earth and Mars and all that with a very small ship.
    One of the issues is that you need to make a lot of He3 to power the reactor. This could be done with dedicated D+D reactors, which would be less efficient and thus probably not as economic to operate. Again, that depends on certain factors. It is just too early to know all that, but the possibilities are intriguing.

  9. I agree. The metric of triple product per $ spent is useful. Doesn’t mean that one approach will work and the other won’t but it is a useful gauge.

  10. No tokamaks want to prevent pinches as they are destructive to the device.

    DPF and Z machine embrace the destructive aspect of parallel electric currents and make it how they accomplish fusion.

  11. Parallel electric currents create magnetic fields around them, such that currents in the same direction nearby are attracted to each other.

    A “Z” pinch runs a strong current around the outside of the fuel, (Along the ‘Z’ axis.) to pinch the fuel down, compressing it, because all those currents around it are attracting each other.

    This sort of compression is unstable, if part of the fuel compresses a tiny bit more than the rest, it compresses even more, and you get the fuel pinched off in lumps instead of uniformly compressed.

    However, if some of the fuel is traveling along the z axis at a different rate than the rest of the fuel, it suppresses this by mixing the degree of compression along the z axis, smoothing out the pinch.

  12. Main concern is D-T.

    Other than that best of luck to them and congrats on the grant money.

  13. Seems like this is where the dense plasma focus was 5ish years ago, and likely to be subject to the same scaling challenges. The main concern being, as they crank up the amps, they’ll start burning off electrode material that will then become impurities in the plasma.

    After a touch more research, it seems the actual Darpa award is “Electrode Technology Development for the Sheared-Flow Stabilized Z-Pinch Fusion Reactor | Zap Energy Inc. | Seattle, WA | $6,767,334”

    So…I guess they’re aware.

  14. One needs to put these results into perspective. How much was spent? How long have the experiments been running? What was the goal of the experiments?
    Shumlak and his team met all of their milestones for the ARPA-E Alpha round and that with relatively low funding, a very small device and in a very short amount of time. That deserves recognition.
    Yes, most if not all of them are lagging behind the big experiments like JET and JT-60 in terms of triple product results, but getting the highest triple product is not necessarily the goal of an experiment. Plus, for the big projects I can only say that it is quite easy to stink if your pants are full.

  15. Was there a graph that showed working fusion with only an extrapolation over 5 orders of magnitude…. yes, yes there is. So just like every other alt-fusion scheme then.

    Alright, let’s look at the Lawson Triple Product. Density x Temperature x Confinement time. The rule is that for D-T (the easiest fusion reaction) the triple product should be at least 3 x E21 keV.s/m^3.

    For this project

    10^17 cm−3 number density, 1 − 2 keV temperature, 0.3 cm pinch radius, and long-lived quiescent periods of approximately 16 µs 

    So convert the units and multiply together and we get

    Hmmm… that’s only 2 orders of magnitude off. Probably I’ve stuffed up somewhere.

  16. Uri Shumlak and his team at Zap Energy Inc are IMHO one of the leading candidates for practical fusion reactors. Their design has a lot of potential because it is so simple and compact and so far scaling laws have been holding up. Could even lead to new space drives with a very high Isp and a good T/W ratio.

Comments are closed.