Z-Pinch Renaissance

[Skipjack]

Finally got to the linked-in video. Less interesting than your post, but confirms they are up around 500KA with scaling intact.

Thanks! I try my best at kremlinology

Frustrating for me that I don't really understand the challenges they face in raising the current. We know MAST is a mega-amp, fwiw. But if the difficulty scales with e.g. the 17th power of current, they might not make it. Just floundering, but I wish them the best: they certainly get the prize for conceptual simplicity....

MAST, Sandia, MIFTI among others use very high currents.
The challanges ZAP faces are in the structure and materials. They want to and have to do several shots a second for a viable power plant. That will cause some abrasion on their electrodes. Also, they have not had a lot of funding until recently. So they were limited in what they could afford to build.
Plus, I know Uri well enough to know that he is extremely cautious. So he likely wanted to test on a smaller scale first and make sure that this is actually working before spending the big bucks. E.g. they went through great lengths to ensure that the neutrons they were getting, were from actual thermonuclear reactions and not some other source, like neutron spallation.

And why bother making the pinch so darn long? 50cm is a hell of a spark-gap.

To the best of my understanding, the longer the pinch, the longer the confinement time.
They are aiming for even longer pinches (10 meters) for their space propulsion designs with advanced fuels.

[RERT]

Thanks. I need to look at where they calculate the 11th power scaling. On the face of it anything which raises current would be a win, but I’d need to try and understand what the scaling law really means.

[Giorgio]

Frustrating for me that I don't really understand the challenges they face in raising the current. We know MAST is a mega-amp, fwiw. But if the difficulty scales with e.g. the 17th power of current, they might not make it. Just floundering, but I wish them the best: they certainly get the prize for conceptual simplicity....

To visualize the challenge you can think to the current into the machine as a viscous fluid, the higher the current (the viscosity) the higher the influences of the MHD instabilities of the boundary on the core pinch.
Thus, to be able to increase the current and overcome the break-even line while keeping a stable Shared flow, the solution is to decrease the pinch radius "a" so that it will not "feel" the boundaries instabilities.

screenshot_Mon_Jun_21_18.03.45.png (36.12 KiB) Viewed 7697 times

And this is why I was asking in my previous post what was the pinch radius of the reported experiment, because a high current without a pinch radius will not allow the black line to cross over the "Q=1", but will transform the black line in an asymptote to "Q=1"
This point (as you can see clearly from the picture down here) will also limit the commercial "Q" of such a reactor to a single digit number, unless they had some new breakthrough that allows the pinch to be stable irrespective of current and pinch diameter.

screenshot_Mon_Jun_21_18.10.57.png (130.12 KiB) Viewed 7697 times

And why bother making the pinch so darn long? 50cm is a hell of a spark-gap.

Because the plasma pinch stability due to flow shear increases with pinch length.

Thanks. I need to look at where they calculate the 11th power scaling. On the face of it anything which raises current would be a win, but I’d need to try and understand what the scaling law really means.

Here on page 3, Point A there is the explanation of how they reached the 11th power scaling:
https://aip.scitation.org/doi/pdf/10.1063/5.0004228

You will see also as the average temperature is correlated with the ion density (that depends on the pinch radius).
Reaching the expected power scaling requires (again) reaching the expected sub millimeter pinch radius.

[Giorgio]

Not that I could see. What they are showing is a graph with the predicted scaling towards Q(sci) and their experiments on that line. So I assume that means that they have kept the other parameters at a useful level.
Here is a screenshot for you, bud:

Thanks a lot!
I projected the "q" values of that diagram onto the chart I got above and I calculated a radius of slightly less than 1 mm, so perfectly in line with FUZE operating parameters.
I would say that this is a pretty good news as for the accuracy of their models, they need to to find a suitable working way to reduce the pinch diameter and verify that the Alpha will escape without thermalizing during the pinch.
If they can manage these two points, overcoming the break even line should be trivial.

I am very interested to see what they will present in the coming conferences.

[RERT]

Because the plasma pinch stability due to flow shear increases with pinch length.

Thanks Giorgio. The above is very counter-intuitive! I had already found and skimmed the paper you cite, but couldn't see any reference to pinch length. Have you got a reference for the above? Also surely creating the sheared flow must be harder over a longer pinch? Similarly couldn't see any relation between pinch length and confinement time, although the 'dilution' of end/electrode leaks is pretty clear.

The paper did obliquely mention length via the statement that the pinch was a uniform linear source of neutrons. Then obviously the longer the better: the same current is constraining more plasma and creating more fusion power just by having a longer pinch. (slaps forehead)

[Giorgio]

The paper did obliquely mention length via the statement that the pinch was a uniform linear source of neutrons. Then obviously the longer the better: the same current is constraining more plasma and creating more fusion power just by having a longer pinch. (slaps forehead)

Exactly, once the pinch is established (and as long as there will be enough plasma and current) the pinch will stay stable, and because fusion is for unit of length, the longer the better.

Here on page 24 you have the general formulation for D-T that they are using for their modelling. You can extrapolate the binding between Power, Pinch Length, Pinch radius, plasma V(z), and all other parameters and respective limits for each.
https://wippl.wisc.edu/pub_files/journal/Shumlak928.pdf

[Skipjack]

I think that keeping the Z-pinch stable for a longer distance is the key here. They think they can keep them stable for 10 meters for D+He3 and 50(!) meters for PB11. Not sure whether they will be able to achieve it, but they are at least thinking it possible:
https://www.researchgate.net/publicatio ... on_Concept

[Giorgio]

I think that keeping the Z-pinch stable for a longer distance is the key here. They think they can keep them stable for 10 meters for D+He3 and 50(!) meters for PB11. Not sure whether they will be able to achieve it, but they are at least thinking it possible:
https://www.researchgate.net/publicatio ... on_Concept

I think that the smaller the pinch radius, the more difficult is to increase the pinch length over a certain value before various instabilities will damage the axial coherence of the Z-Pinch and the plasma.

[Skipjack]

Nice interview with Ben Levitt of ZAP:
https://www.youtube.com/watch?v=rsTKcb5KSig

[Giorgio]

Very interesting video and also the channel was a pleasant surprise as I didn't know it.

The reply I liked more is when he said that they are looking to Q=20 for a 200 MW commercial reactor at the size of a micro-bus.
This really took me by surprise, as the pinch radius would need to be around 0,2 mm. An extremely ambitious goal, but if they can indeed reach it it will really become a versatile machine for everything, from land, marine and space applications.

I am really interested to see what they will be willing to disclose in the coming conferences.

[crowberry]

Zap Energy has published this on Twitter on the 1st of September:

Zap Energy's new facility is fully operational - now producing high performance z-pinch plasmas and generating thermonuclear fusion!

Oh and we got the keys to our second facility today - which doubles our footprint - the team there will be developing the technology we will need on the other side of energy break even

So hopefully we will soon hear what their new device is capable of.

https://twitter.com/energy_zap

[Skipjack]

I am not sure they have fully built their new device yet. IIRC, they are planning for Q(sci) > 1 by 2023. But who knows? Uri is quite conservative with his estimates and predictions. Maybe they get there faster. They got a lot more money now to throw at it too...

[Skipjack]

Benjamin Levitt of ZAP will be presenting at the APS meeting.

2023 break even schedule confirmed:
http://meetings.aps.org/Meeting/DPP21/Session/TP11.53

They have quite a few other presentations scheduled as well.

[Ivy Matt]

These efforts aim to scale the pinch current, plasma density, and plasma temperature to reach scientific breakeven equivalent conditions by early 2023 in the next generation device FuZE-Q, which is currently being commissioned.

I'm guessing this means that they expect to achieve conditions with DD equivalent to scientific break-even conditions if they had been using DT fuel instead. JT-60U achieved this in 1996. Although I suppose if a private fusion company achieved this, it would be a milestone significant enough to attract major investments for a device using DT fuel.

[Skipjack]

These efforts aim to scale the pinch current, plasma density, and plasma temperature to reach scientific breakeven equivalent conditions by early 2023 in the next generation device FuZE-Q, which is currently being commissioned.

I'm guessing this means that they expect to achieve conditions with DD equivalent to scientific break-even conditions if they had been using DT fuel instead. JT-60U achieved this in 1996. Although I suppose if a private fusion company achieved this, it would be a milestone significant enough to attract major investments for a device using DT fuel.

Yeah, that is what I expect as well. Though I don't think that there would be much standing in the way of them doing a few of shots with D-T at the end of the campaign just to drive the point home. Plus, break even with such a tiny device would be very different from JT-60.