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Re: Z-Pinch Renaissance

Posted: Thu Oct 22, 2020 3:27 pm
by Giorgio
williatw wrote:
Thu Oct 22, 2020 11:22 am
Not to interrupt you gentlemen's interesting technical discourse but what about a compromise? Say one of those small modular nuclear reactors of the type that Trump just approved funding for?
What me and Skipjack are digressing about is not on the type of power reactor that is needed but on the need itself of a secondary power source to be coupled to the ZAP engine. In other words we do not agree on the Technology Readiness Level (TRL) of the ZAP design.

We do both agree that if the need of a standby reactor for power production will arise than the whole ZAP engine will lose appeal.

That said, and out of context from the discussion above, a normal fission reactor like the one proposed by NuScale would still be too much massive. For space application I would follow the route of a Molten Salt Reactor, and more specifically of a Liquid Fluoride Thorium Reactor that gives you the lowest footprint and mass for MW. d
Here is a good report on the technology.
Again, this is quite offtopic so if you have any interests or wish to discuss ideas on the LFTR I suggest you ope a new thread.

Re: Z-Pinch Renaissance

Posted: Sat Oct 24, 2020 12:45 am
by Skipjack
Giorgio, the paper you quoted is from 2006. Since then Uri and his team have made a lot of progress and so far the scaling laws are holding, suggesting that thermalization is not a real issue. Back in 2006, they did not even have ZAP-HD yet which scaled the input current to 50 kA and since then their follow up to ZAP- HD, FuZE has scaled up to 400kA and from all that I have read, the scaling laws are holding very well. If thermalization was a big problem, it would likely have reared it's ugly head by now. Don't you think?

Re: Z-Pinch Renaissance

Posted: Sat Oct 24, 2020 3:28 pm
by Giorgio
I am quoting that 2006 paper because is the only paper where they mention the issue. After this paper in no other public paper or presentation that I have read the thermalization issue was ever mentioned as "overcome" or "tested" or "solved".
The scaling laws in the ZAP-HD and FuZE machines are holding for increase in current density and magnetic field, but we are still into the highly stable regime because the pinch radius is still 3 mm with a Q<<1, while all the issues (including thermalization) will appear when the radius start to be reduced to reach Q>1 and you enter the boundary of unstable regimes.

They carefully hinted this in their 2017 paper when they wrote in the conclusions:
"Sheared flow stabilization appears to be robust over a range of plasma parameters as shown in Secs. III and IV.
However, scaling to even higher parameters may introduce phenomena that cannot be stabilized or mitigated by sheared flows."

It might have been just a cautionary statement, but I would really love for them to address this issue in one of the presentations they make because I am sure that I am not the only one seeing the thermalization of Alphas as a big roadblock in front of the ZAP to reach Q>1.

Re: Z-Pinch Renaissance

Posted: Sat Oct 24, 2020 4:10 pm
by Skipjack
They might not be mentioning the issue anymore because it turned out to be a non issue. I mean, we will see what happens. From what we know, they are planning to achieve a notional Q~1 within the next 3 years (I read an earlier statement that said 2 years). Until then, we can only speculate. I prefer to be optimistic.

Re: Z-Pinch Renaissance

Posted: Sun Oct 25, 2020 10:50 am
by Giorgio
Considering the importance of the issues (and the constant need of research funds they have) I would have expected them to rise to general attention the overcoming of this issue as a major point in favor of financing their tech.

Anyhow, I like your optimism and I deeply wish you to be totally right and me totally wrong. We are in dire need to leapfrog the limits in energy production where we have been stuck for the last 60 years.

Re: Z-Pinch Renaissance

Posted: Tue Nov 10, 2020 3:48 pm
by Skipjack
This one will be interesting:
Deformation of Plasma-Facing Surfaces in the ZaP-HD Device:
Target surfaces are analyzed with a scanning electron microscope and energy-dispersive x-ray spectroscopy. Stagnated plasma is found to limit the heat flux to the solid surfaces by slowing the diffusion of the magnetic field into the targets. The orientation of the solid surface to the plasma flow affects the surface topography seen in micrographs. These preliminary results provide a foundation for designing an electrode configuration for a higher-power sheared-flow-stabilized Z pinch device.

Re: Z-Pinch Renaissance

Posted: Sun Dec 06, 2020 2:33 am
by Skipjack
Good and fairly recent presentation by Uri Shumlak: ... QFmFX/view

Re: Z-Pinch Renaissance

Posted: Sun Dec 06, 2020 7:49 pm
by Giorgio
Skipjack wrote:
Sun Dec 06, 2020 2:33 am
Good and fairly recent presentation by Uri Shumlak: ... QFmFX/view
Thanks, it was a very interesting video.
There is lot of new info that I didn't know into this presentation, it helped to clear some doubts I had, but it strengthened some other doubts.

The clarified points:

1) I am convinced that they are indeed measuring neutrons coming from fusion.

2) The "stabilization effect" seems to have been quite well investigated, and it seems to be induced by a "viscous effect" that slows down the faster external front of the plasma wave in a quicker way than the slower front at the core of the plasma wave. This (as they have shown in the slide at t=37.00 min) will tend to normalize the speed of the two front to a more uniform value during the "quiescent period".

The non clarified issues:

1) A low Q value seems still to be the biggest limit.

2) Sheared flow stabilization is not a primary stabilizing effect, but an emerging effect from the primary effect of reaching a period of a more uniform speed over all the plasma front (akin from when a fluid moves from a turbulent to a laminar flow state).

3) Being a viscous type of "speed leveling" effect it will have a limit to the input speed you can assign to the plasma front before the same effect will disrupt the front instead of slowing it down, which means there might be a shear velocity limit (Vz limit) to the plasma that might be the main cause of a low Q (this I believe is one of the issues they was referring to in their 2017 paper I mentioned a couple of posts ago).

4) The slide with the picture of the holographic interferometry measure (t=41.10 min) seems to clearly indicate that the plasma is still fluctuating in a M=1 "kink" mode, but the fluctuation are smaller because the difference in speed between the external front and the core front of the plasma are much smaller in respect to the compressed plasma radius.
So, attempting to reduce the plasma radius to lower values (to increase the Q), might amplify again the M=1 mode type of instabilities as well as bring back the emergence of non linear instabilities on the external surface of the pinched plasma.

Hopefully they will focus on these points in their next experimental run because if unsolved they are a show stopper for this tech, but if solved they might open the road to serious investment and research funds.

Re: Z-Pinch Renaissance

Posted: Sun Dec 06, 2020 8:41 pm
by Skipjack
I agree on most of the points you are making. That said, they do not have to increase the input current that much get a viable reactor (1.2 MA, I believe) and according to Uri, they have some other "knobs" (rather than just the current) that they can still play with to improve performance.
I think they are the most promising team after Helion.
They already got some good private investment from Chevron now and they got more funds from ARPA-E Open funding and I believe also from BETHE.
I think they have a total of around 15 million in funding now. Given that the SFS- Z- Pinch devices are not THAT expensive to build, they should be able to move forward with the break even scale prototype, which is what I am really looking forward to seeing. Well, we will know in 3 years or so, maybe less if things move quickly.

Re: Z-Pinch Renaissance

Posted: Sun Dec 06, 2020 10:02 pm
by Giorgio
Yes, input current needs can eventually be managed if they are able to reduce the radius of the pinch, so the MHD instabilities will be the beast to tame.
I am also very happy to hear that they have enough funds to move on the research to clarify if they can make it feasible.

Let's wait and see what they will find.