Helion Energy to demonstrate net electricity production by 2024

[TallDave]

Loads on the first wall are expected to be in the 1 to 2 MW range.

Hmmm, so 1-2MW sounds like the total load per second from 1-2GW pulses over 1ms.

Say the Polaris reaction chamber interior is a cylinder of 1m radius/base, the surface area is then 12.5 m^2, and at 1GW the instantaneous load would be around 80MW /m^2 which is several times the ITER divertor load. Of course that's not sustained, but I think the concern here is the shock more than the overall load.

No doubt Helion has looked at this problem quite a lot more than I have and has solutions, will be interesting to find out more later this year as they fire Polaris up.

And sometimes progress just requires failure https://www.youtube.com/watch?v=bvim4rsNHkQ I'll be outside, listening for shattering quartz

[mvanwink5]

Power transfer is not thermal; the plasma ions & electron motion produces a magnetic field which is coupled to the compression coils. The power transfer then behaves the same as a utility power transformer, only without the iron core hysteresis losses. The quartz tube will see neutron heating though.

[Skipjack]

The heat load may be instantaneous and it may sound like a lot, but the total amount of energy transferred to the walls is not that high and that is what counts in the end. I would want to think that the people at Helion know what they are doing after they have built how many machines with the same materials now?
There are other parts of the system that are dealing with worse temperature issues. I will say that much.
The walls will get heating from X-rays, mostly, then there is neutrons and a bit of thermal transport. For Polaris none of that is a problem in terms of heating. Power plants will need more cooling, though. But that is for a different time to worry about.

[RERT]

Some posts back I came to understand that the operational picture was circa 40 MJ in, 10MJ of fusion power, 45 MJ out, at 10Hz, delivering 50MW net.

That makes net power the same as waste power, and 50MW heat has to be defrayed somewhere.

Is that right?

The obvious places for heating are walls and coils, but I don’t know…

[RERT]

And yes, it isn’t much compared to a thermal plant, or very large given the size of the machine. It’s just more than people seemed to be discussing just now…

[TallDave]

Power transfer is not thermal; the plasma ions & electron motion produces a magnetic field which is coupled to the compression coils. The power transfer then behaves the same as a utility power transformer, only without the iron core hysteresis losses. The quartz tube will see neutron heating though.

yes to be clear I am only referring to the thermal/brem transfer here... the fact they can recapture ~80% of the energy magnetically is a huge advantage but they still have a load problem for the other 20% at Q=5

The heat load may be instantaneous and it may sound like a lot, but the total amount of energy transferred to the walls is not that high and that is what counts in the end.

well, the instantaneous load matters too... e.g. suppose you have a heater warming you at 1000W for an hour... now compress that 3,600,000 Watt-seconds into 3.6MW over 1 second and suddenly your skin is crispy... but it was the same amount of total power

thermal/brem is going to be at least 20% of total power at Q=5, and higher at lower Qs

although again Helion probably has detailed solutions for both Polaris and reactors

my main concern for Polaris is just getting to >20KeV where Q becomes abundant

[Skipjack]

Bremsstrahlung is not that high. It is more like 5%.

[mvanwink5]

Ions & electrons don't thermalize in a pulse operation which is a big point in a pulse operation and improves direct magnetic recovery efficiency. Quartz is transparent to UV, but I do not know how much of the X-rays will pass, quartz is certainly not opaque to X-rays though and the tube is not that thick judging by the pictures. Quantitative details of energy transfer are important as opposed to hand waving. Are we only able to guess? I had thought Helion said they had over all 95% efficiency fusion energy to electric (presumably for best fuel cycles). SJ?

[Skipjack]

Ions & electrons don't thermalize in a pulse operation which is a big point in a pulse operation and improves direct magnetic recovery efficiency. Quartz is transparent to UV, but I do not know how much of the X-rays will pass, quartz is certainly not opaque to X-rays though and the tube is not that thick judging by the pictures. Quantitative details of energy transfer are important as opposed to hand waving. Are we only able to guess? I had thought Helion said they had over all 95% efficiency fusion energy to electric (presumably for best fuel cycles). SJ?

Ions and electrons start out at a pretty high difference in temperature. That is mainly the result of the acceleration and merging process.
Helion talks about a Te:Ti of 0.1 in their recent paper, but results from Trenta released earlier show an even lower ratio (~0.06) for some of the pulses.
So I assume that 0.1 is conservative.
Over the length of the pulse and especially during the compression phase ions and electrons move closer to equilibrium. My estimate is that starting from a Te:Ti of 0.1, the ratio would not exceed 0.2 over the 1ms pulse length. It could be a lot less and again the 0.1 seems conservative given the results from Trenta.

X-ray absorption into the quartz tube is indeed a thing. They typically deposit the most in the first mm of the thickness of the 5mm thick tube. There is however a soft gradient within the material. So, the is no sharp terminator and that reduces stresses on the material.

As for the conversion efficiency: The 95% refers to the efficiency of the input energy recovery. The fusion energy recovery is somewhat less efficient because of neutrons, X-rays, transport and other losses. Though some of them might be recoverable by other means, at least to some extent.
This was occasionally mentioned in passing. E.g. David Kirtley said in his talk at Princeton that assuming all losses are actual losses in a pulsed system is a "bad assumption to make". I am not sure how to interpret that exactly.
There are also other aspects that come into play. E.g. over the length of the pulse, the FRC will lose particles. So the longer the pulse, the lower the recovery efficiency and fusion rates drop as well. They will have to find the optimal balance.
Helion still keeps that aspect of their design pretty close to their chest and even I don't know everything. I think that they want to see how well all of this works out in Polaris before they talk about it in more detail (if they don't want to keep it a trade secret).

[Skipjack]

Additional:
Thinking about some of the things I remember hearing and reading and looking at the paper again, most particle losses would follow the magnetic field lines and leave the FRC axially towards the divertor. It could be feasible to assume that they would induce charges in the acceleration coils and/or there is some sort of charge exchange happening at the divertor.
That does not affect Bremsstrahlung losses though, which would be largely isotropic in all directions.

[TallDave]

I had thought Helion said they had over all 95% efficiency fusion energy to electric

believe they only said they had recaptured 95% of the compression energy in a smaller machine, which is entirely different from capturing 95% of the total energy of a fusion pulse (maybe someday!)... remains to be seen experimentally what fraction of fusion product energy can be captured magnetically, but keep in mind all energy not in the form of charged products has to be absorbed somewhere else... so if Q is 5 about 10% thermal and 10% brem based on the graph, plus the neutron fusion products

I remember hearing and reading and looking at the paper again, most particle losses would follow the magnetic field lines and leave the FRC axially towards the divertor. I

ahhhhhh yes, that is a good point, especially as the compressed FRC plasma is elongated to avoid tilt modes... if enough of the load is hitting the axial divertors they might not have to worry about shocking the quartz tube

E.g. David Kirtley said in his talk at Princeton that assuming all losses are actual losses in a pulsed system is a "bad assumption to make".

watched that again the other day, in context it's clear he meant "because we don't need to continuously replace that energy to heat the plasma (like a tokamak would)" but that doesn't affect the overall power balance

Helion talks about a Te:Ti of 0.1 in their recent paper, but results from Trenta released earlier show an even lower ratio (~0.06) for some of the pulses

indeed! one reason the Polaris results will be so fascinating is the fuel ion heating by fusion products Kirtley mentioned... if they're really lucky that could supercharge the reaction, further separate Ti from Te, and push Q to significantly higher values... and the higher they can get Q, the less thermal load, the smaller the required reactor, the lower the cost of electricity...

[mvanwink5]

Thermal losses, heat rejection, is perhaps the most major issue for fusion plant siting. Rivers, ocean, lakes (sometimes artificial), cooling towers, these limit how close to ultimate use plants can be. Then there are also environmental issues, the thermal impact on natural bodies of water. Of all the fusion plant designs Helion has the lowest heat rejection by significant factor, whatever that ends up being?

The FRC plus pulse operation is what enables Helion to efficiently extract the energy produced from the fusion reactions directly without a heat cycle. (I have not heard how TAE plans to convert fusion energy but their ultimate planned machine is not pulsed, H + B -> 3 He3).

[Skipjack]

believe they only said they had recaptured 95% of the compression energy in a smaller machine, which is entirely different from capturing 95% of the total energy of a fusion pulse (maybe someday!)... remains to be seen experimentally what fraction of fusion product energy can be captured magnetically, but keep in mind all energy not in the form of charged products has to be absorbed somewhere else... so if Q is 5 about 10% thermal and 10% brem based on the graph, plus the neutron fusion products

The thing is that with a high beta plasma the coupling between the plasma itself and the magnets is very close to 1. So theoretically, they should be just as efficient. But the proof is in the pudding... ehem Polaris
The Bremsstrahlung should be more around 5% from what I have heard. I assume that their graphs and their models are somewhat conservative.

watched that again the other day, in context it's clear he meant "because we don't need to continuously replace that energy to heat the plasma (like a tokamak would)" but that doesn't affect the overall power balance

It's been a while since I watched it and you might be right there. I have to watch it again myself to see.

indeed! one reason the Polaris results will be so fascinating is the fuel ion heating by fusion products Kirtley mentioned... if they're really lucky that could supercharge the reaction, further separate Ti from Te, and push Q to significantly higher values... and the higher they can get Q, the less thermal load, the smaller the required reactor, the lower the cost of electricity...

I wonder whether their formation test section campaign is aiming to achieve just that. To my understanding the separation between Te and Ti happens during the formation, whereas the two temperatures want to return to equilibrium during the compression stage but again, the total pulse length is too short to make much of a difference. We will see how it goes.

[TallDave]

I wonder whether their formation test section campaign is aiming to achieve just that. To my understanding the separation between Te and Ti happens during the formation, whereas the two temperatures want to return to equilibrium during the compression stage but again, the total pulse length is too short to make much of a difference. We will see how it goes.

yes as Kirtley states:

Also, as FRC plasma densities are in the range of 10^21 to 10^23 m-3, they tend to have 1–100 ms equipartition times, which supports the maintenance of this hotter ion temperature in a pulsed system. For adiabatic compression, ions and electrons are heated prportionally, so an initial hotter ion temperature imbalance will be maintained through the entire compression cycle.

however the formation section does not produce any significant fusion, so Helion won't have experimental evidence for ion heating by fusion products at Q>1 conditions till this summer(?) or whenever they start firing the compression

quoting Kirtley again:

One additional physics benefit of D–He-3 systems not explored here, which would further increase the fusion
power output of these systems and maintain a hotter ion temperature ratio, is that a 14.7 MeV proton in a D–He-3
plasma environment will actually impart more energy through direct nuclear elastic scattering with the fuel ions,
than the traditionally modelled Coulomb collisions. This effect is well studied [20] and will both increase heating of
the ions as well as increase the fusion product confinement time. In the present paper, this effect is not included, so the
results are conservative. Not including this effect allows for the decoupling of the evolution of the proton production rate from transport equations

worst-case, at Q>1 fusion products obliterate the stability of the FRC on nanosecond scales (unlikely since they're mainly charged, but hard to rule out entirely)

best-case, significant fusion heats the fuel ions without destabilizing the compressed plasma or raising electron temperatures, pushing Q well over the currently estimated value of 1 at around 10KeV (I've started thinking of this as the "internal combustion FRC engine" model in which the briefly self-ignited plasma functions as a sort of virtual piston)

e.g. with fusion product heating, we might plausibly see average 20KeV ion temps after only directly heating the ions to 10KeV and with minimal additional thermal/brem losses for the extra 10KeV... of course this is all handwaving till we get some results

[Skipjack]

I wonder whether their formation test section campaign is aiming to achieve just that. To my understanding the separation between Te and Ti happens during the formation, whereas the two temperatures want to return to equilibrium during the compression stage but again, the total pulse length is too short to make much of a difference. We will see how it goes.

yes as Kirtley states:

Also, as FRC plasma densities are in the range of 10^21 to 10^23 m-3, they tend to have 1–100 ms equipartition times, which supports the maintenance of this hotter ion temperature in a pulsed system. For adiabatic compression, ions and electrons are heated prportionally, so an initial hotter ion temperature imbalance will be maintained through the entire compression cycle.

however the formation section does not produce any significant fusion, so Helion won't have experimental evidence for ion heating by fusion products at Q>1 conditions till this summer(?) or whenever they start firing the compression

worst-case, at Q>1 fusion products obliterate the stability of the FRC on nanosecond scales (unlikely since they're mainly charged, but hard to rule out entirely)

best-case, significant fusion heats the fuel ions without destabilizing the compressed plasma or raising electron temperatures, pushing Q well over the currently estimated value of 1 at around 10KeV (I've started thinking of this as the "internal combustion FRC engine" model in which the briefly self-ignited plasma functions as a sort of virtual piston)

e.g. with fusion product heating, we might plausibly see average 20KeV ion temps after only directly heating the ions to 10KeV and with minimal additional thermal/brem losses for the extra 10KeV... of course this is all handwaving till we get some results

Yes, the formation test is only about formation of FRCs. It still can help with optimizing and fine tuning the process upfront since the Te:Ti is important.

Helion already was in the 10keV range with Trenta. So the leap to 20 keV is not that large. I doubt we will see a significant change in plasma behavior with that.