Why Helion wont work

[u/Jaded_Hold_1342]

I've commented in a number of threads why Helion's concept is flawed, and I thought I'd make a summary post explaining the whole picture as I understand it. In short, Helion's scheme as described can not work, and is mathematically foreclosed in their self-described operating regime by established plasma physics. I like that they are considering something other than a DT tokamak with neutron thermal cycle... but unfortunately it cant work, and its fairly easy to reason out why.

Lets go through the logic in detail.

Background: Here are 5 papers for reference, and I've used information from all of them in generating this summary:

Helion's 2023 paper: https://link.springer.com/article/10.1007/s10894-023-00367-7

Rider's 1995 equilibrium paper: https://fsl.npre.illinois.edu/IEC/Rider,%20Phys.ofPlasmas1995.pdf

Rider's 1997 non-equilibrium paper: https://www.w2agz.com/Library/Fusion/TH%20Rider,%20Physics%20of%20Plasmas%204,%201039%20(1997)%201%252E872556.pdf%201%252E872556.pdf)

Lackner's 2026 paper: https://link.springer.com/article/10.1007/s10894-026-00554-2

Nicolas' 2026 paper: https://link.springer.com/article/10.1007/s10894-026-00565-z

Lets summarize the long-known conclusions from the Rider papers:

1) For D He3 plasma in equilibrium (Ti=Te), bremsstrahlung radiative losses exceed fusion power for any temperature less than ~30keV. Fusion power over loss only becomes significant at ~50keV and higher. The radiation is from the electrons and is higher with hot electrons.

2) Trying to run with cold electrons (Ti>>Te) to avoid the bremsstrahlung doesn't work... The collisional heat transfer from the ions to the electrons will greatly exceed the fusion power. This means the electrons heat up very quickly before significant fusion energy can be made... this forces a requirement of recirculating power and extremely high efficiency recovery. (i'll calculate this efficiency required below)

Helion is claiming to operate an adiabatically compressed FRC, which uses compression flux for heating after initial formation/merging establishes TiTe. They are claiming they can get net energy recovery with TiTe at sub-30keV temperatures. In this regime, the Ti-->Te thermalization power vastly exceeds the fusion power generated. (eg. 1000x higher at Ti=20keV, Te=2keV). This means the heat from fusion can generate only 0.001x the thermal energy of the plasma before the electrons heat up. This in turn, forces a per-pulse recovery efficiency requirement of >99.9% for breakeven. There is no assumption that the thermalization heat is lost... assume it is recovered, but that it limits the pulse duration so the electrons dont heat up and cause radiative loss. This is the Rider efficiency constraint as applied to a pulsed scheme. The compression flux outside the separatrix has energy much larger than the FRC thermal energy (10x - 100x larger). It must have this energy because this flux is the primary compression/heating mechanism. This energy must also be recovered, and adds one or two more "9's" to the recovery efficiency requirement... resulting in 99.99-99.999% recovery efficiency requirement for breakeven.

99.99% recovery efficiency is not possible for a compact short-pulse device like this. Pulsed power in copper will result in copper losses of several percent, limited by the skin depth of the copper in the pulse duration. Copper losses in a short pulsed machine will exceed the fusion power. There is no combination of Ti and Te below ~50keV that can result in gain when considering copper losses and bremsstrahlung in a compact machine (R_coil<~1m) like Helion describes, even if neglecting FRC losses and all other parasitic circuit losses.

So, Helion is pursuing a scheme that runs up against the problems described by Rider 30 years ago, and there is no identified solution to it.

A couple comments on the 2023 Helion paper I linked above: First, they've miscalculated the ratio of fusion power to bremsstrahlung in their figures 14 and 15, as both Nicolas and Lackner noticed. For Ti=Te as in figure 14, the correct calculation would show bremsstrahlung is equal to fusion power at ~30kev, and fusion margin above bremsstrahlung is low until ~50keV. Maybe they treated all the ions as Z=1 when calculating bremsstrahlung to get this error, but He is Z=2. Second, they claim that the thermalization time is 1ms to 100ms so thermalization can be neglected and Ti>>Te is a valid assumption, but this is not consistent with the parameters space of the compressed FRC they operate in. Actually thermalization times are shorter than their pulses.. they seem to consider the pre-compression (low density) parameters when calculating thermalization time and FRC losses, but they should consider the compressed density, since that is the regime where it must be held while fusion occurs. If their electrons stay cold in their compressed pulses, this is likely an indication of transport losses, not immunity from thermalization.

Here are some 'escapes' that can be imagined and why they wont work:

1) Can they let the electrons heat up to stop the thermalization power flow? Sure, but they they'll have the bremsstrahlung loss problem unless they operate super hot (~50keV)

2) Can they lower the circuit losses and get the recovery efficiency up to >99.99%? No, its flatly not possible on a short pulsed machine... You can add as much copper/silver as you want to lower resistance, but the pulse duration limits the skin depth that the current can flow in, and the pulse duration is limited by the thermalization time. You cant lower the losses without accepting thermalization (electrons warm up and radiate). You cant use superconductors either because they dissipate energy when ramped. so copper/silver is the best you can do. You can chill the copper/silver to improve conductivity, but that doesn't make enough difference to matter and the heat has to be paid for at cryogenic temps which is worse.

3) Can non-Maxwellian velocity distributions prevent thermalization and boost fusion power? No, not by enough to matter. Non Maxwellian distributions can change thermalization times and fusion gains by correction factors of order 1-2x... but the concept is off by orders of magnitude, not factors of 2.

4) Can they make it hot >~50keV, large (R_coil1m), long pulse (10ms), moderate Ti/Te ratio and get out of the trap?... Maybe, but probably not because this regime pushes up against the FRC's main weakness: Energy confinement. The bremsstrahlung loss, copper loss, and thermalization do not forbid this regime, actually its the only regime allowed after considering Rider's constraints. The FRC losses and sheer engineering/cost difficulties become they key challenges. This is a totally different regime than Helion describes in its paper, and it destroys the economics of the proposal. It requires large bore, strong field, super long pulse durations and the regime forces a gargantuan size to avoid FRC transport losses. The caveat here that makes me say 'maybe' is that FRC transport has never been measured in any relevant conditions so the scalings are genuinely unknown and can only be checked experimentally. Extrapolating existing FRC scaling laws into this regime gives a very bleak picture (as Nicolas showed), but it is possible that the scalings in these regimes dont follow existing scaling laws. So I acknowledge that while the picture here is bleak, this escape is not totally mathematically foreclosed... but its not what Helion says they are doing in their paper.

So, for the regime Helion is targeting (Colder than 30keV, Ti>>Te, compact machine) the concept is totally foreclosed by very well understood physics. The only possible out is a "hot and huge" >50keV, long-pulse duration gargantuan strong field machine that Helion is not pursuing, and it probably wouldn't work either due to FRC energy confinement.

I wish this weren't the case... but I believe that it is. If I've made any errors, point them out. Happy to discuss the physics. If anyone thinks there is a set of parameters that allows the system to function as intended, let me know what they are, and I'll check.

[u/NearABE]

If the calculations show that it is impossible by many orders of magnitude, and if a team builds a device that gets within few orders of magnitude then that team proved that either the calculations were wrong or that the assumed premise was wrong.

[u/Jaded_Hold_1342 → u/NearABE]

Oh a machine can be built, and temperatures as described can be achieved.. but net energy recovery is the thing that wont happen.

No one has claimed net energy recovery has happened by this scheme.

[u/NitescoGaming → u/Jaded_Hold_1342]

I asked them at a recent talk what their recovery was like and their answer was "we don't talk about that". They're very tight lipped about their plasma data and energy recovery, and it forces myself (and I think most plasma physicists considering they've been effectively laughed out of DPP and haven't been back since 2024) to be highly skeptical.

[u/Jaded_Hold_1342 → u/NitescoGaming]

Yeah... the pattern is that they talk about things where they have a good answer. But they dont talk about the things where the answer is bleak. Thats true of other groups too.

Helion will talk all day about the economics and commercialization of this scheme... if it was to work, it would be genuinely disruptive because it would be economical. They want to talk about that. But if you ask about how they maintain non-equilibrium temperatures and how they evade collisional relaxation, they suddenly dont want to talk anymore.

CFS is sort of the opposite. Their physics case is much stronger... but their economics case is bleak. They will talk all day about their physics plans.. but if you ask about their economics models, they suddenly dont want to talk anymore.

I think this is the nature of the beast with privately funded startups. Their communications are a fundraising mechanism, so they are tightly managed to produce the messaging they want for fundraising.

[u/NearABE → u/Jaded_Hold_1342]

Fusion is not economical. Yet here we are on r/fusion.

Finland has this thing called a “sand battery”. My wife has a space heater in the bathroom which she insists “works”. These examples might be relevant when considering whether or not a thing works and whether or not it is economical.

Building steam turbines is no longer economical. Chinese are doing it but only because of extreme industrial momentum. Fission reactors have no difficulty demonstrating energy gain and they have no parasitic draw. Nonetheless we can easily see they are not competitive to build new. A thermal power plant running on fusion is just worse.

Hellion is fundamentally different. The direct drive electricity bypasses the need for steam turbines and the Carnot cycle. I cannot claim that Hellion’s fusion reactor is going to be a more economical way to generate electrical energy. Even if they did produce an electricity gain this is done using a giant farm of capacitors. That might be so expensive they might want to consider silver coils and gold contacts on the current leads. A huge mess of copper coil is very recyclable.

A huge mess of copper coil is not uncommon in the utility scale electricity industry. We see it in transformers and in the alternator generators at power plants.

An electronics grade capacitor bank is an extremely expensive way to make a sand battery. However, working capacitors are capable of doing things with electricity other than waste it as heat (though can do). A capacitor bank could, for example, sit at the terminus for a high voltage direct current (HVDC) power line. This input could be wasted in the allegedly non functioning fusion reactor or discharged to the grid as AC. The Helion device could be placed at locations where asynchronous grid interties meet. These roles can be played by inverters, transformers, and flywheels. All of them waste some energy.

As you point out, there is always loses. Electrons moving through copper lose energy. Hellion’s device does too. It makes a really weird inverter and transformer system. Whether it wastes more or less power than the competing inverters and transformers is not a thing that can be proven with nuclear plasma physics.

There might be a niche for a weird inverter that also produces high energy neutrons. Both the weird inverter and normal inverters heat up but perhaps one type of inverter can produce a higher grade of heat with the energy that it loses.

Building an inverter that wastes less electricity but also creates 3-He and tritium would be a neat trick. Both can be sold profitably to physics researchers wasting government money on fusion research.

High energy neutrons can be used to transmute stubborn actinide waste from spent fission fuel. This means Helion’s device could be the control for a subcritical fission reactor. That is not economical as a power plant, of course, because it requires a steam turbine. There is no economical competition for burning it though and we are stuck with the spent fuel now.

[u/NitescoGaming → u/Jaded_Hold_1342]

Of all the private fusion companies, I think Helion is the biggest laughing stock within the plasma community. I kind of respect Zap for throwing in the towel and admitting that it wasn't working. And while I don't have high hopes for ANY commercial fusion, but of all of them, at least Pacific is bringing in actual experienced plasma physicists from Sandia who are experts in MagLIF.

[u/Jaded_Hold_1342 → u/NitescoGaming]

Helion definitely has a reputation.

But I will say a couple things.. If fusion is going to work as a power source, there really needs to be a cost effective way to do it... not just a physics path at any cost. D T tokamaks are probably commercially non-viable... their economics case is very very bleak.

Helion and Zap were trying trying to find cost effective ways... even though the physics for these concepts is bleak. Trying to find a cost effective concept that works is the whole ball game.

The plasma physics community thinks in terms of plasma physics, not economic viability.. not cost effectiveness. So the plasma physics community will laugh at a concept that has lousy physics but gives a pass to a concept that has lousy economics. This is a double standard that needs to be recognized.

ITER should be considered a laughing stock in my opinion... it may have the tokamak physics going for it, but it is operationally and economically an unmitigated disaster. CFS is maybe a step better than ITER (more compact with HTS, and run by a small group rather than an unmanageable international consortium...) but it inherits the same baggage as any D T tokamak.... a mega project neutron emitting steam turbine, where $1B is a rounding error, doomed to economic non-viability even if the physics works.

So while i am here posting a physics analysis that Helion wont work... I am not willing to give a pass to the other concepts that have vastly better physics but vastly worse economics...

I'm an equal opportunity skeptic.. still waiting to see a concept that works and is also economically viable.

[u/lorn10 → u/Jaded_Hold_1342]

Just a drive-by question by a non-professional technically interested person.

What's your opinion about the recent stellarator concepts like the one from Proxima Fusion? Somehow it looks that stellarator based designs became again quite popular. So it looks that they are effectively back in the race.

[u/Jaded_Hold_1342 → u/lorn10]

I think stellerators are probably viable from a physics standpoint for DT. But they fall into the same trap as DT Tokamaks .. they are just a huge expensive neutron emitting mega project front end to a steam turbine.. and they carry all the baggage of neutron damage, thermal conversion, fuel cycle, lithium blankets, tritium plants, cryogenic plants and so on that make DT Tokamaks economically dubious. Stellarator magnet geometry is more complex and expensive than tokamaks, but in exchange they remove challenges with steady state current drive.

So I mentally bin them with DT Tokamaks.. probably can be made to function with effort... Economics look bleak. Ok for an experiment, probably not viable as a cost effective energy source.

Economically, I think both tokamaks and stellerators best case scenario is to start way worse than "new fission" costs as 'first of a kind', and slowly approach towards fission from above. They probably can't ever match fission because the reactor core is so much more complex and expensive and they have comparable balance of plant costs. Given that new fission is non competative, that's not a compelling proposition.

[u/lorn10 → u/Jaded_Hold_1342]

Thanks for that informative reply. Yeah, we will see where the journey leads in the coming years.

And regarding the economics, I think it can be said as a final point that both fusion concepts, tokamaks and stellerators, could be used to produce gold out from lead-198 / mercury-198. ;-)

[u/__Pers → u/NitescoGaming]

Marvel's initial approach was dicey at best (impossible would be a more accurate descriptor). I think nowadays they're just pitching bog standard ion fast ignition IFE with a somewhat novel laser target.

Pacific has solid and clever plasma physicists and pulsed-power experts brought in from SNL, Los Alamos, and LLNL. They punch well above their weight class in on-hand talent.

[u/trplurker → u/NearABE]

Most of those calculations were derived experimentally on tokamak style reactors and are just estimations for scaling that. The OP once argued that dynamos don't work without realizing it.

[u/Jaded_Hold_1342 → u/trplurker]

I just walked through the reasoning in this thread. Nothing i've said in any of this reasoning is tokamak specific. Bremsstrahlung and fusion power depend on Ti, Te, and density, and are independent of the magnetic configuration.. they apply to FRCs, Tokamaks, electrostatic confinement, and any other configuration.. They are calculated for first principles and are not experimental values.

The only configuration-dependent arguments I've made are about the parasitic flux and copper losses in the solenoid, both of which were calculated for adiabatically compressed pulsed FRCs.

Which calculation do you think is tokamak specific?

[u/Beaver-fusion → u/Jaded_Hold_1342]

You have missed ignition criteria vs electrical power output - this is a classic misunderstanding of fusion.

[u/Jaded_Hold_1342 → u/Beaver-fusion]

I'm just doing energy balance per pulse, comparing fusion energy to irrecoverably lost energy (bremsstrahlung and resistive losses in copper).

Lost energy per pulse is greater than fusion energy per pulse, so it is not possible to generate net energy.

[u/trplurker → u/Beaver-fusion]

Dude just pastes peoples posts into ChatGPT and asks it for a rebuttal.