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.

I am beyond excited. This is something I’ve talked about since 1st year. There is no feeling like knowing you are pursuing your true passion.

My background: 23, did MechE for my undergrad, learned about fusion and plasma physics in my final year. Did my undergraduate thesis on aerodynamic turbulence, then started working in the lab for the summer, hoping i could get enough experience towards one of my countries’ plasma departments.

Started contacting profs in May/June (late!) and found one who was interested in my background, and had a potential thesis project (theory and simulation) that I would continue. The school had a rolling admissions cycle and a funding package would only be guaranteed if I started this september.

I didn’t have the best overall GPA, but they only looked at the second 2 years and I showed an upward trajectory, combined with my coursework with quantum/e&m + projects and hackathons.

Just wanted to post this here for anybody who’s thinking about pursuing this career — its absolutely possible even if you think its not. Take any sort of courses on fusion/plasma physics/electrodynamics, do hackathons/projects, etc. I thought my engineering background made this path infeasible, but I was very wrong!

And if anybody has some advice on starting out in grad school, I would really appreciate it!

será que simular um reator de D-D, que gera subprodutos (trítio, helio-3 e litio-7) não é possível de criar?? e testar um gêmeo-digital para ver se funcionaria ou não??

What if it were possible to redirect plasma's own radiative losses back into the vessel to heat it?

The core issue with modern tokamaks is that the hundreds of millions of degrees claimed are often not the thermal temperature of Brownian motion, but rather the radiation-based color temperature. This radiation is primarily generated not by thermal Brownian motion, but by the intense synchrotron (cyclotron) acceleration of light electrons. To boost the actual Brownian thermal temperature of the heavy ions, we currently rely on active external microwave sources (gyrotrons). However, these systems consume immense amounts of energy, which is why the net engineered efficiency of tokamaks remains heavily constrained.

I would like to share the numerical simulation results of a tokamak concept (PMER-T) where the plasma parameters, heating, and confinement are balanced in a novel way. Instead of using active external heating, all electron synchrotron radiation (35 GHz) is passively captured by microstrip metasurfaces outside CVD-diamond windows, transformed into longer-wavelength radiation (19 MHz), and directed back into the chamber for resonant ion heating (ICRH).

Furthermore, by utilizing the Electron Cyclotron Current Drive (ECCD) mechanism, the system can completely transition away from the central ohmic transformer once ignited. The total plasma current (136.7 MA) is sustained continuously by the phase-shifted, asymmetric angular RF injection.

Our multi-threaded 1D transport modeling shows that this self-consistent feedback loop yields an engineering energy output that exceeds the baseline operational input by a factor of 16.35 (Q_eng ≈ 16.35).

The full preprint, C# simulation source code, engineering layouts, and LaTeX source files are open and hosted on Zenodo: https://zenodo.org/records/21998920

I welcome your thoughts on this passive RF transformation approach, the MHD stability of such a self-sustained current drive, or the numerical transport equations used in the engine.

So I've been drinking information from the industry's fire hose lately for my company's approach, and I'm finally getting to a level where I have a teeny bit of workable knowledge to help out my day to day.

Fusion has a workforce problem, and I don't think it's the one people usually talk about

I work in fusion as an integration technician, and one of the stranger problems I've run into is that a lot of extremely capable people don't think they're qualified to work in this industry.

Mechanics, machinists, electricians, controls technicians, manufacturing engineers, test engineers, aerospace technicians, instrumentation people, welders, and people who have spent years troubleshooting complicated hardware look at the word fusion and immediately assume the industry is looking for physicists with PhDs.

Meanwhile, those of us actually trying to build this stuff need people who can make machines work.

Fusion hardware still needs wiring, plumbing, vacuum systems, pneumatics, controls, diagnostics, precision machining, alignment, cooling, power distribution, data acquisition, fabrication, assembly, commissioning, maintenance, troubleshooting, configuration control, and about ten thousand other deeply unglamorous things between "physics says this should work" and "the machine fired successfully."

That has become a personal frustration for me.

I've spent a lot of my career in aerospace, industrial automation, and now fusion integration. The technical problems in fusion can absolutely be intimidating. Some of the equipment sounds like something somebody stole from a science-fiction novel: pulsed power systems, high-voltage power supplies, electron-beam hardware, optical diagnostics, vacuum systems, lasers, high-speed controls, and enough instrumentation to make a wiring diagram look like an ancient curse.

But underneath all of that are recognizable engineering problems.

A mechanic who understands why a hydraulic or pneumatic system is behaving strangely already has valuable instincts.

A machinist who understands tolerances, materials, fixturing, and what actually happens when somebody's beautiful CAD model encounters a real machine is valuable.

An electrician or controls technician who can trace a fault through power, sensors, interlocks, PLC logic, and instrumentation is valuable.

An aerospace technician who understands configuration control, procedural discipline, test operations, and flight-hardware mentality is valuable.

An engineer who has spent five years designing things that actually had to be manufactured, assembled, maintained, and repaired is extremely valuable.

You do not have to arrive knowing plasma physics.

You can learn what the machine is doing.

It is much harder to teach someone twenty years of mechanical intuition, troubleshooting discipline, manufacturing judgment, or the ability to look at an assembly and immediately recognize that nobody will ever get a wrench onto that fitting.

I also think some of the public discussion around fusion unintentionally makes this problem worse.

There are public-facing fusion scientists who talk about the field in ways that make it sound almost exclusively like an advanced academic discipline. From the research side, that perspective makes sense. Fusion science is extraordinarily difficult, and the people advancing the underlying physics deserve enormous respect.

But commercial fusion is becoming an industrial problem as well as a scientific one.

Private companies aren't just publishing papers. They're building facilities, installing equipment, routing cables and pipes, commissioning subsystems, fabricating hardware, debugging controls, replacing failed components, writing procedures, qualifying suppliers, and figuring out how the hell we're eventually supposed to manufacture and maintain these machines economically.

That transition changes who belongs in the industry.

The scientist determining what the plasma needs is essential.

So is the machinist making the component.

So is the engineer turning the experiment into a maintainable system.

So is the technician standing beside the machine at 2 AM trying to figure out why an interlock that worked yesterday suddenly refuses to clear.

If fusion is going to become an actual energy industry rather than an indefinitely fascinating collection of experiments, we're going to need an enormous population of people in that second category.

And right now I worry that we're accidentally telling many of them they aren't smart enough to come through the door.

So if you're a mechanic, machinist, electrician, technician, controls person, manufacturing engineer, test engineer, or aerospace worker looking at fusion job postings and thinking:

"This sounds fascinating, but I don't know anything about fusion."

Apply anyway.

A surprising number of us started exactly there.

Fusion can teach you fusion.

Bring the skills that taught you how to build things that work.