Response to Lackner et. al. 2026 critique of Kirtley 2023
Posted: Wed Feb 18, 2026 2:55 am
In a highly delayed letter, Lackner et. al. provide a critique of sorts to David Kirtley's 2023 article published in the Journal of Fusion Energy (JFE).
This letter is available free of charge here: https://link.springer.com/article/10.10 ... 26-00554-2
Discalimer: I am an electrical engineer with plasma physics experience, but not fusion experience. I trust the formulae I find in the field without fully understanding all of them. I have no connection to, or inside knowledge of, Helion's implementations. My analysis includes "informed' speculation at best. AI tools were used, in addition to more focused plasma modeling tools in developing this rebuttal. I am not paid to do this. I've been mostly "lurking" on Talk-Polywell for over 10 years, enjoying the discussions as a "hobby interest". The reason I have confidence in the claims stated here comes largely from interacting and challenging my calculations with AI LLMs from ChatGPT, Grok and Google AI, which has rapidly confirmed, refuted, or refined my initial calculations and assumptions. I make no representation that anything in this analysis is factual or confirmed by me empirically. That said, let's begin:
For brevity and to avoid redundancy (just read Lackner, it's well written and pretty easy to understand), here's a brief summary of conerns raised in Lackner 2026:
The Helion topology, including for both Trenta and Polaris, accelerates two toriodal plasmoids at speeds around Mach 2000 (yes, two thousand) toward each other, compressing them as they collide in the center, squished into a cigar shape and attaining fusion temperature conditions, all in about 150 microseconds. That's 150 microseconds from initial acceleration from "rest" on either end of the device to peak fusion conditions in the subsequently collided plasmoid combined and compressed at rest in the center reaction chamber.
Now, as fusion begins, the ion/electron temperature ratio Ti/Te is around 10, according to both Kirtley and Lackner. This high ratio thermal disequilibrium increases fusion reaction occurrence, as Kirtley 2023 describes. Lackner et. al. then make a strong case with supporting calculations to show how rapidly the ratio returns to temperature equilibration (Ti = Te), where fusion reaction collisions occur at a lower rate. In Helion's case, that time is short, around 500 microseconds, whether in Polaris at about 15 Tesla magnetic B field or in the still under-construction commercial electricity producing Orion device with a "guestimated" 30T B field.
So Lackner is correct on this: the Ti >> Te fusion reaction efficiency gain is all gone within a mere 500 microseconds.
Lackner et. al. further make a plot (Figure 2) using "fusion breakeven" to "normalize" the fusion reaction time plot, showing the extremely short duration of expected TI >> Te compared to the "fusion breakeven" time. And this is where Lackner 2026 goes completely off the rails: the calculated "breakeven" time is calculated assuming NO RECAPTURE of the plasmoid formation and compression energy - ZERO. Which leads Lackner et. al. to mistakenly conclude that "breakeven" takes a long time to achieve. The problem is, this is steady state fusion "breakeven", which has absolutely no relevance to Kirtley 2023. The point is that this "breakeven time" might be a reasonable calculation for steady state fusion topologies as in Tokomaks or Spheromaks, but it COMPLETELY IGNORES the >90% EMF energy recovery described in Kirtley 2023. This oversight completely destroys any significant relevance of Lackner et. al. conclusions.
And there's another issue: while Lackner et. al. obsess on thermal equilibrium concerns (they do it twice - in the first third AND again in the last third of the letter), they never present an estimate of non-thermal operation applied to Kirtley 2023. Based on their own equations and a few assumptions attainable from Kirtley 2023 and Trenta/Polaris reports, and Integrating the "boosted" but rapidly declining non-thermal enhanced collision rate over the short time to thermal equilibrium yields an approximate threefold boost in fusion collision reaction rate. Threefold boost is "not nothing", and Lackner et. al. wrongly concludes that it doesn't apply to commercial net power configurations when it actually does, but it's not that big a factor either.
This would seem to support Lackner et. al.'s concerns: the "boost" is only on the order of 3X and it's transient at only 500 microseconds.
And that's the thing that is difficult, apparently, for steady state ignition focused plasma scientists to wrap their head around (at least as evidenced by Lackner et. al.): During this "extremely short" first 150 microsecond compression to peak fusion and additional 350 microsecond relaxation phase, an estimated seventy percent of the fusion energy "harvest time" has been accomplished! In fact, starting around that 500 microsecond Ti = Te equilibration mark is the reaction "quench" phase.
What is the "quench" phase? It's the final \ field maintenance that is applied and maintained upon the plasmoid in order to start shutting down and reduce losses and protect the chamber walls. This is key: all the bad things that happen in FRC plasmas (plasmoid tilt, bremsstrahlung, synchrotron and transport losses) have "inertia". They don't start significantly kicking in until that thermal equilibrium 500 microsecond time, and they grow worse and worse from then on. As
One more thing: the Helion design is able to inject high fuel density in the plasmoid, knowing that only a small fraction (estimated at <3%) will be consumed. Unlike steady state fusion designs, they can optimize the density without being constrained by steady state conditions. The considerable amount of unused fuel gets vacuumed out through the diverter and is separated for subsequent recycled use.
Regarding the electromagnetic plasma formation B field, Kirtley makes the STRONG assertion of B field "efficient recovery" repeatedly in Kirtley 2023, always noting in analysis graphs that the plasma characteristics "assume no recovery" (six times this is stated). But the efficient B field recovery is CRITICALLY IMPORTANT: Helion only needs fusion to add enough energy in order to exceed the sum of EMF-generated B field formation/acceleration/compression losses and the thermal, bremsstrahlung, synchrotron and transport losses. Lackner misses high B field energy recovery entirely. It's not even mentioned in the letter, despite it being THE CENTRAL MECHANISM facilitating net fusion energy in the Helion topology.
The Helion design implements fine-grained control with nanosecond precision in timing, using fiber optic-controlled switches, attention to cable length, and high speed FPGA logic to optimize the acceleration, compression and fusion reaction harvesting, the "quench" phase, and the evacuation phase. Add to this the optimization of the fuel ratio and density.
Lackner et. al. conclude that "tight constraints" will be needed in Helion. That's true. Just not new. Kirtley and team have known that for well over a decade. It's all in their design and experimental, empirical work. Kirtley confirmed all of this with data from Trenta, as published in Kirtley 2023. Now, in 2026, Kirtley has confirmed that Polaris has the same or better control.
Lackner 2026 also mentions that they can't replicate Helion's bremsstrahlung loss. That's because Lackner's bremsstrahlung estimates are empirically determined steady state estimates. Which is well over one order of magnitude higher than what can be calculated mathematically under Helion conditions. Spin instability and synchrotron losses are essentially non-existent in this short time window.
Lackner also implies concern that even tiny impurities squelch the reaction, gumming it up. Again, this would be true steady state, but there simply is not enough time for the plasma to hit the wall and trigger impurities that would then travel back and interfere with the fusion reaction. The reaction is already over. And the reactor chamber is being evacuated by then, cleaning it out, and making it ready for the next shot.
It's likely that due to physical restraints, the pulse rate in Orion will max out around 10 Hz. At that rate, with the total acceleration, compression, relaxation and quench portion of the cycle under 500 microseconds in duration, that leaves a remaining 99.5 MILLI-seconds to regroup for the next shot: a 0.5% duty cycle. This, indeed, is mind blowing to continuous ignition fusion plasma physicists. Lackner et. al. 2026 letter, ends up harping on issues that don't apply to Helion's topology, demonstrating the incredulity by seasoned, subject matter experts that have a hard time grappling with the Helion difference.
Kirtley and the Helion team have spent well over a decade designing and optimizing fuel mix, density, compression time, relaxation time and radius, plasma pressure, initial ion and electron temperatures, final plasmoid radius and temperature, field strength, bremsstrahlung, synchrotron, and transport losses, neutron flux, cooling and evacuation time. They discovered a clear path to commercial fusion direct energy production. And they are moving as fast as they can to achieve it. Lackner et. al. 2026 expose their own "outside looking in" Tokomak thinking, and somewhat astonishingly, completely fail to comprehend the Helion topology described by Kirtley 2023.
This letter is available free of charge here: https://link.springer.com/article/10.10 ... 26-00554-2
Discalimer: I am an electrical engineer with plasma physics experience, but not fusion experience. I trust the formulae I find in the field without fully understanding all of them. I have no connection to, or inside knowledge of, Helion's implementations. My analysis includes "informed' speculation at best. AI tools were used, in addition to more focused plasma modeling tools in developing this rebuttal. I am not paid to do this. I've been mostly "lurking" on Talk-Polywell for over 10 years, enjoying the discussions as a "hobby interest". The reason I have confidence in the claims stated here comes largely from interacting and challenging my calculations with AI LLMs from ChatGPT, Grok and Google AI, which has rapidly confirmed, refuted, or refined my initial calculations and assumptions. I make no representation that anything in this analysis is factual or confirmed by me empirically. That said, let's begin:
For brevity and to avoid redundancy (just read Lackner, it's well written and pretty easy to understand), here's a brief summary of conerns raised in Lackner 2026:
- The asserted fusion efficiencies due to Ti >> Te (the ion temperature much higher than electron), relax so quickly that they are negligible and therefore much too optimistic for applying to commercially viable fusion
- Bremsstrahlung radiation will be much higher than asserted by Kirtley,
- Tilt axis plasma instability will occur, along with other concerns like chamber scraping and impurity "gumming" of fusion reactions
- and finally, once again for good measure, Ti will equal Te, very quickly, so Kirtley's Ti>> Te assertion will not meaningfully apply.
The Helion topology, including for both Trenta and Polaris, accelerates two toriodal plasmoids at speeds around Mach 2000 (yes, two thousand) toward each other, compressing them as they collide in the center, squished into a cigar shape and attaining fusion temperature conditions, all in about 150 microseconds. That's 150 microseconds from initial acceleration from "rest" on either end of the device to peak fusion conditions in the subsequently collided plasmoid combined and compressed at rest in the center reaction chamber.
Now, as fusion begins, the ion/electron temperature ratio Ti/Te is around 10, according to both Kirtley and Lackner. This high ratio thermal disequilibrium increases fusion reaction occurrence, as Kirtley 2023 describes. Lackner et. al. then make a strong case with supporting calculations to show how rapidly the ratio returns to temperature equilibration (Ti = Te), where fusion reaction collisions occur at a lower rate. In Helion's case, that time is short, around 500 microseconds, whether in Polaris at about 15 Tesla magnetic B field or in the still under-construction commercial electricity producing Orion device with a "guestimated" 30T B field.
So Lackner is correct on this: the Ti >> Te fusion reaction efficiency gain is all gone within a mere 500 microseconds.
Lackner et. al. further make a plot (Figure 2) using "fusion breakeven" to "normalize" the fusion reaction time plot, showing the extremely short duration of expected TI >> Te compared to the "fusion breakeven" time. And this is where Lackner 2026 goes completely off the rails: the calculated "breakeven" time is calculated assuming NO RECAPTURE of the plasmoid formation and compression energy - ZERO. Which leads Lackner et. al. to mistakenly conclude that "breakeven" takes a long time to achieve. The problem is, this is steady state fusion "breakeven", which has absolutely no relevance to Kirtley 2023. The point is that this "breakeven time" might be a reasonable calculation for steady state fusion topologies as in Tokomaks or Spheromaks, but it COMPLETELY IGNORES the >90% EMF energy recovery described in Kirtley 2023. This oversight completely destroys any significant relevance of Lackner et. al. conclusions.
And there's another issue: while Lackner et. al. obsess on thermal equilibrium concerns (they do it twice - in the first third AND again in the last third of the letter), they never present an estimate of non-thermal operation applied to Kirtley 2023. Based on their own equations and a few assumptions attainable from Kirtley 2023 and Trenta/Polaris reports, and Integrating the "boosted" but rapidly declining non-thermal enhanced collision rate over the short time to thermal equilibrium yields an approximate threefold boost in fusion collision reaction rate. Threefold boost is "not nothing", and Lackner et. al. wrongly concludes that it doesn't apply to commercial net power configurations when it actually does, but it's not that big a factor either.
This would seem to support Lackner et. al.'s concerns: the "boost" is only on the order of 3X and it's transient at only 500 microseconds.
And that's the thing that is difficult, apparently, for steady state ignition focused plasma scientists to wrap their head around (at least as evidenced by Lackner et. al.): During this "extremely short" first 150 microsecond compression to peak fusion and additional 350 microsecond relaxation phase, an estimated seventy percent of the fusion energy "harvest time" has been accomplished! In fact, starting around that 500 microsecond Ti = Te equilibration mark is the reaction "quench" phase.
What is the "quench" phase? It's the final \ field maintenance that is applied and maintained upon the plasmoid in order to start shutting down and reduce losses and protect the chamber walls. This is key: all the bad things that happen in FRC plasmas (plasmoid tilt, bremsstrahlung, synchrotron and transport losses) have "inertia". They don't start significantly kicking in until that thermal equilibrium 500 microsecond time, and they grow worse and worse from then on. As
One more thing: the Helion design is able to inject high fuel density in the plasmoid, knowing that only a small fraction (estimated at <3%) will be consumed. Unlike steady state fusion designs, they can optimize the density without being constrained by steady state conditions. The considerable amount of unused fuel gets vacuumed out through the diverter and is separated for subsequent recycled use.
Regarding the electromagnetic plasma formation B field, Kirtley makes the STRONG assertion of B field "efficient recovery" repeatedly in Kirtley 2023, always noting in analysis graphs that the plasma characteristics "assume no recovery" (six times this is stated). But the efficient B field recovery is CRITICALLY IMPORTANT: Helion only needs fusion to add enough energy in order to exceed the sum of EMF-generated B field formation/acceleration/compression losses and the thermal, bremsstrahlung, synchrotron and transport losses. Lackner misses high B field energy recovery entirely. It's not even mentioned in the letter, despite it being THE CENTRAL MECHANISM facilitating net fusion energy in the Helion topology.
The Helion design implements fine-grained control with nanosecond precision in timing, using fiber optic-controlled switches, attention to cable length, and high speed FPGA logic to optimize the acceleration, compression and fusion reaction harvesting, the "quench" phase, and the evacuation phase. Add to this the optimization of the fuel ratio and density.
Lackner et. al. conclude that "tight constraints" will be needed in Helion. That's true. Just not new. Kirtley and team have known that for well over a decade. It's all in their design and experimental, empirical work. Kirtley confirmed all of this with data from Trenta, as published in Kirtley 2023. Now, in 2026, Kirtley has confirmed that Polaris has the same or better control.
Lackner 2026 also mentions that they can't replicate Helion's bremsstrahlung loss. That's because Lackner's bremsstrahlung estimates are empirically determined steady state estimates. Which is well over one order of magnitude higher than what can be calculated mathematically under Helion conditions. Spin instability and synchrotron losses are essentially non-existent in this short time window.
Lackner also implies concern that even tiny impurities squelch the reaction, gumming it up. Again, this would be true steady state, but there simply is not enough time for the plasma to hit the wall and trigger impurities that would then travel back and interfere with the fusion reaction. The reaction is already over. And the reactor chamber is being evacuated by then, cleaning it out, and making it ready for the next shot.
It's likely that due to physical restraints, the pulse rate in Orion will max out around 10 Hz. At that rate, with the total acceleration, compression, relaxation and quench portion of the cycle under 500 microseconds in duration, that leaves a remaining 99.5 MILLI-seconds to regroup for the next shot: a 0.5% duty cycle. This, indeed, is mind blowing to continuous ignition fusion plasma physicists. Lackner et. al. 2026 letter, ends up harping on issues that don't apply to Helion's topology, demonstrating the incredulity by seasoned, subject matter experts that have a hard time grappling with the Helion difference.
Kirtley and the Helion team have spent well over a decade designing and optimizing fuel mix, density, compression time, relaxation time and radius, plasma pressure, initial ion and electron temperatures, final plasmoid radius and temperature, field strength, bremsstrahlung, synchrotron, and transport losses, neutron flux, cooling and evacuation time. They discovered a clear path to commercial fusion direct energy production. And they are moving as fast as they can to achieve it. Lackner et. al. 2026 expose their own "outside looking in" Tokomak thinking, and somewhat astonishingly, completely fail to comprehend the Helion topology described by Kirtley 2023.