Aneutronic Fusion

Speculative If a proton–boron-11 plasma can be driven to release more fusion power than it loses to bremsstrahlung X-rays — a ratio no experiment has ever measured above 1, and section 7 says what would settle it — the prize is a fusion reactor stripped of almost every subsystem the deuterium–tritium line is built around. The reaction is p + 11B → 3 alpha + 8.7 MeV, and its energy comes out as fast charged alpha particles rather than as the 14.1 MeV neutrons that dominate a D–T reactor.

Established What that removes is specific and large. It removes the tritium fuel cycle that the sibling brief Commercial Fusion identifies as its binding constraint — a 25–30 kg world civil tritium stock against a 1 GW plant that would burn more than 55 kg a year, with no facility having ever bred more than it burned. It removes the 14.1 MeV neutron flux that drives more than 15 displacements per atom per year in a D–T first wall and forces an irradiation-qualification facility that does not yet exist. And the fuel is ordinary matter: boron-11 is roughly 80% of natural boron, and hydrogen is everywhere.

Frontier The second part of the prize is conversion. Because the 8.7 MeV emerges as charged alphas, it can in principle be turned into electricity electrostatically, bypassing the roughly 33–40% ceiling of a steam or gas thermal cycle — a gain the D–T line cannot claim because most of its energy is in neutrons that must first be thermalised in a blanket.

Speculative The distribution of that prize, and its condition, both belong here. The near-term winners are diagnostic, accelerator and laser suppliers, not a grid: every gain to date is a laboratory alpha count, not a watt sold. And the whole case reduces to one number that Rider’s 1995 theorem argues may be unreachable near thermal equilibrium — the steady-state ratio of fusion power to bremsstrahlung power — which is why section 5 is the part of this brief that decides whether any of the above is real.

Established Aneutronic fusion is a fuel choice, not a machine. It names the reactions that release almost all of their energy as charged particles rather than neutrons.

Established The working definition is quantitative. The statutory threshold written into New Jersey research-incentive law is that neutrons carry no more than 1% of the energy released; the point of the choice is to escape the neutron entirely, giving a reactor with no 14.1 MeV wall damage, little neutron activation, no tritium to breed, and the option of converting the products to electricity directly.

Established Three reactions are the real candidates, and they trade against each other. Deuterium–helium-3 (D + 3He → 4He + p + 18.3 MeV) ignites near 58 keV but its side D–D reactions still make neutrons, and helium-3 is scarce on Earth.

Established The purest option is doubly scarce. Helium-3–helium-3 (3He + 3He → 4He + 2p + 12.86 MeV) is the only fully aneutronic reaction but needs two scarce nuclei at once, which is why almost no programme pursues it.

Established Proton–boron-11 is the front-runner precisely because its fuel is abundant, and it is also the hardest of the three. The reaction p + 11B → 3 alpha + 8.7 MeV runs on terrestrial materials, which is the entire reason the field concentrates on the reaction with the worst radiation problem.

Established Proton–boron-11 buys fuel abundance with temperature. Its reaction rate peaks near an ion energy of 600 keV — about 6.6 billion kelvin — and its notional ignition temperature is around 123 keV, roughly nine to ten times the 13.6 keV of D–T.

Established The confinement penalty compounds the temperature penalty. The density–confinement-time product proton–boron-11 needs is about 45 times that of D–T, and the fusion triple product about 500 times; this is the whole bargain, trading the neutron and the tritium loop for a plasma-physics problem an order of magnitude harder.

Frontier The distinction that governs the entire subject is thermal versus beam-target. In a thermal reactor the fuel ions share one temperature and the reaction rate follows from that temperature; in a beam-target reaction a fast beam of protons strikes cold boron and fuses before it equilibrates.

Frontier Every measured proton–boron-11 result to date is beam-target, and the difference is not a detail. Whether in a stellarator, in lasers, or in electrostatic devices, the demonstrations to date show that the reaction occurs; they do not show that a plasma of it can make net power, and those are different achievements.

Frontier The failure mode is radiation, not confinement time. Where D–T is limited by how long you can hold the plasma, proton–boron-11 is limited by how much of its energy pours out as bremsstrahlung X-rays before it can fuse — a loss that scales with the square of ionic charge and is severe for a fuel carrying boron’s charge of five. That radiation loss, not the triple product, is what section 3 is organised around.

Established The reaction is real, its cross-section is measured, and the numbers are not in dispute. Proton–boron-11 has a dominant resonance near 600 keV with a width around 100 keV and a lower-energy resonance near 148 keV.

Established The cross-section has been re-evaluated upward in the last decade. A 2016 compilation by Sikora and Weller consolidated the modern cross-section, a 2026 reanalysis by Wang and colleagues added a further resonance near 4.7 MeV with a width around 153 keV, and together these raised the computed fusion power by roughly a factor of two over the 1979 McNally data that early feasibility studies used — a real correction, and the reason the subject was reopened at all.

Established By reaction count the fuel is close to aneutronic but not free of neutrons. At least 0.1% of reactions in a thermal proton–boron-11 plasma produce neutrons through side channels, and the fast alphas can drive secondary reactions on boron that add more.

Established Low-neutron is not no-neutron. The energy carried by neutrons stays under the 1% aneutronic bar, but the residual flux still activates structure at a level a plant would have to account for, so the “no radioactivity” framing is wrong on its own terms.

Established The anchor for the whole subject is a 2023 measurement in the Large Helical Device, and it is worth stating exactly. Magee and colleagues, a TAE Technologies–National Institute for Fusion Science collaboration, dropped sub-millimetre grains of boron and boron nitride into the LHD stellarator with an impurity powder dropper, reaching boron densities up to 6 × 10¹⁷ m⁻³, and fired three tangential hydrogen neutral beams at 160 kV and 2 MW each into a plasma at 2.75 T with a central electron temperature near 2 keV and a line-averaged density near 2 × 10¹⁸ m⁻³.

Established The count itself is the headline. A silicon detector shielded by tungsten and platinum foil recorded MeV alpha particles at a peak rate around 150,000 counts per second, with a calculated global fusion rate near 10¹⁴ per second — the first realisation of proton–boron-11 fusion in a magnetically confined plasma.

Frontier What the anchor demonstrates is narrower than the headlines it produced. The alphas were made by 160 keV beam protons striking cold boron in a plasma whose own temperature was 2 keV — a beam-target reaction, exactly the non-equilibrium regime Rider warned about, and one that says nothing about whether a hot proton–boron-11 plasma can beat its own radiation.

Established The authors were careful about this, and it matters. They made no claim of net energy and none about bremsstrahlung; the measurement confirms the cross-section inside a real confinement device and does not touch the power balance.

Established The laser record tells the same story at higher intensity. An Osaka experiment reported in 2022 by an HB11 Energy–linked group produced on the order of 10¹⁰ alpha particles per steradian, a crude total near 1.4 × 10¹¹ per shot, from a boron nitride target hit at about 3 × 10¹⁹ W cm⁻², at an energy-conversion efficiency of roughly 0.005% — on the group’s own account four orders of magnitude short of net energy.

Established The peer-reviewed laser yields are competitive but small. A 2025 Physical Review Research paper from Margarone’s group reached about 5 × 10⁷ alphas per steradian per joule from novel targets driven by a 10 J, 800 fs pulse, matching the highest energy-normalised yields on record.

Frontier Every laser result is beam-target too. The alphas come from laser-accelerated protons ploughing into boron, and the yields are quoted per steradian or per joule precisely because a gain figure would be negative; these are cross-section demonstrations, useful as alpha sources for materials and medical work, not evidence about the steady-state radiation balance.

Established The one line that ran on net energy has stalled. Robert Bussard’s Polywell, an inertial-electrostatic-confinement device developed by EMC2, chose proton–boron-11 explicitly for its aneutronic and direct-conversion properties, and the US Navy funded it through the WB-6 (2005), WB-7 (2008) and WB-8 (from 2010, on roughly 7.86 million US dollars of Recovery Act money plus Navy options) devices.

Established Three decades produced no power balance. No peer-reviewed net-energy result ever emerged, a 2019 University of Sydney thesis found the electron confinement would require an unfeasible continuous supply of order 200,000 amperes to sustain, and the company now operates with about five employees — a funded programme that ran for thirty years on this fuel and produced no balance is itself a datum.

Established Against those measurements sits a theorem, and it is the spine of the subject. Todd Rider’s 1995 MIT analysis showed that a proton–boron-11 plasma near thermal equilibrium loses more to bremsstrahlung than it makes in fusion, and that holding the ions hotter than the electrons to escape that loss costs more recirculating power than the reaction yields — on his figures the bremsstrahlung reaches roughly half the fusion power while the power needed to maintain the temperature gap runs many times the fusion power.

Established A second calculation pinned the thermal-equilibrium number. Nevins and Swain’s 2000 result put the thermal-equilibrium bremsstrahlung at no less than 1.74 times the fusion power for proton–boron-11, against 1.39 for helium-3–helium-3; for a plasma at one temperature, the negative result is settled.

Frontier The live science is whether non-equilibrium and updated data reopen the door, and the recent literature genuinely disagrees. With the higher modern cross-sections, a 2024 reassessment of Rider’s constraint found net yield achievable only when the electrons are held near 140 keV against ions at 300 keV, and still concluded net power is unlikely without highly efficient external heat engines.

Frontier The 2026 reanalysis is more permissive but still short of a gain. Wang and colleagues found that a self-consistent treatment in which electrons stay well below the ion temperature opens a positive-balance window between about 0.17 and 0.38 MeV, peaking near 0.25 MeV — concluding proton–boron-11 is “not fundamentally excluded by bremsstrahlung constraints”, while explicitly stopping short of claiming a gain above 1.

Frontier The most careful energy-balance study to date is also the most sobering. Ochs, Kolmes, Glasser and Fisch at Princeton, in a November 2025 analysis of inertial proton–boron-11, found that a plasma transparent to its own bremsstrahlung struggles to exceed a scientific gain of about 2, at an optimum ion temperature near 160 keV and a boron fraction near 0.25.

Frontier The only route to a large gain in that study is extreme density. Gain rises to the 15–20 range only if the plasma is dense enough to reabsorb its own X-rays, which requires an areal density of order 100 g cm⁻² and electron densities near 1.5 × 10²⁸ cm⁻³ — roughly two orders of magnitude beyond what the National Ignition Facility reaches, which the authors call essentially unrealistic in the near future.

Speculative The opposite pole is held by advocates who count on suprathermal ions. A 2024 paper by Ghorbanpour and Belloni, one author affiliated with HB11 Energy, argued that ideal ignition can be reached if a suprathermal population is sustained, computing a fusion-to-bremsstrahlung ratio above 2 at ion densities near 10²⁶ cm⁻³ with ions at 150–340 keV and electrons held at 80–95 keV.

Speculative That premise is the disputed one. Sustained non-equilibrium is exactly what Rider argued is self-defeating, and no experiment has demonstrated that such a temperature gap holds against collisions at reactor conditions.

Frontier So the terminal position is precise. The cross-section is measured and adequate; the reaction has been produced in magnetically confined, laser-driven and electrostatic devices; and no device has ever produced a steady-state plasma in which proton–boron-11 fusion power exceeded bremsstrahlung. The entire question has narrowed to whether a large, sustained ion–electron temperature separation, or bremsstrahlung reabsorption at extreme density, can be realised — and both remain unshown.

Frontier The open questions are no longer about the nucleus; they are about the electrons. The cross-section work of the last decade closed the argument that early feasibility studies used too-low reaction rates, so what remains open is entirely a question of plasma thermodynamics.

Speculative Can a large ion–electron temperature gap be sustained at reactor density? Every optimistic energy balance in the literature — Wang’s window, Ghorbanpour and Belloni’s ignition case, the 2024 Rider reassessment — requires electrons tens of keV colder than the ions.

Frontier The physics fights that gap. Electron–ion collisions equilibrate temperatures, and the colder the electrons the faster they drain energy from the ions; whether any confinement scheme can hold the gap open against that drain, at density and for a confinement time, is the central unproven premise of the whole subject.

Frontier Does bremsstrahlung reabsorption change the balance? The Princeton analysis shows that a plasma optically thick to its own X-rays could reach a gain of 15–20 rather than 2 — a qualitative change — but only at areal densities near 100 g cm⁻².

Speculative And reabsorption may not help the ions. Whether inertial schemes can reach and hold that density with a proton–boron-11 fuel, and whether the reabsorbed energy actually returns to the ions rather than simply reheating escaping electrons, is genuinely unsettled.

Frontier Do fast ions fuse before they thermalise? Beam-driven and avalanche schemes — TAE’s field-reversed configuration, laser block-ignition, the “avalanche” boron reactions HB11 promotes — all bet that a non-thermal ion population can fuse at a useful rate before collisions relax it into the losing thermal distribution.

Speculative That bet is coherent but unbanked. It is precisely the mechanism Rider modelled as a net drain; the measurements are consistent with the reaction happening, but nothing yet demonstrates that the books close in its favour.

Frontier Is synchrotron radiation a second wall? At the fields and temperatures proton–boron-11 needs, electrons also radiate synchrotron X-rays; the recent literature treats bremsstrahlung as dominant, but synchrotron losses are acknowledged and largely unquantified for this fuel, and they run the wrong way as field rises.

Speculative Can direct energy conversion recover enough of the output? The fraction of the total energy that appears as recoverable charged-particle kinetic energy, as opposed to bremsstrahlung and synchrotron X-rays that must be caught thermally, is design-dependent and has never been measured for a burning proton–boron-11 plasma; a converter that is 90% efficient on the alphas it sees is worth little if half the energy left as X-rays first.

Frontier Is there a role short of a power plant? The laser and stellarator results have made proton–boron-11 a competitive laboratory source of MeV alpha particles, with proposed uses in materials testing and in targeted alpha therapy, and whether that matures into a funded field independent of the power dream is an open and quite separate question — possibly where the near-term value actually is.

Established The defining bottleneck is bremsstrahlung, and it is a law of the plasma, not an engineering shortfall. Bremsstrahlung radiated power scales with the effective ionic charge squared, the electron density, the ion density and the square root of the electron temperature; boron carries a charge of five, so a proton–boron-11 plasma radiates far harder than a hydrogenic one at the same density.

Established No engineering lowers a fundamental radiation rate. In thermal equilibrium that radiation exceeds the fusion power — at least 1.74 times, on Nevins and Swain’s figure — and this is the wall the subject keeps hitting.

Established The temperature requirement is the second bottleneck and it compounds the first. Peak reactivity near 600 keV and an ignition temperature near 123 keV mean the plasma must be roughly ten times hotter than a D–T plasma, and the required triple product is about 500 times larger.

Established The two constraints are not independent. Hotter electrons radiate more, so the temperature you need to make the reaction go is also the temperature that makes the radiation loss worse.

Frontier The escape route — holding ions hotter than electrons — has its own cost, and that cost is the third bottleneck. Maintaining a temperature gap against collisional equilibration requires continuously pumping energy into the ions or out of the electrons, and Rider’s result is that this recirculating power generically exceeds the fusion power.

Frontier Any workable design has to beat a generic result. It must show a specific mechanism that defeats Rider’s recirculating-power argument, and none has been demonstrated in a plasma.

Frontier Direct energy conversion is a bottleneck disguised as a solution. Converting MeV alphas to electricity electrostatically has been demonstrated only at small scale and low power; doing it at reactor scale, at high efficiency, with the alpha energy spread a real plasma produces, is unbuilt.

Frontier The converter does not replace the thermal plant. Because a large share of the energy still leaves as X-rays, a proton–boron-11 plant needs both a high-efficiency direct converter and a thermal system to catch the radiation — more plant, not less.

Speculative The heat flux from the radiation itself is an unsolved wall-loading problem. The bremsstrahlung that ruins the power balance does not disappear; it lands on the first wall as a hard X-ray heat load that, for a plant-scale device, would be intense and volumetrically deposited, and no proton–boron-11 wall concept has been engineered against real numbers because no plasma has produced them.

Established Nothing on this map produces the result this brief waits on. The binding constraint is a scientific fact about power balance that no research programme is currently generating: a steady-state plasma in which measured proton–boron-11 fusion power exceeds measured bremsstrahlung.

Established That is a requirement, not an edge. It is recorded in section 14 as a typed requirement rather than an edge to another brief, because no other brief on the map is trying to produce it.

Frontier What it borrows from neighbours it borrows as capability, not as a gate. The high-field magnets that make compact confinement possible come from the same REBCO tape supply that High Temperature Superconductors and Superconducting Infrastructure own; better magnets help every route to the high triple product proton–boron-11 demands, but no magnet result unblocks the radiation problem, so the dependency is real and non-decisive.

Established The fuel supply, uniquely for a fusion concept, is not a dependency at all. Boron-11 is about 80% of natural boron and needs no exotic enrichment; hydrogen is ubiquitous.

Established That is the inverse of the D–T problem. Where Commercial Fusion is gated by a 25–30 kg tritium stock and an unbuilt breeding blanket, this subject has no fuel-cycle dependency to wait on — which is exactly why its entire risk is concentrated in the plasma physics.

Frontier Direct energy conversion is a dependency the field rarely lists as one. The economic case leans on converting charged particles to electricity above the thermal-cycle ceiling, and that hardware is developed nowhere at reactor scale; a proton–boron-11 plant depends on a converter industry that does not exist, on top of the physics result that also does not exist.

Frontier The decisive experiment is a plasma — of any kind, by any confinement scheme — in which the measured proton–boron-11 fusion power exceeds the measured bremsstrahlung power at steady state. Everything else in the subject is instrumentation for, or argument about, this one number.

Frontier It has never been measured above 1. It is the single result that would move this brief’s assessment from “probably barred by radiation” to “a hard but open engineering path”, and no device on the public record is built to produce it.

Established What has been run is the reaction rate, not the power balance. The LHD measurement showed alphas at around 150,000 counts per second from beam-target fusion; the laser experiments showed up to 1.4 × 10¹¹ alphas per shot at 0.005% efficiency.

Established Those experiments are silent on the balance by construction. None was designed to weigh fusion power against radiation, and none did.

Speculative The premise the decisive test would actually probe is sustained ion–electron temperature separation. A cleaner intermediate experiment is to demonstrate, in any device, that electrons can be held tens of keV below the ions in a proton–boron-11-relevant plasma for a confinement time against collisional equilibration, and to measure the recirculating power that costs.

Frontier That intermediate test could close the case without a reactor. If the recirculating power exceeds the fusion power — Rider’s prediction — the concept is closed for near-equilibrium schemes without anyone building a plant.

Frontier The inertial variant of the decisive test is a density measurement. The Princeton analysis makes the whole inertial case turn on whether a proton–boron-11 plasma can reach an areal density near 100 g cm⁻², dense enough to reabsorb its own X-rays, roughly two orders of magnitude beyond current inertial-confinement parameters; demonstrating that density with this fuel, even without net gain, would settle whether the reabsorption route is physical.

Frontier A direct-conversion demonstration is the decisive economic experiment. Recovering the kinetic energy of MeV alphas as electricity at high efficiency and reactor-relevant power, with a realistic energy spread, has never been shown; without it the aneutronic advantage that justifies the harder physics is unpriced.

Established None of these is scheduled. No public facility is being built to test the proton–boron-11 power balance, the temperature-separation premise, the reabsorption density, or the converter at scale; the measurements that exist were opportunistic uses of machines built for D–T or for laser–plasma science.

Speculative The natural-experiment substitute is the funded programmes themselves. TAE Technologies has raised about 1.2 billion US dollars on a field-reversed-configuration route to this fuel; if a beam-driven or field-reversed device reaches burning-plasma conditions this decade and still reports no positive balance, that will be strong evidence the theorem holds in practice, in the same way EMC2’s three decades without a result already are.

Frontier The signature engineering component is the direct energy converter, and it is the least mature part of the whole concept. The physical appeal is real: MeV alphas can be decelerated against an electrostatic field and their kinetic energy collected as current, in principle above the 33–40% ceiling of a thermal cycle.

Speculative Scaling it is unsolved. Converters have been built only at low power, and taking one to a reactor with the broad alpha energy spectrum a real plasma produces, at high efficiency and with manageable voltages, is unsolved engineering resting on unsolved physics.

Established The first wall trades a neutron problem for a photon problem. Removing the 14.1 MeV neutron spares the wall the displacement damage and activation that dominate Commercial Fusion engineering and force an unbuilt irradiation-qualification facility.

Frontier The exchange is not free. The wall must instead absorb an intense, volumetrically deposited bremsstrahlung X-ray load and export it as heat, which means a proton–boron-11 plant still needs a thermal balance-of-plant, alongside its direct converter, rather than instead of one.

Frontier Magnets remain a genuine enabler. The high triple product this fuel demands rewards the highest achievable field, so the REBCO high-temperature-superconductor tape whose supply is owned by High Temperature Superconductors and Superconducting Infrastructure is as central here as in any tokamak line, and its supply constraints carry over unchanged.

Speculative Heat and particle handling at ten times D–T temperatures is unquantified. Sustaining ions near hundreds of keV, injecting the power to hold electrons cold, and exhausting helium ash from a plasma this hot are engineering problems whose specifications cannot be written until a device produces the plasma; every number a designer would need is downstream of the physics result section 7 describes.

Frontier The closest neighbour is the D–T mainline. Commercial Fusion owns the tritium fuel cycle, the breeding blanket and the neutron-irradiation-qualification argument; this brief is the mirror image, taking on a harder plasma to escape all three.

Frontier The two are best read together. The aneutronic case is only worth its physics penalty if the D–T penalties — tritium scarcity, blanket, wall damage — are as binding as that brief argues.

Frontier The magnet briefs are shared infrastructure. High Temperature Superconductors and Superconducting Infrastructure own REBCO as a materials and systems problem; this brief owns only the demand that a higher triple product places on them.

Speculative Space is where the aneutronic advantage is largest. Fusion Spacecraft and Advanced Nuclear Propulsion value a reactor that produces charged particles that can be exhausted directly for thrust or converted without a heavy shield and radiator, which is exactly the aneutronic promise; the temperature problem is the same in orbit as on the ground, but the payoff for solving it is higher where shielding mass is decisive.

Frontier The helium-3 fuels tie this subject to the Moon. The D–helium-3 and helium-3–helium-3 branches depend on a helium-3 supply that Lunar Energy Infrastructure treats as a mining proposition; that dependency is one reason proton–boron-11, whose fuel is terrestrial and abundant, is the branch most work concentrates on.

Established The defining institutional fact is that proton–boron-11 is a second, harder bet in a field that has not proven its first. The overwhelming majority of public fusion money and private capital goes to D–T, whose scientific gain is demonstrated.

Frontier That ordering makes patient capital scarce. An aneutronic programme asks funders to accept a physics risk the mainline has already retired, before the mainline has delivered a plant, and that shapes who can play.

Frontier The funded landscape is narrow and concentrated. TAE Technologies is the principal capitalised proton–boron-11 programme, at roughly 1.2 billion US dollars raised on a field-reversed-configuration route, with a stated aim of a hydrogen–boron plant on the grid in the 2030s; HB11 Energy pursues the laser route; EMC2 continues at minimal scale.

Established The anchor itself came from a public machine used opportunistically. The stellarator result came from LHD, a national facility, not from a device built for this fuel; outside the handful of companies, the subject is a diffuse academic literature rather than a programme.

Established No public facility is designed to answer the decisive question. The irradiation and fuel-cycle facilities governments are building serve D–T; there is no state-funded device whose purpose is to measure the proton–boron-11 power balance or to sustain and diagnose a large ion–electron temperature gap, and no roadmap on the public record proposes to build one.

Frontier Vendor claims outrun independent verification, which is an institutional risk in itself. The strongest public statements — grid power in the 2030s, ignition with suprathermal ions — come from the parties raising money on them, while the independent literature is more cautious, so a reader has to weight the framing by the interest of its source.

Frontier The live ethical issue is that the marketing of “clean, safe, radiation-free” fusion outruns the physics. A proton–boron-11 plant is genuinely low-neutron, but it is not radiation-free.

Established The residual radiation is real. At least 0.1% of reactions make neutrons, side reactions add more, and the bremsstrahlung X-ray flux that limits the power balance is itself an intense radiation field the plant must contain; presenting aneutronic fusion as having no radioactivity is an overclaim, and it is made most often by parties raising capital.

Established The allocation question is opportunity cost, and it is sharp here. Directing scarce fusion capital and talent toward a fuel that must first overturn a thirty-year-old negative theorem, while the D–T line has not yet produced net electricity, is a defensible high-risk bet but should be stated as one.

Frontier The spillovers are the honest part of the case. Research at this scale is cheap against the payoff and produces spillovers in diagnostics, alpha sources and direct conversion; a grid-power promise on a 2030s timeline is a different claim and should not borrow the credibility of the spillovers.

Speculative If it worked, the equity story would be unusually good. A reactor fuelled by abundant boron and hydrogen, with no tritium to safeguard and little neutron activation to manage, would be easier to site and to proliferation-safeguard than either fission or D–T, and its benefits would be hard for any single nation to monopolise through fuel control — a real distributional upside, entirely contingent on the power balance nobody has shown.

Speculative The civilizational prize, if the physics yields, is a fusion source that is compact, siteable and light on shielding. Directly converted charged-particle power with minimal neutron activation would suit distributed generation, industrial heat and above all spaceflight, where the mass saved on shields and radiators is decisive.

Frontier It would be a genuinely different asset. A compact, low-activation, directly converting source is not the same machine as a neutron-heavy D–T plant, and that difference is the reason the harder fuel keeps drawing money.

Frontier The sober terminal position is that proton–boron-11 may never be a power source at all. On the current balance of evidence — a settled thermal-equilibrium negative result, narrow non-equilibrium windows that all depend on an unproven temperature separation, and no measured gain — the most likely long-run outcome is that the reaction remains a valuable laboratory alpha source for materials and medicine rather than a generator.

Speculative A civilization should plan for the dream to stay a dream. The prudent posture is to treat any power outcome as upside rather than as a plan, and to fund the reaction for its near-term uses on their own merits.

Frontier The subject also serves as a discipline on the wider fusion story. Aneutronic fusion is where the gap between what is thermodynamically possible and what is rhetorically promised is widest, so how honestly a society handles the proton–boron-11 claims is a low-stakes rehearsal for how it will handle fusion claims generally.

These horizons track the one measurement that governs the subject — a steady-state plasma in which proton–boron-11 fusion power exceeds bremsstrahlung — and the funded programmes that might reach it.

• 10 yr: Frontier The funded field-reversed and laser programmes resolve one way or another. If TAE’s route reaches burning-plasma conditions and reports a positive balance, the subject transforms; more likely, on the current evidence, is continued beam-target alpha yields and no measured gain, which would be strong practical confirmation of Rider’s theorem alongside Commercial Fusion’s own D–T milestones.
• 25 yr: Speculative A dedicated device built to sustain and diagnose a large ion–electron temperature gap could exist if a positive intermediate result justified it; absent that, the most probable state is a mature laboratory alpha-source field and a settled scientific consensus that near-equilibrium proton–boron-11 power is barred.
• 50 yr: Speculative Any power role would arrive here at the earliest, most plausibly in space applications shared with Fusion Spacecraft, where the shielding-mass payoff justifies a harder physics bet than a terrestrial grid would.
• 100 / 250+ yr: Handwave A civilization operating direct-conversion aneutronic reactors as ordinary infrastructure is a coherent long-horizon picture, but it rests on a chain of results none of which has been demonstrated, and it is offered here as a possibility, not a projection.

• Depends on nothing on this map produces a result this subject waits on. Its binding constraint is a scientific fact — a measured positive power balance — that no brief in the corpus is generating, so no typed depends-on edge is claimed; the magnet briefs help but do not unblock it.
• Requires (not on this map) first, a steady-state plasma in which measured proton–boron-11 fusion power exceeds measured bremsstrahlung, which no device has produced; second, a demonstrated ion–electron temperature separation sustained against the collisions that erase it; third, direct energy conversion of MeV alpha particles at reactor scale and efficiency, which exists nowhere; and fourth, patient capital willing to back a second, harder fusion fuel before the first has produced net electricity.
• Enables if the power balance were ever shown, a fusion source with negligible neutron activation, no tritium fuel cycle, and directly convertible output — enabling compact siteable generation and, most valuably, low-shield-mass space power for Fusion Spacecraft.
• Adjacent to Commercial Fusion as its mirror-image fuel choice, to High Temperature Superconductors and Superconducting Infrastructure for the field it needs, and to Lunar Energy Infrastructure for the helium-3 branches it mostly declines.

Handwave “Aneutronic fusion is neutron-free and radiation-free.” It is neither. At least 0.1% of proton–boron-11 reactions produce neutrons, secondary reactions on boron add more, and the bremsstrahlung X-ray flux that limits the power balance is an intense radiation field in its own right; “aneutronic” is a statutory threshold — neutrons under 1% of the energy — not a physical zero.

Frontier “The LHD and laser results prove proton–boron-11 works as a power source.” They prove the reaction occurs and the cross-section is real inside a plasma and under a laser.

Established But an alpha count is not a plant result. Every one of those results is beam-target and none measured fusion power against radiation loss; treating an alpha count as a plant result is the field’s characteristic error, made by advocates and critics alike.

Established “Boron fusion is cleaner, so it is obviously the fuel to pursue.” It trades a solved-in-principle problem — the D–T neutron and tritium loop — for an unsolved one: beating bremsstrahlung at ten times the temperature. Cleaner at the wall does not mean easier overall, and on present evidence it is considerably harder.

Frontier “Rider’s theorem has been disproven.” It has been narrowed, not overturned.

Frontier The narrowing is on paper only. Updated cross-sections and self-consistent non-equilibrium treatments open small positive-balance windows in calculations, but every one depends on a sustained ion–electron temperature gap that has not been demonstrated, and the most careful recent analysis still caps a bremsstrahlung-transparent plasma near a gain of 2. No measured result contradicts Rider.

Speculative “Direct energy conversion makes efficiency a non-issue.” Only for the charged particles. The energy that leaves as bremsstrahlung and synchrotron X-rays cannot be collected electrostatically and must be caught thermally, so a real plant needs both systems and its overall efficiency is set by how the energy splits — a split no burning proton–boron-11 plasma has ever produced to be measured.

Frontier “A hydrogen–boron plant will be on the grid in the 2030s.” This is a vendor timeline. No device has shown the power balance the claim requires, the most careful energy-balance studies are cautious to negative, and a three-decade funded electrostatic programme on the same fuel produced no net result; the claim should be read as a fundraising target, not a forecast.