Historical research guide · 1023 · 2023
HB11—Understanding Hydrogen-Boron Fusion as a New Clean Energy Source
Warren McKenzie · Dimitri Batani · Thomas A. Mehlhorn · Daniele Margarone · Fabio Belloni · E. Michael Campbell · Simon Woodruff · Jan Kirchhoff · Adrian Paterson · Sergey Pikuz · Heinrich Hora
In one minute
Fuse a proton with a boron-11 nucleus and you get three helium nuclei and 8.7 megaelectronvolts — all of it carried by charged particles you can steer straight into electricity, with no neutron stream to shield against and no radioactive tritium to breed. That is why Heinrich Hora spent a career on it, and why HB11 Energy was founded around his work. Warren McKenzie, Dimitri Batani, Thomas Mehlhorn, Hora and their colleagues here set out where the field actually stands. Because the temperatures for a thermal proton-boron burn are impractical, the route is non-thermal: ultra-short laser pulses accelerate protons directly into a boron target. Since 2005 about ten experiments have done it, and the best shots — at ELI Beamlines in Prague and the LFEX laser in Osaka — now produce around ten to the eleventh alpha particles per steradian. The authors put that at four orders of magnitude below breakeven, name every route they know for closing the gap, and price the reactor that would follow.
Connection
Chapter 12 argues that the fuel choice decides the machine, and this is the clearest published statement of what the aneutronic choice buys and what it costs: no breeding blanket, no activated wall, direct conversion of charged particles to current — in exchange for a reaction that will not burn thermally, so the driver has to be a laser. Chapter 9 meets it at the magnetic-confinement half of the scheme, where a second laser charges a capacitor-coil and pinches the proton and alpha flux inside a kilotesla-class field.
From the source
The reaction is a proton plus boron-11 giving three helium-4 nuclei and 8.7 megaelectronvolts. As a nuclear process it presents an energy density approximately seven orders of magnitude higher than chemical reactions, and because the primary reaction is aneutronic it does not induce activation in materials, leading to negligible radioactive waste. In principle this enables the direct conversion of the kinetic energy of the charged particles into electricity, rather than through a thermal cycle.Introduction, Equation 1
Proton-boron was neglected for a physical reason and rescued by a technological one. The reactivity of the fuel means the temperatures required to achieve a thermal fusion burn are an order of magnitude higher than for deuterium-tritium and far exceed 100 million kelvin, and bremsstrahlung losses are worse because boron carries five units of charge. The answer was to abandon thermal initiation: plasma-block acceleration was proposed in 1978 from early hydrodynamic simulations, chirped pulse amplification made the required pulses real, and the first experimental demonstration of non-thermal hydrogen-boron fusion was performed by Belyaev and colleagues in 2005.Introduction and History and Recent Results
The measured state of the art, stated against its own target. The highest reported alpha-particle flux is of the order of ten to the eleventh per steradian, from a nanosecond PALS shot at ELI Beamlines in Prague and from the picosecond LFEX system at Osaka University. At an average of about 3 megaelectronvolts that flux is about 0.1 joule of alpha energy from a shot delivering of order 1 kilojoule on target — a fusion-to-laser energy efficiency of about 0.01 percent. Breakeven corresponds to 2.15 times ten to the fifteenth alpha particles per kilojoule of laser energy, so the deficit is four orders of magnitude, reached after only about ten experimental demonstrations in total.History and Recent Results, and Pathways to Increase Fusion Gain; Figure 1
HB11 Energy’s initial reactor concept uses two lasers. The first accelerates ions through a cylindrical hydrogen-boron target to initiate the non-thermal reaction; the second irradiates a capacitor-coil target, ejecting hot electrons from one plate so that the potential difference drives a current in a U-turn coil and raises a sub-kilotesla field lasting several nanoseconds, which confines the proton and alpha flux instead of letting it disperse. Quantitatively, direct-drive ignition is estimated to need a 1-picosecond pulse of 30 kilojoules, that is 30 petawatts, focused into a 200-micrometre spot at ten to the twentieth watts per square centimetre, igniting a cylinder 1 centimetre long and 2 millimetres across confined by a 10-kilotesla field raised by a 3-kilojoule nanosecond pulse on the coil.History and Recent Results, The application of magnetic fields; Figure 2
The plant is a power amplifier, not a power source: the fusion power available for conversion is the power on target multiplied by the target gain, and the recirculating power fraction is one divided by the product of generator efficiency, laser efficiency and gain. Engineering breakeven is a recirculating fraction of one; fission plants run near one tenth. That yields the rule of thumb that laser efficiency times gain must exceed 10, and against market boundaries of 35 dollars per megawatt hour of electricity and 1.5 dollars per kilogram of hydrogen, a laser efficiency of 20 percent puts the required target gain between 100 and 300.Commercialisation: Technoeconomic Model and Engineering Challenges; Figure 4
What to watch: the authors name the measurements that would settle the physics. Almost 90 years after the reaction was discovered, the exact shape of the proton-boron cross-section below a few hundred kiloelectronvolts and above 3 megaelectronvolts is still not known, and several experiments are being planned to fill those gaps. The avalanche mechanism — alpha particles elastically knocking bound protons into further fusion reactions — was proposed to explain unusually high measured rates, has been the subject of debate, and is considered one of the most promising single routes to a large increase in gain.Pathways to Increase Fusion Gain, The Avalanche Mechanism; Research Challenges, Material Properties
The way in
https://doi.org/10.1007/s10894-023-00349-9How to cite it
Warren McKenzie, Dimitri Batani, Thomas A. Mehlhorn, Daniele Margarone, Fabio Belloni, E. Michael Campbell, Simon Woodruff, Jan Kirchhoff, Adrian Paterson, Sergey Pikuz, Heinrich Hora (2023) HB11—Understanding Hydrogen-Boron Fusion as a New Clean Energy Source doi:10.1007/s10894-023-00349-9