Historical research guide · 0752 · 2023
First measurements of p11B fusion in a magnetically confined plasma
R. M. Magee · K. Ogawa · T. Tajima · I. Allfrey · H. Gota · P. McCarroll · S. Ohdachi · M. Isobe · S. Kamio · V. Klumper · H. Nuga · M. Shoji · S. Ziaei · M. W. Binderbauer · M. Osakabe
In one minute
A joint team from TAE Technologies and Japan’s National Institute for Fusion Science report the first proton-boron-11 fusion produced inside a magnetically confined plasma. Proton-boron-11 is the aneutronic reaction: a proton and a boron-11 nucleus give three helium nuclei and 8.7 MeV, with no neutrons in the main channel, so a reactor built on it avoids the shielding and material-damage problems that dominate deuterium-tritium designs. Until this experiment the reaction had only been studied in accelerators, in laser-produced plasmas and on paper. Magee and colleagues used Japan’s Large Helical Device, dropped sub-millimetre boron powder into the plasma edge until boron accumulated in the core, then fired three 2 MW hydrogen beams at 160 kV to make the fast protons. A silicon detector tucked below the plasma, out of the plasma’s direct line of sight and fed by alphas steered along the magnetic field, counted the fusion products — about 150,000 counts a second with boron present, under a thousand without.
Connection
Chapter 12 turns on the fuel that returns charged particles rather than neutrons, and this is the paper that moved proton–boron-11 out of the accelerator and into the environment a reactor would actually use. It also names the next lever the site cares about: the fusion rate can be pushed by engineering the particle distribution — alpha channelling, profile tuning, beam-driven waves — rather than only by raising temperature.
From the source
This is the first realization of proton–boron-11 fusion in a magnetically confined plasma: boron powder injection plus high-energy hydrogen neutral beams in the Large Helical Device produced diagnostically significant levels of alpha particle emission, measured with a purpose-built particle detector.Abstract; Results, Measurements
Proton–boron-11 trades downstream engineering problems for present-day physics problems: the reaction yields three alpha particles and 8.7 MeV with no neutrons, so a reactor avoids the roughly 10¹⁹ neutrons per square metre per second of 14 MeV fluence that a deuterium-tritium plasma imposes on first-wall materials, superconducting coils and remote handling.Introduction, paragraphs 1 to 3
With the updated proton–boron-11 cross-section values and kinetic effects properly accounted for, a thermal proton–boron-11 plasma can reach high fusion gain and even ignition, given a low internal magnetic field, electrons held cooler than the ions to cut radiation losses, and a maintained non-equilibrium population of energetic reacting ions.Introduction, paragraph 4
Real-time boron powder injection through the Impurity Powder Dropper accumulated boron in the mid-radius of the plasma at densities up to 6 × 10¹⁷ per cubic metre; with three 2 MW, 160 kV tangential hydrogen beams firing together, calculations predict fusion rates of about 10¹⁴ reactions per second, and the roughly 10 cm alpha Larmor radius sends most alphas to the wall where an external detector can see them.Results, Producing fusion alpha particles in LHD
The signal is correlated with both ingredients: the maximum pulse count rate is about 150 kcps with boron injection and less than 1 kcps without it, the pulses begin at beam turn-on, and the measured count rate tracks the global fusion rate computed by the FBURN code in leading edge, plateau and trailing edge.Results, Measurements and Comparison to numerical simulation; Figures 2 and 3
An absolute comparison of measurement to calculation is not yet possible, because accurate orbit tracing needs the alpha energy spectrum at the source while only the alphas that survive to the detector can be measured; the authors therefore rest the identification on dynamical, relative agreement, and name alpha channelling, profile tuning, phase space engineering, fusion product current drive and collective beam-induced heating as the levers to raise gain next.Results, Comparison to numerical simulation; Discussion
The way in
https://doi.org/10.1038/s41467-023-36655-1How to cite it
R. M. Magee, K. Ogawa, T. Tajima, I. Allfrey, H. Gota, P. McCarroll, S. Ohdachi, M. Isobe, S. Kamio, V. Klumper, H. Nuga, M. Shoji, S. Ziaei, M. W. Binderbauer, M. Osakabe (2023) First measurements of p11B fusion in a magnetically confined plasma doi:10.1038/s41467-023-36655-1