Acoustically driven Magnetized Target Fusion
Michel Laberge · Stephen Howard · D. E. Richardson · Aaron Froese · Victoria Suponitsky · M. Reynolds · David Plant
Abstract and summary · read the original at the source
In one page
Magnetized target fusion sits between the two mainstream routes: make a self-organised ring of magnetised plasma, then crush it with the inertia of a conducting shell. Michel Laberge and his colleagues at General Fusion — a 65-person company with 40 million dollars raised at the time of writing — describe how they intend to do the crushing with sound. Hundreds of pneumatic pistons, fired in a servo-controlled sequence, hammer the outside of a steel sphere filled with spinning liquid lead-lithium; the shock converges on a plasma held in the vortex at the centre, and geometric focusing turns one gigapascal at the wall into ten at the plasma surface. The paper is a progress report as much as a design: a hundred-kilogram hammer timed to two millionths of a second, a fourteen-piston test sphere commissioned in 2013, compact toroids accelerated past a hundred kilometres a second — and a frank account of the two places where the measurements do not yet match the model.
Why it matters hereChapter 12 keeps the ledger of fusion routes, and this is the one that trades expensive pulsed power for cheap compressed air — pneumatic energy storage at a fraction of a dollar per joule against more than two dollars for a capacitor bank. Chapter 9 gets the plasma: a self-confined compact toroid that has to hold its own magnetic shape for the whole implosion, inside a liner made of moving liquid metal.
What it claims
01Magnetized target fusion compresses a self-organised plasma with the inertia of a conductive liner until it meets the Lawson criterion, working in a regime of density and confinement time between magnetic and inertial confinement. General Fusion’s version drives that liner acoustically: modern servo controllers synchronise piston impacts precisely enough to raise a large-amplitude wave in a liquid metal liner and compress the target plasma in under 200 microseconds, which is matched to the lifetimes achievable in present self-organised plasma devices.Section I, Introduction
Designed, not yet built02The reactor concept in full: a pair of magnetised plasma rings is injected into the evacuated free-surface vortex at the centre of a rotating flow of molten lead-lithium eutectic, 83 per cent lead to 17 per cent lithium, and merges into one ring just before the wave arrives. The implosion reduces the cavity volume by three orders of magnitude, taking the plasma from ten to the twenty-second to ten to the twenty-fifth ions per cubic metre, from 0.1 to 10 kiloelectronvolts, and from 2 to 200 tesla. Fusion happens during the roughly 10 microseconds at peak compression; the neutrons heat the liquid metal directly, which is then pumped to a heat exchanger and a turbine.Section II, Fusion by acoustic implosion
Designed, not yet built03The economic argument is the driver. A 100 megajoule acoustic pulse is generated mechanically by a synchronised array of hundreds of pneumatically driven pistons striking the outside of the reactor sphere, and geometric focusing amplifies the pressure from 1 gigapascal to 10 at the liquid-plasma interface. Pneumatic energy storage at the hundred-megajoule scale can be had for under 0.2 dollars per joule, against more than 2 dollars per joule for the high-voltage pulsed power an electromagnetic implosion needs — and in a power plant the same working gas from the high-pressure side of the heat exchanger could drive the pistons directly, with no capacitor bank to recharge and switch.Section II, the paragraphs on the acoustic pulse and its practical advantages
Designed, not yet built04The liquid metal is chosen to do four jobs at once. Lead-lithium has a low melting point and low vapour pressure, breeds tritium, carries enough mass to hold the compression long enough, and has an acoustic impedance close to steel so the pulse crosses into it efficiently. The thick blanket shields the structure by cutting the neutron flux and softening the spectrum, and full coverage gives a tritium breeding ratio of 1.6 to 1.8 — the authors note the difficulty is likely to be too much tritium production rather than too little.Section II, the liner and blanket paragraphs
Designed, not yet built05The hardware existed and the numbers are measured. The driver element is a 100 kilogram, 0.3 metre hammer accelerated by compressed air down a one metre bore, braked electronically onto a stationary anvil; at 50 metres per second it carries 125 kilojoules, about 90 per cent of which goes into the acoustic wave. The HP3b test stand fired 850 impacts in a year including 39 at 50 metres per second, with four consecutive shots landing within 2 microseconds of the target time. In 2013 the Mini-Sphere was commissioned: a one metre sphere of liquid lead with 14 full-scale drivers in two rings of seven, a closed-loop pumping system holding a stable free-surface vortex, and ten shots fired under servo control with the collapse filmed by high-speed camera.Section III, Acoustic driver progress
On the bench now06What to watch, in the authors’ own words rather than a critic’s. On the liner side the vortex wall turns to spray soon after the pressure wave arrives — attributed to Richtmyer-Meshkov instability together with a poorly formed cavitation region — and because the Mini-Sphere is small its 14 pistons make a hyperboloidal rather than the wanted ellipsoidal wavefront, which likely enhances the instability rather than suppressing it; the stated target is a timing spread of plus or minus 10 microseconds at 20 metres per second impact. On the plasma side a compact toroid compressed fourfold in radius conserved poloidal flux and reached 3 tesla, but Thomson scattering gave an electron temperature of only 250 electronvolts, far below the adiabatic expectation, and the paper states plainly that the loss mechanism is not yet identified.Section III, the Mini-Sphere paragraphs; Section IV, the closing paragraphs on acceleration; Section VI, Summary
What to watch
Read it · abstract
Abstract
General Fusion is a 65-employee private company developing fusion energy with $40M of capital to date. This report will describe General Fusion’s design for an acoustically driven Magnetized Target Fusion (MTF) reactor concept. The advantages of this particular MTF scheme will be discussed. Our experimental and numerical work and results so far will be presented, as well as plans for future development.
Michel Laberge, Stephen Howard, D. E. Richardson, Aaron Froese, Victoria Suponitsky, M. Reynolds and David Plant, General Fusion Inc., Burnaby, British Columbia, Acoustically driven Magnetized Target Fusion, in the 2013 IEEE 25th Symposium on Fusion Engineering (SOFE). The paper is at doi.org/10.1109/sofe.2013.6635495.
(Abstract only — no other text of the paper is reproduced here; see the rights note above for what was read and where. On this site, the other standoff-driver route to magnetized target fusion, a liner assembled in flight from a ring of plasma guns, is at /library/stm-2410928ec7; the magnetized liner design at the Z facility, which crushes its target with pulsed power instead of pistons, is at /library/stm-57d0076dfb, with an unexpected pressure measured on that machine at /library/stm-4b4aa19d9f. The survey that places General Fusion among the routes to a power plant is at /library/stm-4fed2cae63, and the axioms this kind of privately funded programme is measured against are at /library/stm-ec19ca9fbf.)
The way in
https://doi.org/10.1109/sofe.2013.6635495PUBLICATION. Proceedings of the 2013 IEEE 25th Symposium on Fusion Engineering, copyright IEEE, which records no licence for it and answers automated retrieval with a challenge rather than content. WHAT WAS READ. General Fusion posts an author copy of this paper on its own site; the live address now returns not found, and the copy read for this page is the Internet Archive capture of 31 May 2023 of generalfusion.com/wp-content/uploads/2022/05/Laberge-2013-Acoustically-Driven-Magnetized-Target-Fusion.pdf — seven pages, read in full on 2026-09-08, and every claim below is located to one of its numbered sections. Because the copyright is IEEE’s, nothing beyond the abstract is reproduced here; the abstract is the paper’s own, identical in that copy and in the publisher’s deposited metadata. Two later open documents were read alongside it and are named where they are used rather than blended into the claims: the Los Alamos and General Fusion Cooperative Research and Development Agreement final report LA12C10675, released as LA-UR-23-33278, which records the joint work on a magnetized plasma target for the acoustic compression scheme; and Brennan and colleagues, A stable corridor for toroidal plasma compression (2021), read from Office of Scientific and Technical Information record 1809084. AUTHORS. Given names are expanded only where the publisher record confirms them — Michel Laberge, Stephen Howard, Aaron Froese, Victoria Suponitsky and David Plant; D. E. Richardson and M. Reynolds stand as recorded. All authors at General Fusion Inc., Burnaby, British Columbia; the corresponding address printed on the paper is Michael Delage’s. RELATED PAGES: see the cross-links at the foot of this page.
How to cite it
Michel Laberge, Stephen Howard, D. E. Richardson, Aaron Froese, Victoria Suponitsky, M. Reynolds, David Plant (2013) Acoustically driven Magnetized Target Fusion. doi:10.1109/sofe.2013.6635495
Where it sits in the curriculum
Lattice confinement fusionPlasmoids, charge clusters and the orbs