Muon-catalyzed nuclear fusion.
(1) A beam of negatively charged muons is produced and injected into a mixed fuel of deuterium and tritium, (2) resulting in the creation of many muonic tritium atoms (tµ). As muons are 207 times heavier than electrons, the muon orbits the nucleus at a much closer distance to the nucleus than electrons. Thus, tµ atoms are extremely small. (3) As the tµ atoms have no electric charge, they readily collide with deuterium atoms without being affected by repulsive electrical force. These collisions produce dtµ molecules, which consist of a muon, a deuterium nucleus and a tritium nucleus. (4) Similar to tµ atoms, dtµ molecules are extremely small. When d–t nuclear fusion occurs in these small molecules, large amounts of energy are released, accompanied by the production of α particles (helium nuclei) and neutrons. (5) The muon is freed and recycled in subsequent nuclear fusion reactions. (6) About 1% of the liberated muons, however, become stuck to helium nuclei.
Teiichiro Matsuzaki, Director of Japan’s RIKEN Facilities, describes the history and planned future work on Muon catalyzed nuclear fusion.
Background on the Muon and the Basics of Muon Catalyzed Fusion
The elementary particle known as a muon, however, provides a means of achieving nuclear fusion at sub-zero temperatures. “Using muons, we can achieve nuclear fusion in a comparatively small facility at reasonable cost,” says Teiichiro Matsuzaki, director of the RIKEN-RAL Muon Facility. Matsuzaki and scientists at the facility have been conducting unique experiments as part of fundamental research into the use of muons to develop industrially viable nuclear fusion technology.
The muon belongs to the lepton group of elementary particles, which includes electrons. It has a lifetime of 2.2µs, and a mass one-ninth that of a proton and 207 times that of an electron. There are positively charged muons and negatively charged muons. In a material, the positive muon acts as a ‘light’ proton, while the negative muon acts as a ‘heavy’ electron.
Muon-based nuclear fusion is conducted using negative muons. A mixed gas of deuterium and tritium is cooled to temperatures below around −250°C, causing the gas to form a liquid or solid. The injection of a beam of muons (µ) into the medium then generates muonic tritium atoms (tµ), which are similar to hydrogen atoms. As muons are 207 times heavier than electrons, the muon orbits the nucleus at a distance much shorter than that for electrons. Thus, tµ atoms are extremely small, and because the tµ atoms have no charge, they collide with deuterium atoms without being affected by repulsive electrical force. This process produces muonic deuterium–tritium molecules (dtµ), which are also similar to hydrogen atoms, and which have a nucleus consisting of a muon, a deuterium nucleus and a tritium nucleus. Similar to the tµ atom, the dtµ molecule is extremely small, which allows the deuterium and tritium nuclei to come into very close proximity, thus inducing d–t nuclear fusion.
After the occurrence of d–t nuclear fusion, the muon in the dt molecule is liberated and becomes available for the creation of a new dtµ molecule. Thus a chain of nuclear fusions occurs. This reaction is called ‘muon-catalyzed nuclear fusion’ because the muons act like a catalyst that drives nuclear fusion.
RIKEN Muon Facility
At the RIKEN–RAL Muon Facility, a beam of muons is injected into about 1 cc of fuel to induce d–t nuclear fusion at a rate of about one million times per second. In general, 5 GeV of energy is required to produce one muon. In the RIKEN–RAL Muon Facility, a single muon is capable of inducing d–t nuclear fusion 120 times before it decays, producing 2 GeV of energy. In other words, 5 GeV of energy is required to generate 2 GeV of energy, corresponding to an energy balance of 40%.
The scientific break-even point for achieving 100% energy balance will be achieved when a single muon can induce d–t nuclear fusion at least 300 times before decaying. Economic nuclear-fusion power generation will clearly require improved efficiency far exceeding the scientific break-even point. The efficiency level required is estimated to be 3–10 times higher than that for scientific break-even. This means that a single muon needs to induce d–t nuclear fusion 1,000–3,000 times before decaying.
A Path To Possible Success, Laser Condensed Muon Fuel
The key to successful research therefore lies in two points: how to strip the muons from the muonic helium atoms efficiently, and how to create dt molecules more efficiently.
If the fuel is made much denser, the muonic helium atoms could be stripped of their muons more easily because of the increased probability of collision with deuterium or tritium atoms. Furthermore, denser fuel will contribute to an increased probability of creating dtµ molecules by more frequently bringing muonic tritium and muonic deuterium atoms into close proximity, as well as increasing the frequency of nuclear fusion induced by a single muon and increasing the efficiency of the nuclear fusion cycle.
If muonic helium atoms can be completely stripped of their muons, at the present level of dtµ creation efficiency, a single muon could induce nuclear fusion 340 times before decaying, which will be close to the scientific break-even condition. Furthermore, if the fuel were five times denser than liquid hydrogen, a single muon could induce nuclear fusion as many as 1,200 times. For example, we could easily create a new fuel that is 5–10 times denser than liquid hydrogen by combining our process with laser-based inertial confinement fusion. I would very much like to undertake a joint study because there have been very few conventional studies on nuclear fusion involving the combination of different methods.
Recent studies by Matsuzaki and his team have shown that the efficiency of the nuclear fusion cycle improves as the temperature of the solid fuel is increased from 5 to 17 K (0 K = –273.15°C). We will attempt to increase the temperature of the solid fuel further to investigate how the efficiency of the nuclear fusion cycle might increase. If the temperature is increased too far, the solid fuel will melt and become a liquid. The fuel, however, stays solid up to temperatures of 30 K provided that the pressure is maintained above 1,000 atmospheres.
Matsuzaki and his team also have many other ideas. Controlling the molecular-excited state of the deuterium in the fuel by irradiating it with a laser beam may enhance the production of dtµ molecules. Furthermore, applying an electric field to the fuel may increase the efficiency of stripping the muons from the muonic helium atoms.
Muon Catalyzed fusion at wikipedia
Muon fusion is just one of several possible technology paths to commercial nuclear fusion.
IEC fusion has received sufficient funding, $8 million, for work to settle theoretical questions of viability over the next 18-24 months
General fusion (magnetized target fusion variant, has gotten about $20 million in private and Canadian goverment funding)
Lawrenceville Plasma (Focus fusion / Dense plasma focus, $1.2 million in funding)
Tri-alpha energy (colliding beam fusion, $40+ million in funding)
Helion Energy (also colliding beam fusion, 1/3 scale was developed with academic funding and needs $20 million for next phase)
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