Deuterium-tritium fusion

Of the several fusion reactions, deuterium tritium fusion is the most feasible, as it has the lowest ignition temperature, 40 million°K. (See Reaction 1.) Deuterium comprises 0.15... 

Deuterium-tritium fusion is considered the most likely process to result in a fusion reactor suitable for electricity production. In this process, a confined gas of deuterium and tritium atoms must be heated to nearly 100,000,000 K. Each fusion of D with T produces a helium nucleus, or alpha particle, and a neutron. The 17.6 million electron volts (MeV) of energy released per reaction are substantial, but only 3.5 MeV are carried away by the charged particle—the more useable form of energy for electricity. Although the method is well understood, it is still highly inefficient much more energy must be put into the process than is produced. Fusion is not expected to be a viable source of power for humankind for at least the next 50 years. 

Fusion research currently relies on the deuterium-tritium fusion reaction to produce useable power, a method that is well understood but still highly ineKI dent—much more energy must be put into the process than is produced. Fusion is not expected to be a viable source of power for humankind for at least the next 50 years. 

Gamma-ray laser action is a further related field which has attracted much efforts [9.306], Laser-driven (inertial confinement) fusion using the largest laser installation is a huge research field for laser-nuclear interaction [9.307]. The laser energy requirements for conventional laser-driven deuterium-tritium fusion seem to be difficult to reach. This has stimulated the development of a modified concept, the /ast igniter scheme, where an extremely intense (petawatt) laser pulse is fired into the pre-compressed plasma [9.308]. 

Of the several fusion reactions, deuterium-tritium fusion is the most feasible, as it has the lowest ignition temperature, 4E7 "K. (See Reaction 1.) Deuterium comprises 0.15 percent of naturally occurring hydrogen, whereas tritium is produced by neutron fission of iithium-6 that is irradiated in a blanket surrounding a nuclear reactor core. Nuclide separation is required to produce the deuterium and possibly the lithium. The... 

The reactions of deuterium, tritium, and helium-3 [14762-55-17, He, having nuclear charge of 1, 1, and 2, respectively, are the easiest to initiate. These have the highest fusion reaction probabiUties and the lowest reactant energies. 

Another result of the cold-fusion epopee that was positive for electrochemistry are the advances in the experimental investigation and interpretation of isotope effects in electrochemical kinetics. Additional smdies of isotope effects were conducted in the protium-deuterium-tritium system, which had received a great deal of attention previously now these effects have become an even more powerful tool for work directed at determining the mechanisms of electrode reactions, including work at the molecular level. Strong procedural advances have been possible not only in electrochemistry but also in the other areas. 

To initiate such a D-T fusion reaction requires temperatures of 10-100 million degrees. Relatively large amounts of deuterium/tritium and/or lithium deuteride can be heated to such temperatures by a fission explosion where the temperature may be 108 K. (Tritium is generated in situ by the neutron bombardment of i during the fusion reaction by the reaction 6Li + n —> 3H + 4He + n + 17 MeV, thus making the overall fusion reaction 6Li + 2H —> 2 4He + 21.78 MeV). 

A single muon stopped in a target of deuterium-tritium mixture can catalyze more than 100 fusions, but this number is limited by two major bottle-necks. One is the rate at which a muon can go through the catalysis cycle before its decay (cycling rate), and another is a poisoning process called p-a sticking in which, with a probability u)s < 0.01, the muon gets captured after the fusion reaction to atomic bound states of the fusion product 4He, and hence lost from the cycle (see Section 5). 

Three promising fusion reactions are D-D (deuterium-deuterium) and D-T (deuterium-tritium) reactions ... 

Tritium is a very sensitive subject for public acceptance of fusion and will play a central role in the operation of a next-step experimental fusion facility, which will routinely use large amounts of tritium as fuel (e.g., 100 times more in ITER than in present experiments) in a mixture with deuterium. Tritium retention is a regulatory issue since the amount that can potentially be released in an accident sets the limits on plasma operation without removal. Fuel economy has never been an issue in deuterium-fuelled experiments and only recently have the limitations associated with the use of tritium, and its incomplete recovery in experiments in TFTR and in JET, brought the issue of fuel retention under closer scrutiny [56,57]. Table 12.3 provides a list of key quantities related to tritium in existing tokamaks and a next-step device [18,57-59]. 

The fusion reaction least difficult to initiate is the deuterium-tritium (DT) reaction which releases a 14.1 MeV neutron and a 3.5 MeV alpha particle. However, because neutrons activate the reactor structure, other fusion reactions have been considered. These reactions are either neutron free, or they produce fewer and less energetic neutrons. The required quality of confinement for these more desirable fusion reactions is much higher than for DT, and it is not yet clear if it will be achieved. Hence, fusion reactor designers have concentrated on the DT reaction for at least the first generation of fusion plants. 

The focus of contemporary fusion research is the deuterium-tritium reaction ... 

Only a small amount deuterium is required to fuel a fusion reactor. Natural sources of hydrogen contain 0.0156% deuterium. A metric ton (1000-kg) of hydrogen from any source contains 156 grams of deuterium. Tritium is unknown in nature however, the neutrons produced by fusion react with lithium to produce tritium. There is sufficient deuterium and lithium to provide energy for thousands of years. 

Several types of energy beams have been tested in research efforts to ignite inertial confined fusion reactions. Multiple laser beams, electron beams and heavy ion beams have been tested. All have shown that heating and compression is possible. Thus far, none have caused the release of more energy from the deuterium tritium pellet than was present in the original laser beams. 

While a deuterium-tritium (D-T) mix is the fuel of choice for sustained fusion research, tritium on Earth is scarce. Produced by cosmic ray protons colliding with nitrogen in the upper atmosphere, trace amounts are found in air and less abundantly in water.That is where lithium comes in. Bombarding lithium 6 or lithium 7 atoms with high-energy neutrons results in atoms of tritium and helium. 

Protium is a stable isotope and makes up more than 99.9% of naturally occurring hydrogen. Deuterium (D) can be isolated from hydrogen it can form compounds such as "heavy water," D2O. Heavy water is a potential source of deuterium for fusion processes. Tritium (T) is unstable, hence radioactive, and is a waste product of nuclear reactors. 

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