The feasibility of using D–3He and D–D fusion fuels

Fusion reactor fuel cycles based on the D–3He and D–D reactions have been advocated as alternatives to deuterium and tritium (D–T). In this paper we make a careful assessment of the feasibility of burning these alternative fuels in a fusion reactor. A zero-dimensional model of the energy balance including radial profile effects for plasma temperature and density with accurate algorithms for synchrotron and bremsstrahlung radiation losses is used to calculate the required plasma conditions. Radiation losses and other factors severely restrict the choice of fuel mixtures that can be brought to ignition—and even under the most favourable assumptions, ignition requires plasma conditions in terms of energy confinement time, density, temperature and beta that are significantly more demanding than the conditions required to burn D–T. These requirements are far beyond the best conditions that have been reached in any present-day magnetic confinement experiments. A very serious issue is the stringent limit on the maximum concentrations of impurities and helium ash that can be tolerated. We consider the extent to which neutrons are reduced and briefly discuss the prospects for direct conversion. Finally we look at the serious problem of supplying 3He fuel in sufficient quantities to sustain a worldwide fusion energy programme and discuss the limitations of lunar sources and the difficulties of manufacturing 3He from D–D.