Considerations in the Design of Electron-Beam-Induced Fusion Reactor Systems

Abstract

Electrical power generation by controlled fusion may provide a partial solution to the world’s long-term energy supply problem. Achievement of a fusion reaction requires the confinement of an extremely hot plasma for a time long enough to allow fuel burnup. Inertial confinement of the plasma may be possible through the use of tightly focused, relativistic electron beams to compress a deuterium-tritium (D-T) fuel pellet. A power balance analysis applied to a conceptual electron-beam fusion power plant indicates that energy gains of between 5 and 16 are required from the fuel pellet for economic feasibility. To deliver an average power of 100 MW(e), the reactor must operate at a pulse rate of ∼35 Hz, assuming an electron-beam energy of 1 MJ per pulse. The use of a fusion-fission hybrid reactor substantially relaxes the pellet gain requirement, and allows breakeven plant operation at near unit pellet gain. Calculations show that x rays and ions will comprise an important part of the total energy release (30% for a pellet gain of 7.9). The x-ray radiation has an ∼350-eV blackbody spectrum. The energy of ions from the gold shell surrounding the D-T fuel lies between 100 and 500 keV. Consideration of the response of diode and first-wall materials to the incident x-ray and ion fluxes shows that wet walls of lithium or tin over niobium are not desirable, due to spallation or other stress wave damage, engineering complexity, and excessive materials usage and cost. A solid wall protected by a graphite cloth shield offers the maximum protection to the surrounding blanket structure.