Efficient High-Power High-Energy Neutral Beams for the Reference Mirror Reactor

The neutral beams for the reference mirror reactor are provided via four separate injectors using negative ions created by charge exchange in a cesium-vapor cell and neutralized by photodetachment. Each of the injectors delivers the equivalent of 1800 A of the desired mixture of 150-keV deuterium and tritium neutrals. Each injector consists of 23 ion sources of a modified Lawrence Berkeley Laboratory/Lawrence Livermore Laboratory type, with an associated cesium-vapor cell that converts 20 percent of the positive-ion output into negative ions D- and T-. The negative ions are accelerated to the desired energy and subsequently pass through a photodetachment cell that is continuously illuminated by eight columns of iteratively pulsed lasers. As much as 95 percent of the negative ions are stripped, producing fast neutrals that pass between the cryopumps and shielding into the reactor. Innovations required to attain an overall efficiency of 81.2 percent include a continuously operating cathode for the ion source, a negative-ion beam line with cooled gids, a high-voltage accelerator with insulators shielded from the neutron and gamma flux, cryopanels that cycle between pumping and outgassing modes, and recovery of the waste thermal energy and charged beam energy.