As part of a study for a mirror fusion-fission hybrid reactor, a preliminary design for a 225-MW neutral beam injector of fast deuteriu m atoms at 100 kV and fast tritium atoms at 150 kV was prepared. The injector layout consists of four assemblies, each comprising 70 ion-sourc e modules mounted in a converging array. An efficient, long-lifetime cathode for the plasma sources is proposed. The requirements for ion extraction and acceleration are satisfied by a two-stage accel -decel-accel-decel grid system designed to operate within th e limitations imposed by beam space charge, beam optics, voltage breakdown, and grid bombardment by secondary ions and electrons. A low-temperature neutralizing cell followed by a system for recovery of the energy of the unneutralized fraction of the beam has been designed to provide an overall injector power efficiency greater than 70%. To maintain required pressures within th e acceleration assemblies, the neutralizers, the beam energy recovery systems, and the beam line itself, pumping systems capable of handling a total gas flow of 2400 Torr·litre·s−1 are required. Problems associated with magnetic shielding of the ion source assemblies from the reactor fringing field as well as the mounting of the accel-decel grids at high voltage and high temperature are evaluated.
Transport of realistic beams in ITER neutral beam injector accelerator