Neutral beam injector research and development at ORNL and LBL/LLL in the United States

Neutral beam injectors have been developed and applied successfully for injection heating of PLT and ISX-B plasmas. Present and near-future injection systems for PDX, ISX-C, DIII, MFTF, and TFTR are similar in principle, although scaled in beam energy, current, and pulse width to meet the machine requirements. In addition, as shown in recent calculations, an INTOR or ETF device will also utilize a positive-ion-based system with possible trade-offs between beam energy, current, and pulse length. That is, beam energies of about 100 keV are acceptable if the current and/or pulse length may be increased to appropriate values. Recent direct energy recovery experiments have shown that a positive-ion-based system can be expected to operate at an overall system efficiency of up to 50% if the beam energy is limited to a value below 75 keV/nucleon. For injection energy above 200 keV, a negative-ion-based neutral beam injector may be needed. In this paper we report the performance highlights of the existing ORNL and LBL/LLL beam systems and the necessary R and D needs for future high-efficiency, long-pulse beam systems