Increased power delivery from the DIII-D neutral beam injection system

The neutral beam system installed on the DIII-D tokamak uses eight 80-kV long pulse sources (LASs) mounted on four beamlines and was originally designed to deliver a nominal 12 MW of H⁰ power to a plasma for pulses of up to 5-s duration. Essentially, all source components are of a common design, making the DIII-D version conservative in its rated parameters. A neutron shield has recently been constructed around the torus hall, allowing D⁰ injection to become routine. Because deuterium beams have a better neutralization efficiency, the nominal power delivery per source has been measured to be approximately 2 MW (for a total of 16 MW) without any modifications. However, by reoptimizing the voltage gradients in the source, the perveance can be increased without degrading the optics. Key features of the neutral beam system are reviewed, and the techniques for raising the delivery power are summarized. The tentative costs of the techniques are included