Neutral beam injection has been shown to create field-reversed configuration plasmas on C-2W. Recent advances in optimization and control of eight neutral beam injectors help deliver customized current drive for a plethora of plasma regimes. The optimization of neutral beam injection (NBI) relies on in situ beam-characterization measurements and carefully executed experiments. During optimization, beam parameters are finely tuned to maximize the beam current injected into the plasma while minimizing gas bleed into the main plasma chamber. Precisely controlled power supplies and fast measurements enable feed-forward waveforms and real-time control of beam current and energy, beyond initial requirements. This includes beam energy modulations up to 7.5 keV (25 mean energy) at rates greater than 3 kHz and stable beam current (3). Subsequently, unique combinations of in phase and out of phase tuning of NBI modulations, in conjunction with the axisymmetric positioning of the tunable energy beams, are shown to enhance fast-ion effects or reduce energetic particle modes within the plasma. These methods are described herein and represent significant advances in NBI operation.
This paper describes advancements in neutral beam injection (NBI) for creating and controlling field-reversed configuration (FRC) plasmas. The researchers optimized the NBI system to precisely control beam parameters, enabling enhanced fast-ion effects and reduced energetic particle modes within the plasma.