High-Harmonic Fast Wave Driven H-mode Plasmas on NSTX

The launch of High‐Harmonic Fast Waves (HHFW) routinely provides auxiliary power to NSTX plasmas, where it is used to heat electrons and pursue drive current. H‐mode transitions have been observed in deuterium discharges, where only HHFW and ohmic heating, and no neutral beam injection (NBI), were applied to the plasma. The usual H‐mode signatures are observed. A drop of the Dα light marks the start of a stored energy increase, which can double the energy content. These H‐mode plasmas also have the expected kinetic profile signatures with steep edge density and electron temperature pedestal. Similar to its NBI driven counterpart — also observed on NSTX — the HHFW H mode has density profiles that feature “ears” in the peripheral region. These plasmas are likely candidates for long pulse operation because of the combination of bootstrap current, associated with H‐mode kinetic profiles, and active current drive, which can be generated with HHFW power.