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Localized electron cyclotron heating (ECH) can have a dramatic effect on neutral beam driven toroidicity induced Alfvén eigenmode (TAE) activity in DIII-D plasmas. In these experiments, ECH with varied current drive phasing was deposited at large radius near the location of TAEs that have been recently reported to locally stabilize ITG turbulence through the generation of sheared flows [1]. The impact of ECH depends drastically on location, with an increase in mode activity observed inside of the deposition location while a local reduction in some TAEs occurs near the deposition location. Modes that are stabilized return rapidly when electron cyclotron power is removed and the effect does not depend on current drive phasing, which indicates the minimal current driven at large radius does not play a large role. In some cases turbulence suppression persists through the EC injection period. In other cases, with EC injection inside of the TAE generated ITB, the electron temperature rises rapidly until the ITB collapses and both the TAEs and turbulence suppression cease. The rapid change in TAE activity with both EC turn-on and turn-off indicate electron collisional damping or electron Landau damping may play a role as opposed to current profile modification effects. To this end, NOVA-K calculations of TAE stability have been carried out for a range of conditions approximating those during a radial and power scan of ECH deposition in the target DIII-D equilibrium. Electron collisional and Landau damping are two of the dominant damping mechanisms found and a factor of three or more variation is predicted to be possible depending on deposition location and power.
*This work was supported by the US Department of Energy under DE-FC02-04ER54698 and DE-SC0026408 and DE-AC02-09CH11466
[1] X.D. Du, et al., Phys. Rev. Lett.66 135, 265101 (2025).