Controlling DIII-D QH-Mode Particle and Electron Thermal Transport with ECH

Quiescent H-mode core particle transport and density peaking are locally controlled by modulated electron cyclotron heating (ECH) at $\rho\sim 0.2$. Gyrokinetic simulations show density gradient driven trapped electron modes (TEMs) are only unstable in the inner core, where the density profile flattens in response to ECH. Thus $\alpha$-heating could reduce density peaking, providing burn control. Density fluctuations from Doppler backscattering intensify at TEM wavenumbers $k_\theta\rho_s\sim 0.8$ during ECH, while new quasi-coherent modes are observed with adjacent toroidal mode numbers consistent with TEMs. Separately, ECH at two-deposition locations ($r/a\sim\rho =0.5$ \& 0.7) varied the electron temperature gradient. A jump in ``heat pulse'' diffusivity during the scan indicates a critical gradient was crossed.