Effect of helicon RF injection on turbulence and transport in the pedestal and SOL regions of the DIII-D Tokamak*

Helicon waves are high harmonic fast waves (500-1500 MHz) designed for off-axis current drive in DIII-D and other tokamaks including DEMO. Helicon RF (~476 MHz) injection is found to modify the pedestal and SOL turbulence as well as the electron density profiles in H-mode plasmas. These modifications are seen 45-60° toroidally away from the helicon antenna with little-to-no change in turbulence 215° toroidally away, indicating a toroidally localized effect. GENRAY simulations of N_|| = 3 helicon indicate the wave makes at least two toroidal passes before it is fully absorbed. Flow velocities and density turbulence (k_θρ_s ≈ 0.15–0.61) amplitudes ñ (from Doppler backscattering) show an increase (~x10) in edge turbulent flow accompanied by smaller increases (≈10%) in the SOL ñ, with little-to-no change in flow velocities closer to the separatrix. Density profiles show an increase in density with a decrease in density gradient in the SOL during helicon injection, with T_e showing no change. Divertor floor Langmuir probes show a slight reduction in both electron density and temperature during helicon wave injection. Density profile and fluctuation changes are significant and their effect on RF propagation, coupling, transport, etc. will be reported on.