Broadband density fluctuation measurements using a heavy ion beam probe on the Texas Experimental Tokamak

Broad bandwidth (60 kHz ≤f≤500 kHz), long wavelength (k̄θ≤2 cm−1) density fluctuation measurements were made using a heavy ion beam probe on the Texas Experimental Tokamak (TEXT) [K. W. Gentle, Nucl. Technol./Fusion 1, 479 (1981)]. Fluctuation amplitudes and correlation length scalings do not correspond to linear or quasilinear drift wave theory. Power-weighted root-mean-square (rms) wave number estimates are much lower (〈k̄θ〉rmsρs≤0.1, ρs=[miTe]1/2/eB) than quasilinear theoretical expectations (k̄⊥ρs∼0.3). Core results indicate strong turbulence with a wave number spread, Δk∼k̄ at fixed frequency f, consistent with strong turbulence predictions, while edge results can be considered consistent with weak turbulence. In between the core and edge (0.6≤r/a≤0.8) is a transition region.