Testing instabilities and microturbulence in TEXT

Abstract

The physical relationship between naturally occurring large scale (m=2) Mirnov oscillations and small scale turbulence in the Texas Experimental Tokamak (TEXT) is described. Dependences on plasma profiles (e.g. density and potential), which are strongly perturbed in the vicinity of the magnetic islands, are unfolded. Theoretical expectations for tearing modes and electron drift waves are compared with the characteristics of the measured mode amplitudes and frequency spectra. The dispersion relation for the turbulent density fluctuations, which propagate in the electron diamagnetic drift direction, is observed to be consistent with that of electron drift wave theory when a Doppler shift due to E*B plasma rotation is included. The fluctuation magnitude is found to correlate with the electron density scale length in a manner following mixing length estimates