Scaling of edge magnetic fluctuations In DIII-D L-mode

Magnetic fluctuations at the divertor hit point were investigated during the L-mode near L-H transitions in DIII-D divertor discharges. These fluctuations show broad-band frequency spectra (15 approximately 35 kHz) with toroidal coherency (0.4 approximately 0.8) and rotate in the electron diamagnetic dift direction. The amplitude and the peak frequency follow different scalings. The parameter dependence of the amplitude is compared with the prediction of the microtearing and drift balloning modes. Both modes are expected to be suppressed with increasing edge electron temperature gradient in the H-mode. The parameter scalings are more consistent with the prediction of drift ballooning modes than they are with the microtearing modes. The scaling of the frequency suggests that the peak frequency is the electron diamagnetic drift frequency for n = 1 and m > 5.