Bursts of turbulence associated with ELMs have been studied systematically in DIII-D with a multichannel phase contrast imaging (PCI) diagnostic, which is sensitive to the long poloidal wavelength components of the density fluctuations in the outer edge of the tokamak. A comparison of the temporal dynamics of the turbulence with the signature D_α signal from the divertor has revealed systematic differences between type Ⅰ and type Ⅲ ELMs: even though precursor fluctuations are sometimes seen before type ⅠELMs, the PCI signal level remains high until the peak in the D_α signal; by contrast, in type Ⅲ ELMs the fluctuation burst precedes the D_α peak by 0.4-0.6 ms.
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