MHD-blob correlations in NSTX

This paper describes a study of the cross-correlations between edge fluctuations as seen in the gas puff imaging (GPI) diagnostic and low frequency coherent magnetic fluctuations (MHD) in H-mode plasmas in NSTX. The main new result was that large blobs in the scrape-off-layer were significantly correlated with MHD activity in the 3–6 kHz range in 21 of the 223 shots examined. There were also many other shots in which fluctuations in the GPI signal level and its peak radius Rpeak were correlated with MHD activity but without any significant correlation of the MHD with large blobs. The structure and motion of the MHD are compared with those of the correlated blobs, and some possible theoretical mechanisms for the MHD-blob correlation are discussed.