Bursty fluctuations in the scrape-off layer (SOL) of Alcator C-Mod have been
analyzed using gas puff imaging data. This reveals many of the same fluctuation
properties as Langmuir probe measurements, including normal distributed
fluctuations in the near SOL region while the far SOL plasma is dominated by
large amplitude bursts due to radial motion of blob-like structures.
Conditional averaging reveals burst wave forms with a fast rise and slow decay
and exponentially distributed waiting times. Based on this, a stochastic model
of burst dynamics is constructed. The model predicts that fluctuation
amplitudes should follow a Gamma distribution. This is shown to be a good
description of the gas puff imaging data, validating this aspect of the model.Comment: 8 pages, 6 figure