  Fluctuations in the boundary region of the Alcator C-Mod tokamak have been
analyzed using gas puff imaging data from a set of Ohmically heated plasma
density scan experiments. It is found that the relative fluctuation amplitudes
are modest and close to normally distributed at the separatrix but become
increasingly larger and intermittent towards the main chamber wall. The
frequency power spectra are nevertheless similar for all radial positions and
line-averaged densities. Predictions of a stochastic model, describing the
plasma fluctuations as a super-position of uncorrelated pulses, are shown to be
in excellent agreement with the measurements. This implies that the pulse
duration is the same, while the degree of pulse overlap decreases radially
outwards in the scrape-off layer. The model also describes the rate of
threshold level crossings, which provide novel predictions of plasma--wall
interactions due to transient transport events.
