  This paper presents the use of a novel modelling technique based around
intermittent transport due to filament motion, to interpret experimental
profile and fluctuation data in the scrape-off layer (SOL) of JET during the
onset and evolution of a density profile shoulder. A baseline case is
established, prior to shoulder formation, and the stochastic model is shown to
be capable of simultaneously matching the time averaged profile measurement as
well as the PDF shape and autocorrelation function from the ion-saturation
current time series at the outer wall. Aspects of the stochastic model are then
varied with the aim of producing a profile shoulder with statistical
measurements consistent with experiment. This is achieved through a strong
localised reduction in the density sink acting on the filaments within the
model. The required reduction of the density sink occurs over a highly
localised region with the timescale of the density sink increased by a factor
of 25. This alone is found to be insufficient to model the expansion and
flattening of the shoulder region as the density increases, which requires
additional changes within the stochastic model. An example is found which
includes both a reduction in the density sink and filament acceleration and
provides a consistent match to the experimental data as the shoulder expands,
though the uniqueness of this solution can not be guaranteed. Within the
context of the stochastic model, this implies that the localised reduction in
the density sink can trigger shoulder formation, but additional physics is
required to explain the subsequent evolution of the profile.

Plasma Physics