  A stochastic model is presented for a super-position of uncorrelated pulses
with a random distribution of amplitudes, sizes, velocities and arrival times.
The pulses are assumed to move radially with fixed shape and amplitudes
decaying exponentially in time due to linear damping. The pulse velocities are
taken to be time-independent but randomly distributed. The implications of a
distribution of and correlations between pulse sizes, velocities and amplitudes
are investigated. Expressions for the lowest order statistical moments,
probability density functions and correlation functions for the process are
derived for the case of exponential pulses and a discrete uniform distribution
of pulse velocities. The results describe many features of high average
particle densities, broad and flat average radial profiles, and
large-amplitude, intermittent fluctuations at the boundary region of
magnetically confined plasmas. The stochastic model elucidates how these
phenomena are related to the statistics of blob-like structures.

Plasma Physics