Universality in scrape-off layer plasma fluctuations: Comparison of experiment to numerical simulations

Particle density time series, sampled in the outboard mid-plane scrape-off layer, are interspersed by large amplitude bursts due to radial propagation of plasma blobs. GPI and Langmuir probe time series measured in the Alcator C-Mod tokamak suggest that conditionally averaged wave forms of large amplitude bursts are well described by a double exponential function. Furthermore remains the ratio of the rise and fall e-folding time of the conditionally averaged wave form constant over a range of line-averaged plasma densities. In this contribution we compare this finding to results from numerical simulations. A two-dimensional drift-fluid model has been used to simulate the propagation of seeded plasma blobs in scrape-off layer plasmas for various initial amplitudes and cross-field sizes. Time traces of the particle density, sampled at a single point, are compared to the conditionally averaged waveform of the experimental data time series. The results are interpreted in the framework of a stochastic model which relates the statistical properties of the SOL fluctuations to the profile scale length.