Relationship between frequency power spectra and intermittent, large-amplitude bursts in the Alcator C-Mod scrape-off layer
arXiv:1702.01104 · doi:10.1088/1741-4326/aa7e4c
Abstract
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.
8 figures
References in corpus (7)
- Scrape-off layer turbulence in TCV: evidence in support of stochastic modelling
- Auto-correlation function and frequency spectrum due to a super-position of uncorrelated exponential pulses
- Statistical properties of a filtered Poisson process with additive random noise: Distributions, correlations and moment estimation
- Convergence of statistical moments of particle density time series in scrape-off layer plasmas
- Level crossings, excess times and transient plasma-wall interactions in fusion plasmas
- Amplitude and size scaling for interchange motions of plasma filaments
- SOL width and intermittent fluctuations in KSTAR
Cited by in corpus (7)
- Intermittent electron density and temperature fluctuations and associated fluxes in the Alcator C-Mod scrape-off layer
- Intermittent fluctuations in the Alcator C-Mod scrape-off layer for ohmic and high confinement mode plasmas
- Probability distribution functions for intermittent scrape-off layer plasma fluctuations
- Comparison between mirror Langmuir probe and gas puff imaging measurements of intermittent fluctuations in the Alcator C-Mod scrape-off layer
- Stochastic modelling of blob-like plasma filaments in the scrape-off layer: Theoretical foundation
- Numerical turbulence simulations of intermittent fluctuations in the scrape-off layer of magnetized plasmas
- Level crossings and excess times due to a super-position of uncorrelated exponential pulses