Now showing items 1-10 of 45
Unified transport scaling laws for plasma blobs and depletions
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-06-14)
We study the dynamics of seeded plasma blobs and depletions in an (effective) gravitational field. For incompressible flows, the radial center of mass velocity of blobs and depletions is proportional to the square root of their initial cross-field size and amplitude. If the flows are compressible, this scaling holds only for ratios of amplitude to size larger than a critical value. Otherwise, the ...
Level crossings and excess times due to a superposition of uncorrelated exponential pulses
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-01-10)
A well-known stochastic model for intermittent fluctuations in physical systems is investigated. The model is given by a superposition of uncorrelated exponential pulses, and the degree of pulse overlap is interpreted as an intermittency parameter. Expressions for excess time statistics, that is, the rate of level crossings above a given threshold and the average time spent above the threshold, are ...
Stochastic modeling of scrape-off layer fluctuations
(Conference object; Konferansebidrag, 2017-08-24)
1. Stochastic model of data time series <br> 2. Comparison to experimental measurements
Velocity scaling for filament motion in scrape-off layer plasmas
(Journal article; Tidsskriftartikkel; Peer reviewed, 2011)
Blob sizes and velocities in the Alcator C-Mod scrape-off layer
(Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
Gas-puff imaging data is used to investigate the dynamics of blob-like structures in the scrape-off layer of Alcator C-Mod. A blob-tracking algorithm is developed and used to compute blob propagation velocities and cross-field sizes for a series of discharges where the line-averaged particle density View the MathML source is varied. We find that the mean radial blob velocity increases from View the ...
20 years of research on the Alcator C-Mod tokamak
(Journal article; Tidsskriftartikkel; Peer reviewed, 2014)
Skewed Lorentzian pulses and exponential frequency power spectra
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-01-18)
Frequency power spectra due to a super-position of uncorrelated Lorentzian pulses with a random distribution of amplitudes are considered. For pulses with a constant duration, there is an exponential frequency spectrum which is independent of the degree of pulse overlap and the pulse amplitude distribution. The spectrum is furthermore shown to be unaffected by skewness of the Lorentzian pulses and ...
Probability distribution functions for intermittent scrape-off layer plasma fluctuations
(Journal article; Peer reviewed; Tidsskriftartikkel, 2018-01-24)
A stochastic model for intermittent fluctuations in the scrape-off layer of magnetically confined plasmas has been constructed based on a super-position of uncorrelated pulses arriving according to a Poisson process. In the most common applications of the model, the pulse amplitudes are assumed exponentially distributed, supported by conditional averaging of large-amplitude fluctuations in experimental ...
Statistical properties of a filtered Poisson process with additive random noise: distributions, correlations and moment estimation
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-04-19)
Filtered Poisson processes are often used as reference models for intermittent fluctuations in physical systems. Such a process is here extended by adding a noise term, either as a purely additive term to the process or as a dynamical term in a stochastic differential equation. The lowest order moments, probability density function, auto-correlation function and power spectral density are derived ...
Relationship between frequency power spectra and intermittent, large-amplitude bursts in the Alcator C-Mod scrape-off layer
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-08-21)
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 skewed towards the main chamber wall. The frequency power spectra are ...