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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
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 ...
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 ...
Statistical properties of the plasma fluctuations and turbulent cross-field fluxes in the outboard mid-plane scrape-off layer of Alcator C-Mod
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-12-29)
The Alcator C-Mod mirror Langmuir probe diagnostic is used to characterize plasma fluctuations in the outboard mid-plane scrape-off layer (SOL). Ohmically heated L-mode plasmas with Greenwald fractions from 0.1 to 0.45 are analyzed. In plasmas with a low line-averaged core density, the radial profiles of the average electron density and temperature feature a two-scale structure with a strong gradient ...
Large amplitude blob propagation in the SOL of Alcator C-Mod and comparison to theoretical model
(Conference object; Konferansebidrag, 2012)
Blob Sizes and Velocities in the Alcator C-Mod Scrape-Off Layer
(Conference object; Konferansebidrag, 2012)
A new blob-tracking algorithm for the GPI diagnostic installed in the outboard-midplane of Alcator C-Mod is developed. I t tracks large-amplitude fluctuations propagating through the scrape-off layer and calculates blob sizes and velocities. We compare the results of this method to a blob velocity scaling from a simple blob-model for sheath-connected blobs. We further present initial results from a ...
Intermittent fluctuations in the Alcator C-Mod scrape-off layer
(Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
Fluctuations in the boundary region of the Alcator C-Mod tokamak have been analyzed using gas
puff imaging data. It is found that the fluctuation amplitudes in the near scrape-off layer follow a
normal distribution while the far scrape-off layer fluctuations are dominated by large amplitude
bursts due to radial motion of blob-like structures and have a positively skewed and flattened
amplitude ...
Plasma fluctuations in the scrape-off layer and at the divertor target in Alcator C-Mod and their relationship to divertor collisionality and density shoulder formation
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-03-15)
Experiments indicate that the formation of density shoulders in the far scrape-off layer (SOL) is associated with an increase in cross-field transport and the propagation of coherent structures of high density known as blobs. It has been suggested that far SOL divertor collisionality (Λ<sub>div</sub>) may be a controlling parameter in this physics, which could be challenging for heat flux mitigation ...
Outlier classification using autoencoders: Application for fluctuation driven flows in fusion plasmas
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-01-16)
Understanding the statistics of fluctuation driven flows in the boundary layer of magnetically confined plasmas is desired to accurately model the lifetime of the vacuum vessel components. Mirror Langmuir probes (MLPs) are a novel diagnostic that uniquely allow us to sample the plasma parameters on a time scale shorter than the characteristic time scale of their fluctuations. Sudden large-amplitude ...
Universality of Poisson-driven plasma fluctuations in the Alcator C-Mod scrape-off layer
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-12-18)
Large-amplitude, intermittent fluctuations are ubiquitous in the boundary region of magnetically confined plasmas and lead to detrimental plasma-wall interactions in the nextgeneration, high duty cycle fusion power experiments. Using gas puff imaging data time
series from the scrape-off layer in the Alcator C-Mod device, it is here demonstrated that
the large-amplitude fluctuations can be described ...