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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 ...
Models for electrostatic drift waves with density variations along magnetic field lines
(Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
Drift waves with vertical magnetic fields in gravitational ionospheres are considered where the unperturbed plasma density is enhanced in a magnetic flux tube. The gravitational field gives rise to an overall decrease of plasma density for increasing altitude. Simple models predict that drift waves with finite vertical wave vector components can increase in amplitude merely due to a conservation of ...
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 ...
Intermittent fluctuations due to uncorrelated Lorentzian pulses
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-01-31)
Fluctuations due to a super-position of uncorrelated Lorentzian pulses with a random distribution of amplitudes and duration times are considered. These are demonstrated to be strongly intermittent in the limit of weak pulse overlap, resulting in large skewness and flatness moments. The characteristic function and the lowest order moments are derived, revealing a parabolic relationship between the ...
Power-law scaling of uncorrelated plasma bursts
(Conference object; Konferansebidrag, 2019-07)
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 ...
Intermittent electron density and temperature fluctuations and associated fluxes in the Alcator C-Mod scrape-off layer
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-04-10)
The Alcator C-Mod mirror Langmuir probe system has been used to sample data time series of fluctuating plasma parameters in the outboard mid-plane far scrape-off layer. We present a statistical analysis of one second long time series of electron density, temperature, radial electric drift velocity and the corresponding particle and electron heat fluxes. These are sampled during stationary plasma ...
Intermittent fluctuations in the Alcator C-Mod scrape-off layer for ohmic and high confinement mode plasmas
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-03-20)
Plasma fluctuations in the scrape-off layer of the Alcator C-Mod tokamak in ohmic and high confinement modes have been analyzed using gas puff imaging data. In all cases investigated, the time series of emission from a single spatially resolved view into the gas puff are dominated by large-amplitude bursts, attributed to blob-like filament structures moving radially outwards and poloidally. There ...
SOL width and intermittent fluctuations in KSTAR
(Journal article; Tidsskriftartikkel; Peer reviewed, 2016-12-27)
Radial profiles of the ion saturation current and its fluctuation statistics are presented from probe measurements in L-mode, neutral beam heated plasmas at the outboard mid-plane region of KSTAR. The results are consistent with the familiar two-layer structure, seen elsewhere in tokamak L-mode discharges, with a steep near-SOL profile and a broad far-SOL profile. The profile scale length in the ...