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dc.contributor.advisorGarcia, Odd Erik
dc.contributor.authorTheodorsen, Audun
dc.date.accessioned2016-02-04T11:36:32Z
dc.date.available2016-02-04T11:36:32Z
dc.date.issued2015-05-15
dc.description.abstractIn the tokamak scrape-off layer, radial motion of blob-like structures is the dominant mechanism for transport of particles and heat. Fixed point probe measurements in the Tokamak à Configuration Variable scrape-off layer reveal highly intermittent fluctuations in the ion saturation current. These measurements are well described by a shot noise process with exponential pulse shapes, exponentially distributed pulse amplitude and pulses arriving according to a Poisson process. The statistical properties of this shot noise process is explored in this thesis. Characteristic functions and probability density functions of the shot noise process have been derived, as well as the joint probability density function between the resulting signal and its derivative. These probability density functions have then been used to derive a general model for the excess statistics of a shot noise process. This model has been explored using synthetically generated shot noise time series. Synthetically generated shot noise time series have also been used to compare results of conditional averaging using various pulse amplitude and waiting time distributions, as well as different pulse shapes. While the pulse shape is well preserved after conditional averaging, the pulse waiting time and amplitude distributions are not. Excess time statistics have been analyzed for the ion saturation current measured by a Langmuir probe at a fixed point in the Tokamak à Configuration Variable scrape-off layer. The general model gives a qualitatively better fit to the data from the measurements than the normal limit does. Probability density functions of the time above threshold per upcrossing have been computed, and reveal exponential tails. It is found that both the average time above threshold per upcrossing and the root mean square value of the time above threshold per upcrossing have very slow decay for large threshold values, underlining the importance of intermittent fluctuations for plasma-wall interactions for tokamak plasmas.en_US
dc.identifier.urihttps://hdl.handle.net/10037/8431
dc.identifier.urnURN:NBN:no-uit_munin_8002
dc.language.isoengen_US
dc.publisherUiT Norges arktiske universiteten_US
dc.publisherUiT The Arctic University of Norwayen_US
dc.rights.accessRightsopenAccess
dc.rights.holderCopyright 2015 The Author(s)
dc.subject.courseIDFYS-3900en_US
dc.subjectVDP::Mathematics and natural science: 400::Physics: 430::Space and plasma physics: 437en_US
dc.subjectVDP::Matematikk og Naturvitenskap: 400::Fysikk: 430::Rom- og plasmafysikk: 437en_US
dc.subjectShot noise processen_US
dc.subjectexcess time statisticsen_US
dc.subjectconditional averageen_US
dc.subjectlevel crossingsen_US
dc.subjectfiltered Poisson processen_US
dc.subjectintermittencyen_US
dc.subjectscrape-off layeren_US
dc.subjectplasma fluctuationsen_US
dc.subjecttokamaken_US
dc.subjectTokamak à Configuration Variableen_US
dc.subjectfusion energyen_US
dc.subjecttime series analysisen_US
dc.titleStochastic modelling of intermittent scrape-off layer plasma fluctuationsen_US
dc.typeMaster thesisen_US
dc.typeMastergradsoppgaveen_US


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