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dc.contributor.authorKube, Ralph
dc.contributor.authorTheodorsen, Audun
dc.contributor.authorGarcia, Odd Erik
dc.contributor.authorLaBombard, Brian
dc.contributor.authorTerry, James L.
dc.date.accessioned2017-03-22T09:34:11Z
dc.date.available2017-03-22T09:34:11Z
dc.date.issued2016-03-30
dc.description.abstractWe study long time series of the ion saturation current and floating potential, sampled by Langmuir probes dwelled in the outboard mid-plane scrape-off layer and embedded in the lower divertor baffle of Alcator C-Mod. A series of ohmically heated L-mode plasma discharges is investigated with line-averaged plasma density ranging from ${{\bar{n}}_{\text{e}}}/{{n}_{\text{G}}}=0.15$ to 0.42, where n G is the Greenwald density. All ion saturation current time series that are sampled in the far scrape-off layer are characterized by large-amplitude burst events. Coefficients of skewness and excess kurtosis of the time series obey a quadratic relationship and their histograms coincide partially upon proper normalization. Histograms of the ion saturation current time series are found to agree well with a prediction of a stochastic model for the particle density fluctuations in scrape-off layer plasmas. The distribution of the waiting times between successive large-amplitude burst events and of the burst amplitudes are approximately described by exponential distributions. The average waiting time and burst amplitude are found to vary weakly with the line-averaged plasma density. Conditional averaging reveals that the radial blob velocity, estimated from floating potential measurements, increases with the normalized burst amplitude in the outboard mid-plane scrape-off layer. For low density discharges, the conditionally averaged waveform of the floating potential associated with large amplitude bursts at the divertor probes has a dipolar shape. In detached divertor conditions the average waveform is random, indicating electrical disconnection of blobs from the sheaths at the divertor targets.en_US
dc.description.sponsorshipAcknowledgements: RK, OEG and AT were supported with financial subvention from the Research Council of Norway under grant 240510/F20. RK would like to thank D Brunner for providing the script used to create figure 1. Work partially supported by US DoE Cooperative agreement DE-FC02-99ER54512 at MIT using the Alcator C-Mod tokamak, a DoE Office of Science user facility. RK and OEG acknowledge the generous hospitality of the Plasma Science and Fusion Center at MIT during a sabbatical stay during which these experiments were performed.en_US
dc.descriptionLink to publishers version: 10.1088/0741-3335/58/5/054001en_US
dc.identifier.citationKube R, Theodorsen A, Garcia OE, LaBombard B, Terry JL. Fluctuation statistics in the scrape-off layer of Alcator C-Mod. Plasma Physics and Controlled Fusion. 2016;58:054001(5):1-13en_US
dc.identifier.cristinIDFRIDAID 1351564
dc.identifier.doi10.1088/0741-3335/58/5/054001
dc.identifier.issn0741-3335
dc.identifier.issn1361-6587
dc.identifier.urihttps://hdl.handle.net/10037/10823
dc.language.isoengen_US
dc.relation.journalPlasma Physics and Controlled Fusion
dc.relation.projectIDNorges forskningsråd: 240510en_US
dc.rights.accessRightsopenAccessen_US
dc.subjectVDP::Mathematics and natural science: 400en_US
dc.titleFluctuation statistics in the scrape-off layer of Alcator C-Moden_US
dc.typePeer revieweden_US
dc.typeJournal article
dc.typeTidsskriftsartikkel


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