Blar i forfatter "Theodorsen, Audun"

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    • SOL width and intermittent fluctuations in KSTAR 

      Garcia, Odd Erik; Kube, Ralph Arthur; Theodorsen, Audun; Bak, J. G.; Hong, SH; Kim, H.S.; KSTAR, project team; Pitts, RA (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 ...

    • Statistical properties of a filtered Poisson process with additive random noise: distributions, correlations and moment estimation 

      Theodorsen, Audun; Garcia, Odd Erik; Rypdal, Martin Wibe (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 ...

    • Statistical properties of fluctuation driven flows in the outboard mid-plane SOL of Alcator C-Mod 

      Kube, Ralph; Garcia, Odd Erik; Theodorsen, Audun; Kuang, Adam; Brunner, Dan; LaBombard, Brian; Terry, Jim L. (Conference object; Konferansebidrag, 2018)
      The scale length of the radial density profile in scrape-off layer plasmas has been shown to depend on the line-averaged plasma density. While first reported on AlcatorC-Mod, recent work verifies this phenomena in JET and ASDEX Upgrade. In low density plasmas with a sheath-limited SOL, the density profiles present a two-scale structure which allows the separation of the SOL into two distinct regions. ...

    • Statistical properties of intermittent fluctuations in the boundary of fusion plasmas 

      Theodorsen, Audun (Doctoral thesis; Doktorgradsavhandling, 2018-06-14)
      Fluctuation-induced plasma–wall interactions is a major concern for the next generation, high duty-cycle magnetic confinement fusion devices. The turbulence is generated in the outboard midplane transition region between the confined core plasma and the scrape-off layer where magnetic field lines intersect material walls. Here, filaments of hot and dense plasma, elongated in the field direction, ...

    • Statistical properties of the plasma fluctuations and turbulent cross-field fluxes in the outboard mid-plane scrape-off layer of Alcator C-Mod 

      Kube, Ralph; Garcia, Odd Erik; Theodorsen, Audun; Kuang, Adam; LaBombard, Brian; Terry, Jim L.; Brunner, Dan (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 ...

    • Stochastic modeling of blob-like plasma filaments in the scrape-off layer: Theoretical foundation 

      Losada, Juan Manuel; Theodorsen, Audun; Garcia, Odd Erik (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-04-25)
      A stochastic model for a superposition of uncorrelated pulses with a random distribution of amplitudes, sizes, and velocities is presented. The pulses are assumed to move radially with fixed shape and amplitudes decaying exponentially in time due to linear damping. The pulse velocities are taken to be time-independent but randomly distributed. The implications of a distribution of pulse amplitudes, ...

    • Stochastic modeling of scrape-off layer fluctuations 

      Kube, Ralph; Theodorsen, Audun; Garcia, Odd Erik; Brunner, Daniel; Kuang, Adam; LaBombard, Brian; Terry, James L. (Conference object; Konferansebidrag, 2017-08-24)
      1. Stochastic model of data time series <br> 2. Comparison to experimental measurements

    • Stochastic modelling of intermittent fluctuations in the scrape-off layer: Correlations, distributions, level crossings, and moment estimation 

      Garcia, Odd Erik; Kube, Ralph; Theodorsen, Audun; Pecseli, Hans (Journal article; Tidsskriftartikkel; Peer reviewed, 2016-05)
      A stochastic model is presented for intermittent fluctuations in the scrape-off layer of magnetically confined plasmas. The fluctuations in the plasma density are modeled by a super-position of uncorrelated pulses with fixed shape and duration, describing radial motion of blob-like structures. In the case of an exponential pulse shape and exponentially distributed pulse amplitudes, predictions are ...

    • Stochastic modelling of intermittent scrape-off layer plasma fluctuations 

      Theodorsen, Audun (Master thesis; Mastergradsoppgave, 2015-05-15)
      In 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 ...

    • Strongly intermittent far scrape-off layer fluctuations in Alcator C-Mod plasmas close to the empirical discharge density limit 

      Ahmed, Sajidah; Garcia, Odd Erik; Q Kuang, Adam; LaBombard, Brian; L Terry, James; Theodorsen, Audun (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-09-07)
      Intermittent plasma fluctuations in the boundary region of the Alcator C-Mod device were comprehensively investigated using data time-series from gas puff imaging and mirror Langmuir probe diagnostics. Fluctuations were sampled during stationary plasma conditions in ohmically heated, lower single null diverted configurations with scans in both line-averaged density and plasma current, with Greenwald ...

    • Universality of intermittent fluctuations in the Alcator C-Mod scrape-off layer 

      Kube, Ralph; Garcia, Odd Erik; Theodorsen, Audun; Brunner, Dan; Kuang, Adam; LaBombard, Brian; Terry, Jim L. (Conference object; Konferansebidrag, 2017)

    • Universality of Poisson-driven plasma fluctuations in the Alcator C-Mod scrape-off layer 

      Theodorsen, Audun; Garcia, Odd Erik; Kube, Ralph; LaBombard, Brian; Terry, James L. (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 ...