Blar i forfatter "Garcia, Odd Erik"

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    • 20 years of research on the Alcator C-Mod tokamak 

      Greenwald, Martin; Bader, A; Baek, S; Bakhtiari, M; Barnard, H; Beck, W; Bergerson, W; Bespamyatnov, I; Bonoli, P; Brower, D; Brunner, D; Burke, W; Candy, J; Churchill, M; Cziegler, I; Diallo, A; Dominguez, A; Duval, B; Edlund, E; Ennever, P; Ernst, D; Faust, I; Fiore, C; Fredian, T; Garcia, Odd Erik; Gao, C; Goetz, J; Golfinopoulos, T; Granetz, R; Grulke, O; Hartwig, Z; Horne, S; Howard, N; Hubbard, A; Hughes, J; Hutchinson, I; Irby, J; Izzo, V; Kessel, C; Labombard, B; Lau, C; Li, C; Lin, Y; Lipschultz, B; Loarte, A; Marmar, E; Mazurenko, A; McCracken, G; McDermott, R; Meneghini, O; Mikkelsen, D; Mossessian, D; Mumgaard, R; Myra, J; Nelson-Melby, E; Ochoukov, R; Olynyk, G; Parker, R; Pitcher, S; Podpaly, Y; Porkolab, M; Reinke, M; Rice, J; Rowan, W; Schmidt, A; Scott, S; Shiraiwa, S; Sierchio, J; Smick, N; Snipes, JA; Snyder, P; Sorbom, B; Stillerman, J; Sung, C; Takase, Y; Tang, V; Terry, J; Terry, D; Theiler, C; Tronchin-James, A; Tsujii, N; Vieira, R; Walk, J; Wallace, G; White, A; Whyte, D; Wilson, J; Wolfe, S; Wright, G; Wright, J; Wukitch, S; Zweben, S (Journal article; Tidsskriftartikkel; Peer reviewed, 2014)

    • Amplitude and size scaling for interchange motions of plasma filaments 

      Kube, Ralph; Wiesenberger, Matthias; Garcia, Odd Erik (Journal article; Tidsskriftartikkel; Peer reviewed, 2016-12-07)
      The interchange dynamics and velocity scaling of blob-like plasma filaments are investigated using a two-field reduced fluid model. For incompressible flows due to buoyancy, the maximum velocity is proportional to the square root of the relative amplitude and the square root of its cross-field size. For compressible flows in a non-uniform magnetic field, this square root scaling only holds ...

    • Apparent universality of 1/f spectra as an artifact of finite-size effects 

      Korzeniowska, Magdalena A.; Theodorsen, Audun; Rypdal, Martin Wibe; Garcia, Odd Erik (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-06-29)
      Power spectral density scaling with frequency f as 1/ f <sup>β</sup> and β ≈ 1 is widely found in natural and socioeconomic systems. Consequently, it has been suggested that such self-similar spectra reflect the universal dynamics of complex phenomena. Here, we show that for a superposition of uncorrelated pulses with a power-law distribution of duration times the estimated scaling exponents β¯ ...

    • Auto-correlation function and frequency spectrum due to a super-position of uncorrelated exponential pulses 

      Garcia, Odd Erik; Theodorsen, Audun (Peer reviewed; Journal article; Tidsskriftsartikkel, 2017-03)
      The auto-correlation function and the frequency power spectral density due to a super-position of uncorrelated exponential pulses are considered. These are shown to be independent of the degree of pulse overlap and thereby the intermittency of the stochastic process. For constant pulse duration and a one-sided exponential pulse shape, the power spectral density has a Lorentzian shape which is flat ...

    • Blob interactions in 2D scrape-off layer simulations 

      Decristoforo, Gregor; Militello, Fulvio; Nicholas, Thomas; Omotani, John; Marsden, Chris; Walkden, Nick; Garcia, Odd Erik (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-12-01)
      Interaction of coherent structures known as blobs in the scrape-off layer of magnetically confined plasmas is investigated. Isolated and interacting seeded blobs, as well as full plasma turbulence, are studied by two-dimensional numerical simulations. The features of the blobs (position, size, amplitude) are determined with a blob tracking algorithm, which identifies them as coherent structures with ...

    • Blob shapes in the scrape-off layer: Comparison of measurements to simulations 

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

    • Blob sizes and velocities in the Alcator C-Mod scrape-off layer 

      Kube, Ralph; Garcia, Odd Erik; LaBombard, Brian; Terry, J.L; Zweben, Stewart (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 ...

    • Blob Sizes and Velocities in the Alcator C-Mod Scrape-Off Layer 

      Kube, Ralph; Garcia, Odd Erik; LaBombard, Brian; Madsen, Jens; Terry, James L.; Zweben, Stewart (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 ...

    • Comparison between mirror Langmuir probe and gas-puff imaging measurements of intermittent fluctuations in the Alcator C-Mod scrape-off layer 

      Kube, Ralph; Theodorsen, Audun; Garcia, Odd Erik; Brunner, D; Labombard, B; Terry, James L. (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-10-30)
      Statistical properties of the scrape-off layer plasma fluctuations are studied in ohmically heated plasmas in the Alcator C-Mod tokamak. For the first time, plasma fluctuations as well as parameters that describe the fluctuations are compared across measurements from a mirror Langmuir probe (MLP) and from gas-puff imaging (GPI) that sample the same plasma discharge. This comparison is complemented ...

    • Convergence of statistical moments of particle density time series in scrape-off layer plasmas 

      Kube, Ralph; Garcia, Odd Erik (Journal article; Tidsskriftartikkel; Peer reviewed, 2015)

    • Effect of dynamical friction on interchange motion of plasma filaments 

      Kube, Ralph; Garcia, Odd Erik (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)

    • Estimation of statistical moments for single point measurements in the Scrape Off Layer 

      Kube, Ralph; Garcia, Odd Erik (Conference object; Konferansebidrag, 2014-03-17)

    • Fluctuation statistics in the scrape-off layer of Alcator C-Mod 

      Kube, Ralph; Theodorsen, Audun; Garcia, Odd Erik; LaBombard, Brian; Terry, James L. (Peer reviewed; Journal article; Tidsskriftsartikkel, 2016-03-30)
      We 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 ...

    • Intermittent electron density and temperature fluctuations and associated fluxes in the Alcator C-Mod scrape-off layer 

      Kube, Ralph; Garcia, Odd Erik; Theodorsen, Audun; Brunner, Daniel; Kuang, Adam; LaBombard, Brian; Terry, James L. (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 due to Lorentzian pulses in turbulent thermal convection 

      Decristoforo, Gregor; Theodorsen, Audun; Garcia, Odd Erik (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-08-03)
      Turbulent motions due to flux-driven thermal convection are investigated by numerical simulations and stochastic modeling. Tilting of convection cells leads to the formation of sheared flows and quasi-periodic relaxation oscillations for the energy integrals far from the threshold for linear instability. The probability density function for the temperature and radial velocity fluctuations in the ...

    • Intermittent fluctuations due to uncorrelated Lorentzian pulses 

      Garcia, Odd Erik; Theodorsen, Audun (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 ...

    • Intermittent fluctuations in the Alcator C-Mod scrape-off layer 

      Garcia, Odd Erik; Fritzner, Sindre Markus; Kube, Ralph; Cziegler, Istvan; LaBombard, Brian; Terry, Jim L. (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 ...

    • Intermittent fluctuations in the Alcator C-Mod scrape-off layer for ohmic and high confinement mode plasmas 

      Garcia, Odd Erik; Kube, Ralph; Theodorsen, Audun; Labombard, B; Terry, J.L (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 ...

    • Large amplitude blob propagation in the SOL of Alcator C-Mod and comparison to theoretical model 

      Kube, Ralph; Garcia, Odd Erik; LaBombard, Brian; Terry, James L.; Zweben, Stewart (Conference object; Konferansebidrag, 2012)

    • Level crossings and excess times due to a superposition of uncorrelated exponential pulses 

      Theodorsen, Audun; Garcia, Odd Erik (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-01-10)
      A well-known stochastic model for intermittent fluctuations in physical systems is investigated. The model is given by a superposition of uncorrelated exponential pulses, and the degree of pulse overlap is interpreted as an intermittency parameter. Expressions for excess time statistics, that is, the rate of level crossings above a given threshold and the average time spent above the threshold, are ...