Intermittent fluctuations due to uncorrelated Lorentzian pulses

Garcia, Odd Erik; Theodorsen, Audun

doi:10.1063/1.5020555

Cited by 4 publications

(4 citation statements)

References 51 publications

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“…For example trapped electron mode turbulence with a strong dependence on collisions [16] does scale differently than ion temperature gradient (ITG) driven turbulence with adiabatic electrons in the collisionless limit [4,17]. However, when considering the influence of collisions [4,13], E × B shear [18] and β stabilisation physics [18] for ITG turbulence the expected scaling with main ion mass will change. A more complete account of the different physics mechanisms depending on the main ion mass can be found in [19].…”

Section: Introductionmentioning

confidence: 99%

The dependence of confinement on the isotope mass in the core and the edge of AUG and JET-ILW H-mode plasmas

et al. 2021

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Experiments in ASDEX Upgrade (AUG) and JET with the ITER-like wall (JET-ILW) are performed to separate the pedestal and core contributions to confinement in H-modes with different main ion masses. A strong isotope mass dependence in the pedestal is found which is enhanced at high gas puffing. This is because the ELM type changes when going from D to H for matched engineering parameters, which is likely due to differences in the inter ELM transport with isotope mass. The pedestal can be matched in H and D plasmas by varying only the triangularity and keeping the engineering parameters relevant for core transport the same. With matched pedestals ASTRA/TGLF (Sat1geo) core transport simulations predict the experimental profiles equally well for H and D. These core transport simulations show a negligible negative mass dependence and no gyro-Bohm scaling is observed. However, to match the experimental observations at medium β it is required to take the fast-ion dilution and rotation into account. This is not enough for high β plasmas where for the first time a profile match between H and D plasmas was achieved experimentally. Under these conditions quasilinear modelling with TGLF over predicts the transport in the core of H and D plasmas alike.

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Section: Introductionmentioning

confidence: 99%

The dependence of confinement on the isotope mass in the core and the edge of AUG and JET-ILW H-mode plasmas

et al. 2021

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“…12, this is better described using a skewed Lorentzian pulse as a fit function with duration 80 and skewness parameter 1 for the x SOL = 50 case. [87][88][89][90] The slightly elevated tails of the conditional burst shape is likely due to finite pulse overlap in the turbulence simulations. 12.…”

Section: Fluctuation Statisticsmentioning

confidence: 99%

Numerical turbulence simulations of intermittent fluctuations in the scrape-off layer of magnetized plasmas

Decristoforo,

Theodorsen,

Omotani

et al. 2021

Preprint

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Intermittent fluctuations in the boundary of magnetically confined plasmas are investigated by numerical turbulence simulations of a reduced fluid model describing the evolution of the plasma density and electric drift vorticity in the two-dimensional plane perpendicular to the magnetic field. Two different cases are considered, one describing resistive drift waves in the edge region and another including only the interchange instability due to unfavorable magnetic field curvature in the scrape-off layer. Analysis of long data time series obtained by single-point recordings are compared to predictions of a stochastic model describing the plasma fluctuations as a super-position of uncorrelated pulses. For both cases investigated, the radial particle density profile in the scrape-off layer is exponential with a radially constant scale length. The probability density function for the particle density fluctuations in the far scrape-off layer has an exponential tail. Radial motion of blob-like structures leads to large-amplitude bursts with an exponential distribution of peak amplitudes and the waiting times between them. The average burst shape is well described by a two-sided exponential function. The frequency power spectral density of the particle density is simply that of the average burst shape and is the same for all radial positions in the scrape-off layer. The fluctuation statistics obtained from the numerical simulations are in excellent agreement with recent experimental measurements on magnetically confined plasmas. The statistical framework defines a new validation metric for boundary turbulence simulations.

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“…where A k and t k are pulse amplitude and arrival time for the pulse labeled k, respectively, and K(T) is the number of pulses present in a time interval of duration T. In the case of Lorentzian pulses, the function ϕ is given by [39][40][41] ϕ(θ) = 1 π…”

Section: Lorentzian Pulsesmentioning

confidence: 99%

“…Recently, the exponential spectrum has been attributed to the presence of uncorrelated Lorentzian pulses in the temporal dynamics. [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] This includes the Lorenz model, which describes chaotic dynamics in Rayleigh-Bénard convection. [23][24][25][26][27][28][29][30] In two-dimensional thermal convection, it is well known that the convection rolls in a horizontally periodic domain can give rise to the spontaneous formation of strong mean flows through a tilting instability.…”

Section: Introductionmentioning

confidence: 99%

Intermittent fluctuations due to Lorentzian pulses in turbulent thermal convection

2020

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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 fluid layer changes from a normal distribution at the onset of turbulence to a distribution with an exponential tail for large fluctuation amplitudes for strongly driven systems. The frequency power spectral density has an exponential shape, which is a signature of deterministic chaos. By use of a novel deconvolution method, this is shown to result from the presence of Lorentzian pulses in the underlying time series, demonstrating that exponential frequency spectra can also persist in turbulent flow regimes.

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Intermittent fluctuations due to uncorrelated Lorentzian pulses

Cited by 4 publications

References 51 publications

The dependence of confinement on the isotope mass in the core and the edge of AUG and JET-ILW H-mode plasmas

The dependence of confinement on the isotope mass in the core and the edge of AUG and JET-ILW H-mode plasmas

Numerical turbulence simulations of intermittent fluctuations in the scrape-off layer of magnetized plasmas

Intermittent fluctuations due to Lorentzian pulses in turbulent thermal convection

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