Level crossings, excess times, and transient plasma–wall interactions in fusion plasmas

Theodorsen, Audun; Garcia, Odd Erik

doi:10.1063/1.4947235

Cited by 25 publications

(67 citation statements)

References 18 publications

(41 reference statements)

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“…VII. Based on the foregoing discussion of pulse propagation, it is of interest to consider a stochastic process given by the super-position of a random sequence of K pulses [34][35][36][37][38][39] …”

Section: A Super-position Of Pulsesmentioning

confidence: 99%

“…[11][12][13][14][15][23][24][25][26][27][28][29][30][31][32] The present study incorporates these features in a stochastic model for intermittent plasma fluctuations in the SOL, described as a super-position of uncorrelated pulses. [34][35][36][37][38][39] This model explains many of the salient experimental findings and empirical scaling relations, including broad plasma profiles and large fluctuation levels, skewed and flattened probability density functions, and a parabolic relation between the skewness and flatness moments. The latter has been observed in the boundary region of numerous experiments on magnetized plasmas.…”

Section: Introductionmentioning

confidence: 99%

“…The relations given in Eq. (39) imply that there is a parabolic relation between the skewness and flatness moments 37…”

Section: B Skewness and Flatnessmentioning

confidence: 99%

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

et al. 2016

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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 given for the lowest order moments, probability density function, auto-correlation function, level crossings, and average times for periods spent above and below a given threshold level. Also, the mean squared errors on estimators of sample mean and variance for realizations of the process by finite time series are obtained. These results are discussed in the context of single-point measurements of fluctuations in the scrape-off layer, broad density profiles, and implications for plasma--wall interactions due to the transient transport events in fusion grade plasmas. The results may also have wide applications for modelling fluctuations in other magnetized plasmas such as basic laboratory experiments and ionospheric irregularities. Published by AIP Publishing.

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Section: A Super-position Of Pulsesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2016

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“…The case of a one-sided exponential pulse function is readily generalized to a pulse shape that is continuous by introducing a finite pulse rise time, 79,82,88 …”

Section: B Two-sided Exponential Pulsementioning

confidence: 99%

“…A n and the mean value for the process is Φ = γ A and the variance is Φ 2 rms = γ A 2 /2. For both one-and two-sided exponential pulses, the characteristic function is C Φ (u) = (1 + iu A ) γ and the probability density function for the random variable is a Gamma distribution 85,86,88 …”

Section: Appendix A: Probability Densitiesmentioning

confidence: 99%

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

Garcia

Theodorsen

2017

Physics of Plasmas

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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 for low frequencies and a power law at high frequencies. The algebraic tail is demonstrated to result from the discontinuity in the pulse function. For a strongly asymmetric two-sided exponential pulse shape, the frequency spectrum is a broken power law with two scaling regions. In the case of a symmetric pulse shape, the power spectral density is the square of a Lorentzian function. The steep algebraic tail at high frequencies in these cases is demonstrated to follow from the discontinuity in the derivative of the pulse function. A random distribution of pulse durations is shown to result in apparently longer correlation times but has no influence on the asymptotic power law tail of the frequency spectrum. The effect of additional random noise is also discussed, leading to a flat spectrum for high frequencies. The probability density function for the fluctuations is shown to be independent of the distribution of pulse durations. The predictions of this model describe the variety of auto-correlation functions and power spectral densities reported from experimental measurements in the scrape-off layer of magnetically confined plasmas.

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On the role of integrated computer modelling in fusion technology

Smolentsev¹,

Spagnuolo²,

Serikov³

et al. 2020

Fusion Engineering and Design

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To assure self-sufficiency of the fusion reactor with regard to tritium (by producing, from lithium, at least the same amount of tritium as consumed in the plasma) 2) To convert fusion energy into heat (to produce electricity by using a turbinedriven generator) 3) To act as a radiation barrier (such that the components behind the breeding blanket receive the lowest possible amount of radiation) The blanket/FW is an in-vessel component located between vacuum vessel and plasma.

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Level crossings, excess times, and transient plasma–wall interactions in fusion plasmas

Cited by 25 publications

References 18 publications

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

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

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

On the role of integrated computer modelling in fusion technology

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