Blob interactions in 2D scrape-off layer simulations

Decristoforo, Gregor; Militello, F.; Nicholas, T.; Omotani, John; Marsden, Chris; Walkden, N.; Garcia, Odd Erik

doi:10.1063/5.0021314

Cited by 12 publications

(6 citation statements)

References 75 publications

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“…Further, it is assumed that s a b = 0.2 cm and Γ a b = 7. The correlation coefficient η = 0.9, signifying strong positive correlation between n b /n 0 and a b [50].…”

Section: Summary and Discussionmentioning

confidence: 97%

Spectral broadening from turbulence in multiscale lower hybrid current drive simulations

et al. 2022

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The scattering of lower hybrid (LH) waves due to scrape-off layer (SOL) filaments is investigated. It is revealed that scattering can account for the LH spectral gap without any ad hoc modification to the wave-spectrum. This is shown using a multiscale simulation approach which allows, for the first time, the inclusion of full-wave scattering physics in ray-tracing/Fokker-Planck calculations. In this approach, full-wave scattering probabilities are calculated for a wave interacting with a statistical ensemble of filaments. These probabilities are coupled to ray-tracing equations using radiative transfer (RT) theory. This allows the modeling of scattering along the entire ray-trajectory, which can be important in the multi-pass regime. Simulations are conducted for lower hybrid current drive (LHCD) in Alcator C-Mod, resulting in excellent agreement with experimental current and hard X-ray (HXR) profiles. A region in filament parameter space is identified in which the impact of scattering on LHCD is saturated. Such a state coincides with experimental LHCD measurements, suggesting saturation indeed occurs in C-Mod, and therefore the exact statistical properties of the filaments are not important.

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“…Further, it is assumed that s a b = 0.2 cm and Γ a b = 7. The correlation coefficient η = 0.9, signifying strong positive correlation between n b /n 0 and a b [50].…”

Section: Summary and Discussionmentioning

confidence: 97%

Spectral broadening from turbulence in multiscale lower hybrid current drive simulations

et al. 2022

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“…In the SOL of C-Mod, mirror Langmuir probe measurements reveal positively skewed PDFs of density fluctuations [31]. SOL fluid codes predict that filament width and density are positively correlated [32]. Therefore, the joint-PDF is reasonably well described by a positivelyskewed Gaussian PDF for each parameter (a b and n b /n 0 ) along with a positive bi-variate correlation.…”

Section: Effective Differential Scattering-width: σ Eff (θ)mentioning

confidence: 89%

A hybrid full-wave Markov chain approach to calculating radio-frequency wave scattering from Scrape-off Layer filaments

Biswas,

Shiraiwa,

Baek

et al. 2021

Preprint

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The interaction of radio-frequency (RF) waves with edge turbulence modifies the incident wave-spectrum, and can significantly affect RF heating and current drive in tokamaks. Previous LH scattering models have either used the weak-turbulence approximation, or treated more realistic, filamentary turbulence in the ray-tracing limit. In this work, a new model is introduced which retains full-wave effects of RF scattering in filamentary turbulence. First, a Mie-scattering technique models the interaction of an incident wave with a single Gaussian filament. Next, an effective differential scattering-width is derived for a statistical ensemble of filaments. Lastly, a Markov chain solves for the transmitted wave-spectrum in slab geometry. This model is applied to LH launch for current drive. The resulting wave-spectrum is asymmetrically broadened in wave-number angle-space. This asymmetry is not accounted for in previous LH scattering models. The modified wave-spectrum is coupled to a ray-tracing/Fokker-Planck solver (GENRAY/CQL3D) to study its impact on current drive. The resulting current profile is greatly altered, and there is significant increase in on-axis current and decrease in off-axis peaks. This is attributed to a portion of the modified wave-spectrum that strongly damps on-axis during first-pass.

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“…Future work will investigate the distribution of filament sizes and velocities by analysis of the velocity fluctuations and applying a blob tracking algorithm as described in Ref. 91.…”

Section: Discussionmentioning

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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Blob interactions in 2D scrape-off layer simulations

Cited by 12 publications

References 75 publications

Spectral broadening from turbulence in multiscale lower hybrid current drive simulations

Spectral broadening from turbulence in multiscale lower hybrid current drive simulations

A hybrid full-wave Markov chain approach to calculating radio-frequency wave scattering from Scrape-off Layer filaments

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

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