Study of turbulence-induced refraction of lower hybrid waves using synthetic scrape-off layer filaments

Biswas, Bodhi; Baek, Seung Gyou; Bonoli, P. T.; Shiraiwa, S.; Wallace, G.; White, Anne

doi:10.1088/1361-6587/abb0d5

Cited by 15 publications

(28 citation statements)

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“…2016; Biswas et al. 2020). Each filament is generated with a randomly picked and with a probability that satisfies the prescribed joint-p.d.f.…”

Section: Verification Of Sas-mc With Numeric Full-wave Solvermentioning

confidence: 99%

“…2010; Biswas et al. 2020). These models also do not account for asymmetric scattering, because they make the ray tracing approximation.…”

Section: Sas-mc Applied To Lower Hybrid Scatteringmentioning

confidence: 99%

“…(More details about this perturbation analysis can be found in Appendix A of Biswas et al. (2020), although in that derivation, terms were erroneously neglected, which led to the dropping of the term in the final ray tracing validity criterion.) At initial launching of the LH wave , but they can both grow to be much larger as the ray continues to propagate.…”

Section: Sas-mc Applied To Lower Hybrid Scatteringmentioning

confidence: 99%

“…Note that the parallel wave vector up-shift from PDI and the perpendicular wave vector rotation from scattering may both be required to bridge the LH spectral gap (Biswas et al. 2020). (The terms ‘perpendicular/parallel’ are used in relation to the local background magnetic field.…”

Section: Introductionmentioning

confidence: 99%

“…A recent study models LH scattering from coherent SOL filaments with ray tracing (Biswas et al. 2020). This results in an increased angle-broadening effect compared with previous models, which in turn leads to a relatively better match with experimental current drive measurement and reduced sensitivity to simulation parameters.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2021

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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 lower hybrid (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 launching for current drive. The resulting wave spectrum is asymmetrically broadened in angular wavenumber 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 the on-axis current and decrease in the off-axis peaks. This is attributed to a portion of the modified wave spectrum that is strongly dampened on-axis during the first pass.

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“…2016; Biswas et al. 2020). Each filament is generated with a randomly picked and with a probability that satisfies the prescribed joint-p.d.f.…”

Section: Verification Of Sas-mc With Numeric Full-wave Solvermentioning

confidence: 99%

“…2010; Biswas et al. 2020). These models also do not account for asymmetric scattering, because they make the ray tracing approximation.…”

Section: Sas-mc Applied To Lower Hybrid Scatteringmentioning

confidence: 99%

Section: Sas-mc Applied To Lower Hybrid Scatteringmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2021

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Interaction of radio frequency waves with cylindrical density filaments: scattering and radiation pressure

Valvis

Ram²,

Hizanidis³

2021

J. Plasma Phys.

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The propagation of radio-frequency (RF) waves in tokamaks can be affected by filamentary structures, or blobs, that are present in the edge plasma and the scrape-off layer. The difference in the permittivity between the surrounding plasma and interior of a filament leads to reflection, refraction and diffraction of the waves. This, in turn, can affect the power flow into the core of the plasma and reduce the efficiency of heating and/or current generation. The scattering of RF waves, lower hybrid, helicon and ion cyclotron waves, by a single cylindrical filament, embedded in a background plasma, is studied using a full-wave analytical theory developed previously (Ram & Hizanidis, Phys. Plasmas, vol. 23, 2016, 022504). The theory assumes that the plasma in and around a filament is homogeneous and cold. A detailed scattering analysis reveals a variety of common features that exist among the three distinctly different RF waves. These common attributes can be inferred intuitively based on an examination of the cold plasma dispersion relation. The physical intuition is a useful step to understanding experimental observations on scattering, as well as results from simulations that include general forms of edge plasma turbulence. While a filament can affect the propagation of RF waves, the radiation force exerted by the waves can influence the filament. The force on a filament is determined using the Maxwell stress tensor. In 1905, Poynting was the first to evaluate and measure the radiation force on an interface separating two different dielectric media (Poynting, London Edinburgh Dublin Philos. Mag. J. Sci., vol. 9, 1905, pp. 393–406). For ordinary light propagating in vacuum and incident on a glass surface, Poynting noted that the surface is ‘pulled’ towards the vacuum. In a magnetized cold plasma, there are two independent wave modes. Even if only one of these modes is excited by an RF antenna, a filament will couple power to the other mode: a consequence of electromagnetic boundary conditions. This facet of scattering has consequences on the radiation force that go beyond Poynting's seminal contribution. The direction of the force depends on the polarization of the incident wave and on the mode structure of the waves inside and in the vicinity of a filament. It can either pull the filament toward the RF source or push it away. For slow lower hybrid waves, filaments with densities greater than the ambient density are pulled in, while filaments with lower densities are pushed out, thereby enhancing the density in front of the antenna. In the case of fast helicon and ion cyclotron waves, the direction of the force depends on the plasma and wave parameters; in particular, on the ambient density. The radiation force, in all three frequency ranges, is large enough to affect the motion of a filament and could be measured experimentally. This also suggests the possibility of modifying the edge turbulence using RF waves.

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Verifying raytracing/Fokker–Planck lower-hybrid current drive predictions with self-consistent full-wave/Fokker–Planck simulations

et al. 2022

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Raytracing/Fokker–Planck (FP) simulations used to model lower-hybrid current drive (LHCD) often fail to reproduce experimental results, particularly when LHCD is weakly damped. A proposed reason for this discrepancy is the lack of ‘full-wave’ effects, such as diffraction and interference, in raytracing simulations and the breakdown of the raytracing approximation. Previous studies of LHCD using non-Maxwellian full-wave/FP simulations have been performed, but these simulations were not self-consistent and enforced power conservation between the FP and full-wave code using a numerical rescaling factor. Here, we have created a fully self-consistent full-wave/FP model for LHCD that is automatically power conserving. This was accomplished by coupling an overhauled version of the non-Maxwellian TORLH full-wave solver and the CQL3D FP code using the Integrated Plasma Simulator. We performed converged full-wave/FP simulations of Alcator C-Mod discharges and compared them with raytracing. We found that excellent agreement in the power deposition profiles from raytracing and TORLH could be obtained, however, TORLH had somewhat lower current drive efficiency and broader power deposition profiles in some cases. This discrepancy appears to be a result of numerical limitations present in the TORLH model and a small amount of diffractional broadening of the TORLH wave spectrum. Our results suggest full-wave simulation of LHCD is likely not necessary as diffraction and interference represented only a small correction that could not account for the differences between simulations and experiment.

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Study of turbulence-induced refraction of lower hybrid waves using synthetic scrape-off layer filaments

Cited by 15 publications

References 50 publications

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

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

Interaction of radio frequency waves with cylindrical density filaments: scattering and radiation pressure

Verifying raytracing/Fokker–Planck lower-hybrid current drive predictions with self-consistent full-wave/Fokker–Planck simulations

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