Limits of applicability of the quasilinear approximation to the lower hybrid wave-plasma interaction

Pavlo, P.; Krlín, L.

doi:10.1088/0741-3335/41/4/006

Cited by 7 publications

(12 citation statements)

References 14 publications

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“…We note that Ref. [8] presented a relativistic extension of the exact nonlinear results of [5][6][7]. Second, we show that the standing wave interaction can be approximated by the "simplified" version of the Fermi-Ulam map [3], which we here generalize to relativistic electron velocities.…”

Section: Introductionmentioning

confidence: 55%

“…To do so, we, first, extend our previous work [4][5][6][7][8] on electron phase space stochasticity caused by electrons repeatedly passing through a spatially localized travelling lower hybrid (LH) wave to the case of electrons passing through a standing wave. We note that Ref.…”

Section: Introductionmentioning

confidence: 99%

“…Most of the transmitted power ends up in non-propagating eigenmodes, only 10% propagates in opposite directions along resonance cones, which due to the lack of phasing also forms a standing wave pattern at the antenna mouth, where the ~MeV electrons were observed [1]. The standing wave field can be described by a relativistic nonconservative and non-autonomous Hamiltonian, which, in contrast to the case of a travelling plane wave with a rectangular envelope [5][6][7][8], is not conserved.…”

Section: Introductionmentioning

confidence: 99%

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Lower hybrid wavepacket stochasticity revisited

Fuchs¹,

Laqua

Krlín³

et al. 2014

AIP Conference Proceedings

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Abstract. Analysis is presented in support of the explanation in Ref. [1] for the observation of relativistic electrons during Lower Hybrid (LH) operation in EC pre-heated plasma at the WEGA stellarator [1,2]. LH power from the WEGA TE11 circular waveguide, 9 cm diameter, un-phased, 2.45 GHz antenna, is radiated into a B 0.5 T, n e 5x10 17 1/m 3 plasma at T e 10 eV bulk temperature wth a EC generated 50 keV component [1]. The fast electrons cycle around flux or drift surfaces essentially without collisions and repeatedly interact with the rf field close to the antenna mouth, gaining energy in the process. Our antenna calculations reveal a standing electric field pattern at the antenna mouth, with which we formulate the electron dynamics via a relativistic Hamiltonian. A simple approximation of the equations of motion leads to a relativistic generalization of the areapreserving Fermi-Ulam (F-U) map [3], allowing phase-space global stochasticity analysis. At typical WEGA plasma and antenna conditions, the F-U model predicts an LH driven current of about 230 A, at about 225 W of dissipated power, in good agreement with the measurements and analysis reported in [1].

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Section: Introductionmentioning

confidence: 55%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Lower hybrid wavepacket stochasticity revisited

Fuchs¹,

Laqua

Krlín³

et al. 2014

AIP Conference Proceedings

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“…We have shown that the broadening of resonance observed in [1] at high electric field amplitudes is due to the overlap of neighbouring spatial modes. Further, a model of interaction of spatially localized LHW with electrons has been proposed.…”

Section: Discussionmentioning

confidence: 82%

“…In Ref. [1], we have compared this value, for a narrow spectrum of waves, with the quasilinear one [2],…”

Section: Introductionmentioning

confidence: 99%

Nonlinear effects in lower hybrid heating and current drive

Pavlo

Krlín

2000

Czech. J. Phys.

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Lower Hybrid Current Drive in High Aspect Ratio Tokamaks

Peysson

Mazon²,

Artaud³

et al. 2020

J Fusion Energ

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A multi-machine study has been carried out to investigate the impact of a strongly bounded wave propagation domain on the Lower Hybrid current drive, a condition which occurs principally in high aspect ratio tokamaks. In this regime, the condition of kinetic resonance can be far above the upper boundary of the propagation domain, and may not be achieved by the usual toroidal upshift. Therefore no tail of fast electrons can be pulled out from the thermal bulk. Nevertheless, while tokamak plasmas are in principle almost transparent to the wave in this regime so-called "unbridgeable spectral gap", full current drive is well achieved for the two tokamaks considered in this study, TRIAM-1M [H. Zushi, et al., Nucl. Fusion 43 (2003) 1600] and WEST [C. Bourdelle, et al., Nucl. Fusion 55 (2015) 063017], both characterized by a very large aspect ratio R/a > 5.5. The case of the high aspect ratio tokamak HL-2A [Y. Liu et al. Nucl. Fusion 45 (2005) S239] for which the wave propagation domain has also an upper boundary, but close to the resonance condition, is considered by comparison. First principles modeling of the rf-driven current and the fast electron bremsstrahlung using the ALOHA/C3PO/LUKE/R5-X2 chain of codes shows unambiguously that the spectral gap must be already filled at the separatrix in order to reproduce quantitatively observations and some important parametric dependencies. This result is an important milestone in the physics understanding of the Lower Hybrid current drive, highlighting the existence of a powerful and likely universal alternative mechanism to bridge the spectral gap, that is not related to toroidal magnetic refraction. With an initially broad power spectrum, lobes with low parallel refractive indexes that carry most of the plasma current can be absorbed in almost single pass, restoring the full validity of the ray-tracing approximation for describing the propagation of the Lower Hybrid wave in cold plasmas.

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Limits of applicability of the quasilinear approximation to the lower hybrid wave-plasma interaction

Cited by 7 publications

References 14 publications

Lower hybrid wavepacket stochasticity revisited

Lower hybrid wavepacket stochasticity revisited

Nonlinear effects in lower hybrid heating and current drive

Lower Hybrid Current Drive in High Aspect Ratio Tokamaks

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