Lower hybrid wave excitation and propagation in the spherical tokamak Globus-M

Abstract

The problem of lower hybrid (LH) wave excitation and current drive (CD) in tokamaks with a small aspect ratio (spherical tokamaks) is discussed. It is proposed to solve this problem by exciting the waves slowed down in the poloidal rather than the toroidal direction. As a result, due to the strong poloidal inhomogeneity of the magnetic field in spherical tokamaks, even the waves with comparatively weak slowing down (N ≈ 3-5) excited by a waveguide antenna in the equatorial plane can penetrate into the dense plasma and be absorbed via the Landau mechanism. This approach was applied for modeling the LHCD experiments in the low aspect ratio tokamak Globus-M (R = 0.36 m, a 0 = 0.24 m, B 0 = 0.4 T, I p = 0.25 MA, vertical elongation k = 1.6, operating frequency 2.45 GHz). The modeling was carried out using four independent codes: (i) the self-consistent antenna coupling code GRILL3D, (ii) the ray-tracing code incorporating a specially developed ray-tracing technique including some corrections necessary in strongly inhomogeneous plasma, (iii) the 2D full-wave code WAVETOP2D and (iv) the Fokker-Plank code combined with the ray-tracing code allowing simulation of the driven current density profile. The results of simulations were cross-checked and appeared to be in a good agreement. It was demonstrated that the proposed scenario provides a possibility for the efficient LHCD in a spherical tokamak.

Fast synthetic X-mode Doppler reflectometry diagnostics for the full-f global gyrokinetic modeling of the FT-2 tokamak

“…were solved numerically by the full-wave code WaveTOP2D 33 initially developed for the ICR frequency range, modernized here and applied in the microwave frequency domain. The boundary conditions at the antenna were modeling the experimentally measured Gaussian wave beam focusing on air at the distance of 14 cm from the antenna where its diameter was equal to 1.5 cm in the poloidal direction.…”

Полноволновое Двумерное Моделирование Распространения И Поглощения Геликонов В Плазме Сферического Токамака Глобус-М2

“…Моделирование выполнялось с помощью двумерного полноволнового кода [12] в рамках модели двумернонеоднородной плазмы токамака Глобус-М2 с полным учетом тороидальных эффектов, формы полоидального сечения и магнитной конфигурации.…”

“…Здесь была введена обобщенная тороидальная система координат [12], привязанная к магнитным поверхностям, в которой ψ -это " потоковая" радиальная координата (ψ равно нулю на оси разряда и единице на границе плазмы), а θ и ϕ -полоидальный и тороидальный углы соответственно. В тороидальном направлении плазма считалась однородной, поэтому отдельные тороидальные моды n ϕ можно было рассматривать независимо друг от друга.…”

Influence of the probing wave phase modulation on the X-mode radial correlation Doppler reflectometry performance in the FT-2 tokamak

“…were solved numerically by full-wave code WaveTOP2D. 36 The boundary conditions at the antenna were modeling the Gaussian wave beam (experimentally measured in the range of not less than 12 dB for the probing power), focusing on air at the distance of 14 cm from the antenna where its diameter was equal to 1.5 cm in the poloidal direction. The infinite size of the beam in the toroidal direction (toroidal mode n ¼ 0) was assumed.…”