Electron Cyclotron Resonance Heating in Spherical Plasmas: O-X-EBW Mode Conversion in MAST

Using a full wave solution, the O-X-EBW mode conversion is examined for density and magnetic profiles in MAST. The effects of magnetic shear and the sharp density pedestal for H-mode operation are considered with an eye to understanding both electron cyclotron emission (ECE) and electron cyclotron resonance heating (ECRH)

On O-X mode conversion in 2D inhomogeneous plasma with a sheared magnetic field

The conversion of an ordinary wave to an extraordinary wave in a 2D inhomogeneous slab model of the plasma confined by a sheared magnetic field is studied analytically.Comment: sub. to PPC

TOPLHA: an accurate and efficient numerical tool for analysis and design of LH antennas

This paper presents a self-consistent, integral-equation approach for the analysis of plasma-facing lower hybrid (LH) launchers; the geometry of the waveguide grill structure can be completely arbitrary, including the non-planar mouth of the grill. This work is based on the theoretical approach and code implementation of the TOPICA code, of which it shares the modular structure and constitutes the extension into the LH range. Code results are validated against the literature results and simulations from similar code

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

The fast linear (Born approximation) version of the X-mode Doppler reflectometry (DR) synthetic diagnostics is developed in the framework of the ELMFIRE global gyrokinetic modeling of the FT-2 tokamak ohmic discharge. The DR signal frequency spectra and the dependence of their frequency shift and shape on the probing antenna position are computed and shown to be similar to those measured in the high magnetic field side probing DR experiment at the FT-2 tokamak. The fluctuation poloidal velocities are determined using the DR experiment and synthetic diagnostics and shown to be within 15%. However, the computed and measured dependences of the DR signal power on the antenna position appear to be different presumably due to underestimation of the small-scale trapped electron mode turbulence component in the measurement region by the code.Peer reviewe

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

The cross-correlation function of high field side radial correlation X-mode Doppler reflectometry (DR) measured in the FT-2 tokamak experiment is shown to be a factor of three narrower than that computed using the fast linear (Born approximation) version of the X-mode DR synthetic diagnostics developed in the framework of the ELMFIRE global gyrokinetic modeling of the FT-2 ohmic discharge. This difference is observed in spite of the fact that the computed DR signal frequency spectra are shown to be similar to those measured. A modest phase modulation of the probing and backscattering waves by the long-scale turbulent density fluctuations is shown, both experimentally and in computation, to be responsible for the observed effect.Peer reviewe

Investigation of nonlinear effects in Doppler reflectometry using full-wave synthetic diagnostics

International audienceIn this work, Doppler reflectometry (DR) and radial correlation DR (RCDR) nonlinear scattering effects were studied using full-wave modeling and a set of representative FT-2 tokamak turbulences as inputs. Narrowing of the RDCR correlation function and widening of the DR poloidal wavenumber spectrum are demonstrated. An effect on the dependence of the DR signal frequency shift on the probing wavenumber is found, namely, this dependence "linearizing" in the nonlinear scattering regime. Nonlinear effects are shown to be weaker for O-mode probing than for X-mode probing, while a faster transition to nonlinear regime is demonstrated for RCDR compared to DR in both probing scenarios

Validation of full-f global gyrokinetic modeling results against the FT-2 tokamak Doppler reflectometry data using synthetic diagnostics

International audienceTwo versions of the X-mode Doppler reflectometry (DR) synthetic diagnostics are developed within the framework of the ELMFIRE global gyrokinetic modeling of the FT-2 tokamak ohmic discharge. In the 'fast' version the DR signal is computed in the linear theory approximation using the reciprocity theorem, utilizing the probing wave field pattern provided by computation and taking into account the 2D plasma inhomogeneity effects; whereas the alternative 'slow' version DR synthetic diagnostic is based on the full-wave code IPF-FD3D describing the probing and scattered wave propagation in turbulent plasma. The DR signal frequency spectra and the dependence of their frequency shift, width and shape on the probing antenna position are computed and shown to be similar to those measured in the high-field side probing DR experiment at the FT-2 tokamak. The geodesic acoustic mode characteristics provided by the measurements and by the synthetic DR are close within a 12% accuracy. However, a substantial difference was found in the decay of the DR signal cross-correlation functions with growing frequency shift in the probing wave channels. The quick decrease in the radial correlation DR coherence observed in the experiment and full-wave synthetic diagnostic, compared to the fast synthetic DR, is attributed to the nonlinear effect of the probing wave phase modulation by the turbulence in the former two cases. The variation in the DR signal at a growing incidence angle in the experiment is also shown to be slower than predicted by both of the synthetic diagnostics, presumably due to underestimation of the probing wave phase modulation and consequent nonlinear saturation of the DR signal at lower incidence angles in modeling

Investigation of nonlinear effects in Doppler reflectometry using full-wave synthetic diagnostics

| openaire: EC/H2020/633053/EU//EUROfusionIn this work, Doppler reflectometry (DR) and radial correlation DR (RCDR) nonlinear scattering effects are studied using full-wave modeling with a set of representative FT-2 tokamak turbulence as inputs. Narrowing of the RCDR correlation function and widening of the DR poloidal wavenumber spectrum are demonstrated. An effect on the dependence of the DR signal frequency shift on the probing wavenumber is found, namely, this dependence 'linearizing' in the nonlinear scattering regime. Nonlinear effects are shown to be weaker for O-mode probing than for X-mode probing, while a faster transition to nonlinear regime is demonstrated for RCDR compared to DR in both probing scenarios.Peer reviewe