Abstract
In this paper we derive the equations of collective Thomson scattering (CTS) for an arbitrarily drifting magnetized plasma described by a bi-Maxwellian distribution. The model allows the treatment of anisotropic plasma with different parallel and perpendicular temperatures (with respect to the magnetic field) as well as parallel and perpendicular plasma drift. As could be expected, parallel observation directions are most sensitive to the parallel temperature and drift, whereas perpendicular observation directions are most sensitive to the perpendicular temperature and the perpendicular drift along the observation direction. The perpendicular drift can be related to the radial electric field. Measurements with a spectral resolution better than 0.5 MHz are necessary for the inference of the radial electric field. This spectral resolution and the required scattering geometry are attainable with the current setup of the CTS diagnostic on Wendelstein 7-X.
Highlights
The most advanced fusion concepts, the tokamak and the stellarator, both rely on thermonuclear reactions in a magnetized plasma sustained in toroidal geometry
We calculated spectra for the three observation angles φ = 10○, φ = 80○ and φ = 90○ and for each case, we investigated the effects of changing the parallel and perpendicular temperatures
The forward model based on the outlined equations (17), (21) and (22) should be used for interpretation of collective Thomson scattering (CTS) measurements in drifting bi-Maxwellian plasmas produced by NBI or ICRH heating in which the anisotropy in temperature has to be taken into account
Summary
The most advanced fusion concepts, the tokamak and the stellarator, both rely on thermonuclear reactions in a magnetized plasma sustained in toroidal geometry. The value of the radial electric field can be calculated from measurements of the perpendicular flow velocity provided the other parameters are known or that the first term on the right side of equation (1) can be neglected. We start by introducing the building blocks of our newly derived CTS model for an arbitrarily drifting bi-Maxwellian distribution function and discuss the chosen coordinate system with respect to the applied magnetic field, emphasizing the optimal scattering geometry for perpendicular drift velocity measurements (Section II).
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