Abstract
The electron cyclotron emission (ECE) diagnostic provides routinely electron temperature (T e ) measurements. At ASDEX Upgrade an electron cyclotron forward model, solving the radiation transport equation for given T e and electron density profile, is used in the framework of integrated data analysis. With this method T e profiles can be obtained from ECE measurements even for plasmas with low optical depth. However, due to the assumption of straight lines of sight and an absorption coefficient in the quasi-perpendicular approximation this forward model is not suitable for the interpretation of measurements by ECE diagnostics with an oblique line of sight.Since radiation transport modelling is required for the interpretation of oblique ECE diagnostics we present in this paper an extended forward model that supports oblique lines of sight. To account for the refraction of the line of sight, ray tracing in the cold plasma approximation was added to the model. Furthermore, an absorption coefficient valid for arbitrary propagation was implemented. Using the revised model it is shown that for the oblique ECE Imaging diagnostic at ASDEX Upgrade there can be a significant difference between the cold resonance position and the point from which most of the observed radiation originates.
Highlights
For the measurement of both, the electron temperature (Te) profile and Te fluctuations, Electron Cyclotron Emission (ECE) is a widely used diagnostic
At ASDEX Upgrade an electron cyclotron forward model, solving the radiation transport equation for given Te and electron density profile, is used in the framework of integrated data analysis. With this method Te profiles can be obtained from electron cyclotron emission (ECE) measurements even for plasmas with low optical depth
Since radiation transport modelling is required for the interpretation of oblique ECE diagnostics we present in this paper an extended forward model that supports oblique lines of sight
Summary
For the measurement of both, the electron temperature (Te) profile and Te fluctuations, Electron Cyclotron Emission (ECE) is a widely used diagnostic. Every ECE diagnostic inherently measures radiation temperature (Trad) and not Te. For many cases it is possible to assume that fluctuations in Trad are identical to Te fluctuations at cold resonance. For many cases it is possible to assume that fluctuations in Trad are identical to Te fluctuations at cold resonance This procedure fails if absorption is low near the cold resonance and/or if the line of sight (LOS) is not perpendicular to the magnetic field lines. If the ECE diagnostic is located on the low field side (LFS), the down-shifted emission can be reabsorbed close to the cold resonance, but the up-shifted emission cannot. In this article an electron cyclotron forward model is introduced that allows the determination of the region in the plasma that contributes to the measured Trad. In the second section that follows this introduction the forward model is introduced.
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