Abstract
Interpretation of the Electron Cyclotron Emission (ECE) and ECE Imaging (ECE-I) measurements concerning the measurement position and the radiation temperature (Trad) at the plasma edge is associated with significant uncertainty. Various limitations such as low and high-density limits, relativistic and Doppler shift-broadening, mode overlap were identified in the past. Here, we analyse the influence of density profile variation onto the radiation temperature in H-mode plasmas at ASDEX Upgrade tokamak. We show that, in the region of steep gradients, the variation of the density profile leads to an outward-shift of the measurement position, towards lower Trad. The analysis is extended towards the study of the contribution of the ordinary mode (O-mode) emission to the measured Trad at the plasma edge. With this analysis, we show the qualitative agreement between experimental observations and modeling when taking into account the O-mode contribution to the ECE measurements. All of these effects are assessed via the Electron Cyclotron Radiation transport forward model that is now routinely used to model the response of the ECE-I and ECE systems in different plasma scenarios.
Highlights
The Electron Cyclotron Emission (ECE) diagnostic is widely used to measure the electron temperature (Te) and electron temperature fluctuations [1]
The radiation transport model enables us to model the response of the electron cyclotron emission imaging (ECE-I) and ECE systems to different plasma scenarios at the ASDEX Upgrade tokamak
Of special interest are H-mode plasmas with pronounced density fluctuation at the plasma edge region during the inter-ELM periods. We have modeled such a scenario and shown the effect of the density at the pedestal top on an ECE-I and ECE channels both being shifted towards lower magnetic fields and lower radiation temperatures
Summary
The Electron Cyclotron Emission (ECE) diagnostic is widely used to measure the electron temperature (Te) and electron temperature fluctuations (δTe) [1]. To probe the emission volume for each channel and interpret the radiation temperature Trad we use the electron cyclotron radiation transport model. At ASDEX Upgrade we routinely use the radiation transport model for interpreting measurements of ECE and ECE-I diagnostics [12, 13].
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