Physics Aspects of ECE T_e Measurements in ITER

Abstract

This paper summarises the study which has been made of the physics of ECE for ITER. Two ECE simulation codes have been used to obtain quantitative information about the spatial localisation and accessibility limits of T_e measurements. The calculations include the effects of spatial averaging due to the antenna pattern. Results are presented for three different scenarios: the core of full performance plasmas, the edge region and the startup plasma. It is shown that for thermal plasmas it will generally be possible to make core T_e measurements with spatial resolution at or close to the ITER target (∼0.1 m) using the second harmonic extraordinary mode, although access to the plasma centre will be limited at high T_e. Access is better for the first harmonic ordinary mode, but the resolution is poor. Edge T_e measurements using ECE will have a spatial resolution <50 mm, much worse than the ITER target (5 mm), and it will generally not be possible to measure low values of T_e (<1 keV) close to the separatrix. It is shown that it will be possible to make core T_e measurements during much of the discharge startup if there is a suitable sightline.