Proposal of Reflectometry System for ITER

Abstract

Reflectometry is now widely used in tokamak experiment. It may provide the measurements of a number of important plasma characteristics with minimum requirements to the entrance ports. It uses well developed mm wave band and the launched and received waves may be easily transported to and away from tokamak by means of long transmission lines. Significant experience was gained in reflectometry since the first experiments on ATC tokamak¹, but it still in process of development. It means, that there is no final universal version of reflectometry scheme and there is a number of questions connected with the interpretation of reflectometry data. The radial localization of measured phase fluctuations, experimentally appeared to be much more localized then predicted by one or two dimensional calculations⁶. It was shown in⁴, that at high turbulence^2,3,4,5 level, the measured radial correlation length may be greatly reduced with respect to the real length and even distort the observed frequency spectrum. The problem of so called ″phase run away″ is discussed in^7,8,9, which is thought to be connected with the Doppler frequency shift associated with the poloidal rotation of the grating-like cut off layer surface⁹. Thus it is possible to conclude, that reflectometry is powerful diagnostic for ITER, but additional experimental work have to be done to solve some problems.