Baseline Design of a Multi-Channel Interferometer and Polarimeter System for Density Measurements on ITER

Abstract

A design of a multi-channel system to measure line average plasma density for ITER has been developed using vibration compensated interferometry and Faraday rotation measurements. The purpose of this study is to establish a consistent design based on current technology, that can be used to examine performance and reliability issues and to evaluate the effect of future design improvements. The system uses a vibration compensated interferometer, with a CO2 laser at 10.6 μm for the probe beam and a CO laser at 5.2 μm for the vibration compensation. The CO2 laser probe beam also allows Faraday rotation measurements to be made along the tangential beam path. This improves the reliability of the system because density measurements made from the Faraday rotation, although less accurate than interferometry, do not require cumulative knowledge of the phase shift over the long time scales expected in ITER. Plasma effects on both types of measurements and ITER specific operational considerations, such as plasma start-up, pulse length, and vibration effects will be discussed. Survivability and placement of the plasma facing optics in the ITER structure are critical issues and a discussion of the material selection, and integration into the ITER design are given.