Conceptual Design of Electron Density Measurement System for DEMO-Relevant Helical Plasmas∗)

Electron density measurement remains indispensable to control fueling on a DEMO reactor. For steadystate operation of the DEMO reactor, density measurement should be highly reliable and accurate. A dispersion interferometer and a Faraday polarimeter are free from measurement errors caused by mechanical vibrations. Hence combination of the two diagnostics yields a suitable system for density measurement on future steadystate fusion reactors. A wavelength around 1μm is one of the desirable candidates in terms of the fringe shift and the Faraday rotation angle, the variety of optical components, and the efficiency of frequency doubling for the dispersion interferometer. This paper presents a conceptual design for the dispersion interferometer and Faraday polarimeter with a 1 μm light source.