A spectrometer with multilayer filters for line intensity measurements in the RFX experiment

The role played by light impurities in influencing the power balance of Reversed Field Pinch (RFP) plasmas is usually very important. This is the case for RFX, a large Reversed Field Pinch experiment (R=2 m, a=0.457 m) which has recently started its operation in Padova, whose first wall is completely covered by 2016 graphite tiles. Carbon and Oxygen line emissions are in this initial low-current operational phase of RFX key-factors in understanding the plasma confinement. In this paper we present a simple spectrometer with multifoil filters which we have developed as an on-line monitor of line emission from the H and He-like C and O ions. In section II the basic principle of the measurement and the experimental apparatus are described, in section III we discuss the initial experimental results and in section IV the project for a new multichord diagnostic is briefly presented. (author) 7 refs., 6 figs., 1 tab