Continuous plasma density measurement in TJ-II infrared interferometer-Advanced signal processing based on FPGAs

This work presents the behavioral simulation in an FPGA of a novel processing system for measuring line average electronic density in the Ti-II stellarator diagnostic, Infra-Red Two-Color Interferometer. Line average electronic density is proportional to phase difference between probing and reference signals of the interferometer, as the Appleton-Hartree cold plasma model states. The novelty of the approach is the development of a real time measuring system where research work has been carried out in two ways: a new interpolation algorithm and the implementation of a new specific processor on an FPGA. The main goal of this new system is to measure line plasma electronic density for several channels in real time, also it will be useful to eliminate intermediate mixing frequency stages (the output signals coming from the interferometer are going to be directly sampled) and finally to generate real time density signals for control purposes in Ti-II and in other diagnostics. This device is intended to be the new data acquisition-processing system for the future six channel infrared interferometer that requires at least 14 input signals. The knowledge acquired could be useful in the design of W7-X and ITER IR-interferometer data acquisition and processing systems (C) 2010 Elsevier B.V. All rights reserved.