Multichannel HCN interferometer for electron density profile measurements of tokamak plasmas

Abstract

A multichannel interferometer, designed for tokamak plasma-density measurements, is described. The phase shift experienced by the probing beam is transferred to a low-frequency signal obtained by Doppler shifting the frequency of the reference beam. This ensures a sensitivity of 10−2 fringe. The source is a cw HCN waveguide laser, with a 150-mW-output power. Eight channels are in operation on TFR. The variation of the line density as a function of time for each channel is deduced from the phase shift measurement by an on-line computer.