On the measurement of poloidal field distributions in Tokamaks by far-infrared polarimetry

In 1972, De Marco and Segre showed, theoretically, that it should be possible to measure the poloidal magnetic field in Tokamak plasmas on the basis of the Faraday effect. Preliminary polarimetric model experiments with an HCN laser are not reported and the author is optimistic that the problems of measuring small rotation angles in the far IR can be solved. With the improvements suggested, at least a sufficiently precise measurement of small Faraday rotation angles in a Tokamak experiment should be possible. Besides the precision with which the Faraday rotation angles can be measured, the precision with which the poloidal field can finally be deduced from such measurements, depends on other factors such as the measuring precision of the electron density profile, the diameter of the probing beam and the deviation of the plasma from circular symmetry.