Theoretical considerations and preparatory experiments for poloidal field measurements in tokamaks by far-infrared polarimetry

First measurement of poloidal-field-induced Faraday rotation in a tokamak plasma

“…It can be shown by calculations similar to those in Ref. [2 ] that for actual TFR 600 parameters the HCN laser wavelength (X = 337 ;um) is within the optimum wavelength range for Faraday rotation measurements, where the influence of the linear birefringence caused by the toroidal magnetic field is negligible. The maximum rotation angles expected for this wavelength and TFR data are of the order of few degrees.…”

“…2a. The discharge parameters were a maximum discharge current of 207 kA, a line integral of the electron density across the centre of the vessel given by /n e dfi= 3.4 X 10 19 m" 2 signal should follow the temporal development of the line integral of the electron density. Figure 2b shows the corresponding line density evaluated from the simultaneously operated signal of the adjacent channel of the HCN interferometer (distance from the axis 0.177 m).…”

“…Further efforts should now be directed towards the development of a multi-channel set-up in order to determine the radial poloidal field distribution and thus the current density distribution. The inversion of the relevant integral equation has been investigated numerically with regard to the precision of the measurements required for reliable results [2].…”

“…An analysis of the potential accuracy of the technique is given in Ref. [2 ]. Thereby, FIR lasers instead of visible lasers should be used since the rotation angles increase as X 2 at longer wavelengths.…”