It is shown that it is possible to measure both the plasma density and the poloidal magnetic field simultaneously by polarimetry, purely from phase measurements. The latter are advantageous compared with previously proposed amplitude measurements. The phase measurements can be performed either by modulating the input polarization (two alternative configurations for this modulation are considered), or by modulating the output polarization. The merits of the three schemes are discussed. The polarimeter required for these measurements is simpler and more robust than the conventional interferometer - polarimeter presently used for the combined density and magnetic field measurements.
First measurements of line-integrated electron density in an ITER-like configuration using the JET far infrared polarimeter diagnostic