Far Infrared Faraday Rotation Measurement CN ZT-40

The poloidal magnetic field in ZT-40 (LASL's newest toroidal reversed-field-pinch controlled fusion experiment) is being measured by Faraday rotation of the 164 micron emission of a CO2-pumped CH3OH laser. The essence of this method, which is independent of spurious intensity modulations, is to monitor the phase distortion of a regular beat frequency. This beating is produced when two oppositely circularly polarized components, frequency shifted with respect to each other and both passed through a magnetized plasma, are transmitted through a linear polarization analyzer. The same concept has been independently described by Dodel and Kunz [1].