Faraday rotation measurements on compact helical system by using a phase sensitive heterodyne polarimeter

A phase sensitive heterodyne polarimeter was installed on compact helical s ystem (CHS). An HCN laser (337 mu m) and Schottky barrier diodes are used f or the radiation source and for detection, respectively. By using a phase s ensitive heterodyne scheme, the Faraday rotation angle can be measured from the phase variations caused by the phase difference between the right- and left-handed waves in the magnetized plasma. The purpose of the polarimeter on CHS is for a stable density monitor which is free from fringe jump and for the measurements of the internal magnetic field induced by the plasma c urrent. The present resolution of the Faraday rotation angle is 0.1 degrees with 10 ms time resolution and 1 degrees with 1 ms. These are mainly deter mined by the laser instability. (C) 1999 American Institute of Physics. [S0 034-6748(99)50701-6].