Upgrade of far infrared three-wave polarimeter–interferometer system on Joint-TEXT

The far infrared polarimeter–interferometer system (POLARIS) on the Joint-TEXT has been upgraded recently. A new support structure has been applied to the mixer array of the POLARIS for adjusting the position of the mixers precisely. Five detection chords have been added to the system on the low field side by optimizing the utilization efficiency of the laser beams on both sides of the beam splitting grid. The spatial resolution can be improved from 3 to 1.5 cm. A better measurement on plasma electron density and current density has been obtained after the system is upgraded. The initial experimental result will be introduced along with the upgrade details.