Precision Signal Conditioning Electronics for Cryogenic Temperature and Magnetic Field Measurements in SST-1

As a part of refurbishment of Steady-state Superconducting Tokamak-1 (SST-1) at the Institute for Plasma Research, India, all 16 toroidal field (TF) magnets of SST-1 have been individually tested in cold with nominal current in a dedicated experimental cryostat. The magnets were cooled down to 4.5 K using either supercritical or two-phase helium, after which they were charged up to 10 kA of transport current. Precise cryogenic temperature and magnetic field measurements in the experimental configuration were mandatory. Temperatures were required to be accurately measured at several locations in the magnet and hydraulic circuits, whereas the field measurements were carried out at few predefined locations on the magnet case. Highly accurate in-house modular signal conditioning electronics had been developed for low temperature and high magnetic field measurements for such large magnets. This paper describes the scheme of the measurement, precautions taken for enhanced reliability, precautions taken for long-term offset stability in cryogenic environment, and the results of SST-1 TF magnet tests.