I. Introduction
Superconducting magnet system (SCMS) of tokamak SST-1 [1] consists of 16 numbers D-shaped toroidal field (TF) coils and 9 numbers circular poloidal field (PF) coils. The conductors used for the superconducting coils are Nb-Ti based cable in conduit conductor (CICC) having 40% void fraction for coolant flow. Each TF coil is divided into 12 flow paths having 48 m length. PF coils have different flow paths and length. PF3 coil has maximum number of flow path (8) among all the PF coils. Coolant adopted for all the superconducting coils for the SCMS of SST-1 is forced flow supercritical helium (SHe) at 4 bar and 4.5 K. The source of the coolant is a refrigerator/liquefier (R/L), of 650 W refrigeration and 200 l/h liquefaction capacity, supplied by M/s Air Liquide DTA, France as per the SST-1 cryogenic requirement [2], [3]. The thermodynamic process of R/L is designed with 3 numbers turbines, designated as A, B and C. Turbine A and B are connected in series with each other. Turbine C is a hypercritical turbine, which gives additional cooling power for the R/L. A cold circulator (CC) with associated sub-systems has been implemented with the cold-box of the R/L to maintain a constant flow rate through the SCMS. Total flow requirement for the SCMS has been estimated as 240 g/s for TF coil systems, 35 g/s for the PF coil system, 13 g/s for the case cooling of the TF coil system and 12 g/s for the TF/PF superconducting bus bars [4]. The flow rate for all the superconducting coils has been establiSHed to satisfy the cryogenic stability of the coils during normal and transient operation i.e., current ramp up/down, plasma disruption etc.