Prediction of Helium Vapor Quality in Steady-State Two-Phase Operation of SST-1 Superconducting Toroidal Field Magnets

Steady-state superconducting tokamak (SST-1) at the Institute for Plasma Research is the first superconducting tokamak in India and is an “operational device.” Superconducting magnets system (SCMS) in SST-1 comprises sixteen toroidal field (TF) magnets and nine poloidal field magnets employing cable-in-conduit conductor of multifilamentary high-current-carrying high-field-compatible-multiply-stabilized NbTi/Cu superconducting strands. SST-1 superconducting TF magnets are successfully and regularly operated in a cryostable manner being cooled with two-phase (TP) flow helium. The typical operating pressure of the TP helium is 1.6 bar (a) and the operating temperature is the corresponding saturation temperature. The SCMS cold mass is nearly 32 t and has a typical cool-down time of about 14 days from 300 K down to 4.5 K using the helium refrigerator/liquefier (HRL) system of an equivalent cooling capacity of 1350 W at 4.5 K. Using the available experimental data from the HRL, we have estimated the vapor quality during the cryostable operation of the TF magnets using the well-known correlation of TP flow. In this paper, we report the detailed characteristics of TP flow for given thermohydraulic conditions during long steady-state operation of the SST-1 TF magnets as observed in the SST-1 experimental campaigns.