Overall behaviour of PFC integrated SST-1 vacuum system

As a part of phase-I up-gradation of Steady-state Superconducting Tokamak (SST-1), Graphite Plasma Facing Components (PFCs) have been integrated inside SST-1 vacuum vessel as a first wall (FW) during Nov 14 and May 2015. The SST-1 FW has a total surface area of the installed PFCs exposed to plasma is similar to 40 m(2) which is nearly 50% of the total surface area of stainless steel vacuum chamber (similar to 75 m(2)). The volume of the vessel within the PFCs is similar to 16 m(3). After the integration of PFCs, the entire vessel as well as the PFC cooling/baking circuits has been qualified with an integrated helium leak tightness of < 1.0 x 10(8) mbar 1/s. The pumping system of the SST-1 vacuum vessel comprises of one number of Roots' pump, four numbers of turbomolecular pumps and a cryopump. After the initial pump down, the PFCs were baked at 250 degrees C for nearly 20 hours employing hot nitrogen gas to remove the absorbed water vapours. Thereafter, Helium glow discharges cleaning were carried out towards the removal of surface impurities. The pump down characteristics of SST-1 vacuum chamber and the changes in the residual gaseous impurities after the installation of the PFCs will be discussed in this paper.