A steady state superconducting tokamak (SST-1) has been commissioned after the successful experimental and engineering validations of its critical sub-systems. During the 'engineering validation phase' of SST-1; the cryostat was demonstrated to be leak-tight in all operational scenarios, 80 K thermal shields were demonstrated to be uniformly cooled without regions of 'thermal runaway and hot spots', the superconducting toroidal field magnets were demonstrated to be cooled to their nominal operational conditions and charged up to 1.5 T of the field at the major radius. The engineering validations further demonstrated the assembled SST-1 machine shell to be a graded, stress-strain optimized and distributed thermo-mechanical device, apart from the integrated vacuum vessel being validated to be UHV compatible etc. Subsequently, 'field error components' in SST-1 were measured to be acceptable towards plasma discharges. A successful breakdown in SST-1 was obtained in SST-1 in June 2013 assisted with electron cyclotron pre-ionization in the second harmonic mode, thus marking the 'first plasma' in SST-1 and the arrival of SST-1 into the league of contemporary steady state devices.Subsequent to the first plasma, successful repeatable plasma start-ups with E ∼ 0.4 V m −1 , and plasma current in excess of 70 kA for 400 ms assisted with electron cyclotron heating pre-ionization at a field of 1.5 T have so far been achieved in SST-1. Lengthening the plasma pulse duration with lower hybrid current drive, confinement and transport in SST-1 plasmas and magnetohydrodynamic activities typical to large aspect ratio SST-1 discharges are presently being investigated in SST-1. In parallel, SST-1 has uniquely demonstrated reliable cryo-stable high field operation of superconducting TF magnets in the two-phase cooling mode, operation of vapour-cooled current leads with cold gas instead of liquid helium and an order less dc joint resistance in superconducting magnet winding packs with high transport currents. In parallel, SST-1 is also continually getting up-graded with first wall integration, superconducting central solenoid installation and over-loaded MgB 2 -brass based current leads etc. Phase-1 of SST-1 up-gradation is scheduled by the first half of 2015, after which long pulse plasma experiments in both circular and elongated configurations have been planned in SST-1.

The SST-1 is a super conducting tokamak, which is in the final phase of assembly and commissioning. The super conducting magnet system of SST1 comprises of Toroidal field (TF) and Poloidal field (PF) coils. The 16 TF coils are nosed and clamped towards the in-board side and are supported toroidally with inter-coil structure at the out-board side, forming a rigid body system. The 9 PF coils are clamped on the TF coils structure. The integrated system of TF coils & PF coils forms the cold mass of @ 50 Ton weight. This cold mass is accommodated inside the cryostat and freely supported on the rigid support ring at 16 locations and support ring in-turn supported on 8 columns of machine support structure. During the operation this cold mass attains a cryogenic temperature of 4.2K in the hostile environment of high vacuum. The thermal excursion of cold mass and its supporting structure during this cool down results into severe frictional forces at the supporting surfaces. There is a design requirement of introducing a thin layer of solid lubricant film of MOS2 having coefficient of friction 0.05 between the sliding surfaces to control the stress contribution due to the friction.To ascertain the compatibility of molybdenum disulphide (MOS2) as a solid lubricant in high vacuum and very low temperature environment, we have carried out qualification tests on various samples and measured the coefficient of friction in both the room temperature conditions and at high vacuum & after thermal shocking to 4.2K temperatures. After successful qualification tests actual components are fabricated and integrated in the cold mass support structure assembly. This paper presents the design requirement, qualification tests performed and details about the integration of thin solid lubricant film of MOS2.

Under the 'SST-1 mission mandate' recently, all the sixteen Steady State Superconducting Tokamak (SST-1) Toroidal Field (TF) magnets have been successfully tested at their nominal currents of 10000 A in cold under supercritical helium (SHe) flow conditions. The TF magnets test campaign have begun in an experimental cryostat since June 2010 with the SST-1 Helium cryogenics facility, which is a 1.3 kW at 4.5 K helium refrigerator-cum-liquefier (HRL) system. The HRL provides ~300 g-s -1 supercritical helium (SHe) with cold circulator (CC) as well as ~ 60 g-s -1 without cold circulator to fulfill the forced flow cooling requirements of SST-1 magnets. In case of single TF coil tests, we can adjust HRL process parameters such that an adequate amount of required supercritical helium is available without the cold circulator. In this paper, the complete process is describing the Process Flow Diagram (PFD) of 1.3 kW at 4.5 K HRL, techniques to generate supercritical helium without using the cold-circulator and the results of the cooldown, steady state characteristics and experience of supercritical helium operations during the TF coils test campaign have been discussed.

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