SST-1

Abstract: The Steady State Superconducting Tokamak (SST-1) is currently being refurbished in a mission mode at the Institute for Plasma Research with an ultimate objective of producing the first plasma in early 2012. Since January 2009, under the SST-1 Mission mandate, a broad spectrum of refurbishment activities have been initiated and pursued on several subsystems of SST-1. Developing sub-nano-ohm leak-tight joints in the magnet winding packs, developing single-phased LN2-cooled thermal shields, developing supercritical-helium-cooled 5-K thermal shields for magnet cases, ensuring thermal and electrical isolations between various subsystems of SST-1, testing of each of the SST-1 toroidal field (TF) magnets at 4.5 K with nominal currents, testing each of the modules and octants of the SST-1 machine shell in representative experimentally simulated scenarios, augmentation and reliability establishment of the SST-1 vacuum vessel baking system, time synchronizations among various heterogeneous subsystems of SST-1, large data-storage scenarios, and integrated engineering testing of the first phase of the plasma diagnostics are some of the major refurbishment activities. Presently, the SST-1 device integration is in full swing. The cold test of the assembled SST-1 TF and poloidal field magnets began in December 2011. Following the successful testing of the SST-1 superconducting magnet system and engineering validations of the machine shell, the first plasmas will be attempted in SST-1. The first plasma will be ~ 100-kA limiter assisted with the available volt-seconds and could possibly be assisted by ECCD/LHCD.

Abstract: All SST-1 superconducting Toroidal Field (TF) and Poloidal Field (PF) magnets have been refurbished, integrated, and assembled onto the SST-1 machine shell in mid of 2012. Fabrication of sub nano-ohm, leak tight DC joints in superconducting magnets winding packs, enhancing the insulation strength in operating conditions, and test qualifying all the magnets prior to their integration in SST-1 machine shell were the primary refurbishment aspects. All assembled SST-1 TF magnets in SST-1 machine shell have since been successfully cooled down employing 1.3 kW SST-1 Helium Refrigerator/Liquefier system maintaining helium leak tightness under all temperature conditions. The TF magnets have experimentally demonstrated thermo-mechanical behavior as per the design as well as excellent flow uniformity amongst various parallel paths. Subsequently, these TF magnets have been increasingly charged so as to create a magnetic field of 1.5 T at the SST-1 major radius of 1.1 m. This is the first occasion, when cable-in-conduit wound toroidal field magnets have been successfully operating with two phase flow in a Tokamak application. The first plasma in SST-1 has been successfully obtained in June 2013 where the SST-1 TF magnets have demonstrated excellent functional characteristics. The confidence boosting engineering and functional validation test results of SST-1 TF magnets as well as its performance during the recent SST-1 plasma campaign have been elaborated in this paper.

Abstract: Electron Cyclotron Resonance Heating (ECRH) system will play an important role in plasma formation, heating and current drive in the Superconducting Steady state Tokamak (SST-1). Commissioning activity of the machine has been initiated. Many of the sub-systems have been prepared for the first plasma discharge. A radial and a top port have been allotted for low field side (LFS) and high field side (HFS) launch of O and X- modes in the plasma. The system is based on a gyrotron source operating at a frequency of 82.6±0.1GHz (GLGD-82.6/0.2) and capable of delivering 0.2 MW / 1000s with 17% duty cycle. The transmission line consisting of ~15 meters length 63.5mm corrugated wave guide, DC break, wave guide switch, mitre bend, polariser, bellows that terminates with a vacuum barrier CVD window. A beam launching system used to steer the microwave beam in the plasma volume is connected between the end of the transmission line and the tokamak radial and top ports. A VME based real time data acquisition and control (DAC) system is used for monitoring, acquisition and control. Hard-wired interlock operates a rail-gap based crowbar system in less than 10µs under any fault condition. Burn patterns are recorded at various stages in the transmission line. The gyrotron is tested for ~200 kW / 1000s operation on a water dummy load. Transmission line is tested at various power levels for long pulse operation. The paper highlights the experimental results of successful commissioning of the system.

Abstract: Steady state super-conducting tokamak-1 (SST-1) is a medium sized tokamak, which has been designed to produce a ‘D’ shaped double null divertor plasma and operate in quasi steady state (1000 s). SST-1 vacuum system comprises of plasma chamber (vacuum vessel, interconnecting rings, baking and cooling channels), and cryostat all made of SS 304L material designed to meet ultra high vacuum requirements for plasma generation and confinement. Prior to plasma shot and operation the vessel assembly is baked to 250/150 °C from room temperature and discharge cleaned to remove impurities/trapped gases from wall surfaces. Due to baking the non-uniform temperature pattern on the vessel assembly coupled with atmospheric pressure loading and self-weight give rise to high thermal-structural stresses, which needs to be analyzed in detail. In addition the vessel assembly being a thin shell vessel structure needs to be checked for critical buckling load caused by atmospheric and baking thermal loads. Considering symmetry of SST-1, 1/16th of the geometry is modeled for finite element (FE) analysis using ANSYS for different loading scenarios, e.g. self-weight, pressure loading considering normal operating conditions, and off-normal loads coupled with baking of vacuum vessel from room temperature 250 °C to 150 °C, buckling and modal analysis for future dynamic analysis. The paper will discuss details about SST-1 vacuum system/cryostat, solid and FE model of SST-1, different loading scenarios, material details and the stress codes used. We will also present the thermal structural results of FE analysis using ANSYS for various load cases being investigated and our observations under different loading conditions.