[en] Highlights: •SST-1 Tokamak was successfully commissioned. •Vacuum vessel and cryostat were pumped down to 6.3 × 10⁻⁷ mbar and 1.3 × 10⁻⁵ mbar. •Leaks developed during baking were detected in-situ by RGA and confirmed later on. •Cryo-pumping effect was observed when LN2 thermal shields reached below 273 K. •Non-standard aluminum wire-seals have shown leak tightness < 1.0 × 10⁻⁹ mbar l/s. -- Abstract: Steady-state Superconducting Tokamak (SST-1) was installed and it is commissioning for overall vacuum integrity, magnet systems functionality in terms of successful cool down to 4.5 K and charging up to 10 kA current was started from August 2012. Plasma operation of 100 kA current for more than 100 ms was also envisaged. It is comprised of vacuum vessel (VV) and cryostat (CST). Vacuum vessel, an ultra-high (UHV) vacuum chamber with net volume of 23 m³ was maintained at the base pressure of 6.3 × 10⁻⁷ mbar for plasma confinement. Cryostat, a high-vacuum (HV) chamber with empty volume 39 m³ housing superconducting magnet system, bubble thermal shields and hydraulics for these circuits, maintained at 1.3 × 10⁻⁵ mbar in order to provide suitable environment for these components. In order to achieve these ultimate vacuums, two numbers of turbo-molecular pumps (TMP) are installed in vacuum vessel while three numbers of turbo-molecular pumps are installed in cryostat. Initial pumping of both the chambers was carried out by using suitable Roots pumps. PXI based real time controlled system is used for remote operation of the complete pumping operation. In order to achieve UHV inside the vacuum vessel, it was baked at 150 °C for longer duration. Aluminum wire-seals were used for all non-circular demountable ports and a leak tightness < 1.0 × 10⁻⁹ mbar l/s were achieved

[en] Steady-state Superconducting Tokamak (SST-1) was installed and it's commissioning for overall vacuum integrity, magnet systems functionality in terms of successful cool down to 4.5 K and charging up to 10 kA current was started from August 2012. Plasma operation of 100 kA current for more than 100 ms was also envisaged. It is comprised of vacuum vessel (VV) and cryostat (CST). Vacuum vessel, an ultra-high (UHV) vacuum chamber with net volume of 23 m"3 was maintained below 1.0 10"-"7 mbar for plasma confinement. Cryostat, a high-vacuum (HV) chamber with empty volume 39 m"3 housing superconducting magnet system, bubble thermal shields and hydraulics for these circuits was maintained below 1.0 10"-"5 mbar in order to provide suitable environment for these components. In order to achieve these ultimate vacuums, two numbers of turbo-molecular pumps (TMP) are installed in vacuum vessel while three numbers of turbo-molecular pumps are installed in cryostat. Initial pumping of both the chambers will be carried out by using suitable Roots pumps. PXI based real time controlled system is used for remote operation of the complete pumping operation. In order to achieve UHV inside the vacuum vessel, it was baked at 150 °C for longer duration. Aluminium wire-seals were used for all non-circular demountable ports and a leak tightness < 1.0 10"-"9 mbar l/s were achieved. (author)

[en] Density control feedback system for SST-1 is designed using heterodyne density signal as a feedback signal. During operation and control, the heterodyne system measures the plasma density and generates a signal in the form voltage ranging from 0 to 5 VDC. The generated one voltage each corresponds to a density value of 8.0 x 10"1"2 /cm''3. This signal is compared with the reference value using comparator devices. The feedback system will start when the plasma current reaches 80% and the plasma density reaches to 8.0 x 10"1"2 /cm"3. Once the plasma density reaches a maximum valve of 3.8 x 10"1"3 cm"3 or the plasma current start decaying, the feedback system will stop gas puffing. This density control feedback system will also be used to control the plasma density in H-mode plasma operation. The detailed design and implementation part of the control circuit is discussed in this paper. (author)

[en] Steady-state superconducting Tokamak (SST-1) is currently under refurbishment in a mission mode at Institute for Plasma Research. In this mission, leak tightness of all the cryogenic components of SST-1 under all operational scenarios is evaluated. Cryogenic components include TF coils, 80 K thermal shields, Helium and Nitrogen Manifolds, Isolators, Tubing, Headers etc. Toroidal field (TF) magnets of SST-1 have been refurbished and have been tested in cold condition with current. Leak tightness of the entire superconducting magnets winding-pack including joints and helium manifolds were necessarily to be ensured at room temperature (RT) as well as in cold (∼ 5 K) with and without current. Nearly twenty five campaigns involving SST-1 TF coils have been made where the vacuum leak tightness was monitored and ensured including those of the partial pressure of the residual gases. This paper will elaborate these experiments including methods adopted at ensuring leak tightness in cold. This paper will elaborate these experiments including methods adopted at ensuring leak tightness in cold condition and Partial pressure measurement during all the campaigns of Coils and other component testing. (author)

[en] Steady State Tokamak (SST-1) vacuum vessel baking as well as baking of the first wall components of SST-1 are essential to plasma physics experiments. Under a refurbishment spectrum of SST-1, the nitrogen gas heating and supply system has been fully refurbished. The SST-1 vacuum vessel consists of ultra-high vacuum (UHV) compatible eight modules and eight sectors. Rectangular baking channels are embedded on each of them. Similarly, the SST-1 plasma facing components (PFC) are comprised of modular graphite diverters and movable graphite based limiters. The nitrogen gas heating and supply system would bake the plasma facing components at 350°C and the SST-1 vacuum vessel at 150°C over an extended duration so as to remove water vapour and other absorbed gases. An efficient PLC based baking facility has been developed and implemented for monitoring and control purposes. This paper presents functional and operational aspects of a SST-1 nitrogen gas heating and supply system. Some of the experimental results obtained during the baking of SST-1 vacuum modules and sectors are also presented here. (fusion engineering)

[en] SST-1 Tokamak is under commissioning at Institute for Plasma Research in mission mode. It comprises of a toroidal doughnut shaped plasma chamber, surrounded by liquid helium cooled superconducting magnets and LN₂ thermal shields, housed inside the cryostat chamber. The superconducting magnet system of SST-1 consists of toroidal field (TF) magnets and poloidal field (PF) magnets and will be operated at internal supercritical helium pressure of 4.5 bar (a) under very low temperature of 4.5 K and carrying a DC current of 10 kA. High-vacuum compatibility up to low-pressure ≤ 1 × 10⁻⁵ mbar is one of the most essential features of these superconducting magnets in order to avoid the heat losses due to conduction and convection. This paper describes the extensive tests carried out under representative conditions to ensure the high-vacuum compatibility of the SST-1 magnets before assembly to the main system.

[en] Helium leak testing is the most versatile form of weld qualification test for any vacuum application. Almost every ultra-high vacuum (UHV) system utilizes this technique for insuring leak tightness for the weld joints as well as demountable joints. During UHV system under operational condition with many other integrated components, in-situ developed leaks identification becomes one of the prime aspect for maintaining the health of such system and for continuing the experiments onwards. Since online utilization of leak detector (LD) has many practical limitations, residual gas analyser (RGA) can be used as a potential instrument for online leak detection. For this purpose, a co-relation for a given leak rate between Leak Detector and RGA is experimentally established. This paper describes the experimental aspect and the relationship between leak detector and RGA.

[en] The Steady-state Superconducting Tokamak (SST-1) is an indigenously built medium sized fusion device at IPR designed for plasma duration of 1000 seconds. It consists of two large vacuum chambers – Vacuum Vessel (16 m³) and Cryostat (39 m³) which will be pumped to UHV and HV pressures respectively using a set of turbo molecular pumps, Cryo-pumps and Roots pumps. The total as well as the partial pressure measurement in these chambers will be carried out using a set of Pirani gauges, Bayard Alpert type gauges, Capacitance manometers and Residual Gas Analyzers (RGA). A reliable and accurate pressure measurement is essential for successful operation of SST-1 machine. For this purpose a gauge calibration system is set up in SST-1 Vacuum laboratory based on Spinning Rotor Gauge which can measure absolute pressure in the range 1.0 mbar to 1.0 × 10⁻⁷ mbar. This system is designed to calibrate up to five gauges simultaneously for different gases in different operating pressure ranges of the gauges. This paper discusses the experimental set-up and the procedure adopted for the calibration of such vacuum gauges.

[en] Vacuum system of steady-state Superconducting Tokamak (SST-1) has a very essential role during SST-1 plasma operation. For this purpose, its data acquisition and control system should be reliable and accurate. The PXI based faster real time data acquisition and control system were used for performing various operations like online data measurements, control, display, status indication in form of graphical visualization and storing the data for future analysis. We developed such PXI based vacuum control and implemented to our ongoing experimental set-up. This paper will describe the detailed information and guidance on PXI based platform for data acquisition and control used during the campaign.

[en] SST-1 tokamak is a long pulse tokamak designed for the plasma operation up to 1000 sec duration. Gas feed system and gas exhaust management will play a very crucial role during plasma discharge. During the different type of operations of tokamak like wall conditioning, diverter operation and neutral beam injection, a large amount of gas will be fed into the vacuum chamber at different locations. Also during plasma operations, the gas will be fed both in continues and pulse mode. Gas feed will be carried out mainly using piezo-electric valves controlled by PXI based data acquisition and control system. Such operations will lead to a huge amount gas exhaust by the main system which requires good exhaust facility to searches, great care should be taken in constructing both. Also initial pumping of cryostat and vacuum vessel of SST-1 will release a large amount of gas. Exhausted gases from SST -1 will be Hydrogen, Nitrogen, Mixture gases or some toxic gases. Dedicated exhaust system controlling the different gases are installed. Special treatment of hazardous/explosive gases is done before releasing to the atmosphere. This paper describes design and implementations of the complete gas feed and exhaust system of SST-1.