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Limiter based ADITYA tokamak has been upgraded in the divertor configured ADITYA-U tokamak. The ADITYA tokamak upgradation includes the replacement of rectangular cross section vacuum vessel by circular cross section vacuum vessel to accommodate additional poloidal (divertor) coils in space between the new vessel and toroidal field coils. The major radius (0.75 m) and minor radius (0.25 m) has been kept same as of old torus so as to accommodate the new torus inside the toroidal field coils. In order to accommodate as many numbers of diagnostics as possible, the ADITYA-U vessel is designed to have 111 port openings directly on the vessel. The leak proof, UHV condition, precise dimensions and lots of weld and demountable joints in the new vessel made the fabrication job very challenging. The ADITYA-U vacuum vessel of SS304L has been precisely fabricated as per IPR design by Godrej & Boyce Mfg. Co. Ltd. under the supervision of IPR scientists. The factory and IPR site acceptance tests of new vessel had been completed successfully, such as dimensional measurement, leak test, pressure, baking. The final acceptable tests had been carried out successfully as results of local leak rate 150 °C. After external testing, the vessel has been installed successfully in ADITYA-U tokamak structure. In this paper, we present the all details of ADITYA-U vacuum vessel like design, analysis, fabrication, acceptance, installation and operation to ascertain its suitability for the plasma experiments.

Plasma position control is essential for obtaining repeatable high temperature, high-density discharges of longer duration in tokamaks. Recently, a set of external coils is installed in the vertical field mode configuration to control the radial plasma position in ADITYA tokamak. The existing capacitor bank cannot provide the required current pulse beyond 200 ms for position control. This motivated to have a DC power supply of 500 A to provide current pulse beyond 200 ms for the position control. The automatization of the DC power supply mandated interfaces with the plasma control system, Aditya Pulse Power supply, and Data acquisition system for coordinated discharge operation. A high current thyristor circuit and a timer circuit have been developed for controlling the power supply automatically for charging vertical field coils of Aditya tokamak. Key protection interlocks implemented in the development ensure machine and occupational safety. Fiber-optic trans-receiver isolates the power supply with other subsystems, while analog channel is optically isolated. Commissioning and testing established proper synchronization of the power supply with tokamak operation. The paper discusses the automation of the DC power supply with main circuit components, timing control, and testing results.

The first Indian tokamak ADITYA, operated over 2 decades with circular poloidal limiter has been upgraded to a tokamak named ADITYA Upgrade (ADITYA-U) for attaining shaped-plasma operations with open divertor in single and double-null configurations. The experimental research in ADITYA-U has made significant progress, since last FEC 2016. After installation of PFC and standard tokamak diagnostics in ADITYA-U, the Phase-I plasma operations has been initiated from December 2016 with graphite toroidal belt limiter. Ohmically heated circular plasmas supported by filament pre-ionization with plasma parameters, Ip ~ 80 – 95 kA, duration ~ 80 – 180 ms with maximum toroidal field ~ 1T and chord-averaged electron density ~ 2.5 x 10^19 m^-3 has been successfully obtained. The runaway electron (RE) generation, transport and mitigation experiments along with MHD activities and density enhancement with H2 gas puffing experiments have carried out in Phase-I, which is completed in March 2017. The Phase-II operation preparation in ADITYA-U includes calibration of magnetic diagnostics followed by commissioning of major diagnostics and installation of baking system. After repeated cycles of baking the vacuum vessel up to ~ 135°C, the Phase-II operations resumed from February 2018 and are continuing to achieve plasma parameters close to the design parameters of circular limiter plasmas using real time plasma position control. The plasma current has been raised to ~ 135 kA in phase-II with maximum chord averaged electron density of ~ 4 x 10^19 x m^-3. Hydrogen gas breakdown has been observed in more than ~ 2000 discharges including Phase-I and Phase-II operation without a single failure. Several experiments, including the control of REs with fuelling of Supersonic Molecular Beam Injection as well as sonic H2 gas puffing during current flat-top, MHD modes studies using multiple periodic gas puffs and radiative improved modes using Neon gas puff have been carried out. The experimental results from Phase-I and Phase-II operations of ADITYA-U tokamak are discussed in this paper.