Recent high current plasma discharges operations with booster power supply assisted vertical magnetic field in aditya tokamak

Abstract

ADITYA tokamak, an air-core, mid-sized (R0 = 75 cm, a = 25 cm) ohmically heated circular limiter tokamak, regularly being operated to carry out several experiments related to controlled thermonuclear fusion research. During recent operation campaign, special efforts are made to enhance the discharge performance as well as plasma parameters. Repeatable plasma discharges of maximum plasma current of ∼ 160 kA and discharge duration beyond ∼ 230 ms with plasma current flattop duration of ∼ 140 ms with negative converter operation and Booster Power Supply assisted vertical magnetic field has been obtained for the first time in the first Indian tokamak ADITYA. The chord-averaged electron density ∼ 3.0 – 4.0 × 1019 m−3 using multiple hydrogen gas puffs, plasma temperature of the order of ∼ 500 – 700 eV has been achieved and maintained till the end of the discharges. It is observed that with Booster operation, we could achieve higher plasma current rise initially of the order of 5 – 8 MA/Sec which is helpful for rising plasma current at very faster rate and achieving higher plasma current above 150 kA, which was not possible with existing power supply. The current rise in VF magnets was limited due higher inductance of the coils. The main difference between previous Thyristor based converter system and Booster switching based system is that the present Booster system having faster response time (< 0.1 ms) for voltage rise. The Booster power supply has two stages chopper based power supply of 800 V each using high power IGBT modules giving 1600 V, and series turn on thyristor in each module. Each chopper output is prefixed and fired in series give maximum rise rate accordingly plasma current rises to higher value so that ∼100 KA of plasma current could rise within 20 ms duration. The breakdown is achieved at ∼20 V peak loop voltages and then maintain discharge plateau at ∼ 2 V of loop voltages. The peak plasma current of 140 to 160 KA is achieved in 40–60 ms time scale. The role of Booster power supply in Vertical field for achieving higher plasma current in ADITYA tokamak will be discussed in this paper.