The refurbishment of damaged toroidal magnetic field coils for Aditya upgrade

Aditya tokamak (R₀ = 75 cm, a = 25 cm), is a machine in which high temperature plasma is produced and contained using magnetic fields. After 25 years of Aditya tokamak operation, Upgradation of the Aditya tokamak with limiter configuration to Aditya-U tokamak with divertor configuration is under progress. There are 20 numbers of toroidal magnetic field coils which produces 1.5 Tesla of magnetic field at plasma centre, when 50 kA of current is passed through them. Each of the TF coils is a picture frame type coil, with a bore of 0.78 m x 0.9 m and outer dimension of 1.03 m x 1.26 m, having weight of 500 kg each. A single TF coil is made up of two C's (Big-C and Small-C) joined together using 16 bolts. Each C is made up of six C shaped copper plates pressed together with pre-impregnated epoxy glass insulation between the copper plates. For joining the two C's to make one picture frame type TF coil, at the open ends of C, all six plates are tapered to accommodate the respective open ends of small C which has similar tapering. The tapered portion of each C is named as Fingers. Each Finger in both the C's is silver plated having dimension of 160 mm x 160 mm x 6.5 mm thickness and 6.5 mm apart from each other. During the dis-assembly of Toroidal magnetic field (TF) coils, it was realised that 6 numbers of TF coils (Coil No. 2, 3, 8, 9, 17 and 20) are damaged at the fingers joints of two C's sections constituting a TF coil. The copper material have been melted and eroded mainly at the edges of fingers joints of small-C and big-C of TF coils especially in the middle fingers. Large depositions of carbon have been found near melted copper. The Aditya Upgrade team has found in house technique of refurbishing these TF coils. After repairing the damaged TF coils, they are assembled one by one on Test Stand by joining both C's sections and the electrical parameter testing (Resistance and Inductance) of these coils have been carried out. The resistance and inductance measurements of each damaged coil after repairing showed that electrical parameters are within satisfactory limits and are in good condition to be reused again. This remarkable task has saved lot of cost and time for Aditya Upgrade re-assembly. The details of damaged TF coils refurbishment and its electrical parameters measurements will be discussed in this paper. (author)