EMC improvement of an ECH power supplies system at TCV

Three RHVPSs (regulated high voltage power supplies, 85 kV/80 A/2 s) are installed and have been operated at the Swiss Plasma Center for more than 20 years. Each RHVPS supplies a cluster of three gyrotrons. Two clusters are composed of diode-type gyrotrons operating at the second harmonic of the TCV electron-cyclotron frequency (X2, 82.74 GHz); the third is a cluster of triode-type gyrotrons operating at the third harmonic (X3, 118 GHz). During the design and installation period, grounding (earthing) was primarily considered to the point of view of safety. EMC (electro magnetic compatibility) was not a major consideration; so, the ECH plant operation produced strong electromagnetic interference with other tokamak's systems. This article focuses on the EMC problems inherent to power converters. The mechanism by which these converters influence their environment is explained. Solutions to minimise the emission of interference are given. Finally, first results of real-time X3 RF power tuning during TCV shots are shown. EMC improvements make possible extended TCV heating scenarios.