New design of the gyrotron used for ECRH experiments on Tore Supra

For ECRH (Electron Cyclotron Resonance Heating) and current drive experiments on the tokamak Tore Supra, gyrotrons have been developed thanks to a collaboration between TED (Thales Electron Devices), Association Euratom-Confederation Suisse, Association Euratom-FZK and Association Euratom-CEA. Limitations on pulse length (about 110 s) have been observed on the first series gyrotron during tests in Cadarache. These limitations have been attributed to inadequate cooling and subsequent overheating of internal components in the tube. Moreover, the geometry of the launcher seems to be at the origin of spurious oscillations inside and at the output of the gyrotron, possibly leading to degraded performances. To improve the gyrotron, new studies involving the same partners have been undertaken and a new tube has just been manufactured by TED, with the main modifications being the introduction of a new cooling system and a launcher with a different geometry. The factory acceptance tests were completed in January 2004; the gyrotron is now installed on the Cadarache test bed where long pulse tests (up to 600 s) will begin by mid June. (authors)