Max-Plank-Institut für Plasmaphysik, EURATOM-IPP, Boltzmannstr.2, D-85748 Garching, Germany

M. Thumm¹, R. Heidinger², I. Danilov², G. Gantenbein¹, J. Flamm¹

Forschungszentrum Karlsruhe, EURATOM-FZK

¹Institut für Hochleistungsimpuls- und Mikrowellentechnik,

²Institut für Materialforschung,

PO Box 3640, D-76021 Karlsruhe, Germany

W. Kasparek

Institut für Plasmaforschung, Universität Stuttgart, Pfaffenwaldring 31,

D-70569 Stuttgart, Germany

A.G. Litvak³, L.G. Popov⁴, V.O. Nichiporenko⁴, V.E. Myasnikov⁴, G.G. Denisov³,

E.M. Tai⁴, E.A. Solyanova⁴, S.A. Malygin⁴

³ Institute of Applied Physics, RAS, 46 Ulyanov St., Nizhny Novgorod, 603950, Russia

⁴ GYCOM Ltd, 46 Ulyanov St., Nizhny Novgorod, 603155, Russia

A two-frequency GYCOM gyrotron, Odissey-2, has been installed and put into operation in the new multi-frequency ECRH system at the ASDEX Upgrade tokamak experiment. It works at 105GHz and 140GHz with output power 640kW and 880kW respectively at a pulse length of 10s. Meanwhile, the first two-frequency gyrotron Odissey-1, which was damaged last year, is back at GYCOM for repair. It will be equipped with a broadband Brewster output window and therefore become a multi-frequency gyrotron. A further extension of the system with 2 more gyrotrons is underway. Depending on the success of Odissey-1, these gyrotrons will also be step-tunable and operate at two additional intermediate frequencies between 105 and 140GHz. Construction and cold test of a first broadband double-disc torus window are completed. The transmission to the torus is in normal air, through corrugated aluminum HE11 waveguides with I.D.=87mm over a total length of about 70m. Calorimetric measurements gave a total transmission loss of only 12% at 105GHz and 10% at 140GHz. The variable frequency will significantly extend the operating range of the ECRH system with respect to the applied toroidal magnetic field. A feedback system for the mirror control is under development, to keep the ECRH deposition on the resonant q-surface while the plasma is evolving. This is required for applications such as the suppression of neoclassical tearing modes.