Progress of the 1 MW, 140 GHz, CW Gyrotron for W7-X

G.Dammertz1, S.Alberti2, A.Arnold 1,3, E.Borie1, V.Erckmann4, G. Gantenbein5, E.Giguet6,

R. Heidinger1a, J.P. Hogge2, S.Illy1, W.Kasparek5, K.Koppenburg1, M.Kuntze1, H.P.Laqua4, G. LeCloarec6, F. Legrand6, W.Leonhardt1, C.Lievin6, R. Magne7, G.Michel4, G.Müller5, G.Neffe1, B.Piosczyk1, M.Schmid1, K. Schwoerer5, M.Thumm1,3, M.Q.Tran2

1Forschungszentrum Karlsruhe, 1Institut für Hochleistungsimpuls- und Mikrowellentechnik, 1a Institut für Materialforschung I, Association EURATOM-FZK, Postfach 3640, D-76021 Karlsruhe, Germany

2Centre de Recherche en Physique des Plasmas, Association Euratom-Confédération Suisse, EPFL Ecublens, CH-1015 Lausanne, Suisse

3Universität Karlsruhe, Institut für Höchstfrequenztechnik und Elektronik,

Kaiserstr. 12, D-76128 Karlsruhe, Germany

4Max-Planck-Institut für Plasmaphysik, Teilinstitut Greifswald, Association EURATOM,

Wendelsteinstr. 1, D-17491 Greifswald, Germany

5Institut für Plasmaforschung, Universität Stuttgart, Pfaffenwaldring 31, D-70569 Stuttgart, Germany

6Thales Electron Devices, 2 Rue de Latécoère, F-78141 Vélizy-Villacoublay, France

7Association Euratom-CEA, Départment de Recherches sur la Fusion Controlée, F-13108, Saint Paul Lez Durances, France





The development of high power gyrotrons in continuous wave operation for heating of plasmas used in nuclear fusion research has been in progress for several years in a joint collaboration between different European research institutes and industrial partners. The 140 GHz gyrotron is designed for an output power of 1 MW in continuous wave operation and is operated in the TE28,8 mode. The first tube "Maquette" was tested at the Forschungszentrum Karlsruhe. Long pulse operation of the gyrotron was possible but it was limited by the behaviour of the RF-load and by the pressure increase inside the tube. Modulation experiments with an amplitude between 0.1-0.8 kW were performed up to a modulation frequency of 50 kHz sinusoidally.

A visual inspection of the tube showed some melted spots in the mirror box. An improved tube (Protoype 1) with better cooling and an additional relief window at the mirror box has been built and tested. Without optimisation of the parameters in short and long pulse operation, an output power of 0.85 kW could be achieved with a pulse length of 180 s and 0.97 kW for 12 s with an efficiency of 44% (depression voltage: 26 kV). Even for long pulse operation the pressure increase inside the tube was moderate. The limitations were caused by mode-loss and/or by increased cathode current connected with parasitic oscillations.