M. Thumm1a,2, A. Arnold1a,2, G. Dammertz1a, G. Gantenbein1a, R. Heidinger1b, S. Illy1a, W. Leonhardt1a, G. Neffe 1a, B. Piosczyk1a, M. Schmid1a

1Forschungszentrum Karlsruhe, Association EURATOM-FZK aIHM, bIMF I,

Hermann-von-Helmholtz-Platz 1; D-76344 Eggenstein-Leopoldshafen, Germany

2Universität Karlsruhe, IHE, D-76131 Karlsruhe, Germany


S. Alberti, J.P. Hogge, M.Q. Tran

Centre de Recherche en Physique des Plasmas, Association EURATOM-Conféd., EPFL,

CH-1015 Lausanne, Suisse


V. Erckmann, H. Laqua, G. Michel

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

D-17491 Greifswald, Germany


W. Kasparek

Institut für Plasmaforschung, Universität Stuttgart,
D-70569 Stuttgart, Germany


R. Magne

CEA/Cadarache, F-13108 Saint Paul-lez-Durance, France


E. Giguet, F. Legrand, C. Lievin

Thales Electron Devices, F-78141 Vélizy-Villacoublay, France


The development of gyrotrons with 1-MW output power at the Forschungszentrum Karlsruhe (FZK) in collaboration with EURATOM Associations and Thales Electron Devices for continuous wave (CW) operation at 140 GHz is linked with the construction of the new 10 MW ECRH system of the superconducting Stellarator Wendelstein 7-X at the Institute of Plasma Physics (IPP) Greifswald, Germany.

The first series tube tested at FZK yielded a total output power of 980 kW with an efficiency of 31% in short pulse operation and of 920 kW in pulses of 180 s (efficiency of 45% at a collector depression voltage of 29 kV). The Gaussian mode output power was 906 kW. The pulse length at full power is limited at FZK by the available power supply. At reduced  electron beam current, it is possible to operate at longer pulse lengths. At an output power of 570 kW (beam current of 29 A), the pulse length was increased to 1893s. There was no physical reason for a limitation of this pulse: the pressure increase during the pulse was less than a factor of two and ended up at a very low value in the 10-9 mbar range. The tube was delivered to IPP for tests at full power and up to 30 minutes pulse length. The Gaussian mode RF output power measured in a calorimetric load after a 25 m long quasioptical transmission line with 5 smooth mirrors and 2 reflection grating polarizers was 870 kW at a total output power of 920 kW in 30 min. pulses. The Gaussian output mode purity is 97.5%. Again, no indications for a limitation in pulse length was found.

The second and third series tubes were delivered to FZK in November 2005 and March 2006, respectively. The Gaussian mode purity of the output beams of these tubes was determined to be also around 97%. However, optimum long pulse operation has not been achieved up to now in both cases.