Progress of the European 2 MW, 170 GHz Coaxial Cavity

Gyrotron for ITER


M. Thumm1,2, S. Alberti3, F. Albajar4, K. Avramidis5, P. Benin6, T. Bonicelli4, S. Cirant7,
O. Dumbrajs8, D. Fasel3, J. Flamm2, G. Gantenbein1, T. Goodman3, J.-P. Hogge3, S. Illy1, S. Jawla3, J. Jin1, S. Kern1, C. Lievin6, I. Pagonakis5, B. Piosczyk1, O. Prinz1, T. Rzesnicki1, M.Q. Tran3


1Forschungszentrum Karlsruhe, Association EURATOM-FZK,

Institut für Hochleistungsimpuls- und Mikrowellentechnik (IHM),

D-76021 Karlsruhe, Germany

2Universität Karlsruhe, Institut für Höchstfrequenztechnik und Elektronik (IHE),

D-76131 Karlsruhe, Germany

3Centre de Recherche en Physique des Plasmas (CRPP), Association EURATOM–Confedération Suisse, Ecole Polytechnique Fédérale de Lausanne,

CH-1015, Lausanne, Switzerland

4The European Joint Undertaking for ITER (F4E), 0801 9 Barcelona, Spain

5National Technical University of Athens (NTUA), Association EURATOM-Hellenic

Republic, GR-15772 Athens, Greece

6Thales Electron Devices (TED), F-78141 Vélizy-Villacoublay, France

7Instituto di Fisica del Plasma Consiglio Nazionale delle Ricerche, I-20125 Milano, Italy

8Helsinki University of Technology, Association EURATOM-TEKES,

FIN-02150 Espoo, Finland



The development of a 2 MW, 170 GHz gyrotron for ITER is taking place in Europe as a cooperative effort between research institutions and tube industry. The design of the first prototype tube is based on previous results obtained at FZK with a short pulse experimental coaxial cavity gyrotron operated at 165 GHz. To verify the design extensive studies have been performed on a short pulse 170 GHz pre-prototype coaxial gyrotron which utilizes the same cavity and mm-wave output coupler and a similar coaxialelectron gun as the 1st industrial prototype tube.

In the meantime the industrial prototype has been fabricated and is presently under test at CRPP Lausanne where a suitable test facility has been constructed. In short pulse operation (~ 1ms) stable single mode excitation of the nominal TE34,19 mode at 170 GHz has been obtained. At reduced parameters (83.5kV/72A) with a corresponding velocity ratio a @ 1, a maximum mm-wave output power of 1.4 MW has been measured. A further increase of the accelerating voltage was limited by arcing; parasitic LF oscillation around 170 MHz occur simultaneously. The origin of the LF oscillations, which begin typically at cathode voltages above ~ 77 kV, is not clear up to now. The measured mm-wave power is about 15% less than the corresponding value obtained from self-consistent simulations. The agreement between experiment and simulations is better for lower voltages. Presently a conditioning and optimization of the tube towards operation at nominal beam parameters (90kV/75A) and at pulses up to 1 s is underway. In parallel to the experimental studies on the first prototype tube, the basic investigations on the experimental 170 GHz pre-prototype tube have been continued.

The results obtained will be reported and discussed.