Progress of the European 2 MW, 170 GHz Coaxial Cavity

Gyrotron for ITER

M. Thumm^1,2, 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

E-mail: manfred.thumm@ihm.fzk.de

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 TE_34,19 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.