A 2 MW, CW, 170 GHz COAXIAL CAVITY GYROTRON FOR ITER

B. Piosczyk¹, S. Alberti², A. Arnold^1,3, D. Bariou⁴, A. Beunas⁴, T. Bonicelli⁵, H. Budig¹,

G. Dammertz¹, O. Dumbrajs⁶, O. Drumm^1,3, T. Goodman², J.P. Hogge², S. Illy¹, J. Jin¹,

C. Lievin⁷, P.L. Mondino⁵, M. Thumm^1,3, M.Q. Tran² , I. Yovchev²

¹Forschungszentrum Karlsruhe, Association EURATOM-FZK, Institut für Hochleistungsimpuls- und Mikrowellentechnik, 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

⁴Thales Electron Devices, 2 Rue de Latécoère, F-78141 Vélizy-Villacoublay, France

⁵EFDA Close Support Unit - Garching, Germany

⁶ Department of Engineering Physics and Mathematics, Helsinki University of Technology,

Association EURATOM TEKES, FIN-02150 Espoo, Finland.

e-mail: bernhard.piosczyk@ihm.fzk.de

To reduce the costs of the installations of the electron cyclotron wave (ECW) system at ITER and to allow a compact upper port launcher an increase of the output power per unit is desirable. Coaxial cavity gyrotrons have the potential to fulfil this requirement since very high-order volume modes can be used. This is because the presence of the coaxial insert practically eliminates the restrictions of voltage depression and limiting current and in addition, the problem of mode competition is reduced by the selective influence of the diffractive quality factor of the competing modes.

Within a development program performed as an ITER task at Forschungszentrum Karlsruhe (FZK) the feasibility of manufacturing a multi-megawatt coaxial gyrotron operated in continuous wave (CW) has been demonstrated and all information necessary for a technical design and industrial manufacturing has been obtained. Based on these results the development of a coaxial cavity gyrotron with an RF output power of 2 MW, CW at 170 GHz as could be used for ITER started recently in cooperation between European Associations (CRPP Lausanne, FZK Karlsruhe and HUT Helsinki) together with European tube industry (Thales Electron Devices, Velizy, France). The nominal design parameters of the gyrotron are: beam current I_b = 75 A, accelerating voltage U_b = 90 kV, RF-output power P_out = 2 MW, output efficiency h_out ³ 45 %. In a first step an engineering design of such a gyrotron is underway. This includes as well a technical design of all components, integration of the tube and design and specification of auxiliary components as superconducting magnet and power supplies. At the end of the design phase (end of 2003) technical drawings and specifications for a first prototype will be available. For testing the gyrotron a test facility is under preparation at CRPP Lausanne.

In parallel to the design work the experimental short pulse (5 - 10 ms) 165 GHz, TE_31,17 coaxial gyrotron at FZK will be modified for operation at 170 GHz in the TE_34,19 cavity mode. This modified tube will be used to test the design of the most critical components as electron gun, cavity and the quasi optical RF output system under realistic conditions. In particular the cavity and the RF-output system with a specific dimpled-wall launcher will be identical as designed for the industrial tube.