GYROTRON DEVELOPMENT FOR ITER
O. Dumbrajs,
B. Piosczyk and G. Dammertz (Forschungszentrum Karlsruhe, Germany),
Y. Kominis and K.A. Avramides (National Technical University of Athens, Greece),
G.S. Nusinovich (University of Maryland, College Park, USA).

The development of high-power high-frequency gyrotrons is strongly driven by the needs of fusion technology. Gyrotrons are superior to other rf sources in the frequency range relevant for electron cyclotron resonance heating (ECRH), or about 170 GHz for ITER. To make an ECRH system cost-effective, the output power of a single gyrotron should be around 2 MW continuous power. Coaxial cavity gyrotrons have the potential to fulfil this requirement as has been experimentally demonstrated within the development program performed as an ITER task at Forschungszentrum Karlsruhe (FZK). In proof of principle experiments carried out at FZK Karlsruhe on a 165 GHz coaxial cavity gyrotron during the last years, the feasibility of manufacturing a 2 MW, CW coaxial gyrotron at 170 GHz has been demonstrated and information necessary for a technical design has been obtained. Based on these results and on the experience acquired during the development of the 1MW, CW, 140 GHz gyrotron for W7-X, the technical feasibility of a 2 MW, CW, 170 GHz coaxial cavity gyrotron has been studied before EFDA has placed a contract with Thales Electron Devices (TED) for procurement of a first industrial prototype of such a coaxial gyrotron tube. The development work is done in cooperation between European research centers together with TED, the main European tube manufacturer. Within this cooperation both physical specifications and design of gyrotron components have been done by the research institutions whereas TED is responsible for the technological aspects and manufacturing of the tube. In the meantime the fabrication of the prototype gyrotron has been finished and the tube will be delivered to CRPP Lausanne where the tests will be performed. A suitable superconducting magnet is expected to be available in spring 2007. Therefore, experimental operation of the gyrotron experiments could start in summer 2007.

Our laboratory in collaboration with Forschungszentrum Karlsruhe, School of Electrical and Computer Engineering, National Technical University of Athens, and University of Maryland, College Park, has participated in this development. In parallel many theoretical investigations have been performed. Most recently, the effect of microwave reflections in gyrotrons with radial output and consequences for the ITER coaxial gyrotron was studied, azimuthal instability in gyrotrons with overmoded resonators was investigated, feasibility of coaxial super power (4 MW) was examined, Hamiltonian map description of electron dynamics in gyrotrons was proposed, eigenvalues and ohmic losses in coaxial gyrotron cavity were reexamined by means of a novel method. The past, present and future of coaxial gyrotrons has been reviewed in a special invited paper.

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