2.2 MW Record Power of the 0.17 THz European Pre-Prototype Coaxial-Cavity Gyrotron for ITER

Manfred Thumm ^1,2*, Tomasz Rzesnicki ¹, Bernhard Piosczyk ¹, Jens Flamm ², Gerd Gantenbein ¹, Stefan Illy ¹, Jianbo Jin ¹, Stefan Kern ¹, Andrey Samartsev ¹, Andreas Schlaich ²
Karlsruhe Institute of Technology (KIT), Association EURATOM-KIT
¹ Institute for Pulsed Power and Microwave Technology (IHM)
² Institute of High Frequency Techniques and Electronics (IHE),
Kaiserstr. 12, 76131 Karlsruhe, Germany
^*2 Email: manfred.thumm@kit.edu

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Abstract: A 2 MW, CW, 0.17 THz coaxial-cavity gyrotron for electron cyclotron heating and current drive in the International Thermonuclear Experimental Reactor (ITER) is under development within an European Gyrotron Consortium (EGYC*), a cooperation of several European research institutions. To support the development of the industrial prototype of a CW gyrotron, a short pulse tube (pre-prototype) is used at KIT Karlsruhe (former FZK, Karlsruhe) for experimental verification of the design of critical components, like the electron gun, beam tunnel, cavity and quasi-optical (q.o.) mm-wave output coupler. Recently a significant progress has been achieved which will be reported here after a general introduction to the principles of gyrotrons. In particular, an output power of up to 2.2 MW with 30 % output efficiency (non-depressed collector operation) has been obtained in single-mode operation at 0.17 THz. Further on, with a newly designed mm-wave output coupler an efficient conversion of the generated mm-wave power into a fundamental Gaussian output beam, with a Gaussian mode content of almost 96 %, has been successfully performed. Recently, the narrow-band fused silica output window has been replaced by a broadband SiN Brewster window in order to be able to study the excitation of additional modes in the frequency range between 0.13 and 0.17 THz (tunable multi-frequency gyrotron). In first experiments an output power of 1.8 MW with an efficiency of 26% has been obtained in the TE_28,16 mode at 0.1413 THz. In addition, in the next azimuthal neighbor mode TE_29,16 at 0.1433 THz, an output power of 1.25 MW has been generated with an efficiency of 23%. Measurements of the power profiles of the mm-wave output beams have confirmed numerical simulations resulting in a very high efficiency and good mode purity of the q.o. output coupler also for these other frequencies and modes.

Keywords: Gyrotron, Coaxial cavity, Quasi-optical output coupler, Frequency step tuning, Parasitic oscillations, Electron cyclotron heating and current drive of thermonuclear fusion plasmas.

Published: 2010-3-30

Acknowledgments: This work was supported by Fusion for Energy (F4E) under the grant contract No.F4E-2008-GRT-08(PMS-H.CD)-01 and within the European Gyrotron Consortium (EGYC). The views and opinions expressed herein reflect only the author's views. Fusion for Energy is not liable for any use that may be made of the information contained therein.

The authors are grateful to Dr. T. Shimozuma from the National Institute for Fusion Science (NIFS), Toki, Japan, for the supply of the silicon-nitride Brewster-window, and to R. Lang,W. Leonhardt, D. Mellein, D. Papenfu?, M. Schmid, W. Spiess, J. Szczesny and J. Weggen of the KIT gyrotron team technical staff for the mechanical design and careful assembly of the tube, for running the gyrotron test facility as well as for their assistance during the experiments. We also wish to express our deep gratitude to Mrs. Huber and Mrs. Kastner for their careful typing of this manuscript.

Cite this article:
Manfred Thumm, Tomasz Rzesnicki, Bernhard Piosczyk, Jens Flamm, Gerd Gantenbein, Stefan Illy, Jianbo Jin, Stefan Kern, Andrey Samartsev, Andreas Schlaich. 2.2 MW Record Power of the 0.17 THz European Pre-Prototype Coaxial-Cavity Gyrotron for ITER[J]. International Journal of Terahertz Science and Technology, 2010, Vol.3, No.1: 1-20.  DOI:10.11906/TST.001-020.2010.03.01

URL: http://www.tstnetwork.org/10.11906/TST.001-020.2010.03.01