Experimental Investigations and Analysis of Parasitic RF Oscillations in High-Power Gyrotrons

Gantenbein, G.; Dammertz, G.; Flamm, J.; Illy, S.; Kern, Stefan; Latsas, George P.; Piosczyk, B.; Rzesnicki, T.; Samartsev, A.; Schlaich, A.; Thumm, M.; Tigelis, I. G.

doi:10.1109/tps.2010.2041366

Cited by 84 publications

(47 citation statements)

References 15 publications

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“…2). The ceramic rings attenuate unwanted modes, thereby lowering the quality factor in order to increase the starting current of possible unwanted oscillations.Due to the low surface currents of the azimuthally symmetric TE 0,n -modes on the surface of the beam tunnel, an additional technique is employed for their suppression [11]. The azimuthal symmetry of the beam tunnel is broken by introducing irregular indentations on the copper rings.…”

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confidence: 99%

From Series Production of Gyrotrons for W7-X Toward EU-1 MW Gyrotrons for ITER

Jelonnek

Albajar

Alberti

et al. 2014

IEEE Trans. Plasma Sci.

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Abstract-Europe is devoting significant joint efforts to develop and to manufacture MW-level gyrotrons for electron cyclotron heating and current drive of future plasma experiments. The two most important ones are the stellarator Wendelstein W7-X at Greifswald and the tokamak ITER at Cadarache. While the series production of the 140 GHz, 1 MW, CW gyrotrons for the 10 MW ECRH system of stellarator W7-X is proceeding, the European GYrotron Consortium (EGYC) is presently developing the EU-1 MW, 170 GHz, CW gyrotron for ITER. The initial design had already been initiated in 2007, as a risk mitigation measure during the development of the advanced ITER EU-2 MW coaxial-cavity gyrotron. The target of the ITER EU-1 MW conventional-cavity design is to benefit as much as possible from the experiences made during the development and series production of the W7-X gyrotron and of the experiences gained from the earlier EU-2 MW coaxial-cavity gyrotron design. Hence, the similarity of the construction will be made visible in the present article. During 2012, the scientific design of the ITER EU-1 MW gyrotron components has been finalized. In collaboration with the industrial partner Thales Electron Devices (TED), Vélizy, France, the industrial design of the technological parts of the gyrotron is being completed. A short-pulse prototype is under development to support the design of the CW prototype tube. The technological path towards the EU ITER-1MW gyrotron and the final design will be presented. . Both experiments are relying on electron cyclotron resonance heating (ECRH) as the main heating method for steady state operation, while in addition it is planned for ITER to apply electron cyclotron resonance technique for current drive (ECCD). ECRH & ECCD offer the compatibility to the various physics demands, such as controlled plasma start-up, steady state plasma control, and performance optimization by plasma profile shaping. It offers excellent coupling to the plasma, remote launching and very good localization of the absorbed power. Index Terms-PlasmaThe construction of the stellarator W7-X is almost completed and the device is approaching the commissioning phase [3]. W7-X operation will be supported by a 10 MW continuous wave ECRH system working at 140 GHz in 2 nd harmonic X-or O-mode. To date, the ECRH-system of W7-X is in stand-by with already 5 out of 10 gyrotrons operational. The series production of the W7-X 1 MW, CW gyrotrons [4,5] for the 10 MW ECRH system is proceeding.The European gyrotron development for ITER started with an advanced 170 GHz, 2 MW coaxial-cavity design. RF tests with an industrial CW prototype were done at the European test facility at EPFL-CRPP Lausanne in December 2011 [6]. The prototype did show an excellent voltage stand-off. It was directly possible to excite the nominal operating TE 34,19 -mode. The output RF-beam intensity was in good agreement with the expected one. Without further optimization, the RF output power reached the level of almost 2.1 MW in short-pulse (1 ms) operation with sin...

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confidence: 99%

From Series Production of Gyrotrons for W7-X Toward EU-1 MW Gyrotrons for ITER

Jelonnek

Albajar

Alberti

et al. 2014

IEEE Trans. Plasma Sci.

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“…However, beam currents up to 50 A have been used in the experiments. Details of the gyrotron can be found in [14]. The electron gun is a diode type magnetron injection gun which was designed and manufactured by the Institute of Applied Physics (IAP), Nizhny Novgorod, Russia [15].…”

Section: Experimental Set_upmentioning

confidence: 99%

First Operation of a Step-Frequency Tunable 1-MW Gyrotron With a Diamond Brewster Angle Output Window

Gantenbein

Samartsev

Aiello

et al. 2014

IEEE Trans. Electron Devices

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Abstract-Experimental results using a step-frequency tunable D-band gyrotron are reported. The short-pulse (~3 ms) gyrotron is equipped with an elliptically brazed CVD diamond Brewster angle output window. It is designed for the operation in the frequency range from 111.6 GHz up to 165,7 GHz. Operating parameters for 10 different frequencies corresponding to an equal number of different cavity operating modes has been measured. A minimum output power of 830 kW and a peak output power of 1.3 MW have been realized. For all frequencies the parameters of the RF beam generated by the internal quasioptical converter, such as fundamental Gaussian contents and beam waist, are sufficiently good to allow an efficient coupling of the RF power out of the window. This is the first time a diamond Brewster angle window has been used in a high power gyrotron (~ 1 MW). Such a system offers the path to a simple and compact window solution for high power broadband applications using gyrotrons.

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“…Here, parasitic oscillations in the beam tunnel of W7-X gyrotron SN4 were diagnosed, located and removed by a dedicated design change [4].…”

Section: Improvement Goalsmentioning

confidence: 99%

“…Figure 3 contains the relative received power for a synthesizer signal in the frequency range up to 2 f N directly applied to the scope. 4 ("scope LP"). Without additional measures for aliasing suppression, the aliasing free dynamic range (AFDR) would be less than 30 dB.…”

Section: Bandwidthmentioning

confidence: 99%

Systematic Observation of Time-Dependent Phenomena in the RF Output Spectrum of High Power Gyrotrons

Schlaich

Gantenbein

Kern

et al. 2012

EPJ Web of Conferences

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Abstract.At IHM/KIT, high power gyrotrons with conventional cavity (e.g. 1 MW CW at 140 GHz for the stellarator Wendelstein 7-X) and coaxial cavity (2 MW shortpulse at 170 GHz for ITER) for fusion applications are being developed and verified experimentally. Especially with respect to the problem of parasitic RF oscillations in the beam tunnel of some W7-X tubes, investigations of the gyrotron RF output spectrum have proved to be a valuable source of diagnostic information. Signs of transient effects in millisecond pulses, like frequency switching or intermittent low-frequency modulation, have indicated that truly time-dependent measurements with high frequency resolution and dynamic range could give deeper insight into these phenomena. In this paper, an improved measurement system is presented, which employs a fast oscilloscope as receiver. Shorttime Fourier transform (STFT) is applied to the time-domain signal, yielding time-variant spectra with frequency resolutions only limited by acquisition length and STFT segmentation choice. Typical reasonable resolutions are in the range of 100 kHz to 10 MHz with a currently memory-limited maximum acquisition length of 4 ms. A key feature of the system consists in the unambiguity of frequency measurement: The system receives through two parallel channels, each using a harmonic mixer (h = 9 − 12) to convert the signal from RF millimeter wave frequencies (full D-Band, 110 − 170 GHz) to IF (0 − 3 GHz). For each IF output signal of each individual mixer, injection side and receiving harmonic are initially not known. Using accordingly determined LO frequencies, this information is retrieved from the redundancy of the channels, yielding unambiguously reconstructed RF spectra with a total span of twice the usable receiver IF bandwidth, up to ≈ 6 GHz in our case. Using the system, which is still being improved continuously, various transient effects like cavity mode switching, parasitic oscillation frequency variation, and lowfrequency modulation have been documented.

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Experimental Investigations and Analysis of Parasitic RF Oscillations in High-Power Gyrotrons

Cited by 84 publications

References 15 publications

From Series Production of Gyrotrons for W7-X Toward EU-1 MW Gyrotrons for ITER

From Series Production of Gyrotrons for W7-X Toward EU-1 MW Gyrotrons for ITER

First Operation of a Step-Frequency Tunable 1-MW Gyrotron With a Diamond Brewster Angle Output Window

Systematic Observation of Time-Dependent Phenomena in the RF Output Spectrum of High Power Gyrotrons

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