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Description
The dual-frequency gyrotron TH1510 [1] represents a collaborative achievement involving SPC, KIT and Thales, within the context of the TCV tokamak upgrade. SPC and KIT were involved in the gyrotron design, while Thales served as the manufacturer. The gyrotron is designed to generate a 1MW, 2seconds RF wave at 84 and 126 GHz, corresponding to the second and third harmonics of the tokamak magnetic field. The pulse duration limitation is associated with the TCV maximum plasma duration.
The gyrotron features a triode gun design, a hybrid-type launcher and a non-depressed collector incorporating a longitudinal sweeping coil. Two gyrotrons have already been successfully integrated into the TCV tokamak ECRH system, actively contributing to daily plasma experiments. Following the success of this project, a third gyrotron has been recently ordered.
Before the gyrotron were incorporated into the TCV tokamak ECRH system, an extensive characterization of their behaviour has been performed. The use of a CNR load and temperature measurements on all the gyrotron component cooling circuits allows for precise calorimetry. This paper focuses on presenting the results of these experiments for the two operating frequencies.
The power measurements are systematically compared with numerical simulations, using the optical-beam code ARIADNE and the interaction code TWANG (cf. Figure 1). This comparison will highlight the impact of After Cavity Interaction (ACI [2,3,4]), a crucial factor that must be considered for achieving a reasonable agreement between theoretical predictions and experimental results. The last part of the paper is dedicated to a numerical study on the dependencies of ACI.
![RF power measured and simulated for different cathode voltage on the TCV dual-frequency gyrotron at 126GHz][1]
References
[1] J.-P. Hogge, S. Alberti, K. A. Avramidis, A. Bruschi, W. Bin, F. Cau, F. Cismondi, J. Dubray, D. Fasel, G. Gantenbein, S. Garavaglia, J. Genoud, T. P. Goodman, S. Illy, J. Jin, F. Legrand, R. Marchesin, B. Marlétaz, J. Masur, A. Moro, C. Moura, I. Gr. Pagonakis, E. Périal, L. Savoldi, T. Scherer, U. Siravo, M. Thumm, M. Toussaint, M.-Q. Tran; Megawatt power generation of the dual-frequency gyrotron for TCV at 84 and 126 GHz, in long pulses. AIP Conf. Proc. 16 September 2020; 2254 (1): 090006. https://doi.org/10.1063/5.0014343.
[2] E. M. Choi, M. A. Shapiro, J. R. Sirigiri, R. J. Temkin; Experimental observation of the effect of aftercavity interaction in a depressed collector gyrotron oscillator. Phys. Plasmas 1 September 2007; 14 (9): 093302. https://doi.org/10.1063/1.2776911.
[3] S. Kern et al., "Simulation and experimental investigations on dynamic after cavity interaction (ACI)," 35th International Conference on Infrared, Millimeter, and Terahertz Waves, Rome, Italy, 2010, pp. 1-2. https://doi.org/10.1109/ICIMW.2010.5612609.
[4] K. A. Avramidis, Z. C. Ioannidis, S. Illy, J. Jin, T. Ruess, G. Aiello, M. Thumm, and J. Jelonnek, “Multifaceted simulations reproducing experimental results from the 1.5 MW 140 GHz pre-prototype gyrotron for W7-X”, IEEE Trans. Electron Devices, vol. 68, No. 6, pp. 3063 - 3069, May 2021. https://doi.org/10.1109/TED.2021.3075653.
