Erlangen 2018 – scientific programme
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P: Fachverband Plasmaphysik
P 26: Magnetic Confinement II - Helmholtz Graduate School V
P 26.1: Talk
Thursday, March 8, 2018, 14:00–14:25, A 0.112
Improved Measurements of Satellite Modes in 140 GHz Wendelstein 7-X Gyrotrons: An Approach towards an Electronic Stability Control — •Fabian Wilde1,2, Torsten Stange1, Hans Oosterbeek1, Stefan Marsen1, Heinrich Laqua1, Konstantinos Avramidis2, Ioannis Pagonakis2, Stefan Illy2, Manfred Thumm2, Gerd Gantenbein2, John Jelonnek2, Robert Wolf1, and W7-X Team1 — 1Max-Planck Institute of Plasmaphysics, Wendelsteinstraße 1, 17491 Greifswald, Germany — 2Institute for Pulsed Power and Microwave Technology, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
The stellarator Wendelstein 7-X (W7-X) uses electron cyclotron resonance heating (ECRH) by high-power microwave sources (gyrotrons). At the limit of operational stability, the stray radiation level in the gyrotron is increased due to excitation of parasitic and satellite modes, often resulting in a mode loss. The stray radiation by those modes is proposed as a mode-loss precursor. The hysteretic gyrotron behavior after a mode loss was investigated to demonstrate the feasibility of an automated mode recovery. The satellite modes around 137.3 GHz and 142.5 GHz were identified as possible mode-loss precursor candidates in shot spectrograms of the stray radiation at the gyrotron relief window. The activity of the latter was measured with a 142 GHz highpass filter and upto two RF detectors. In order to improve the signal stability, an overmoded setup was evaluated, using a satellite mode bandpass, realized as a dielectric disc filter in an overmoded waveguide and a resonator volume with upto five RF detectors.