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P: Fachverband Plasmaphysik

P 3: Magnetic Confinement II

P 3.5: Vortrag

Montag, 16. März 2026, 18:05–18:20, KH 02.016

Demonstrating the capabilities of the Electron Cyclotron Absorption (ECA) Diagnostic at W7-X in a case study. — •Jonas Zimmermann, Torsten Stange, Sergiy Ponomarenko, Heinrich Laqua, and W7-X Team — Institut für Plasmaphysik, Greifswald, Deutschland

Electron cyclotron resonance heating (ECRH) is the primary heating system of the Wendelstein 7-X (W7-X) device and a major component of the heating mix of most next-generation magnetically confined plasma experiments. Ensuring high heating efficiency is important for machine safety, experimental success, and cost-effectiveness. The propagation and absorption of a heating beam depend on plasma parameters as well as the coupling of the beam to the X- or O-mode at the plasma edge. The electron cyclotron absorption (ECA) diagnostic at W7-X measures ECRH beam shine-through, providing a first-pass heating efficiency measure. During X-mode operation, where full absorption is expected, shine-through power of a few percent was detected. A detector channel was upgraded to include a motorized polarization rotator. With this, the unabsorbed power could be attributed to partial O-mode coupling. Full absorption was finally achieved using a systematic optimization procedure for the coupled polarization. It was possible to measure the magnetic shear induced polarization rotation of the ECRH beam. Comparison of this measurement with the expected change in rotational transform (iota) along the beam path suggests the effective ECRH coupling point lies radially outward of the previously assumed last closed flux surface.

Keywords: W7-X; ECRH; Diagnostic; Iota; Microwaves