Göttingen 2025 – scientific programme
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P: Fachverband Plasmaphysik
P 17: Poster Session II
P 17.27: Poster
Wednesday, April 2, 2025, 16:15–18:15, ZHG Foyer 1. OG
First successful plasma start-up with X2 ECRH at a reduced field of 1.8T at W7-X — •Niklas Simon Polei, Torsten Stange, Heinrich Peter Laqua, Kai Jakob Brunner, Juan Fernando Guerrero Arnaiz, Georg Schlisio, and W7-X Team — Max-Planck-Institut für Plasmaphysik, 17491 Greifswald, Germany
At Wendelstein 7-X (W7-X) the nominal magnetic field strength is 2.5T, but operation at a lower magnetic field strength is desired to achieve higher plasma beta (ratio of kinetic and magnetic pressure). The electron cyclotron resonance heating (ECRH) operates at 140GHz, corresponding to third harmonic (X3) heating at 1.8T. A plasma start-up is not possible with X3-heating, but one gyrotron was successfully tuned to 101GHz for an X2 start-up with 250kW. A multi-pass scenario was developed to ensure six passes close to the magnetic axis to increase the effective power in the first few milliseconds and allow a plasma breakdown even at low power. Neutral beam injection (NBI) with a power of 3MW was expected to be able to takeover the plasma from the X2 ECRH, increasing the electron temperature up to 1keV, so that X3 ECRH can take over.
The foreseen start-up scenario was successfully demonstrated in the last operational phase OP 2.2. The X2 ECRH alone can create a central plasma with a peak temperature of several keV and line integrated densities above 5· 1018m−2. The plasma can be taken over by the NBI to increase temperature and density, for subsequent X3 ECRH take-over to maintain a steady plasma. This enables the low field operation of W7-X.
Keywords: ECRH; Wendelstein 7-X; Gyrotrons; Plasma start-up