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P: Fachverband Plasmaphysik

P 6: Helmholtz Graduate School I

P 6.5: Poster

Montag, 13. März 2017, 16:30–18:30, HS Foyer

Study of the gas balance of Wendelstein 7-X — •Georg Schlisio¹, Uwe Wenzel¹, Thomas Sunn Pedersen¹, Tom Wauters², and W7-X Team¹ — ¹Max-Planck-Institute for Plasma Physics, Greifswald — ²KMS/RMA, Brussels, Belgium

The Wendelstein 7-X (W7-X) stellarator experiment is currently being prepared for its plasma operation phase OP1.2 with an island divertor. In the first operation phase (OP1.1) in 2016 the device was operated in a limiter configuration. We studied the gas balance during OP1.1 by balancing the neutral particle input and output. The components in the plasma vessel interact with the neutral gas, i.e. by wall pumping or outgassing. The neutral gas pressure and its constituents have a strong influence on the plasma performance. In order to gain a quantitative understanding of the gas balance, we are studying and modeling the sources and sinks.
To assess the gas removal rate, given by Q = p · S (p pressure, S pumping speed), an accurate calibration of the neutral pressure gauges is required. For OP1.2 an effective calibration scheme is presented that allows fast calibration of all pressure gauges simultaneously. Data collected in OP1.1 is analyzed to better understand neutral gas effects such as wall pumping, outgassing and runtime effects. We found that the gas balance was dominated by the effect of net outgassing. We studied the dependence on the magnetic configuration and on the heating power. We present an outline of the plans for assessing the gas balance in OP1.2, with pulse lengths of tens of seconds. We also present elements of a gas balance model being developed for OP2 (30min pulses).