Erlangen 2018 – scientific programme

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P: Fachverband Plasmaphysik

P 11: Helmholtz Graduate School - Poster

P 11.26: Poster

Tuesday, March 6, 2018, 16:15–18:15, Redoutensaal

First gas balance studies of Wendelstein 7-X — •Georg Schlisio, Uwe Wenzel, Thomas Sunn Pedersen, and W7X Team — MPI für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany

The advanced optimized stellarator Wendelstein 7-X (W7-X) is currently in its second operation phase (OP 1.2), featuring now a graphite island divertor. The first wall consists of graphite tiles and stainless steel panels. Both divertor and first wall are inertially cooled. With a divertor, plasma-wall interaction changes significantly compared to the first operation with a graphite limiter.

The first wall can act as a source or sink for particles depending on the conditions. This has great influence on the plasma particle balance. The overall gas balance consists of all sources and sinks of particles.

We discuss the methods of the gas balance of OP1.2a with an assessment of all sinks and sources. Since the wall source is not directly accessible, it has to be determined indirectly via the other terms of the balance.

A major part of the gas balance is determined by the particle removal rate Q given by Q=p*S, wherein p is the divertor pressure measured by a set of ASDEX pressure gauges at different locations in the sub-divertor region of W7-X, and S is the effective pumping speed.

Experience from OP1.1 and OP1.2a shows the critical importance of these studies for density control already for the plasmas in OP1.2b but especially for the long-pulse discharges in the upcoming next operational phases with discharge lengths that eventually will exceed 1000s.