Speaker
Joris Fellinger
(Max-Planck-Institut für Plasmaphysik)
Description
The modular stellarator Wendelstein 7-X in Greifswald (Germany) successfully started operation in 2015 with short pulse limiter plasmas. In 2017, the next operation phase (OP) OP1.2 will start once 10 uncooled test divertor units (TDU) with graphite armor will be installed. The TDUs allow for plasma pulses of 10 s with 8 MW heating. OP2, allowing for steady state operation, is planned for 2020 after the TDUs will be replaced by 10 water cooled CFC armored divertors.
Due to the development of plasma currents like bootstrap currents in long pulse plasmas in OP2, the plasma could hit the edge of the divertor targets which has a reduced cooling capacity compared to the central part of the target tiles. To prevent overloading of these edges, a so-called scraper element can be positioned in front of the divertor, intersecting those strike lines that would otherwise hit the divertor edges. As a result, these edges are protected but as a drawback the pumping efficiency of neutrals is also reduced. As a test an uncooled scraper element with graphite tiles will be placed in two out of ten half modules in OP1.2. A decision to install ten water cooled scraper elements for OP2 is pending on the results of this test in OP1.2.
To monitor the impact of the scraper element on the plasma, Langmuir probes are integrated in the plasma facing surface, and a neutral gas manometer measures the neutral density directly behind the plasma facing surface. Moreover, IR and VIS cameras observe the plasma facing surface and thermocouples monitor the temperatures of the graphite tiles and underlying support structure.
This paper describes the integration of the scraper element and its diagnostics in Wendelstein 7-X.
Co-authors
Arnold Lumsdaine
(Oak Ridge National Laboratory, Oak Ridge, TN 37831, United States)
Dean McGinnis
(Oak Ridge National Laboratory, Oak Ridge, TN 37831, United States)
Doug Loesser
(Princeton Plasma Physics Laboratory, James Forestall Campus, Princeton, NJ 08542, United States)
Glen Wurden
(Los Alamos National Laboratory, Los Alamos, NM 87545, United States)
Han Zhang
(Princeton Plasma Physics Laboratory, James Forestall Campus, Princeton, NJ 08542, United States)
Hutch Neilson
(Princeton Plasma Physics Laboratory, James Forestall Campus, Princeton, NJ 08542, United States)
John Mitchell
(Princeton Plasma Physics Laboratory, James Forestall Campus, Princeton, NJ 08542, United States)
Jorg Wendorf
(Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
Joris Fellinger
(Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
Kerstin Rummel
(Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
Klaus Grosser
(Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
Marc Sibilia
(Princeton Plasma Physics Laboratory, James Forestall Campus, Princeton, NJ 08542, United States)
Peter Titus
(Princeton Plasma Physics Laboratory, James Forestall Campus, Princeton, NJ 08542, United States)
Soren Klose
(Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
Team W7-X
(Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
Uwe Schultz
(Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
Uwe Wenzel
(Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
