Speaker
Christian Brandt
(Max-Planck-Institute for Plasma Physics)
Description
The quasi-steady state high power plasma experiments at Wendelstein 7-X are expected to become pioneering research benchmarking the advanced stellarator concept. The results will bring comparisons to the huge amount of experimental findings in other stellarator and tokamak devices. After the successful start of hydrogen plasmas in February 2016, the set of plasma diagnostics will be extended during the shutdown phase (between OP1.1 and OP1.2, to start in 2017). The soft X-ray multi-camera tomography system (XMCTS), a key diagnostic for the detection of high-frequency instabilities and MHD-mode dynamics, is planned to be included in OP 1.2. Twenty pinhole cameras aligned on a poloidal circumference are installed inside the plasma vessel within a segmented stainless steel support structure. Each camera is fitted with a silicon diode array (AXUV) and a curved beryllium filter (transparent for photon energies >1keV). For design, engineering and manufacturing of the mechanic and electronic components of the XMCTS an extensive set of requirements had to be met, that are special for operation in such a long discharge plasma device. This includes for instance the handling of sputtering of wall material, which can be comparable to one month of operation in usual short-pulsed fusion plasma devices and the need for active cooling. Especially here the welding procedure of the pipes (water cooling, signal) in the complex 3D geometry is very sophisticated. During plasma operation inaccuracies of the diagnostic from misalignment can result due to thermal movement of in vessel components. Other issues as electronic pickup during ECRH heating or the influence of the variances of the thicknesses of the Be-filter on the results of tomography are also discussed. This paper provides a summary of technical issues solved, electronic demands fulfilled and results from tomographic reconstruction of synthetic emissivity distributions modulated in time and in space assuming high-frequency MHD-modes.
Co-authors
Christian Brandt
(Max-Planck-Institute for Plasma Physics, 17491 Greifswald, Germany)
Henning Thomsen
(Max-Planck-Institute for Plasma Physics, 17491 Greifswald, Germany)
Mathias Schulke
(Max-Planck-Institute for Plasma Physics, 17491 Greifswald, Germany)
Mirko Marquardt
(Max-Planck-Institute for Plasma Physics, 17491 Greifswald, Germany)
Paolo Franz
(Consorzio RFX, 35127 Padova, Italy)
Sven Weißflog
(Max-Planck-Institute for Plasma Physics, 17491 Greifswald, Germany)
Thomas Sieber
(Max-Planck-Institute for Plasma Physics, 17491 Greifswald, Germany)
Torsten Broszat
(Max-Planck-Institute for Plasma Physics, 17491 Greifswald, Germany)
