Speaker
Dr
Samuel Lazerson
(Princeton Plasma Physics Laboratory)
Description
The measurement and correction of error fields in Wendelstein 7-X (W7-X) is critical to long pulse high beta operation, as small error fields may cause overloading of divertor plates. Accordingly, as part of a broad collaborative effort, the detection and correction of error fields on the W7-X experiment has been performed using the U.S. supplied trim coil system [1] in conjunction with the flux surface mapping diagnostic [2] and the U.S. supplied high resolution infrared camera [3]. In the early commissioning phase of the experiment, the trim coils were used to open an n/m=1/2 island chain in a specially designed magnetic configuration [3]. The flux surfacing mapping diagnostic was then able to directly image the magnetic topology of the experiment, allowing the inference of a small ~4 cm intrinsic island chain [4]. Scaled to the planned operating field (2.5 T), such error fields would be correctable using less than 10% the rated trim coil capacity. The suspected main source of the error field, slight misalignment of the superconducting coils, is then confirmed through a synthetic flux surface mapping diagnostic and detailed measurements of the coil positions. Confirmation of the error fields allows the assessment of magnetic fields which resonate with the n/m=5/5 island chain. Predictions of the extent to which these error fields, if left uncorrected, could limit plasma performance are presented. Plasma experiments without applied correcting fields show a significant asymmetry in neutral pressure (centered in module 4) and light emission (visible, H-alpha, and carbon). Such pressure asymmetry is associated with divertor heat load asymmetries between the modules. Application of trim coil fields with n=1 waveform correct the imbalance. Observations of the limiters temperatures in module 5 shows a clear dependence of the limiter heat flux pattern as the perturbing fields are rotated.
[1] Rummel T et al. “The Wendelstein 7-X Trim Coil System” IEEE Trans. Appl. Super. 24(3), 2014
[2] Otte M et al. “Setup and initial results form the magnetic flux surface diagnostics at Wendelstein 7-X“, submitted to Plasma Physics and Controlled Fusion
[3] Wurden et al., this conference
[4] Lazerson S et al. “First measurements of error fields on W7-X using flux surface mapping.” submitted to NF
| Country or International Organization | United States of America |
|---|---|
| Paper Number | EX/P5-5 |
Primary author
Dr
Samuel Lazerson
(Princeton Plasma Physics Laboratory)
Co-authors
Dr
Christoph Biedermann
(Max-Planck-Institut für Plasmaphysik)
Dr
David Gates
(PPPL)
Dr
Gabor Kocsis
(Wigner Research Center for Physics)
Dr
Glen Wurden
(Los Alamos National Laboratory)
Dr
Joachim Geiger
(Max-Planck-Institut für Plasmaphysik)
Dr
Marcin Jakubowski
(Max-Planck-Institut für Plasmaphysik)
Dr
Matthias Otte
(Max-Planck-Institut für Plasmaphysik)
Dr
Sergey Bozhenkov
(Max-Planck-Institut für Plasmaphysik)
Dr
Tamara Andreeva
(Max-Planck-Institut für Plasmaphysik, Teilinstitut Greifswald, Germany)
Dr
Tamas Szepesi
(Wigner Research Center for Physics)
Prof.
Thomas Sunn Pedersen
(Max-Planck-Institut für Plasmaphysik)
Dr
Uwe Wenzel
(Max-Planck-Institut für Plasmaphysik)
