Speaker
Dr
Joon-Wook Ahn
(Oak Ridge National Laboratory)
Description
Understanding of underlying physics processes that determine non-axisymmetric divertor footprints is crucial for ITER’s long pulse operation scenario in the presence of 3-D fields, as they will cause asymmetric erosion and re-deposition of divertor material. It has been recently found that plasma response plays a key role in the formation of 3-D lobe structure and divertor footprints by the applied 3-D fields in NSTX and KSTAR.
Work in NSTX showed that ideal plasma response from the IPEC modeling can significantly shield or amplify vacuum footprints from field line tracing. Comparison of footprint measurements by visible and IR cameras to the data from field line tracing reveals that n=1 magnetic perturbations are significantly amplified while n=3 perturbations are shielded. The mechanism of amplification and shielding is determined by the competition between shielding of resonant components and excitation of non-resonant components of applied 3-D fields, demonstrated in the poloidal field spectrum when including plasma response in the modeling. Connection length (Lc) profile from the IPEC modeling for n=1 case shows that Lc rapidly begins to decrease in a significantly deeper region, compared to the vacuum case where it only drops near the very plasma edge, corresponding to a dramatic amplification of vacuum footprint splitting.
Shielding and amplification of applied 3-D fields have been also observed in KSTAR by IPEC plasma response modeling. A full phase shift scan was conducted for n=1 perturbations, while two distinctive phases (90 deg for resonant and 0 deg for non-resonant coil configuration) were closely examined for n=2 perturbations. As in NSTX, non-resonant components of applied fields are amplified due to kink excitation while resonant components are strongly shielded, which produces net amplification (shielding) effect of applied fields that strengthens (weakens) footprint splitting, depending on which action is more dominant for a specific phase shift. Radial location of lobes in the measured heat flux profile shows better agreement with that from the field line tracing when plasma response is taken into account for calculation.
This work was supported by the US Department of Energy, contract numbers DE-AC05-00OR22725 (ORNL), DE-AC02-09CH11466 (PPPL), DE-FC02-04ER54698 (GA), and DE-AC52-07NA27344 (LLNL), and DE-SC0013911 (UW).
| Country or International Organization | USA |
|---|---|
| Paper Number | EX/P4-30 |
Primary author
Dr
Joon-Wook Ahn
(Oak Ridge National Laboratory)
Co-authors
Dr
Adam McLean
(Lawrence Livermore National Laboratory)
Dr
Alberto Loarte
(ITER Organization)
Dr
Alexis Briesemeister
(ORNL)
Dr
Chan Soo Kang
(National Fusion Research Institute)
Mr
Filippo Scotti
(LLNL)
Dr
Gustavo Canal
(General Atomics)
Dr
Hyung Ho Lee
(National Fusion Research Institute)
Dr
Jaehyun Kim
(National Fusion Research Institute)
Dr
Jeremy Lore
(ORNL)
John Canik
(Oak Ridge National Laboratory)
Dr
Jong-Kyu Park
(Princeton Plasma Physics Laboratory)
Dr
Kimin Kim
(Korea Advanced Institute of Science and Technology)
Dr
Oliver Schmitz
(University of Wisconsin - Madison, Department of Engineering Physics)
Dr
Rajesh Maingi
(Princeton Plasma Physics Laboratory)
Dr
Richard Pitts
(ITER Organization)
Dr
Si-Woo Yoon
(National Fusion Research Institute)
Dr
Travis Gray
(Oak Ridge National Laboratory)
Dr
Won Ha Ko
(Korea, Republic of)
Dr
Yongkyoon In
(National Fusion Research Institute)
Dr
YoungMu Jeon
(National Fusion Research Institute)
