Speaker
Prof.
Byron Peterson
(National Institute for Fusion Science)
Description
Various noble gasses have been seeded in the Large Helical Device (LHD) to reduce the divertor heat load through enhanced radiation [1]. At the vertically elongated cross-section, in the case of N_2 seeding, bolometric images show additional outboard radiation, while in the case of Ne, only inboard radiation is observed. With N_2 seeding, radiation is observed by two imaging bolometers [2], viewing the same poloidal cross-section from top and bottom ports, respectively, at a location which is 36 degrees toroidally removed from the N_2 gas puff nozzle located at the bottom of the machine. These measurements both confirm that the additional radiation from the outboard side is coming exclusively from the top of the cross-section, indicating poloidal asymmetry. Triangulation between the two imaging bolometer signals indicates that the additional outboard radiation is coming from near the upper part of the last closed flux surface, and that the standard inboard radiation is coming from the upper x-point region. With N_2 seeding the radiation enhancement is observed to be from 20 - 100% depending on the discharge, while the reduction in divertor heat load indicated by I_sat was more than 50% in some locations but varied strongly toroidally, while in the case of Ne the I_sat signals are quite uniform toroidally. Modelling by EMC3-EIRENE [3] shows that the outboard radiation is enhanced with N_2 (versus Ne) seeding and with reduced recycling (0 versus 100 %) indicating that the localized outboard radiation may be attributed to reduced recycling of N2. Also, modelling with EMC3-EIRENE using a 90 degree (toroidally) model can reproduce the upper localization of the radiation at a cross-section which is 36 degrees toroidally separated from the N_2 source located at the bottom of the cross-section as is the case in the experiment.
[1] K. Mukai et al., Nucl. Fusion 55 (2015) 083016.
[2] B.J. Peterson et al., Rev. Sci. Instrum. 74 (2003) 2040.
[3] G. Kawamura et al., Contrib. Plasma Phys. 54 (2014) 437.
| Country or International Organization | Japan |
|---|---|
| Paper Number | EX/P8-6 |
Primary author
Prof.
Byron Peterson
(National Institute for Fusion Science)
Co-authors
Dr
Gakushi Kawamura
(National Institute for Fusion Science)
Dr
Gen Motojima
(National Institute for Fusion Science)
Dr
Hirohiko Tanaka
(National Instutute for Fusion Science)
Dr
Junichi Miyazawa
(National Institute for Fusion Science)
Dr
Kiyofumi Mukai
(National Institute for Fusion Science)
Dr
Masahiro Kobayashi
(NIFS)
Dr
Motoshi Goto
(National Institute for Fusion Science)
Prof.
Noriyasu Ohno
(Graduate School of Engineering, Nagoya University)
Dr
Ryuichi Sakamoto
(National Institute for Fusion Science)
Dr
Ryuichi Sano
(National Institute for Fusion Science)
Dr
Shuyu Dai
(Dalian University of Technology)
Dr
Shwetang Pandya
(Institute for Plasma Research)
Prof.
Suguru Masuzaki
(National Institute for Fusion Science)
Prof.
Tomohiro Morisaki
(National Institute for Fusion Science)
Dr
Tsuyoshi Akiyama
(National Institute for Fusion Science)
