Speaker
Mr
Shohei Yamoto
(Faculty of Science and Technology, Keio University, Japan)
Description
With the move in current and future fusion devices to all-metal walls, and particularly with tungsten (W) plasma-facing components, understanding heavy ion impurity transport processes in the Scrape-Off Layer (SOL)/divertor region is becoming one of the most critical issues for tokamak operation. To improve this understanding, we are continuing to develop the kinetic SOL/divertor impurity transport code IMPGYRO (IG), which tracks the trajectory of impurity ions in the plasma, resolving their full gyro-orbits.
For the W transport in the SOL/divertor region, the friction force, the thermal force, the E×B drift and the anomalous radial transport are traditionally regarded as the dominant factors. In addition to these, it has recently been pointed out that neoclassical transport processes can have non-negligible effects on transport in the SOL/divertor region. In this paper, we mainly focus on neoclassical transport processes associated with the parallel transport of W impurities in single null divertor configurations.
We focus the IG simulations using a plasma background obtained with the SOLPS5.0 plasma boundary code suite on the magnetic equilibrium of the JT-60U pulse #49540. When the background plasma is in a high recycling state, the W particles have been pushed upstream by the strong thermal force and transported to the top region of the SOL due to the existence of a steep parallel temperature gradient in front of the divertor plate. The W particles then stagnate near the top of the SOL where the parallel thermal force and the friction force are in balance. The W impurities then penetrate into the main plasma due to the grad-B drift and curvature drifts, which are automatically taken into account in the IG modelling, causing a net inward perpendicular flux.
In order to better understand the W penetration process, we compare the IG model to a simpler guiding centre model with an anomalous transport. We find that in general the IG radial velocities tend to be larger than those from the guiding centre model. As a consequence, localized impurities have a larger radial flux in the IG calculation. The results suggest that not only the anomalous diffusion but also the drifts, specifically the grad-B drift and the curvature drift, should be taken into account in order to correctly predict the W core accumulation.
| Country or International Organization | Japan |
|---|---|
| Paper Number | TH/P6-23 |
Primary author
Mr
Shohei Yamoto
(Faculty of Science and Technology, Keio University, Japan)
Co-authors
Prof.
Akiyoshi Hatayama
(Faculty of Science and Technology, Keio University, Japan)
Mr
Haruyuki Inoue
(Faculty of Science and Technology, Keio University, Japan)
Dr
Kazuo Hoshino
(Japan Atomic Energy Agency, Japan)
Dr
Richard Pitts
(ITER Organization, France)
Dr
Steve Lisgo
(ITER Organization, France)
Dr
Xavier Bonnin
(ITER Organization, France)
Dr
Yuki Homma
(Japan Atomic Energy Agency, Japan)
