Speaker
Costanza Maggi
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.111.pdf
Scientific results of the collaboration on tokamak pedestal physics between
Europe and the Asia-Pacific region (2018 PPCF Dendy Award)
Hajime Urano1, Costanza Maggi2, Ohjin Kwon3, Samuli Saarelma2
1
National Institutes for Quantum Radiological Science and Technology, Naka Fusion
Institute, Naka, 311-0193 Japan
2
CCFE, Culham Science Centre, Abingdon, OX14 3DB, UK
3
Daegu University, 201 Daegudaero,Gyeongsan, Gyeongbuk, 38453 Republic of Korea
The collaboration has expanded the understanding of tokamak pedestal physics
through multimachine experiments, in particular JET and JT-60U, and theoretical analysis.
The issues considered were plasma shape (including X-point location), neutrals, global
plasma beta, TF ripple and edge rotation. The work has led to more accurate models for
predicting ITER and DEMO pedestals.
In both JET and JT-60U a robust correlation was found between total and pedestal
thermal stored energy and improved edge stability was correlated with increasing total
poloidal normalized pressure [1]. Despite their similar plasma size, the plasma performance
of the two tokamaks can be different, which arises from machine-related aspects, such as
shape, aspect ratio, TF ripple. The effects of TF ripple and edge rotation on the pedestal
structure were investigated by the collaboration between the two tokamaks [2]. The effect of
plasma shape on the pedestal width was examined focusing on the different operational areas
of JET and JT-60U [3]. The effects of plasma triangularity, global beta and neutrals on
pedestal confinement and stability were investigated in JET with the Be/W ITER-like wall
[4]. On the theoretical side, the collaboration initially focussed on the effect of the X-point
on pedestal stability. The X-point, depending on its poloidal location, can have opposite
effects on peeling and ballooning modes, the two instabilities that govern linear MHD
pedestal stability [5]. Analysis of simulated ITER plasmas has shown that, unlike most
currently operating tokamaks that are limited by coupled peeling-ballooning modes, ITER
pedestals are likely to be limited by low-n peeling modes due to very low collisionality and,
consequently, high bootstrap current [6]. Pedestal predictions for the European DEMO have
indicated that the beneficial effect of triangularity on pedestal stability saturates at a certain
triangularity value, giving an upper limit for system studies for the maximum pedestal that
can be achieved by plasma shaping alone.
The Award recipients feel privileged that their collaborative work was highly
recognized.
[1] CF Maggi et al., Nucl. Fusion 47 (2007) 535; [2] H Urano et al., Nucl. Fusion 51 (2011) 113004;
[3] H Urano, S Saarelma et al., Proc. IAEA FEC 2016, Kyoto, EX/3-4.; [4] CF Maggi et al., Nucl.
Fusion 55 (2015) 113031; [5] S Saarelma, OJ Kwon et al., Plasma Phys. Control. Fusion 53 (2011)
025011; [6] S Saarelma et al., Nucl. Fusion 52 (2012) 103020.
