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research article

The negative triangularity tokamak: stability limits and prospects as a fusion energy system

Medvedev, S. Yu.
•
Kikuchi, M.
•
Villard, L.
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2015
Nuclear Fusion

The paper discusses edge stability, beta limits and power handling issues for negative triangularity tokamaks. The edge magnetohydrodynamic stability is the most crucial item for power handling. For the case of negative triangularity the edge stability picture is quite different from that for conventional positive triangularity tokamaks: the second stability access is closed for localized Mercier/ballooning modes due to the absence of a magnetic well, and nearly internal kink modes set the pedestal height limit to be weakly sensitive to diamagnetic stabilization just above the margin of the localized mode Mercier criterion violation. While a negative triangularity tokamak is thought to have a low beta limit with its magnetic hill property, it is found that plasmas with reactor-relevant values of normalized beta beta(N) > 3 can be stable to global kink modes without wall stabilization with appropriate core pressure profile optimization against localized mode stability, and also with increased magnetic shear in the outer half-radius. The beta limit is set by the n = 1 mode for the resulting flat pressure profile. The wall stabilization is very inefficient due to strong coupling between external and internal modes. The n > 1 modes are increasingly internal when approaching the localized mode limit, and set a lower beta in the case of the peaked pressure profile leading to a Mercier unstable core. With the theoretical predictions supported by experiments, a negative triangularity tokamak would become a prospective fusion energy system with other advantages including a larger separatrix wetted area, more flexible divertor configuration design, wider trapped particle-free scrape-off layer, lower background magnetic field for internal poloidal field coils, and larger pumping conductance from the divertor room.

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Type
research article
DOI
10.1088/0029-5515/55/6/063013
Web of Science ID

WOS:000356236500015

Author(s)
Medvedev, S. Yu.
Kikuchi, M.
Villard, L.
Takizuka, T.
Diamond, P.
Zushi, H.
Nagasaki, K.
Duan, X.
Wu, Y.
Ivanov, A. A.
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Date Issued

2015

Publisher

IOP Publishing Ltd

Published in
Nuclear Fusion
Volume

55

Issue

6

Article Number

063013

Subjects

tokamak

•

power exhaust handling

•

MHD stability

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
SPC  
Available on Infoscience
September 28, 2015
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/119324
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