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research article

Impact of heat deposition profile on global confinement of NBI heated plasmas in the LHD

Yamada, H.
•
Murakami, S.
•
Yamazaki, K.
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2003
Nuclear Fusion

Energy confinement and heat transport of net-current-free NBI heated plasmas in the large helical device (LHD) are discussed with emphasis on density and power deposition profile dependences. Although the apparent density dependence of the energy confinement time has been demonstrated in a wide parameter range in LHD, the loss of this dependence has been observed in the high density regime under specific conditions. Broad heat deposition due to off-axis alignment and shallow penetration of neutral beams degrades the global energy confinement while the local heat transport maintains a clear temperature dependence, lying between Bohm and gyro-Bohm characteristics. The central heat deposition tends towards an intrinsic density dependence like tau(E) alpha ((n) over bar (e)/p)(0.6) from the state where density dependence is lost. The broadening of the temperature profile due to the broad heat deposition profile contrasts with the invariant property that has been observed widely as profile resilience or stiffness in tokamak experiments. The confinement improvement as a result of the inward shift of the magnetic axis is obvious in the core region, which emphasizes the improvement of transport because of the geometry being unfavourable for the central heating of NBI in this configuration. The edge pressure, clearly, does not depend on the magnetic axis position. Unlike a tokamak H-mode, the edge pressure is determined by transport and can be increased by increasing the heating power.

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Type
research article
DOI
10.1088/0029-5515/43/8/317
Web of Science ID

WOS:000185180800017

Author(s)
Yamada, H.
Murakami, S.
Yamazaki, K.
Kaneko, O.
Miyazawa, J.
Sakamoto, R.
Watanabe, K. Y.
Narihara, K.
Tanaka, K.
Sakakibara, S.
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Date Issued

2003

Publisher

IOP Publishing Ltd

Published in
Nuclear Fusion
Volume

43

Issue

8

Start page

749

End page

755

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
CRPP  
SPC  
Available on Infoscience
April 16, 2008
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/21899
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