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The merits of ion cyclotron resonance heating schemes for sawtooth control in tokamak plasmas

Part of: Focus on Fusion Culham Thesis Prize Winners

Published online by Cambridge University Press:  21 September 2015

I. T. Chapman ,
J. P. Graves ,
M. Lennholm ,
J. Faustin ,
E. Lerche ,
T. Johnson ,
S. Tholerus  and
JET contributors
I. T. Chapman*
Affiliation:
EUROfusion Consortium, JET, Culham Science Centre, Abingdon OX14 3DB, UK CCFE, Culham Science Centre, Abingdon OX14 3DB, UK
J. P. Graves
Affiliation:
EUROfusion Consortium, JET, Culham Science Centre, Abingdon OX14 3DB, UK Ecole Polytechnique Federale de Lausanne, Centre de Recherches en Physique des Plasmas, 1015 Lausanne, Switzerland
M. Lennholm
Affiliation:
EUROfusion Consortium, JET, Culham Science Centre, Abingdon OX14 3DB, UK European Commission, JET Exploitation Unit, Culham Science Centre, Abingdon OX14 3DB, UK
J. Faustin
Affiliation:
EUROfusion Consortium, JET, Culham Science Centre, Abingdon OX14 3DB, UK Ecole Polytechnique Federale de Lausanne, Centre de Recherches en Physique des Plasmas, 1015 Lausanne, Switzerland
E. Lerche
Affiliation:
EUROfusion Consortium, JET, Culham Science Centre, Abingdon OX14 3DB, UK LPP-ERM/KMS, TEC Partner, Brussels, Belgium
T. Johnson
Affiliation:
EUROfusion Consortium, JET, Culham Science Centre, Abingdon OX14 3DB, UK VR, KTH, SE-100 44 Stockholm, Sweden
S. Tholerus
Affiliation:
EUROfusion Consortium, JET, Culham Science Centre, Abingdon OX14 3DB, UK VR, KTH, SE-100 44 Stockholm, Sweden
*
†Email address for correspondence: ian.chapman@ccfe.ac.uk
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Abstract

JET experiments have compared the efficacy of low- and high-field side ion cyclotron resonance heating (ICRH) as an actuator to deliberately minimise the sawtooth period. It is found that low-field side ICRH with low minority concentration is optimal for sawtooth control for two main reasons. Firstly, low-field side heating means that any toroidal phasing of the ICRH ( $-90^{\circ }$ , $+90^{\circ }$ or dipole) has a destabilising effect on the sawteeth, meaning that dipole phasing can be employed, since this is preferable due to less plasma wall interaction from Resonant Frequency (RF) sheaths. Secondly, the resonance position of the low-field side ICRH does not have to be very accurately placed to achieve sawtooth control, relaxing the requirement for real-time control of the RF frequency. These empirical observations have been confirmed by hybrid kinetic–magnetohydrodynamic modelling, and suggest that the ICRH antenna design for ITER is well positioned to provide a control actuator capable of having a significant effect on the sawtooth behaviour.

Type
Research Article
Information
Journal of Plasma Physics , Volume 81 , Issue 6 , December 2015 , 365810601
Copyright
© UK Atomic Energy Authority 2015 

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