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S. Coda, MHD workshop, PPPL, 22 Nov. 2004S. Coda, MHD workshop, PPPL, 22 Nov. 2004
Advances in sawtooth controlfor NTM prevention in JET
S. Coda1, L.-G. Eriksson2, J. Graves1, R. Koslowski3,F. Nave4, P. Belo4, R.J. Buttery5, S. Cowley6,
P. de Vries5,7, M.J. Mantsinen8, M.-L. Mayoral5,A. Mück1, O. Sauter1, E. Westerhof7,
and JET-EFDA contributors1CRPP, EPFL, Association Euratom-Fédération Suisse, Lausanne, Switzerland2Association Euratom-CEA, DRFC, Cadarache, France3Association Euratom-FZ Jülich, Institut für Plasmaphysik, TEC, Jülich, Germany4Associação Euratom-IST, Centro de Fusão Nuclear, Lisbon, Portugal5Euratom-UKAEA Fusion Association, Culham Science Center, United Kingdom6Department of Physics, Imperial College, London, United Kingdom7Association Euratom-FOM, FOM-Rijnhuizen, TEC, Nieuwegein, The Netherlands8Association Euratom-Tekes, Helsinki University of Technology, Finland
S. Coda, MHD workshop, PPPL, 22 Nov. 2004Sawtooth control in JET
Outline
• NTM triggering by long sawteeth
• Sawtooth destabilization by ICCD
• Sawtooth destabilization by counter-NBI
S. Coda, MHD workshop, PPPL, 22 Nov. 2004Sawtooth control in JET
Long sawteeth trigger (3,2) NTMs
at low N
O. Sauter et al., PRL 88, 105001 (2002)
Avoidance strategy:
destabilize sawteeth
keep seed island small
S. Coda, MHD workshop, PPPL, 22 Nov. 2004Sawtooth control in JET
Fishbones are less of a concern
S. Coda, MHD workshop, PPPL, 22 Nov. 2004Sawtooth control in JET
Discrete jump in N at long Tst…
S. Coda, MHD workshop, PPPL, 22 Nov. 2004Sawtooth control in JET
…but N vs. Tst not really so simple
S. Coda, MHD workshop, PPPL, 22 Nov. 2004Sawtooth control in JET
ICRH control of sawtooth period
• +900 at center: max fast-ion stabilization• -900 at q=1: max ICCD destabilization
M.-L. Mayoral et al., PoP 11, 2607 (2004)
Both effects increase with ICRH power
S. Coda, MHD workshop, PPPL, 22 Nov. 2004Sawtooth control in JET
ICCD destabilizationof fast-particle-stabilized
sawteeth• ITER simulation:
-particles ICRH-accelerated fast ions• ICCD at q=1 to keep sawteeth short:
tested only without strong fast particle pressure(crash criterion different)
• need 2 ICRH frequencies (H minority)• It works! Must still apply to NTM scenario
(NBI)L.-G. Eriksson et al., PRL 92, 235004 (2004)
S. Coda, MHD workshop, PPPL, 22 Nov. 2004Sawtooth control in JET
Control experiments:fast ions vs. ICCD
S. Coda, MHD workshop, PPPL, 22 Nov. 2004Sawtooth control in JET
Control experiments: B-field scan
S. Coda, MHD workshop, PPPL, 22 Nov. 2004Sawtooth control in JET
Sawtooth destabilizationby counter-NBI
• Sawteeth shorter with counter- than co-NBI
S. Coda, MHD workshop, PPPL, 22 Nov. 2004Sawtooth control in JET
Rotation scan in counter-NBI• Sawtooth period is minimum at P~4 MW
S. Coda, MHD workshop, PPPL, 22 Nov. 2004Sawtooth control in JET
Minimum Tst found at finite rotation
Explanation?• NBCD unlikely• Fast ions
unlikely• Promising
candidate: internal kink stabilization by sheared rotation
S. Coda, MHD workshop, PPPL, 22 Nov. 2004Sawtooth control in JET
Shape also affects sawteeth
S. Coda, MHD workshop, PPPL, 22 Nov. 2004Sawtooth control in JET
Conclusions
• NTMs are expected to be excited in ITER by long sawteeth stabilized by -particles
• ICCD at q=1 has been proven to be an effective means of shortening sawteeth, even with large fast-ion pressure, thus preventing NTMs
• Additional sawtooth destabilization tools demonstrated on JET: rotation in counter-NBI and higher elongation
S. Coda, MHD workshop, PPPL, 22 Nov. 2004Sawtooth control in JET
Plans for coming campaigns
• Demonstrate NTM prevention scenario with combined sawtooth stabilization/destabilization scheme– Attempt feedback on ICRH frequency for scenario
optimization– Use new ICRH antenna for better coupling during
ELMs
• Further characterize NTM triggering in a wider range of plasma parameters
S. Coda, MHD workshop, PPPL, 22 Nov. 2004Sawtooth control in JET
N *
• Modified Rutherford equation:
– small island effects cause a * dependence wpol *
N * criterion
– usually assumes a given seed size
S. Coda, MHD workshop, PPPL, 22 Nov. 2004Sawtooth control in JET
New JET-EP ICRH antenna
• Better coupling esp. during ELMs