Advances in sawtooth control for NTM prevention in JET

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 sawteethkeep 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