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O. Sauter, JA-2, 2015.10.01, p.1
Multiple NTM modes in experiment
and nonlinear coupling
O. Sauter
Ecole Polytechnique Fédérale de Lausanne (EPFL)
Swiss Plasma Center (SPC)
Lausanne, Switzerland
http://infoscience.epfl.ch/record/212765
O. Sauter, JA-2, 2015.10.01, p.2
Outline
• Several cases, mainly taken from published data
• Coupling (locked frequencies) can have little effects or
stabilizating effects
• No «dramatic» effects observed so far…
O. Sauter, JA-2, 2015.10.01, p.3
«Standard» case when increasing power
R. Buttery, Nucl. Fus. 43 (2003) 69, JET
• Increasing power• 4/3 appears• Then 3/2• Finally 2/1,
which locks «whole» plasma(E. Lazzaro, PoP 9 (2002) 3907)
O. Sauter, JA-2, 2015.10.01, p.4
«Standard» case when increasing power
• DIII-D/JET similarities• At 2/1 onset, little change of 3/2, which continues.
T. Hender et al, IAEA 2002, JET
•While 2/1 locks, 3/2 can lock to 2/1 with little effects
O. Sauter, JA-2, 2015.10.01, p.5
Large trigger can yield several modes
R. Buttery, IAEA 2004, JET
• 3 modes triggered together• 2/1 leads the locking• Termination seems similar to
when only 2/1 mode present
O. Sauter, JA-2, 2015.10.01, p.6
TCV
O. Sauter, JA-2, 2015.10.01, p.7
Non-harmonic coupling
D. Raju, PPCF 45 (2003) 369
O. Sauter, JA-2, 2015.10.01, p.8
4/3 effect on 3/2 mode
D. Raju, PPCF 45 (2003) 369
O. Sauter, JA-2, 2015.10.01, p.9
4/3 effect on 3/2 mode=> constant D’coupling<0
O. Sauter, PPCF 44 (2002) 1999
2 consecutive ST crashestrigger and stabilize 4/3
3/2 evolution consistentwith a constant negativeD’ in modif. Ruth eq.
JET
O. Sauter, JA-2, 2015.10.01, p.10
3/2 preemption may also help for 2/1 preemption
D. Kim, PhD thesis No 6539, EPFL, 2015
2/1 mode avoided with 3/2 preemption: preliminary resultsMay indicate coupling, marginal conditions, q profile changes: to checkDifficult to trigger 2/1 without first a 3/2 mode…
TCV
O. Sauter, JA-2, 2015.10.01, p.11
Changing q profile does play a role
E. Lazzaro, Nucl. Fusion 55 (2015) 093031D. Kim, PhD thesis No 6539, EPFL, 2015
• Same power ramp but different co/cnt components of beams
• Onset at different power levels
• 3/2 mode contribution before 2/1 onset is different as well
TCV
O. Sauter, JA-2, 2015.10.01, p.12
Some conclusions
•Multiple modes can co-exist without coupling (most cases)•Usually the mode with larger r(q=m/n) dominates•Mode can couple: best analysis is bi-coherence•Need to check exact frequency coupling•Need to check effective effects on island widths(t)
(nonlinear/frequency coupling does not necessarily mean «strong» coupling)•Word of caution: 2/1 modes tend to kill rotation over whole
plasma thus all modes "will" «lock» during the process•Role if any of 3/2 preemption on 2/1 avoidance may
provide more insight