1. 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

2. 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…

3. 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)

4. 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

5. 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

6. O. Sauter, JA-2, 2015.10.01, p.6 TCV

7. O. Sauter, JA-2, 2015.10.01, p.7 Non-harmonic coupling D. Raju, PPCF 45 (2003) 369

8. O. Sauter, JA-2, 2015.10.01, p.8 4/3 effect on 3/2 mode D. Raju, PPCF 45 (2003) 369

9. O. Sauter, JA-2, 2015.10.01, p.9 4/3 effect on 3/2 mode=> constant  ’ coupling <0 O. Sauter, PPCF 44 (2002) 1999 2 consecutive ST crashes trigger and stabilize 4/3 3/2 evolution consistent with a constant negative  ’ in modif. Ruth eq. JET

10. 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 results May indicate coupling, marginal conditions, q profile changes: to check Difficult to trigger 2/1 without first a 3/2 mode… TCV

11. O. Sauter, JA-2, 2015.10.01, p.11 Changing q profile does play a role E. Lazzaro, Nucl. Fusion 55 (2015) 093031 D. 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

12. 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  ( 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