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