O. Sauter “Robust” NTM Control: The AMN-system O. Sauter for the TCV and AUG teams Ecole Polytechnique Fédérale de Lausanne (EPFL) Centre de Recherches en Physiques des Plasmas (CRPP) Lausanne, Switzerland

O. Sauter Outline Introduction TCV developments and results Introduction into AUG RT-control and results Conclusions

O. Sauter Introduction (1) We know we can stabilize NTMs with localized ECCD We know we need deposition within w cd /2 (=> some power within island) We can use RT-equil and RT-ray-tracing to match  dep with  (q=m/n) We «know» we never get a perfect match within w cd /2 How do we deal with this problem? Question even more relevant in larger machines, since w cd typically stays constant but minor radius increases

O. Sauter Introduction (2) Improve RT-equilibrium and add an «offset» to provide  (q=m/n+offset) =>  eff (q=m/n) => This usually works only in «similar scenarios», similar betas Feedback control mirrors towards best position, checking largest effect on mode width, and stay there => This works best if there is a mode, thus not for pre-emption Inline ECE to measure exact deposition position relative to ECE perturbation, avoids offset from RT-equil => works only when there is a mode, not for pre-emption Main strategies so far: New strategy proposed (based on above results): Recognise minimum offset ~  =0.05 «Continuously» move mirrors around  eff (q=m/n)±0.05 Make sure ECCD crosses island location Works for stabilization and pre-emption

O. Sauter Previous TCV results Felici et al, Nucl. Fusion 52 (2012) ECCD deposition approaches island position (2/1 mode) from inside and outside, then stays

O. Sauter Previous TCV results Felici et al, Nucl. Fusion 52 (2012) Mirror angle = 19.9 o and 18 o (  V =0.04)

O. Sauter Similar results for 2/1 and 3/2 2/1 mode 3/2 mode Felici et al, Nucl. Fusion 52 (2012) Need to «be» at the island position Fast stabilization once at right position No «bad effects» when not at the island position, either outside or inside W sat slightly larger when inside consistent with slightly larger bootstrap of larger heat flux For both 3/2 and 2/1 cases:

O. Sauter Simple solution => «robust» NTM control Add  (t) to  target from RT-equil D. Kim, PhD thesis 6539 (2015) infoscience.epfl.ch/record/205040

O. Sauter Can stabilize NTM even with on purpose misalignement q target =2.5,  =0.1 q target =1.6,  =0.1 TCV Note: no destabilization with sweeping either sides

O. Sauter Determination of optimum  (t) q target cst  =0.04, f=10Hz  =0.08, f=3Hz freq too high, mirror cannot follow => equivalent to constant Amplitude too high for small freq => too much time «outside» the good position Easy to determine optimum for given mirror characteristics

O. Sauter Preemption and marginal power Pre-emption works since beam position does not depend on mode Yields much better P marg results Previous results need to be revisited D. Kim, PhD thesis 6539 (2015) infoscience.epfl.ch/record/205040

O. Sauter AUG: demonstration adding sweeping Destabilize mode then to 10MW NBI Add 1 beam, then a 2 nd, then a 3rd  (3/2)+  (t) same for all beams (then rt-TORBEAM calculates angles) Results as predicted from TCV: Mode stabilized more and more Mode not destab. more and more

O. Sauter Alternative phases of stabilization and «no stabilization» Time-regions when island decreases consistent with deposition close to rt-rho(3/2)

O. Sauter Zoom in shows corresponding effect on harmonic Small effects with 1 beam Clear effect with 2 beams Full stabilization with 3 beams w marg almost obtained with 2 beams Smaller island yields smaller harmonic coupling

O. Sauter

AMN-system: anti-miss NTM control New strategy for NTM control is proposed Valid for stabilization and pre-emption using SAME method «Simpler the better» With mode use extremum seeking (Schuster et al 2012) Based on the fact that stabilization ~ dirac around  (m/n) Based on the fact that stab(  mn )>>destab(  mn ±w/2) Keep sweeping across island to ensure max. stabil. effects Similar to ABS system: best for efficient breaking is just before wheel slips (tyre def. before slip) Thus rt-control to keep «crossing» this point Crossing (solid) versus cst 1/4-efficient (dashed) versus crossing far away (red)

O. Sauter backups

O. Sauter Moving beams can move  (m/n) as seen with sawteeth Sweeping up to 5.5s, then cst angle Mode stabilized at 5.65s: why not before? Actually mode moves away (+) when beams move towards mode position and do not cross during sweeping Plasma evolves and makes island to cross beams when angle cst Thus same effect Important to compare «similar» shots

O. Sauter Even with beam short pulses get information

O. Sauter Even with beam short pulses get information 2 beams for a short time