Active Control of Alfvén Eigenmodes in the ASDEX Upgrade tokamak

Active Control of Alfvén Eigenmodes in the ASDEX Upgrade tokamak M. Garcia-Munoz, S. E. Sharapov, J. Ayllon, B. Bobkov, L. Chen, R. Coelho, M. Dunne, J. Ferreira, A. Figueiredo, M. Fitzgerald, J. Galdon-Quiroga, D. Gallart, B. Geiger, J. Gonzalez-Martin, V. Igochine, T. Johnson, P. Lauber, M. Mantsinen, F. Nabais, V. Nikolaeva, M. Nocente, T. Odstrcil, J. Rivero- Rodriguez, M. Rodriguez-Ramos, L. Sanchis-Sanchez, P. Schneider, M. Schubert, A. Snicker, J. Stober, W. Suttrop, G. Tardini, Y. Todo, P. Vallejos, B. Vanovac, M. A. Van Zeeland, E, Viezzer, F. Zonca, the ASDEX Upgrade and the EUROfusion MST1 Team

Active Control of Fast-Ion Driven MHD Fluctuations Might Be Mandatory in Future Devices Good confinement of fast-ions - fusion reactions, Neutral Beam Injection (NBI) and RF heating - is essential for Fusion performance / NBI current drive Device integrity Fast-ion driven MHD fluctuations might be controlled via external actuators such as Localized ECRH/ECCD Externally applied 3D fields RF beatwaves AE induced fast-ion losses in AUG* ECRH at r/a = 0.33 *M. Garcia-Munoz et al., Phys. Rev. Lett.104 (2010)

Active Control of Fast-Ion Driven MHD Fluctuations Might Be Mandatory in Future Devices AE control through localized ECRH / ECCD AE induced fast-ion losses in AUG* AE control through fastion phase-space engineering via externally applied 3D fields ECRH at r/a = 0.33 *M. Garcia-Munoz et al., Phys. Rev. Lett.104 (2010)

Near Axis ECRH Suppresses NBI Driven RSAEs Experiments carried out during current ramp-up phase to have elevated q-profile and high fast-ion pressure Multiple RSAEs flatten fast-ion profile In the absence of RSAEs classical fast-ion profiles are measured M. Garcia-Munoz et al., IAEA TM EP 2015

NBI Driven RSAEs Are Suppressed Due To n=0 Frequency Upshift M. Garcia-Munoz et al., IAEA TM EP 2015 M. A. Van Zeeland et al., Nucl. Fusion 2016 S. E. Sharapov et al., EPS 2017 Local ECRH can modify n=0 continuum / GAM frequency by means of changes in T e, T i and related gradients The RSAE frequency band between GAM and TAE frequency shrinks as pressure and pressure gradients increases TAEFL, LIGKA and NOVA modelling shows no-sweeping RSAEs are not eigenfunction of the system with large mode growth rate drops

Off-Axis ECRH Facilitates ICRH Driven TAEs In AUG TAEs are driven unstable by supra-alfvénic ICRH ions during current flat-top Off-axis ECRH facilitates TAEs during entire flat-top ECRH effect is stronger as q-profile relaxes and system is closer to stability limit TAE activity changes on ms time-scale

On-Axis ECRH Blips Have Strong Impact on TAE Frequency But Not on Amplitude Short ECRH blips to avoid L-H transition, i.e. rapid density changes TAE frequency drops with on-axis ECRH as T e rises collisionality drops ECRH at r/a = 0.0 Overall stronger TAE activity with higher collisionality and elevated q-profile

Simulations Suggest Larger Fast-Ion Energy Content During ECRH Facilitates TAE Drive ICRH produces up to 40% larger fast-ion energy content during ECRH phases due to longer fast-ion slowing down time (higher T e ) SELFO Fast-ion pressure gradient is significantly higher during ECRH Additional drive overcomes larger ion Landau and radiative damping Local changes at i/e waveparticle resonances may explain ms time-scales S. E. Sharapov et al., EPS 2017

Externally Applied n=2 3D Fields Are Used To Manipulate Fast-Ion Distribution Through Their Poloidal Spectrum 3D fields poloidal spectrum is modified by applying a toroidal phase difference between the upper and lower sets of coils, ΔΦ UL = Φ upper - Φ lower AUG AUG B-coils Δφ UL MARS-F

Differential Phase Scan To Identify Optimal Coils Configuration For Fast-Ion Losses Differential phase scan applied in NBI heated discharges with elevated q-profile 5 MW NBI heating with tangential and radial beams to probe different fast-ions phase-space volumes 2 MW ECCD to keep high q- profile Clear modulation in fast-ion losses observed in FILD measurements with maximal losses for Δφ=100 and minimal for Δφ~-50

Calculations of Fast-Ion δp Φ due to 3D Fields Reveal Transport is Resonant and Localized Around Separatrix* ASCOT is used to calculate fast-ion δp Φ for all ΔΦ UL using realistic NBI distribution δp Φ (a.u.) P Φ = mrv Φ ZeΨ p Vacuum and MARS-F n=2+6 3D fields No TF-ripple No collisions Realistic 3D wall δp Φ < 0 (blue-black) outwards transport δp Φ > 0 (yellow-white) inwards transport *see L. Sanchis-Sanchez Oral on Thursday

Overlapping of Multiple Linear / Non-Linear Resonances Creates an Edge Resonant Transport Layer (ERTL) Orbital resonances intrinsic to magnetic background ω pol /ω tor =n/p perfectly match δp Φ regions Maximum transport caused by resonance overlap Non-linear resonances* seem to play key role ΔΦ UL =40º ω pol /ω tor =n/p Trapped/ Passing Boundary <δp Φ > Separatrix Poloidal spectrum determines in/outwards transport δp Φ < 0 (blue-black) outwards transport δp Φ > 0 (yellow-white) inwards transport *L.Chen and F. Zonca Rev. Mod. Phys. 88, 015008 (2016)

Changes in ERTL Due to 3D Fields Explain Measured Fast-Ion Losses Maximum and minimum losses observed for n=2 RMP with Δφ~100º and Δφ~-50º respectively NBI#8

TAEs Suppressed / Excited on Command Varying Poloidal Spectrum of Externally Applied 3D Fields NBI driven TAEs in advanced scenario with elevated q-profile TAEs become weaker as q-profile relaxes TAEs are mitigated or even suppressed with Δφ=100 RMPs TAEs are excited with Δφ~-50 RMPs in plasma with slightly higher radiative damping due to higher T e

Full TAE Suppression Through Fast-Ion Phase-Space Engineering Externally applied 3D fields eject fast-ions driving TAEs unstable RMPs TAEs

Full TAE Suppression Through Fast-Ion Phase-Space Engineering Externally applied 3D fields eject fast-ions driving TAEs unstable FILD measurements help identifying the wave-particle resonances responsible for TAE mitigation/suppression RMPs TAEs

FILD Measures Velocity-Space of 3D Fields Induced Fast-Ion Losses Gyroradius (cm) Several populations affected by 3D fields with a dominant one at NBI injection energy and two different pitch-angles Most affected ions are on trapped orbits with dominant signal coming from barely trapped ions 7 6 5 4 3 2 FILD AUG #34570 1 40 50 60 70 80 Pitch Angle (º)

Neutron Spectrometer Measures Clear Changes in Fast-Ion Distribution With RMP Configuration Neutron spectra measures up to x2 larger neutron rate in Δφ=-50º than Δφ=100º Pulse height spectrum Significant differences in neutron spectra shape suggest fast-ion redistribution / loss Missing tail in #34570

Orbit Simulations Suggest Redistribution is Highly Localized in Velocity-Space Impact depends on 3D fields poloidal spectrum and fast-ion distribution 3D fields could lead to dramatic changes in certain phase-space volumes redistributing particles thus changing gradients (drive) ASCOT

Magnetics, ECE, Reflectometry and SXR Are Used To Identify And Localize Modes TAEs span over large frequency range Dominant modes have n=2-4 Magnetics #34570

Magnetics, ECE, Reflectometry and SXR Are Used To Identify And Localize Modes TAEs span over large frequency range Dominant modes have n=2-4 Magnetics #34570 n=4

Magnetics, ECE, Reflectometry and SXR Are Used To Identify And Localize Modes TAEs span over large frequency range Dominant modes have n=2-4 Magnetics n=4 #34570 n=3

Magnetics, ECE, Reflectometry and SXR Are Used To Identify And Localize Modes TAEs span over large frequency range Dominant modes have n=2-4 Magnetics #34570 n=2

Magnetics, ECE, Reflectometry and SXR Are Used To Identify And Localize Modes TAEs span over large frequency range Dominant modes have n=2-4 Magnetics #34570 n=2 TAEs are within ρ pol = 0.6 with some edge coupling

3D Hybrid MHD MEGA* Code Modified to Include RMP Fields J. Gonzalez-Martin Kinetic fast-ion contribution include in MHD code through current terms AUG Two configurations of n=2 RMPs (#34570 & #34571) simulated n=2 & n=6 (main components of RMP fields) vacuum fields included in magnetic equilibria RMP modelling requires full toroidal geometry *Y. Todo, Phys. Plasma 13, 082503 (2006) MEGA

Realistic NBI Blip Distribution for Beams #7 and #8 Considered Anisotropic slowing down fast-ion distribution, peaked in the center with pitch angle given by NBI injection geometry

MEGA Finds Most Unstable Modes in Good Agreement With Experimental Observations Most dominant mode spatial localization found in MEGA is in good agreement with ECE measurements Perfect frequency match in both discharges Mode frequency depends on 3D fields poloidal spectrum

Growth Rate of Dominant Mode Depends on 3D Fields Poloidal Spectrum n=2 dominant mode grows rapidly with RMP Δφ=-50º (#34571) and remains at low amplitude for RMP Δφ=100º (#34570)

Main Wave-Particle Resonances for TAE Drive Overlap With ERTL AUG Orbit, mode and resonance width allows interaction of certain particle population with both AE and RMP fields simultaneously and thus TAE drive / resonance manipulation MEGA fields

Summary and Conclusions Localized ECRH and ECCD have strong impact on AE activity modifications of thermal plasma profiles seem to be key Externally applied 3D fields can be used to manipulate the fastion distribution in phase-space Suppression / excitation of NBI driven TAEs is obtained by varying the poloidal spectrum of the applied 3D fields

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Simulations Suggest Larger Fast-Ion Energy Content During ECRH Facilitates TAE Drive ICRH produces up to 40% larger fast-ion energy content during ECRH phases due to longer fast-ion slowing down time (higher T e ) Fast-ion pressure gradient is significantly higher during ECRH ρ pol Additional drive overcome larger ion Landau and radiative damping Local changes at wave-particle resonances may explain timescales ρ pol S. E. Sharapov et al., EPS 2017