Impact of Localized ECRH on NBI and ICRH Driven Alfven Eigenmodes in the ASDEX Upgrade Tokamak

Impact of Localized ECRH on NBI and ICRH Driven Alfven Eigenmodes in the ASDEX Upgrade Tokamak M. Garcia-Munoz M. A. Van Zeeland, S. Sharapov, Ph. Lauber, J. Ayllon, I. Classen, G. Conway, J. Ferreira, J. Galdon, B. Geiger, N. Lazanyi, F. Nabais, V. Nikoleva, D. C. Pace, L. Sanchis-Sanchez, A. Snicker, J. Stober, M. Weiland and the ASDEX Upgrade Team

DIII-D Observations Showed ECRH Can Have a Major Impact on NBI Driven AE Stability Localized ECRH has strong impact on RSAEs With on-axis ECRH deposition, strong RSAEs are observed With near q min ECRH deposition, RSAEs are mitigated TAEs still unstable though weaker M. A. Van Zeeland et al., PPCF 50 035009 (2008) Mitigation mechanism still under investigation (ITPA EP-7) M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 2

DIII-D Observations Showed ECRH Can Have a Major Impact on NBI Driven AE Stability Localized ECRH has strong Impact on RSAEs With on-axis ECRH deposition, strong RSAEs are observed With near q min ECRH deposition, RSAEs are mitigated TAEs still unstable though weaker M. A. Van Zeeland et al., PPCF 50 035009 (2008) Mitigation mechanism still under investigation (ITPA EP-7) M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 3

Goal of Experiments Investigate impact of localized ECRH on both NBI and RF tail driven Alfven Eigenmodes Check reproducibility of DIII-D result on NBI driven modes Extend studies to RF tail driven modes to test sensitivity to underlying distribution function Document change in AE stability with ECRH injection location and EP distribution Document resultant change in EP profiles and EP transport ECRH Near Axis #31541 RSAEs ECE Spectrogram Near q min BAAEs ECRH Near q #31545 min Model ECRH impact on AE stability and associated transport M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 4

Outline Introduction and Motivation Impact of localized ECRH on NBI Driven AEs Impact of localized ECRH on ICRH Driven AEs Modeling of Experimental Observations M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 5

Early NBI and ECRH Heating Used to Create Reversed Magnetic Shear and Drive Alfven Eigenmode Activity Beam (60kV) and ECRH heating begin t~0.2s M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 7

Early Beam and ECRH Heating Used to Create Reversed Magnetic Shear and Drive Alfven Eigenmode Activity ~r qmin Beam (60kV) and ECRH heating begin t~0.2s ECH deposition location scanned in series of discharges (positions 1-5) M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 8

Low and Reproducible Density from Discharge to Discharge Maintaining a repeatable density essential for isolating physics changing mode stability Low density important for EP population and mode drive M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 9

With ECRH Near Magnetic Axis Broad Spectrum of RSAE, TAE, and BAAE Driven Clear RSAE activity as qmin evolves #31541, ECRH #1 (Near Axis) ECE R~1.81m RSAEs ECE R~1.86m RSAEs BAAEs ECE R~1.90m RSAEs M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 10

Early Beam Heating With ECRH Near Mid-Radius (~q min ) Had Much Reduced AE Activity #31545, ECRH #4 (Near q min ) ECE R~1.81m Some MHD events visible q-profile still reversed as low-level RSAEs appear again later ECE R~1.86m Drastic changes like this in mode stability provide excellent tests for simulations validation ECE R~1.90m M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 11

Reflectometer Confirms Large Change in AE Stability Between ECRH Near-Axis and Near qmin ECRH Near Axis ECRH Near q min M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 12

Discharges with Suppressed RSAE Activity Show Classical Fast-Ion Profiles ECE Spectrogram Near q min ECRH Near Axis #31541 RSAEs BAAEs ECRH Near q #31545 min M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 13

RF-Tail Driven AE Portion of Experiment Also Used Early On-axis ECRH and Beams to Create Reversed Shear All RF discharges had same startup until t=0.6s on-axis ECRH and constant beam On-axis ECH ECH location varies shot to shot After t=0.6s ICRH (fundamental Hydrogen minority) NBI blips for diagnostics Gyrotrons that are scanned radially from shot to shot M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 15

RF-Tail Drives TAEs Preferentially and ECRH Impact on Modes is Not the Same as NBI Driven AEs ECE R~1.86m TAEs #31567 At switch to ICRH, TAEs become unstable RSAEs ICRH + ECRH On-axis BAAEs? also observed at very low frequency (low rotation) M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 16

RF-Tail Drives TAEs Preferentially and ECRH Impact on Modes is Not the Same as NBI Driven AEs ECE R~1.86m TAEs #31567 At switch to ICRH, TAEs become unstable RSAEs ECE R~1.86m RSAEs ICRH + ECRH On-axis #31569 TAEs ICRH + ECRH near q min BAAEs? also observed at very low frequency (low rotation) Switch to ECRH near q min produces little change of RF driven TAEs M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 17

RF-Tail Drives TAEs Preferentially and ECRH Impact on Modes is Not the Same as NBI Driven AEs ECE R~1.86m TAEs #31567 At switch to ICRH, TAEs become unstable RSAEs ECE R~1.86m RSAEs FILD ECE R~1.81m ICRH + ECRH On-axis #31569 TAEs ICRH + ECRH near q min #31569 RSAEs ICRH + ECRH near q min BAAEs? also observed at very low frequency (low rotation) Switch to ECRH near q min produces little change of RF driven TAEs With ECRH near q min, RSAEs also appear during ICRH phase FILD measures TAE induced losses M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 18

First Modelling Attempts Focus on Stability of NBI Driven AEs ECE Spectrogram Near q min Well modelled fast-ion distribution Based on TRANSP runs: linear analysis Higher density in 31545 higher damping Very different ratio Te/Ti all low-f modes are weakly damped due to reduced ion Landau damping Large Te/Ti BAAEs in 31541 ECRH Near Axis #31541 RSAEs BAAEs ECRH Near qmin #31545 M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 20

First Modelling Attempts Focus on Stability of NBI Driven AEs Well modelled fast-ion distribution Based on TRANSP runs: linear analysis Higher density in 31545 higher damping Very different ratio Te/Ti all low-f modes are weakly damped due to reduced ion Landau damping Large Te/Ti BAAEs in 31541 M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 21

Different q-profiles Lead to Significant Changes in Spectra RSAEs TAEs RSAEs TAEs LIGKA calculates kinetic continuum with and without fast-ions n=0 continua below TAE gap Small shear in #31545 changes spectra significantly Wider modes expected in #31545 q #31545 #31541 ρ pol M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 22

LIGKA Predict Broader Eigenfunctions w/o Fast-Ions in #31545 ES potential ES potential M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 23

LIGKA Calculates Kinetic Continuum Including Fast-Ion Effects Maxwellian fast-ion distribution with T eff = 25 kev P equi #31545 Fast-ion pressure comparable to total plasma pressure P EP P el FOW effects are not considered P ion ρ pol TRANSP M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 24

Fast-Ion Pressure Leads to n=0 Upshift No EP FOW effects for continuum lead to an overestimation of EP contribution to the pressure upshift but reasonable agreement with experimental observation 150 khz 75 khz Simulations upshift to 150 khz / Measured frequency 120 khz M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 25

Fast-Ion Pressure Leads to n=0 Upshift No EP FOW effects for continuum lead to an overestimation of EP contribution to the pressure upshift but reasonable agreement with experimental observation n=3 n=3, EP n=0 n=0, EP #31545 150 khz 75 khz Simulations upshift to 150 khz / Measured frequency 120 khz 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 ρ pol Due to peaked EP profile, maximum in continuum vanishes n=0 continuum reaches background particles only TAE gap M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 26

Modes Develop Continuum Interaction as EP Density Increases Ideal RSAEs transition to EPM as EP density increases in LIGKA systematic scan Modes start to develop a continuum interaction that moves radially outward 20% TRANSP EP pressure 100% TRANSP EP pressure #31545 n=3 #31545 n=3 ρ pol ρ pol Mode is damped by rather slow and cold part of the EP distribution function (n EP being rather large) M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 27

The Beta Suppression Mechanism * May Explain Some Features of Measured Spectra The coupling to GAM / BAEs may explain the absence of RSAEs ω AC has a mínimum when q min = m/n, i.e. k =0 As the temperature and density rise, the TAE frequency drops and the GAM frequency increases When beta is high enough so that the range of the frequency sweep is zero * E. D. Fredrickson et al., Phys. Plasmas 14, 102510 (2007) M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 28

Conclusions / Outlook ECRH can have a major impact on AE stability First complete suppression of NBI driven RSAEs observed in Impact on ICRH driven AEs still contradictory Discharges with suppressed RSAE activity show classical fast-ion profiles Standard AEs cause significant fast-ion losses as routinely observed Systematic scans still need to be done to isolate the effect of different parameters changing with applied ECRH, e.g. q-profiles, Te/Ti, fast-ion pressure, etc The beta suppression mechanism may explain some features of the observed spectra Fast-ion effect must be taken into account in modelling to explain observations M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 30

Back-up slides

AEs Cause Significant Coherent Fast-Ion Losses Scintillator based Fast-Ion Loss Detector (FILD) measures coherent losses induced by RSAEs and TAEs FILD FILD Spectrogram #30370 Both RSAEs and TAEs cause similar coherent losses Resonant losses found only for trapped particles M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 16

AEs Cause Significant Coherent Fast-Ion Losses Scintillator based Fast-Ion Loss Detector (FILD) measures coherent losses induced by RSAEs and TAEs FILD Both RSAEs and TAEs cause similar coherent losses Resonant losses found only for trapped particles M. Garcia-Munoz 14 th IAEA Technical Meeting on Energetic Particles Vienna, Austria 3 rd September 2015 Page 16

The Primary Diagnostic Used for These Experiments is the Fast-Ion Loss Detector (FILD*) FILD is a magnetic spectrometer provides energy and pitch resolved measurements of escaping ions using collimator and tokamak magnetic field ion fast ions v tot v aperture v // Local velocity-space measurements like these help to isolate fundamental mechanisms Plasma *M. Garcia-Munoz et al., RSI. 80, 053503 (2009)

The Primary Diagnostic Used for These Experiments is the Fast-Ion Loss Detector (FILD*) FILD is a magnetic spectrometer provides energy and pitch resolved measurements of escaping ions using collimator and tokamak magnetic field Local velocity-space measurements like these help to isolate fundamental mechanisms fast ions v tot v v // Scintillator Image with Energy and Pitch ion Plasma aperture M. Garcia-Munoz et al., RSI. 80, 053503 (2009)