impact of localized ecrh on nbi and icrh driven alfven … · 2015. 9. 3. · aug #31545, ecrh #4...

Impact of Localized ECRH on NBI and

ICRH Driven Alfven Eigenmodes in the

ASDEX Upgrade TokamakM. 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

M. Garcia-Munoz | 14th IAEA Technical Meeting on Energetic Particles | Vienna, Austria | 3rd September 2015 | Page 2

DIII-D Observations Showed ECRH Can Have a

Major Impact on NBI Driven AE Stability

M. A. Van Zeeland et al., PPCF 50 035009 (2008)

Localized ECRH has

strong impact on

• With on-axis ECRH

deposition, strong

RSAEs are observed

• With near qmin ECRH

deposition, RSAEs are

mitigated

• TAEs still unstable

though weaker

• Mitigation mechanism

still under investigation

(ITPA EP-7)

Localized ECRH has

strong Impact on

• With on-axis ECRH

deposition, strong

RSAEs are observed

• With near qmin ECRH

deposition, RSAEs are

mitigated

• TAEs still unstable

though weaker

• Mitigation mechanism

still under investigation

(ITPA EP-7)M. A. Van Zeeland et al., PPCF 50 035009 (2008)

DIII-D Observations Showed ECRH Can Have a

Major Impact on NBI Driven AE Stability

• 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

• Model ECRH impact on AE stability and

associated transport

Goal of AUG Experiments

AUGECRH Near qmin#31545

ECRH Near Axis #31541

ECE Spectrogram Near qmin

Outline

• Introduction and Motivation

• Impact of localized ECRH

on NBI Driven AEs

on ICRH Driven AEs

• Modeling of Experimental

Observations

Outline

on NBI Driven AEs

on ICRH Driven AEs

Observations

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

~rqmin

• Beam (60kV) and ECRH heating begin t~0.2s

• ECH deposition location scanned in series of

discharges (positions 1-5)

Early Beam and ECRH Heating Used to Create Reversed

Magnetic Shear and Drive Alfven Eigenmode Activity

• Maintaining a

repeatable density

essential for isolating

physics changing

mode stability

• Low density important

for EP population and

mode drive

Low and Reproducible Density from Discharge

to Discharge

AUG #31541, ECRH #1 (Near Axis)

With ECRH Near Magnetic Axis Broad

Spectrum of RSAE, TAE, and BAAE Driven

• Clear RSAE

activity as qmin

evolves

ECE R~1.81m

ECE R~1.86m

ECE R~1.90m

• Some MHD events

visible

• q-profile still reversed as

low-level RSAEs appear

again later

• Drastic changes like this

in mode stability provide

excellent tests for

simulations – validation

AUG #31545, ECRH #4 (Near qmin)

Early Beam Heating With ECRH Near Mid-Radius

(~qmin) Had Much Reduced AE Activity

ECE R~1.81m

ECE R~1.86m

ECE R~1.90m

Reflectometer Confirms Large Change in AE

Stability Between ECRH Near-Axis and Near qmin

ECRH Near qmin

ECRH Near Axis

Discharges with Suppressed RSAE Activity

Show Classical Fast-Ion Profiles

AUGECRH Near qmin#31545

Outline

on NBI Driven AEs

on ICRH Driven AEs

Observations

• All RF discharges had

same startup until

t=0.6s

on-axis ECRH and

constant beam

• After t=0.6s

ICRH (fundamental

Hydrogen minority)

NBI blips for

diagnostics

Gyrotrons that are

scanned radially from

shot to shot

On-axis ECH

ECH location varies shot to shot

RF-Tail Driven AE Portion of Experiment Also Used Early

On-axis ECRH and Beams to Create Reversed Shear

RF-Tail Drives TAEs Preferentially and ECRH Impact

on Modes is Not the Same as NBI Driven AEs

• At switch to ICRH,

TAEs become unstable

• BAAEs? also observed

at very low frequency

(low rotation)ICRH + ECRH On-axis

#31567AUG

ECE R~1.86m

(low rotation)

• Switch to ECRH near

qmin produces little

change of RF driven

ICRH + ECRH On-axis

ICRH + ECRH near qmin

#31567

#31569

ECE R~1.86m

(low rotation)

• Switch to ECRH near

qmin produces little

change of RF driven

• With ECRH near qmin,

RSAEs also appear

during ICRH phase

• FILD measures TAE

induced losses

ICRH + ECRH On-axis

#31567

#31569

ECE R~1.86m

#31569ECE R~1.81m

ECE R~1.86m

Outline

on NBI Driven AEs

on ICRH Driven AEs

Observations

First Modelling Attempts Focus on Stability

of NBI Driven AEs

AUGECRH Near qmin #31545

• 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

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

Different q-Profiles Lead to Significant

Changes in Spectra

• 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

#31545

#31541

TAEsRSAEs TAEs

LIGKA Predict Broader Eigenfunctions

w/o Fast-Ions in #31545

ES potential ES potential

LIGKA Calculates Kinetic Continuum Including

Fast-Ion Effects

#31545

• Maxwellian fast-ion

distribution with Teff = 25 keV

• Fast-ion pressure

comparable to total plasma

pressure

• FOW effects are not

considered

PionTRANSP

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

• Simulations upshift to 150 kHz

/ Measured frequency 120 kHz

75 kHz

150 kHz

Fast-Ion Pressure Leads to n=0 Upshift

• Simulations upshift to 150 kHz

/ Measured frequency 120 kHz

75 kHz

150 kHz

No EP FOW effects for continuum lead to an overestimation of EP

contribution to the pressure upshift but reasonable agreement with

experimental observation

• Due to peaked EP profile, maximum

in continuum vanishes

• n=0 continuum reaches“background

particles only” – TAE gap

n=3 n=3, EP n=0 n=0, EP #31545

0.0 0.1 0.2 0.4 0.5 0.6 0.70.3ρpol

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

• Mode is damped by rather slow and cold part of the EP distribution

function (nEP being rather large)

20% TRANSP EP pressure

#31545 #31545 n=3n=3

100% TRANSP EP pressure

ρpolρpol

The Beta Suppression Mechanism* May Explain

Some Features of Measured Spectra

• ωAC has a mínimum when qmin = 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)

The coupling to GAM / BAEs may explain the absence of RSAEs

The Beta Suppression Mechanism* May Explain

Some Features of Measured Spectra

• ωAC has a mínimum when qmin = 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)

The coupling to GAM / BAEs may explain the absence of RSAEs

Conclusions / Outlook

• ECRH can have a major impact on AE stability

• First complete suppression of NBI driven RSAEs observed in AUG

• 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

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

• Both RSAEs and TAEs cause similar coherent losses

• Resonant losses found only for trapped particles

Resonance calculator

FILDFILD Spectrogram

#30370

• Both RSAEs and TAEs cause similar coherent losses

• Resonant losses found only for trapped particles

AEs Cause Significant Coherent Fast-Ion Losses

Scintillator based Fast-Ion Loss Detector (FILD) measures

coherent losses induced by RSAEs and TAEs

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 tokamakmagnetic field

Local velocity-spacemeasurements like thesehelp to isolatefundamental mechanisms

*M. Garcia-Munoz et al., RSI. 80, 053503 (2009)

//vvvtot

fast ions

Plasma

aperture

• FILD is a magnetic spectrometer

provides energy and pitch resolved measurements of escaping ions using collimator and tokamakmagnetic field

Local velocity-spacemeasurements like thesehelp to isolatefundamental mechanisms

Scintillator Image with Energy and Pitch

M. Garcia-Munoz et al., RSI. 80, 053503 (2009)

//vvvtot

fast ions

Plasma

aperture

The Primary Diagnostic Used for These

Experiments is the Fast-Ion Loss Detector (FILD*)

impact of localized ecrh on nbi and icrh driven alfven … · 2015. 9. 3. · aug #31545, ecrh #4...

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