alcator c-mod icrf research program · icrf provides bulk auxiliary heating power in c-mod. •...

Alcator C-Mod ICRF Research Program

MIT Plasma Science and Fusion CenterJanuary 27-29, 2010

S J W kit h b h lf f ICRF GS.J. Wukitch on behalf of ICRF Group

Overall Themes:Develop ICRF heating and flow/current drive actuator for optimization of high

performance plasmas.Experimental validation of advanced simulation tools scalable to ITER andExperimental validation of advanced simulation tools scalable to ITER and

reactors.Demonstrated integration of ICRF and LHRF.

Outline:Context of C-Mod ICRF programOverview of ICRF system and capabilitiesProposed research

• ICRFICRF• ICRF-LHRF interactions

12010 C-Mod PAC Meeting

ICRF Challenges Impacting Utilization

ICRF heating has been experimentally demonstrated to be effective and is planned to be utilized in both ITER 2

4 PRF (MW)

BT=5.4 T, IP=1 MA 10504260226

p a ed to be ut ed botand future devices.

Wave propagation and absorption.• Assess ICRF as potential flow/current

2

0.1

0.2

0.3WMHD (MJ)

• Assess ICRF as potential flow/current drive actuator.

• Physics and simulation validation.• Interaction at the plasma edge.

2

3

4 Te0 (keV)

20 3Interaction at the plasma edge.Antenna compatibility.

• Impurity production.• Development and validation of

2

4

2 Rneut (x1014 s-1)

ne (x1020 m-3)

• Development and validation of antenna simulation code.

• Load/transient event tolerance.• Voltage and power handling.

1

neut ( )

2

3PRad (MW)

Voltage and power handling.• Antenna conditioning.• Robust long-distant coupling.

Sources are 2 MW and most efficient of

0.6 0.8 1 1.2 1.4

1

Time (s)

Sources are 2 MW and most efficient of all auxiliary heating power sources.

C-Mod ICRF within ITER Needs/ReNEW/ITPA Context

ITER Needs• ICRF impurity production and erosion - compatibility with metal PFCs.

ReNEWThrust 4: Qualify operational scenarios and supporting physics basis for ITER

• ICRF compatibility (impurity production) with high performance plasmas.• Flow drive (MC Flow Drive).

A t ti l d t l d lt / h dli• Antenna operation: load tolerance and voltage/power handling.• Sawtooth destabilization/stabilization with RF.

Thrust 5: Expand limits for controlling and sustaining fusion plasmas• Demonstrate integrated ICRF and LHRF.Demonstrate integrated ICRF and LHRF.• Develop and test temperature, current, density, and rotation velocity profile control

methods in DEMO-relevant conditions.Thrust 6: Develop predictive models

• Strong emphasis on experimental validation of simulations• Strong emphasis on experimental validation of simulations.Thrust 10: Science and technology of plasma-surface interactions

• Evaluation of refractory metal RF armor and antenna.

ITPA :• TC-14: Assess RF driven rotation• IOS 5.2: Maintaining ICRH Coupling in expected ITER regime• MHD WG3: Assess the power requirements for ICRH and ECCD for control ofMHD WG3: Assess the power requirements for ICRH and ECCD for control of

sawteeth in ITER

C-Mod ICRF Program

Primary goal of ICRF physics program is to:• Provide first principle understanding of ICRF physics including antenna

coupling and wave absorption andp g p• Develop a reliable heating and current/flow drive actuator that can be utilized

to optimize overall plasma performance with minimum negative impact on plasma.p

ICRF provides bulk auxiliary heating power in C-Mod.• Fundamental minority, mode conversion, and second harmonic minority ion

cyclotron scenarios are extensively investigated and have begun examinationcyclotron scenarios are extensively investigated and have begun examination of Fast Wave electron heating.

Emphasize validating physics and computational models through comparison of simulations to experimentsof simulations to experiments.• Access to wide range of RF absorption scenarios, diagnostics, and advanced

simulation codes.I i d d l l i h l i l d h i iInvestigate and develop solutions to technological and physics issues

associated with the antenna/coupler and operations to enable successful RF operation.• Fast ferrite tuning network and tetrode anode analysis are current examples.


High Priority Research Areas

High priority research includes issues where C-Mod can make a unique contribution.• High leverage physics issues, support for ITER, and student theses.High leverage physics issues, support for ITER, and student theses.

Assess and develop fundamental understanding of mode conversion flow drive. (Y. Lin)

ICRF ibili i i iICRF compatibility: impurity generation.• Identify primary ICRF impurity source locations. (S. Wukitch)• Rotate antenna to reduce impurity production. (M. Garrett)• Characterize impact of ICRF power on SOL density profile (C. Lau).• Characterize ICRF sheaths with additional emissive and B-dot probes.

Compatibility of simultaneous LH and ICRF coupling.Compatibility of simultaneous LH and ICRF coupling.Validation of physics and simulations in concert with RF-SciDAC.

• Importance of finite banana width on RF absorption (A. Bader)V lid ti f TORIC i d i ith PCI t (N T jii)• Validation of TORIC in mode conversion with PCI measurements (N. Tsujii)

• TOPICA validation with loading, antenna impedance, and SOL density profile measurements. (C. Lau)


Secondary Research Topics

Assess RF physics of ITER scenarios, particularly non-activated phase.• Hydrogen plasmas are generally more time consuming due to high H fraction

following a particular H run.g p• He plasmas are more compatible but performance is often worse than in D

plasmas.Fast wave electron heating and current drive will focus on validation ofFast wave electron heating and current drive will focus on validation of

simulation codes.• I-mode has enabled experiments to measure power deposition.

S t th d t bilit ti / t bili ti i ti i ki ti h i dSawtooth destabilitzation/stabilization via energetic ion kinetic mechanism and traditional current drive techniques.• Recent experiments have been in support of ITPA WG3 (Assess the power

requirements for sawtooth control in ITER).Antenna power and voltage handling studies are proceeding in test stand.

• Have begun investigation of new materials in effort to improve antenna g g pvoltage handling.


ICRF Antenna Configuration (FY’10)

E F

D

E

G

F

D & Eantennas

D & E Antenna

GH FullLimiterIp

C H

J antennaLH

Coupler

B JAB SplitLimiter K midplane

LimiterJ antenna

A K

Frequency 80 MHz 40-80 MHz

Power 2 x 2 MW 4 MW

Antenna 2 x 2 Strap 4 StrapAntenna 2 x 2 Strap 4 Strap

Phase fixed variable


E FNew 4-strap antenna installed in J port

(2010).• A rotated antenna designed to D

E

G

F

D & Eantennas

glower the impurity production.

• Achieving present power density, ~10 MW/m2, the injected power

GH FullLimiterIp

would be limited to 2 MW.▪ For present J antenna, 3 MW is

typical maximum injected power

C H

J antennaLH

Coupler

power.

Real time matching (double stub FFT system ) on all antennas


Limiter system ) on all antennas.• This investment has been shifted

forward due to available stimulus funds.Frequency 80 MHz 40-80 MHz

A K

• Result in delay in making all transmitters tune-able from 50 MHz-80 MHz.

Power 2 x 2 MW 4 MW

Antenna 2 x 2 Strap 4 StrapAntenna 2 x 2 Strap 4 Strap

Phase fixed variable


E FNew 4-strap antenna installed at E

port.• If rotated antenna is successful in D

E

G

FE antenna

reducing impurities, raising the power density limit will become increasingly important.

GH FullLimiterIp

• High melting, high strength materials offer a path to increased voltage and power handling.N i l i f d

C H

J antenna

LH

Couplers

• Nearing completion of test stand to allow high power and high voltage testing under controlled conditions


Limiter conditions.

Variable phasing available for both

A K

Frequency 80 MHz 40-80 MHz

antennas.Power 4 MW 4 MW

Antenna 4 Strap 4 Strap


Antenna 4 Strap 4 Strap

Phase variable variable

Rotated ICRF Antenna

Underlying cause of impurity generation is thought to be generation of E||.

Rotate antenna structure 10º to beRotate antenna structure 10 to be perpendicular to total B field. • Along a field line E|| will cancel due to

symmetry. • For [0, π], estimated sheath field is

reduced ~3-10.• For [0,0], sheath field is negligible –

a surprising prediction.p g p

For comparison, present antennas are operated in dipole [0, π] phasing to reduce impurities

Schedule:reduce impurities.• Estimated sheath field is 2-3 times

lower than [0,0] phasing.

Power density at 2 MW (3 MW) is 9 8

Complete construction by end of June ’10 and power test in test stand by end of August ’10.

Fi t f dth i b i d fPower density at 2 MW (3 MW) is 9.8 MW/m2 (14.8 MW/m2)

Similar vacuum spectrum as present J

First feedthru is being prepared for assembly and braze.• Next four will follow after

inspection.antenna.

p

2010 C-Mod PAC Meeting 10

ICRF Simulation Tools

Codes:• Microwave Studios and COMSOL finite element

electromagnetic commercial codes.TOPICA 3 D d li f ICRF t d• TOPICA: 3-D modeling of ICRF antenna code with full wave plasma model (TORIC) in collaboration with Polytechnico di Torino and RF Sci-DAC (CSWPI).

• TORIC for wave propagation, power deposition, and current drive calculations.▪ Coupled with Fokker Planck codes, DKE, and

CQL3DCQL3D.• Access to finite banana width Monte Carlo code

with self consistent RF wave fields through RF Sci-DAC.

Synthetic Diagnostics:• Synthetic phase contrast imaging diagnostic to

model measured density fluctuations in TORIC.• Synthetic active charge exchange neutral particle• Synthetic active charge exchange neutral particle

analyzer (50-350 keV) implemented in CQL3D.• Plan to implement synthetic charge exchange

recombination spectroscopy for fast ions in CQL3D.


Diagnostics

Present status:• 32 channel PCI diagnostic for density

fluctuations associated with RF waves. (N Tsujii)(N. Tsujii)

• 4-channel CNPA (compact neutral particle analyzer) and 8 channel are operational. (A. Bader)

• Reflectometer microwave electronics are operational and LH SOL horns have been manufactured. (ORNL, C. Lau)

• Background data taken for proof of• Background data taken for proof of principal fast ion charge exchange (FICX). (K. Liao - UT)

Plans:• SOL reflectometers in new 4-strap

antennas.• Edge probes at RF limiters and plasma

li it i i d RF tilimiters: emissive and RF magnetic probes.

• Assess FICX diagnostic when beam becomes available.


Mode Conversion Flow Drive (MCFD)

Goals:Develop external actuator to control/modify

plasma rotation profile (ITPA TC-14)plasma rotation profile. (ITPA TC-14)• Characterize mode conversion flow

drive.• Develop understanding of mode• Develop understanding of mode

conversion flow drive such that one can reliably predict future experiments and devicesdevices.

Status:Dependence on plasma current, density,

3temperature, antenna phase, and 3He concentration investigated.

Found rotation in counter current direction in JET experiments.

H-mode plasmas response to MCFD is as expected from scalingexpected from scaling.


MCFD: Plans

Examine MCFD in low density H-mode plasmas.

Investigate MCFD in He and H majority plasmas.• Examine influence of single pass g p

absorption (higher and broader in He than D majority and lower and narrower in H majority).E i d d tt• Examine dependence on wave pattern.

• ICW perpendicular wavelength is inversely proportional to Alfven speed.

Investigate off-axis flow drive for control/modification of rotation profile.

Compare MCFD at 5 T, 50 MHz and 8 T, 80 MHz.

I fl d i d d ll l• Is flow drive dependent on wave parallel velocity?


ICRF Compatibility: Impurity Production

Goals:• Identify location of RF impurity sources.• Develop understanding of underlying physics.• Examine antenna designs to minimize RF• Examine antenna designs to minimize RF

sheaths.• Assess mitigation techniques.

Status:Status:• Coated outer divertor shelf tiles and limiters with

~100 μm of boron (~50% density).▪ Molybdenum brightness no longer scales with RF

power and is controlled for significantly increasedpower and is controlled for significantly increased number of RF Joules.

• Confinement is maintained for ~ 100 MJ of RF injected – about twice previous.• Installed B-dot and emissive probe on A-B limiter.

B d d l l l i hi i li d h i i d▪ B-dot and plasma voltage relationship is more complicated than anticipated.Plans:

• Assess boron coating to identify regions of interest.▪ Remove coating from regions where coating is unnecessary (remove one location)Remove coating from regions where coating is unnecessary (remove one location)▪ Improve coating quality (working with Plasma Processes Inc.) for use on antennas.

• Characterize impact of ICRF power on SOL density profile.▪ Assess gas puffing effectiveness for modifying the SOL density profile (IOS-5.2)

• Characterize ICRF sheaths with additional emissive and B dot probes• Characterize ICRF sheaths with additional emissive and B-dot probes.▪ Second set of emissive probes to allow radial scan from shot to shot.▪ Additional B-dot and emissive probe on new 4-strap antenna.


VPS Boron on Antenna and Molybdenum Tiles

Boroncoated

16Boron coated RF limiter tile

Boron Coating on Outer Divertor Shelf

Remote camera inspection sho s some loss of boron coatingRemote camera inspection shows some loss of boron coating.• Antenna limiters and plasma limiters except K limiter appear in reasonable

condition.M di h lf il l i bl di i• Most outer divertor shelf tiles also appear in reasonable condition.

Coating removal is non-uniform.• Suggests idea of measuring coating thickness is too simple minded.• Surface characterization awaits manned access.

ICRF Compatibility: Antenna Performance

Goal:Fault free, high power operation with

minimal negative impact on plasma.

N2 gas puff

Status:Found nitrogen or neon seeded discharges

provided much improved ICRFprovided much improved ICRF performance.• Molybdenum radiation is well

controlled.I j i f d di• Injections from antenna and divertorare eliminated.

• Antenna faulting greatly reduced.• Zeff increased to ~2.eff

Impurity control with seeding was unexpected since one might expect

tt i t i ith li ht i itsputtering to increase with light impurity species.• Improved antenna operation is

encouraging but not yet understood.g g y

18

ICRF Compatibility: Plans

Compare rotated and standard antenna characteristics.

• Impurity and gas productionImpurity and gas production.• ICRF impact on SOL density

profile.• Sheaths characteristics dependence

on RF absorption scenarios.Impurity dependence on antenna

phasing.M d li d• Modeling suggest rotated antenna will have different impurity dependence on antenna phase.

I i l f i i di i i i i i i dInvestigate role of impurity seeding in improving impurity generation and power handling.

Develop analysis tools for investing sheath mitigation techniques through collaboration with RF Sci DACcollaboration with RF-Sci DAC.• Utilize TOPICA coupled to FELICE (1-D) and cold plasma model in SOL region

with real density profiles.• Replace cold plasma model of SOL with finite element full wave solver in

analysis packageanalysis package.Assess what makes RF sources the dominant core Mo contributor.


Wave Propagation: Validate ICRF Simulations

Goal: Validate simulations for wide range of experimental regimes.

Scenario Characteristics StatusD(H) Strong single pass absorption,

Fields are toroidally localized.Have a 3 (F-top) and 6 (J-top) channel CNPA operational.FICX has been implemented.y pSynthetic CNPA implemented in AORSA-CQL3D – will need to be updated for active charge exchange.

Mode i

Long and short wavelength modes Investigating difference between measured and i l i ibl lib i d 3 D fi ldconversion present simulations: possible calibration and 3-D field

reconstruction effects.

D(3He) Single pass absorption is ~10% H-mode performance was much more sensitive to 3He concentration making reproducible H-modes difficult.g p

H-mode performance was independent of location of impurity resonances.

Fast Wave Electron heating I-modes plasmas are good target plasmas due to their high d l i l hi h l βSingle pass from 1-10% temperature and relatively high electron β.

2nd Harmonic 2nd harmonic H at low fieldMagnetic field scan to investigate 2nd

harmonic D absorption

Access to upgraded simulation capability including finite orbit effects.


harmonic D absorption.

Wave Propagation: Validate ICRF Simulations Plans

D(H) 1st

and 2nd

harmonic

Measure tail energy and spatial distribution.

Examine tail formation time (RF-SciDAC).

Scan impressed nφ spectrum.

Mode Scan minority concentration from conversion minority to mode conversion regime.

Utilize D(3He), 4He(3He), D(H), and H(3He) discharges.

M b lit dMeasure wavenumbers, wave amplitude, wave spatial distribution, and deposition profiles.

3HeMinority

Direct comparison of D(3He) and 4He(3He) discharges – dependence on 3He fraction and single pass absorption.g p p

Fast Wave Vary target plasma temperature and electron β.β

Scan impressed nφ spectrum.


ICRF and LHRF Interactions: Coupling

Goal:• Demonstrate compatibility between

ICRF and LHRF to enable tokamakperformance optimization.

0.4

0.5

n (

Γ2

) L and H-mode

LH Couplingpe o a ce opt at o .

Status:• Coupled LH power into H-mode and

L-mode ICRF heated discharges.• LH faults are significantly increased

0.2

0.3

ow

er Fra

ctio

n

• LH faults are significantly increased with neighboring ICRF antenna operation.

• Gas puffing in coupler box had mixed results 0 2 4 6 8

0.1

Refl.

Po

H-mode (LSN)

L-Mode (USN)

resultsPlans:

• Measure local density profile with reflectometer.

0 2 4 6 8

ngrill (x1018 m-3)

• Examine influence of ICRF and LH modification of the SOL density and density profile.

• Investigate influence of boronizationgand gas puffing on coupling.

• Examine density and power dependence of reflected power fraction.


IC and LH Waves Interactions: Fast ions and LH

Goal:• Evaluate fast ion absorption of LH waves (important issue for ITER).

Motivation:• Parasitic LH wave absorption on fusion α-particles needs to be limited.• A secondary issue is absorption by fast ions generated by ICRF.• JET reported interaction at ¼ the expected energy but latter experiments failed to

reproduce resultsreproduce results.• Tore Supra has not observed interaction.

Status:• Initial C-Mod experiment was complicated by x-ray sensitivity to plasma density• Initial C-Mod experiment was complicated by x-ray sensitivity to plasma density.

Plans:• Key is to identify plasmas where then density is under better control

▪ Discharges with cryopump or He majority gas may prove to be better targets.g y p p j y g y p g• Inject fixed LHRF power, scanning n|| from (1.5 – 3.5) on different discharges until

an interaction is observed with the minority tail:• Measure hard X-ray profile to evaluate the effect on the generation of fast

l t d CNPA t i t f t i di t ib tielectrons and CNPA to assess impact on fast ion distribution.• Model process with GENRAY – CQL3D.• Scan ICRF power to vary the minority tail energy.• Change B to move the ICRF resonance positionChange B to move the ICRF resonance position.• Vary the LH wave n|| to change the LH wave phase speed.


Summary

Proposed ICRF physics program’s goal is to:• provide first principles understanding of ICRF antenna coupling and wave

absorption physicsp p y• demonstrate that ICRF can be a reliable heating/current drive/flow drive

actuator with minimum negative impact on the plasma.High priority research areas are:High priority research areas are:

• Mode conversion flow drive assessment and characterization.• ICRF compatibility: antenna performance and impurity production.• E i t l lid ti f i l ti• Experimental validation of simulation.• Compatibility of LH and ICRF coupling.

Second tier research issues have lower priority unless developments warrant more resources or an opportunity arises.• Experiments to validate ITER scenarios, particularly non-activated phase.• Evaluate Fast wave heating and current drive for central seed current.• Sawtooth destabilization/stabilization via kinetic mechanisms, heating and

current drive.• Fast ion absorption of LH waves.p• Antenna power and voltage handling studies.


alcator c-mod icrf research program · icrf provides bulk auxiliary heating power in c-mod. •...

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