work in progress: dependence of rmp elm suppression on width of the island overlap region

M E Fenstermacher Thrust 1 YearEnd Rev 04/22/23 02:12 AM 1

M.E. Fenstermacher 12th PEP/8th DIVSOL ITPA04/22/23 02:12 1

Work in Progress: Dependence of RMP ELM Suppression on Width of the Island Overlap

Region

M.E. Fenstermacheron behalf of

the Thrust IT-1 ELM Control for ITER Group

Special Thanks to M. Aldan, T.E. Evans, P. Gohil, A.W. Leonard, R.A. Moyer, T.H. Osborne, M.

Schaffer

Presented at the12th Pedestal and Edge Physics ITPA Meeting

IPP, Garching, GermanyMay 7-10, 2007



• Goals:

– Develop an ELM suppression criterion based on the required width of the stochastic region that could be used for comparative evaluation of different proposed ITER RMP coil designs

– Determine the effect of toroidal rotation on the penetration of the RMP fields in the plasma.

• Width of the Island Overlap Region Varied in 5 Different Ways in ITER Similar Shape Plasmas, at ITER e*, at feedback controlled N = 1.9

– q95 scans --- Changes in q95 and q-shear affect island overlap

– I-coil current scans --- Amplitude of RMP affects island size

– 2 toroidal rotation values --- Screening of RMP affected by rotation

– ODD parity I-coil at high q95 ~ 7 --- n=3 modes pitch resonant for odd parity and high q95

– C-Coil amplitude variation --- Mixture of n=1 modes used to “fill in” edge mode spectral density

Recent Experiments (April 3 & 6) Focused on Width of Island Overlap Region Needed for Complete ELM Suppression



Combination of Internal I-coils and External C-coils Used for RMP ELM Control and Error Field Correction

• Strength of n=3 RMP from I-coil depends on up/down parity of coil sets

• Increasing C-coil current increases strength of n=1 RMP beyond nominal error field correction

Schaffer


ITER Similar Shape plasmas (ISS) have higher magnetic shear and a narrower resonant window

• Larger RMP coil current needed in ISS plasmas for ELM control• Resonant window smaller in ISS plasmas with larger RMP current

– May be a signature of increased RMP screening

Evans, SFP Talk



Changes in plasma profiles previously suggested that effect of the RMP in the region 0.85 < N < 0.95 might be important

Evans, SFP TalkEvans, SFP Talk



For q95=3.6 in Resonance Window, Higher RMP Coil Current Suppresses ELMs, Vacuum Islands Overlap in to N = 0.78

Schaffer

ELMSuppressedI: 6.3 kAC: 1x EFC

• Clear gap at N = 0.78 between 7/3 and 4/2 islands



While ELMing, Overlap of Vacuum Magnetic Islands for q95=3.6 in Resonance Window Extends to N=0.87

Schaffer

ELMingI: 4 kAC: 1x EFC

• Small gap at N = 0.867 between 3/1 and 8/3 islands



Region Where Island Overlap Boundary Changes Inside of Location of Maximum Pressure Gradient Change

• Islands well overlapped at pedestal top in both cases

• Change from ELMing to ELM Suppressed for change in overlap well inside pedestal top (vacuum fields)

• ELMing stoc

vac / pped = 1.9

• ELM Suppressed stoc

vac / pped = 4.4

Schaffer

pedptot

pedptot

pTOT| (kPa/N)


ELMSuppressedI: 6.3 kAC: 1x EFC

stocvac

stocvac



Pedestal Width Extracted from Fits to Thomson and CER Data, example 6.4 kA, q95=3.6, ELM suppressed

Osborne

fz

Te

ne

Ti

pe i



For q95=3.8 Outside Resonance Window, Small Increase of C-coil Current Achieves ELM Suppression

Icoil 3 kA

C-coil

1.2x

Icoil 3 kA

C-coil

1.0x

ne

q95

Icoil

vrotcore

vrotedge

D

D

Ccoil

Ip

Pinj

Bdotodd

Bdoteven



Comparison Suggests that Vacuum Island Overlap in to N < 0.9 Required for ELM Suppression

Schaffer, Aldan

pedptot

pedptot

pTOT| (kPa/N)


ELMSuppressedI: 3 kAC: 1.2 x EFC

stocvac

stocvac

• ELMing stoc

vac / pped = 2.5


vac / pped =

3.5



For q95=3.2 Lower than Resonance Window, Increased I-coil plus C-coil Current Produced ELM Suppression

ne

q95

Icoil

vrotcore

vrotedge

D

D

Ccoil

Ip

Pinj

Bdotodd

Bdoteven

Icoil 4 kA

C-coil

2x

Icoil 3 kA

C-coil

1.0x



pedptot

pedptot


ELMSuppressedI: 4 kAC: 2x EFC

stocvac

stocvac

pTOT| (kPa/N)

ELM Suppression at Low q95 =3.2 Outside Resonance Window Achieved by Broadening Island Overlap Region

Schaffer, Aldan

• n=1 islands from C-coil used to “fill-in” edge mode spectral density

• ELMing stocvac

/ pped = 2.4


vac / pped = 4.5



ELM Suppression Achieved with Odd Parity I-coil Pitch Resonant at high q95 ~ 7.2

Icoil 6.4 kA

C-coil

1x

Icoil 0.0 kA

C-coil

1x

ne

q95 - 5

Icoil

vrotcore

vrotedge

D

D

Ccoil

Ip

Pinj

Bdotodd

Bdoteven



At high q, ODD parity Vacuum Island Overlap for ELM Suppression Extends in to N = 0.77

Schaffer, Aldan

pedptot

pedptotELMing

I: 0 kAC: 1x EFC

ELMSuppressedI: 6.4 kAC: 1x EFC stoc

vac

stocvac

pTOT| (kPa/N)• Large number of

islands give deep overlap at high q95

• ELMing stocvac

/ pped = 0.4


vac / pped =

3.8



At q95=3.8 ELM Suppression Obtained by Increasing I-coil Current from 3 kA to 4 kA

Icoil 4 kA C-coil

1x

Icoil 3 kA C-coil

1x

ne

q95

Icoil

vrotcore

vrotedge

D

D

Ccoil

Ip

Pinj

Bdotodd

Bdoteven



Again ELM Suppression Correlated with Increase in Width of the Vacuum Island Overlap Region

Aldan, Schaffer

pedptot

pedptot

pTOT| (kPa/N) ELMingI: 3 kAC: 1x EFCELM

SuppressedI: 4 kAC: 1x EFC

stocvac

stocvac

• Small increase in overlap changes ELMing character

• ELMing stocvac

/ pped = 3.75


vac / pped = 7.1



Analysis needed to develop criteria for ITER coil evaluation in progress - contains linked components

• Goal is to evaluate the degree of island overlap and the radial width of the overlap region

• Plot we want is WELM / Wped as function of stoc / pped --> sequence:

– Thomson profiles, pped - needs Thomson re-calibration Done

– CERFIT analysis, pped - done for previous good shots Done

– Kinetic efits, Wped Some Shots

– SURFMN analysis of island structure (w/ Fitzpatrick In Progress corrections), stoc and Chirikov parameter,

– Fast magnetics analysis and evaluation of WELM In Progress

– TRIP3D calc. of field line loss fraction and connection lengths

• Initial analysis with vacuum fields and MSE EFITs suggests:

– ELMing for 0 <= stocvac / p

ped <~ 3.5

– ELM Suppressed for 3.5 <~ stocvac / p

ped < 7



Profile data from spatial sweeps sufficient quality for kinetic EFITs, example 4 kA, q95=3.8, ELM suppressed

Osborne

fz

Te

ne

Ti

pe i



Kinetic EFITs make a significant difference in the edge q-profile - 3 kA EVEN, q95=3.8, ELMing (80-99% of cycle)

• EFITs with model p’ and ff’ and constrained only by MSE data do not represent edge bootstrap current peak

• Kinetic EFIT shows different q-shear in the pedestal

Osborne

q

<J//>

•Black - EFIT02 w/ MSE

•Magenta - Kinetic EFIT a



At q95~4, increase in Width of the Island Overlap Region for ELM Suppression Less in Kinetic EFIT than in MSE EFIT

Aldan, Schaffer

pedptot

pedptot

pTOT| (kPa/N)

ELMing KineticI: 3 kAC: 1x EFC

ELMSuppressedKineticI: 4 kAC: 1x EFC

stocvac

stocvac

• Island overlap width less in both cases

• Change for ELM suppression less

• ELMing stoc

vac / pped = 3.0


vac / pped =

5.4



At High q95~7.5 Little Difference in Vacuum Width of Island Overlap Region in Kinetic vs MSE EFITs

Aldan, Schaffer

pedptot

pedptotELMing

KineticI: 0 kAC: 1x EFC

ELMSuppressedKineticI: 6.4 kAC: 1x EFC

stocvac

stocvac

pTOT| (kPa/N)• Overlap width

may be slightly larger

• Different than low q kinetic EFIT case

• ELMing stocvac

/ pped ~ 2.5


vac / pped =

5.4



Discharges with ELM Suppression Show Consistently Higher Normalized Island Overlap Region Width

Shot 126435 126442 128371 128372 128376 128377 128474 128475 128464 128466

Q95, Icoil, Ccoil

3.6 4 kA 1x

3.6 6.3 kA 1x

3.8 3 kA 1x

3.8 3 kA 1.2x

3.8 3 kA 1x

3.8 4 kA 1x

3.2 4 kA 2x

3.2 3 kA 1x

7.2 6.4 kA 4x

7.2 0 kA 1x

ELMs? Yes No Yes No Yes No No Yes No Yes

stocvac .135 .222 .10 .14 .15 .2 .16 .09 .228 .03

pped .07 .05 .04 .04 .04 .028 .035 .04 .06 .06

stocvac /

pped 1.9 4.4 2.5 3.5 3.75 7.1 4.5 2.4 3.8 0.4

• Initial analysis with vacuum fields and MSE EFITs suggests:– ELMing for 0 <= stoc

vac / pped <~ 3.5

– ELM Suppressed for 3.5 <~ stocvac / p

ped < 7



Conclusion - Initial Analysis Points to Correlation Between Width of Vacuum Island Overlap Region and ELM Suppression

• Correlation suggests criteria for comparison of candidate coils designs for ITER could be developed

– Very preliminary analysis: stocvac / p

ped > 3.5 for ELM Suppression

• Many upgrades to this analysis are necessary:

– Kinetic EFITs for accurate q-profiles in island overlap region

– Calculation of field line loss fraction with TRIP3D including effect of relative toroidal phases between I-coil, C-coil and Error Field perturbations

– Corrections to RMP penetration strength due to toroidal rotation screening - use formulation of Fitzpatrick theory

– Need to compare cases based on pedestal energy loss during remaining transients, not just based on D intensity

• Updates will be presented: May 24 at ITPA MHD Group, July 3 at EPS poster, Various ITER Design Review WG1 DRPO Meetings (if requested)



Back-up Slides



Width of q resonance window expands with I-coil and C-coil current

4 kA Icoil, 2x C-coil q95=[3.2, 3.8]

3 kA I-coil, 2x C-coil

3 kA I-coil, 1.2x C-coil

3 kA I-coil, 1.0x C-coil,

Q95=[3.45, 3.6]

ne

q95

C79

IU30

D

D

D

D



Increasing C-coil Current for Fixed ODD Parity I-coil can Produce ELM Suppression

ne

q95

IU30 vrotT1

vrotT23

gapoutD

q0

D

C79

Ip

Pinj

Bdotodd

Bdoteven

Icoil 6.4 kA

C-coil

4x

Icoil 6.4 kA

C-coil

1x



Island overlap at high q, ODD parity

Aldan, Schaffer

ELMing

ELM Suppressed

Icoil 6.4 kA C-coil

4x

Icoil 6.4 kA C-coil

1x



For q95=3.8 Outside Resonance Window, Small Increase of C-coil Current Achieves ELM Suppression

ne

q95

IU30 vrotT1

vrotT23

gapout

D

q0

D

Ip

Pinj

Bdotodd

Bdoteven

Icoil 3 kA

C-coil

1.2x

Icoil 3 kA

C-coil

1.0x

C79



Combination of Internal I-coils and External C-coils Used for RMP ELM Control and Error Field Correction

• Strength of n=3 RMP from I-coil depends on up/down parity of coil sets

• Increasing C-coil current increases strength of n=1 RMP beyond nominal error field correction



Are transients that return at low rotation driven by NTMs in core?

ne

dB/dt odd

vrotT9

D

n3rms

D

pr12 esl079

vrotT7

n2rms

n1rms

dB/dt even



RMP H-modes have reduced particle confinement times compared to ELMing H-modes

• Three small ELM-like D bursts are triggered during the HFS pellet ablation phase but do not persist.

Evans, SFP Talk



In new ODD Parity RMP Shots Pellet Density Perturbation Evolution Different from Low q95 EVEN Parity Cases

Jernigan, Baylor

D

D

ne ne

ne ne

D

D



Splitting of OSP j_sat on floor probes using radial SP sweeps - useful for validation of RMP penetration Models

• New ODD parity I-coil case at q95 = 7.2

• Peak near separatrix

• Additional peaks in SOL

• Also peak in PF region – Similar to

features seen at low q95, EVEN parity

Watkins



ISP Splitting of C1+ emission at 150º Depends on I-coil Parity/Phase - Useful for Validation of RMP Penetration

128465 @ 5365 ms L-mode Odd parity 0° Phase

128473 @ 5428 msL-mode Even Parity60° Phase

C II 514 nm

West, Schmitz



Plasma profiles look good with 2007 Leonard/Bray calibration - 4 kA, q95=3.8, ELM suppressed

Osborne

fz

Te

ne

Ti

pe i



Width of the Island Overlap Region Varied in 5 Different Ways in ITER Similar Shape Plasmas at ITER n*e

• q95 scans

– Changes in q95 and q-shear affect island overlap

• I-coil current scans

– Amplitude of RMP affects island size

• 2 toroidal rotation values

– Screening of RMP affected by rotation

• ODD parity I-coil at high q95 ~ 7

– N=3 modes pitch resonant for odd parity and high q95

• C_Coil amplitude variation

– Add mixture of n=1 modes to “fill in” edge mode spectral density




Aldan, Schaffer

ELMing

Icoil 0.0 kA C-coil

1x




Aldan, Schaffer

ELM Suppressed

Icoil 6.4 kA C-coil

1x



I-coil parity controls pedestal island overlap

Both parities suppress ELMsOdd (weak RMP) small islands little or no change in pedestalEven (strong RMP) stochastic transport / pedestal control

Evans EPS05

work in progress: dependence of rmp elm suppression on width of the island overlap region

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