r. maingi 1 , a. hubbard 2 , h. meyer 3 , the alcator c-mod, mast, and nstx teams
DESCRIPTION
Office of Science. Supported by. Status of Small ELM Comparison Experiments: Comparison of Small ELMs in Alcator C-MOD, MAST, and NSTX (ITPA PEP-16, XP721). R. Maingi 1 , A. Hubbard 2 , H. Meyer 3 , the Alcator C-MOD, MAST, and NSTX Teams 1 Oak Ridge National Laboratory 2 MIT 3 UKAEA Fusion - PowerPoint PPT PresentationTRANSCRIPT
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Status of Small ELM Comparison Experiments: Comparison of Small ELMs in Alcator C-MOD,
MAST, and NSTX (ITPA PEP-16, XP721)R. Maingi1, A. Hubbard2, H. Meyer3, the Alcator C-
MOD, MAST, and NSTX Teams
1 Oak Ridge National Laboratory2 MIT3 UKAEA Fusion
NSTX Results ReviewPrinceton NJ
July 23-24, 2007
Supported by Office ofScience
Columbia U.
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Goals of PEP-16
• Identify similarities and differences between the EDA-H-mode in C-MOD and the Type V ELMy H-mode in NSTX:– Does the same physics govern these regimes (and the HRS-mode on JFT-2M)? – Is the Type V ELMy H-mode specific to ST’s?
• Establish dimensionless pedestal comparison with small ELMs between C-MOD, MAST, and NSTX– Match q95 and range in ped
* – Perform a scan in ped (and ped
*?) to find small ELM thresholds– Compare structure of small ELMs with imaging diagnostics
• This XP is ITPA PEP-16– Follows a successfully completed comparison (PEP-12) which established
similarity between C-Mod EDA and JFT-2M HRS regime at higher R/a and identified q95, * as key parameters.
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Small, irregular ELMs appear in C-MOD on top of EDA H-mode at higher edge and lower *
Mossessian, PoP 2003
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Small ELMs appear in wide and * space in NSTX
2
3
4
5
6
7
0.1 1 10
MixedType V
∗
e5
6
7
8
9
10
0.1 1 10
MixedType V
∗
e
=2.2 d=0.75
PNBI=3 MW #112507
PNBI=4 MW #112498
PNBI=5 MW #112502
PNBI=6 MW #112499
• Mixed between larger ELMs at highest
Maingi, JNM 2007 Maingi, PoP 2006
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PEP-16 Status
• C-MOD: Some data in ‘06; MP448 planned summer ‘07• MAST: M6/059 (2 sessions in May 2007)
– Mapping of existence space of small ELMs• 5 point power scan 1 MW < PNBI < 3 MW
– More data on ELM structure and pedestal parameters• PhD project on inter ELM filaments (N. Ben-Ayed, EPS 2007)
– Failed to access regime in L-SN with drsep < -8 mm.• NSTX: XP721 (3 sessions in 2007)
– scan in L-SN (drsep = -6 mm).• 3 point power scan 2 MW < PNBI < 4 MW.
– scan in DN (drsep = -2 mm).• 3 point scan 1 MW < PNBI < 3 MW.
– Failed to access H-mode w/drsep < -8 mm (high X-point)– scan in L-SN (drsep = -15 mm) at higher q95
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Difficult to reproduce small ELM regime in C-MOD
• 4.7 MW RF• N~1.3• Pe,ped~19 kPa• Good H-mode• No evident ELMs,
why?
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MAST: Small ELMs vanish at high input power
• Even with PNBI=1 MW small ELMs are present.– Mixed with threshold
Type III ELMs• With PNBI = 3.2 MW
small ELMs appear only during early H-mode.
• Pressure pedestal seems to be narrow compared to ELM free phases (PEP-9).– Width ~ 1.5%-2.5% of yN
(half of the width seen in PEP-9)
– Higher pressure gradient.
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MAST: No small ELMs at low * and high ped
• Small ELMs exist over a wide range in * and ped.• At low power they are mixed with type-III ELMs
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MAST summary
• Lower power threshold hard to determine– Small ELMs mixed in between type-III ELMs
• Small ELMs disappear at high power and low collisionality * < 1.5 and high ped
LFS
• High n filaments rotate co-current, not all of them detach.
– Larger ELMs: all filaments detach, medium n.• The characteristics seem different from type-V ELMs. • Failed to access H-mode with drsep < -8 mm with < 1.7 with PNBI < 3.4 MW.
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NSTX: H-mode access at low difficult in LSN
• No H-mode access at <1.7 with with drsep = -15 mm.– Max PNBI
= 6 MW.• No problems at >
1.9
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NSTX: Small ELMs observed close to DN
• Observed between 2 MW < PNBI < 3 MW.• Probably not type-V ELMs, may be similar to MAST small ELMs in DN.
drsep ~ -0.3 cm dr
sep ~ -0.6 cm
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NSTX: Power scan with small ELMs in LSN with lower X-point and increased q95
123644 @ 0.28s124657 @ 0.22s
NSTX (H-mode OK) NSTX (no H-mode)
Type V’s Type V’s
Type V’s Type V’s?
Type V’s?
No Type V’s
124658
124657
124656
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NSTX summary
• Small ELMs observed only close DN at ~ 1.8 and high X-point– Small ELMs vanish at high power– These ELMs appear to drift vertically down, in ion grad-B drift
direction and opposite to type-V ELMs
• Failed to access H-mode with drsep < -8 mm with < 1.7 with PNBI < 6 MW and high X-point
• Type V ELMs obtained with lower X-point, drsep ~ -15 mm
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Plans
• In discussion: consider re-running XPs on NSTX and MAST with X-point shifted downward, perhaps forgoing the q95 match for a qcyl match
• Re-establish small ELMs in C-MOD at higher N
• Report results of ELM structure comparison and edge stability analysis at IAEA 2008
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Backup
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Background (PEP-12): H-mode operating spaces in q95 vs * on C-Mod (R/a~3) and JFT-2M (R/a~5) proved very similar
• Steady EDA or HRS regime at high * (> 1.5).• ELMy regime with low D at low * (<0.4).• Some overlap in ELM, H-mode types at intermediate *:
‘Mixed’ or EDA+ELM regime at higher , ELMy at lower on C-Mod.
C-Mod
Hubbard, Kamiya et al, H-mode workshop 2005, Russia
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The structure of the small ELMs in this experiment is different from type-V ELMs
• Small ELMs: – high mode
number, multiple-filaments moving downwards in video
• Type-V ELM: – single filament
moving upwards in video.
• Small ELMs are similar to the ones observed on MAST
R. Maingi, Phys. Plasmas 13, 092510 (2006)R. Maqueda, PSI-17, to appear in J. Nucl. Mater. (2007)
Small ELM DN Type-V ELM
R. Maqueda
QuickTime™ and a decompressorare needed to see this picture.QuickTime™ and a decompressorare needed to see this picture.
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MAST: Small ELMs appear as co-Ip rotating high-n mode
QuickTime™ and a decompressor
are needed to see this picture.