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S.L. Allen/IAEA FEC/November, 2012
S. L. Allen, V. A. Soukhanovskii, T.H. Osborne, E. Kolemen, J. Boedo, N. Brooks, M. Fenstermacher, R. Groebner, D. N. Hill, A. Hyatt, C. Lasnier, A. Leonard, M. Makowski, W.H. Meyer, A. McLean, T. Petrie, D. Ryutov, J. Watkins IAEA Fusion Energy Conference, San Diego, CA October 8-12, 2012
Results From Initial Snowflake Divertor Physics Studies on DIII-D
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S.L. Allen/IAEA FEC/November, 2012
• Theory1 predicts second order null of SF Divertor (∇BP~0) – Multiple strike points, increased volume and connection lengths – Increased edge shear, influencing pedestal stability
• Experiments2 have made progress on comparisons
• DIII-D adds new data: Focus on SF(-) configuration
DIII-D Experiments focus on SF(-) configuration
1D. D. Ryutov, PoP 14, 064502 2007, TH/P4-18 2Vijvers EX/P5-22, 3Soukhanovskii EX/P5-21
2nd X-Point in Private Flux
2nd X-Point in SOL
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S.L. Allen/IAEA FEC/November, 2012
• Theory1 predicts with second order null of SF Divertor (∇BP~0) – Multiple strike points, increased volume and connection lengths – Increased edge shear, influencing pedestal stability
• Experiments2 have made progress on comparisons
• DIII-D adds new data: Focus on SF(-) configuration – Experience on NSTX
• Possible heat flux control for future compact machines
DIII-D Experiments focus on SF(-) configuration
1D. D. Ryutov, PoP 14, 064502 2007, TH/P4-18 2Vijvers EX/P5-22, 3Soukhanovskii EX/P5-21
2nd X-Point in SOL
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S.L. Allen/IAEA FEC/November, 2012
• Recent DIII-D long pulse (3s) results at high τ- H(89P) ≥ 2 in SF(-) configuration: – Divertor “attached” during SF (C III images) – 2 – 3 X Heat flux reduction due to SF geometry (IR camera) – Constant: Pedestal Profiles, Divertor Radiated Power (Bolometer) – Reduced ΔW(ELM) and ELM heat flux on divertor
in SF(-) with Gas Puffing: – Divertor detaches, large radiating volume – Further heat flux reduction – Heat flux during ELM reduced
DIII-D data adds new insight into Snowflake divertor
Divertor Heat Flux
Snowflake
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S.L. Allen/IAEA FEC/November, 2012
Compare DIII-D Normal Divertor with SF(-)
• Use NSTX control algorithm • 2- External coils control strike points
(F4B and F8B) • 1- External coil moves 2nd null point
(F5B) • DIII-D and NSTX use similar
Plasma Control Systems (PCS)
√√ Standard DIII-D Divertor
√√ Snowflake (-)
3mm Flux Line at Midplane
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S.L. Allen/IAEA FEC/November, 2012
• Ip=1.2 MA, Bt=2 T • PNBI= 3-5 MW
• SF(-) maintained for è 3s
• Flux expansion é 2.5X
• Radiated Power è similar
• Confinement è similar
• Heat Flux reduced ê 2.5X
2.5X Divertor Heat Flux Reduction due to geometry
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S.L. Allen/IAEA FEC/November, 2012
New LLNL Periscope: IR image shows 3-D features of SF(-) operation on DIII-D
Pellet Pellet triggered ELM
Strike Point Splitting During SF
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S.L. Allen/IAEA FEC/November, 2012
Lower Divertor C III Shows Attached SF Divertor
Shot 150673, 3056-3654ms, CIII (465nm)
SF(-): Between ELMs, Additional Strike Point
Before SF(-): CIII extends to outer strike point (attached divertor)
Post-Snowflake
SF(-): During ELM, profile broadens
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S.L. Allen/IAEA FEC/November, 2012
• No significant change in divertor bolometer radiation • Small recombination (Balmer n= 7-2 line ) • Tangential divertor Dα and C III cameras show no detachment • In contrast with NSTX where SF(-) detaches
SF(-) divertor conditions similar to “attached” divertor
Inverted Rad. Power Standard Divertor
Inverted Rad. Power During SF(-)
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S.L. Allen/IAEA FEC/November, 2012
Divertor Peak Heat Flux Reduced 2.5X in SF due to changes in divertor geometry
Standard Divertor
Snowflake Snowflake
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S.L. Allen/IAEA FEC/November, 2012
Pedestal profiles between ELMs very similar with and without SF(-)
• Slightly steeper and higher ne, lower and flatter Te with SF-
Electron Density ne Electron Temperature Te
Note: BLUE is
SF
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S.L. Allen/IAEA FEC/November, 2012
Detailed ELM analysis before/during SF shows:
• Pedestal Energy (WPEDESTAL)
Constant
• Confinement Constant
• Change in stored energy lost
per ELM (ΔWELM) is reduced
• Consistent with Loarte
connection length scaling
Detailed ELM Analysis: ΔW(ELM) decreased, W pedestal constant in SF
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S.L. Allen/IAEA FEC/November, 2012
New opportunity to study details of SOL transport in attached SF divertor; study ELMs
Standard Divertor
Snowflake
Divertor Heat Flux – Expanded Scale
Major Radius Divertor Plate
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S.L. Allen/IAEA FEC/November, 2012
New opportunity to study details of SOL transport in attached SF divertor; study ELMs
ELMs are Variable, Show Additional Strike points
Standard Divertor
Snowflake
Ryutov
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S.L. Allen/IAEA FEC/November, 2012
• Shot with gas puffing only (black lines)
• Compared with: – SF – SF + Gas puff
• Reduced ELM peak heat load with SF + Gas Puff
SF + gas puffing reduces divertor ELM peak heat load
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S.L. Allen/IAEA FEC/November, 2012
SF + Gas Puff Reduced ELM divertor heat flux over GP alone
Gas Puff
SF + Gas Puff
SF D2
D2
Major Radius
Gas Puff
Gas Puff & SF
Expanded Divertor Radiation Zone in Both Cases
Divertor Heat Flux
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S.L. Allen/IAEA FEC/November, 2012
SF + Gas Puff (expanded scale)
Gas Puff
SF + Gas Puff
Gas Puff
Gas Puff & SF
Major Radius
Expanded Divertor Radiation Zone in Both Cases
D2
SF D2
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S.L. Allen/IAEA FEC/November, 2012
• Recent DIII-D long pulse (3s) results at high τ- H(89P) ≥ 2 in SF(-) configuration: – Divertor “attached” during SF (C III images) – 2 – 3 X Heat flux reduction due to SF geometry (IR camera) – Constant: Pedestal Profiles, Divertor Radiated Power (Bolometer) – Reduced ΔW(ELM) and ELM heat flux on divertor
in SF(-) with Gas Puffing: – Divertor detaches, large radiating volume – Further heat flux reduction – Heat flux during ELM reduced
DIII-D data adds new insight into Snowflake divertor
Divertor Heat Flux
Snowflake
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S.L. Allen/IAEA FEC/November, 2012
• Recent DIII-D long pulse (3s) results at high τ- H(89P) ≥ 2 in SF(-) configuration: – Divertor “attached” during SF (C III images) – 2 – 3 X Heat flux reduction due to SF geometry (IR camera) – Constant: Pedestal Profiles, Divertor Radiated Power (Bolometer) – Reduced ΔW(ELM) and ELM heat flux on divertor
in SF(-) with Gas Puffing: – Divertor detaches, large radiating volume – Further heat flux reduction – Heat flux during ELM reduced
• Future snowflake studies: • Integration with high-δ Advanced Tokamak Scenarios • Clarification of detachment threshold w.r.t. standard divertor • Study of parallel versus perpendicular SOL transport – SOL Physics • Heat flux control in compact machines, new regimes
DIII-D data adds new insight into Snowflake divertor
Divertor Heat Flux
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S.L. Allen/IAEA FEC/November, 2012
Snowflake Divertor Results at the IAEA Conference: DIII-D adds recent new data
Ryutov – Original Theory TH/P4-18
TCV Heat Flux Reduction –
Vijvers EX/P5-22
NSTX Heat Flux Reduction –
Soukhanovskii EX/P5-21
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S.L. Allen/IAEA FEC/November, 2012
Backup Slides
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S.L. Allen/IAEA FEC/November, 2012
Initial DIII-D snowflake divertor results very encouraging and motivate further studies
ü Demonstrated steady-state (2 s) snowflake-minus and plus configurations at σ = dX-X/aminor=0.15-0.20 § Optimized divertor geometry and plasma shape for pedestal profile
measurements, analysis commencing
ü Demonstrated beneficial magnetic geometry properties ü Demonstrated between-ELM peak divertor heat flux reduction
via geometry ü Favorable comparison with standard divertor geometry ü Snowflake divertor attached at PNBI=3-5 MW , 0.5 x n/nG
ü High confinement maintained (HL89~2.1, H98(y,2)~1.2-1.3)
ü Demonstrated radiative detachment at 0.55-0.75 x n/nG ü Density scan using D2 puffing ü Significant reduction of peak divertor heat flux, Pdiv-rad ≤0.75 Ptot ü Formation of MARFE-like X-point region outside of separatrix (?) ü Up to 20 % confinement degradation at higher densities
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S.L. Allen/IAEA FEC/November, 2012
• SF configuration reduces heat flux 2-3X by flux expansion
• Divertor heat flux reduced
• ∆W(ELM) reduced • Core confinement (H98 > 2)
and pedestal constant
Snowflake divertor configuration reduces ELM and steady state heat flux
Snowflake
Standard Divertor Snowflake
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S.L. Allen/IAEA FEC/November, 2012
• SF configuration reduces heat flux 2-3X by flux expansion
• Divertor heat flux reduced
• ∆W(ELM) reduced • Core confinement (H98 > 2)
and pedestal constant • ELM heat flux reduced
dramatically with gas puffing
Recent DIII-D Snowflake divertor experiments show heat flux reduction by flux expansion, ELM reduction
Snowflake
Snowflake
Snowflake Snowflake Major Radius
3.
4.
6.
ReducedDivertor Heat Flux
Increased Divertor Radiation
SF 5.
Time(s)