pkm- NCSX CDR, 5/21-23/2002 1 Power and Particle Handling in NCSX Peter Mioduszewski 1 for the NCSX...
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Transcript of pkm- NCSX CDR, 5/21-23/2002 1 Power and Particle Handling in NCSX Peter Mioduszewski 1 for the NCSX...
1pkm- NCSX CDR, 5/21-23/2002pkm- NCSX CDR, 5/21-23/2002
Power and Particle Handling in NCSXPower and Particle Handling in NCSX
Peter MioduszewskiPeter Mioduszewski11
for the NCSX Boundary Group:for the NCSX Boundary Group:
M. FenstermacherM. Fenstermacher22, A. Grossman, A. Grossman33, A. Koniges, A. Koniges22, L. Owen, L. Owen11, T. , T. RognlienRognlien22, M. Umansky, M. Umansky22
1 1 Oak Ridge National LaboratoryOak Ridge National Laboratory2 2 Livermore National LaboratoryLivermore National Laboratory
33University of California at San Diego University of California at San Diego
NCSX Conceptual Design ReviewNCSX Conceptual Design Review
Princeton, May 21-23, 2002Princeton, May 21-23, 2002
2pkm- NCSX CDR, 5/21-23/2002pkm- NCSX CDR, 5/21-23/2002
ObjectivesObjectives
The task of the plasma boundary group is to develop techniques for improving plasma performance by controlling the plasma boundary:
Heat removal: avoid excess temperatures, materials choice (C, W, Mo?), configuration of plasma-facing components (PFCs)
Impurity control: materials, wall conditioning, specific PFC design and location, control of plasma edge parameters (e.g. control Te, screening, etc.)
Recycling control: positioning of the recycling sources away from critical locations, baffled and/or pumped divertors, and wall conditioning.
3pkm- NCSX CDR, 5/21-23/2002pkm- NCSX CDR, 5/21-23/2002
Phased PFC Development will be Guided by Phased PFC Development will be Guided by Experiment and Modeling Experiment and Modeling
1st generation of PFCs: initial poloidal limiters at = 60º Phase 1: Machine shake-down Phase 2: Vacuum and flux surface mapping Phase 3: Ohmic operation: 100-300 kW
2nd generation of PFCs: wall armor for thermal-, fast particles, NBI
Phase 4: Auxiliary heating: 3 - 6 MW, first opportunity to measure finite beta edge configurations for a data base for divertor design
3rd generation of PFCs: divertor operation in baffle mode Phase 5: Confinement and beta limits
4th generation of PFCs: divertor operation in pumping mode
Phase 6: Long-pulse operation: (~1.2 s pulse does not need real-time cooling)
4pkm- NCSX CDR, 5/21-23/2002pkm- NCSX CDR, 5/21-23/2002
1st Generation PFCs: Poloidal Limiters at 1st Generation PFCs: Poloidal Limiters at = = 60º60º
The initial set of limiters will protect the walls and allow for initial Ohmic operation.
Poloidal cross-section at = 60º
Plasma
Vacuum Vessel
poloidal limiters
Plan view of vacuum vessel and plasma
5pkm- NCSX CDR, 5/21-23/2002pkm- NCSX CDR, 5/21-23/2002
2nd Generation PFCs: Graphite Wall Armor 2nd Generation PFCs: Graphite Wall Armor (Liner) (Liner)
The 2nd generation of PFCs will consist on graphite panels attached to the vacuum vessel and bakeable to 350ºC.
This configuration will provide the first opportunity to diagnose the plasma boundary with finite beta plasmas.
Experiments and modeling in this configuration will provide the basis for the divertor design.
= 0o
2nd generation: wall armor
wall armor
plasma
6pkm- NCSX CDR, 5/21-23/2002pkm- NCSX CDR, 5/21-23/2002
Experience in W7-AS indicates that substantial plasma performance improvement can be expected through systematic control of plasma-wall interactions with a divertor:
E increases steeply with density,
p and imp decrease with increasing density
Record value of <ß> ~ 3% achieved (at B = 1.25 T) Full density control Plasma heating at extremely high density with EBW
Although the NCSX configuration is somewhat different, the W7-AS results provide a compass for the direction of our boundary program.
The key to good plasma performance in NCSX is most likely boundary control with divertor-like
configurations.
7pkm- NCSX CDR, 5/21-23/2002pkm- NCSX CDR, 5/21-23/2002
Long Connection Lengths Are Needed Between LCMS and Long Connection Lengths Are Needed Between LCMS and Divertor For Sufficient Temperature SeparationDivertor For Sufficient Temperature Separation
.
The divertor-LCMS temperature difference for NCSX can be calculated with the “2-point-model”
The figure shows: Lc = 100 m -> sufficient divertor-separatrix temperature separation
Lc = 5 m -> temperature separation insufficient, even at high ne
.
0 1 2 3 4 50
40
80
120
160
200
Tsep100
Tdiv100
Tsep5
Tdiv5
nsep (1019m-3)
3 MW
0 1 2 3 4 50
40
80
120
160
200Tsep100
Tdiv100 Tsep5
Tdiv5
nsep (1019m-3)
6 MW
8pkm- NCSX CDR, 5/21-23/2002pkm- NCSX CDR, 5/21-23/2002
The NCSX Boundary Has Long Connection The NCSX Boundary Has Long Connection Lengths ! Lengths !
Poincaré plots, generated with the MFBE* and Gourdon codes: 20 field-lines were started at the outer/inner midplane (0-1 cm) and followed for 20 toroidal revolutions (Lc~180 m)
Significant flux expansion Long connection lengths: here up to 180 m Kolmogorov lengths are ~30-50 m Suitable for divertor operation
A. Grossman
*E. Strumberger
50 cm
0º 30º 60º 90º
9pkm- NCSX CDR, 5/21-23/2002pkm- NCSX CDR, 5/21-23/2002
3rd and 4th Generation PFCs : Divertor 3rd and 4th Generation PFCs : Divertor
vacuum vessel
divertor pump (e.g.Ti)
3rd Generation“baffle mode”
4th Generation“pumping mode”
divertor plateand baffles
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pkm- NCSX CDR, 5/21-23/2002pkm- NCSX CDR, 5/21-23/2002
Neutrals Penetration Is Low in the Neutrals Penetration Is Low in the Limiter and Liner ConfigurationsLimiter and Liner Configurations
Plasma efflux based on: ne=5x1019m-3, assuming p= 20 ms, flux ampl.= 5x modeling indicates low neutral density in the confinement zone
W7-AS has no problem with a smaller waist than NCSX (16 vs.24cm)
Rec.loc. Rec.loc.
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pkm- NCSX CDR, 5/21-23/2002pkm- NCSX CDR, 5/21-23/2002
In the Divertor Configuration, Neutrals Are In the Divertor Configuration, Neutrals Are Contained by the Divertor Plasma/Baffles Contained by the Divertor Plasma/Baffles
10 7
10 8
10 9
10 10
10 11
0 5 10 15 20 25Radius in outer midplane (cm)
Core SOLDivertor
φ=0poloidalcrosssectionsimulation
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pkm- NCSX CDR, 5/21-23/2002pkm- NCSX CDR, 5/21-23/2002
SummarySummary
Improved performance in W7-AS has recently demonstrated that power and particle control are essential tools for improving plasma performance in stellarators.
For initial operation, our understanding of the NCSX boundary will be limited and we will start with a simple limiter configuration.
The boundary in NCSX is stochastic, with Kolmogorov lengths measuring several toroidal revolutions !
This guarantees sufficiently long connection lengths which - in conjunction with the observed flux expansion - are suitable for divertor operation.
As our understanding of the boundary grows, we will improve impurity and neutrals control by developing divertor configurations.
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pkm- NCSX CDR, 5/21-23/2002pkm- NCSX CDR, 5/21-23/2002
ExtrasExtras
14
pkm- NCSX CDR, 5/21-23/2002pkm- NCSX CDR, 5/21-23/2002
The new divertors enable access to a new regime with NBI at very high
density (up to ne~ 3.5 x 1020 m-3 ) with promising confinement properties:
- E increases steeply with density,
- p and imp decrease with increasing density
courtesy of P. Grigull
Record value of <ß> ~ 3% achieved (at B = 1.25 T)
Full density control already without Ti- gettering.
Quasi-steady state operation also including partial detachment.
Radiation stays always peaked at the edge.
Plasma heating at extremely high density by HF (EBW 140 GHz) is
successfully demonstrated.
Divertor Operation has Dramatically Divertor Operation has Dramatically Improved Plasma Performance in W7-ASImproved Plasma Performance in W7-AS
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pkm- NCSX CDR, 5/21-23/2002pkm- NCSX CDR, 5/21-23/2002
Toroidal Decay of Neutral Density Recycled at Toroidal Decay of Neutral Density Recycled at = 0º= 0º
0
5 10 10
1 10 11
1.5 10 11
0 10 20 30 40 50 60
n(H0
) (cm
-3)
Toroidal angle φ( .)deg
Just insideseparatrix
Just inside the vacuum vessel wall
Midplane simulations( ) Recycle puff at φ=0
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pkm- NCSX CDR, 5/21-23/2002pkm- NCSX CDR, 5/21-23/2002
Initial Results of Poincaré Plots With Field-Line Diffusion- Initial Results of Poincaré Plots With Field-Line Diffusion- Field-Lines Launched Just Inside the Last Closed Field-Lines Launched Just Inside the Last Closed
Magnetic Surface Magnetic Surface A. Koniges
Field-line expansionat tips of bean section looks promising for divertor operation.
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pkm- NCSX CDR, 5/21-23/2002pkm- NCSX CDR, 5/21-23/2002
Initial Foot-Prints Used For Divertor Plate Initial Foot-Prints Used For Divertor Plate Design Indicate Nearly Full Toroidal Coverage of Design Indicate Nearly Full Toroidal Coverage of
DivertorDivertor
A. KonigesA. Koniges
toroidaltoroidal
poloidalpoloidal
outeroutermidplanemidplane
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pkm- NCSX CDR, 5/21-23/2002pkm- NCSX CDR, 5/21-23/2002
Kolmogorov Length for Field-Lines Kolmogorov Length for Field-Lines Launched At Outside MidplaneLaunched At Outside Midplane
Lk ~ 40 m
Lc ~ 180 m
0.001
0.01
0.1
1
0 50 100 150 200 250
Kolmogorov Length: FL 1 and 2 mm outside
Dist:1-2 (m)
y = 0.010152 * e^(0.025256x) R= 0.79601
Dist:1-2 (m)
Tor.Distance (m)Toroidal Distance (m)
Dis
tan
ce b
etw
een
Fie
ld-L
ines
(m
)