1 pkm- NCSX CDR, 5/21-23/2002 pkm- NCSX CDR, 5/21-23/2002 Power and Particle Handling in NCSX Power and Particle Handling in NCSX Peter Mioduszewski Peter Mioduszewski 1 for the NCSX Boundary Group: for the NCSX Boundary Group: M. Fenstermacher M. Fenstermacher 2 , A. Grossman , A. Grossman 3 , A. Koniges , A. Koniges 2 , L. Owen , L. Owen 1 , T. , T. Rognlien Rognlien 2 , M. Umansky , M. Umansky 2 1 1 Oak Ridge National Laboratory Oak Ridge National Laboratory 2 2 Livermore National Laboratory Livermore National Laboratory 3 University of California at San Diego University of California at San Diego NCSX Conceptual Design Review NCSX Conceptual Design Review Princeton, May 21-23, 2002 Princeton, May 21-23, 2002
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pkm- NCSX CDR, 5/21-23/2002 1 Power and Particle Handling in NCSX Peter Mioduszewski 1 for the NCSX Boundary Group: for the NCSX Boundary Group: M. Fenstermacher.
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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
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
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
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
In the Divertor Configuration, Neutrals Are In the Divertor Configuration, Neutrals Are Contained by the Divertor Plasma/Baffles Contained by the Divertor Plasma/Baffles
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.
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.
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