ARIES Compact Stellarator Reactor

1
NCSX Construction Progress and Research Plans
Hutch Neilson for the NCSX Team Princeton Plasma
Physics Laboratory Oak Ridge National Laboratory
IEEE/NPSS Symposium on Fusion
Engineering Knoxville, TNSeptember 27, 2005
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Topics

• NCSX Mission
• Design, Key Requirements.
• Construction Progress.
• Research Plans.
• Theme Realizing complex geometry requirements in
  the finished product.

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Compact Stellarator Benefits to Magnetic Fusion

• Stellarators solve critical problems.
• Steady state without current drive.
• No disruptions stable without feedback control
  or rotation drive.
• Unique flexibility to resolve 3D plasma physics
  issues.

• Compact Stellarators have additional
• benefits
• Magnetic quasi-symmetry. In NCSX
• Quasi-axisymmetric configuration with effective
  ripple lt1.5.
• Low flow damping, tokamak-like orbits? enhanced
  confinement
• Makes full use of tokamak advances, allowing
  rapid and economical development.
• Lower aspect ratio than typical stellarators.
• 4.4 in NCSX vs. 11 in W7-X.

NCSX has low effective ripple.
4
Stellarator Benefits Are Due to its 3D Geometry

• Stellarators create confining magnetic
  configuration with magnets alone.
• Robust mode of operation, simple control.
• Compact stellarators take advantage of 3D shaping
  flexibility to design for additional attractive
  properties.
• Compactness, good confinement, high-? stability,
  etc.

Engineering challenge geometry and tight
tolerances in magnets and associated
structures. NCSX Project objective engineering
realization of a system to test the physics
benefits of compact stellarators.
Plasma and Coil Design for the National Compact
Stellarator Experiment (NCSX)
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NCSX Mission Compact Stellarator Attractiveness

• Acquire the physics data needed to assess the
  attractiveness of
• compact stellarators advance understanding of 3D
  fusion science.
• Understand
• Beta limits and limiting mechanisms.
• Effect of 3D magnetic fields on disruptions
• Reduction of neoclassical transport by QA design.
• Confinement scaling reduction of anomalous
  transport.
• Equilibrium islands and neoclassical tearing-mode
  stabilization.
• Power and particle exhaust compatibility w/good
  core performance.
• Alfvénic mode stability in reversed shear compact
  stellarator.
• Demonstrate
• Conditions for high-beta, disruption-free
  operation.

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NCSX Physics Design

• Plasma / coil configuration was optimized to
  realize target physics properties.

Plasma Cross Sections

• Physics Properties
• 3 periods, low R/?a? (4.4).
• Quasi-axisymmetric w/ low ripple.
• Stable at ?4.1 to specific MHD instabilities.
• Reverse shear q-profile.
• 25 of transform from bootstrap.
• Good magnetic surfaces at high ?.
• Constrained by engineering feasibility metrics
• coil-coil spacing
• min. bend radius
• tangential NBI access
• coil-plasma spacing.

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NCSX Coils Flexibility to Vary Physics Properties
rotational transform
Shear controlled by varying plasma shape ?4.2,
full current, fixed profiles.

• Magnet system has 4 coil sets
• Modular, TF, PF, trim.

normalized radius

• Also
• Can externally control iota.
• Can increase ripple by 10x, preserving
  stability.
• Can lower theoretical b-limit to 1.
• Can cover wide operating space in ? (to at least
  6), IP, profile shapes.

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Modular Coil Design Meets Physics Requirements

• 18 modular coils (3 shapes)
• Robust structural shell design minimizes
  deflections.
• Toroidal and poloidal breaks inhibit eddy
  currents.
• Lead arrangement minimizes field errors.

Modular Coil Structure
Winding form (one per coil).
Winding current centers follow physics-optimized
design to 1.5 mm (0.1) accuracy.
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Vacuum Vessel Design Meets Physics Requirements

• Physics Requirements
• High-vacuum environment for good plasma
  performance.
• Sufficient interior space for plasma, boundary
  layer, and PFCs.
• Access for heating and diagnostic viewing.
• Low field errors.

• Engineering constraint be able to
• slide the modular coils over the
• vacuum vessel (w/ ports removed).
• Design
• Vacuum boundary inside coils, as far from plasma
  surface as possible.
• Shell geometry similar to plasmas. Tolerance
  3 mm.
• About 100 ports, filling all available openings
  in surrounding magnets.
• Inconel material.
• Bakeable to 350 C.

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NCSX Can Produce Required Plasma Conditions.
Stellarator Major radius 1.4 m Magnetic Field
(B) _at_ 0.2 s pulse 2.0 T _at_ 1.7 s pulse 1.2
T Plasma current 350 kA. Plasma Heating
(planned) NBI 6 MW (tangential) ICH 6 MW
(high-field launch) ECH 3 MW

• High ? (4) Plasma Scenario
• B 1.2 T, P 6 MW
• (?E  2.9 ? ISS95 L-mode assumed)
• ne 6 ? 1019 m-3
• Ti(0)  1.8 keV
• ?i  0.25

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Construction

• Key engineering challenge accurate realization
  of the geometries
• required in the magnets, vacuum vessel, and
  associated structures.
• NCSX Project Strategy
• Manufacturing RD Develop critical processes
  prior to construction.
• Modular coil winding forms / structures.
• Modular coil windings.
• Vacuum vessel.
• System engineering Manage flow-down of
  requirements from physics specification to
  finished product.

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Vacuum Vessel Manufacturing RD

• Scoping studies during conceptual design
• Manufacturing analyses by 5 industrial suppliers.
• Examined process issues.
• Shell segmentation to minimize welding.
• Weld fixturing to minimize distortion.
• Port attachment.
• Prototyping and supplier qualification during
• preliminary design.
• Two competing suppliers, cost-type contracts.
• Developed manufacturing and QA plans for NCSX
  specs.
• Built 20-degree prototype sectors.
• Submitted sound proposals for production order.
• Production Contract awarded Sept., 2004
• Major Tool and Machine, Inc.

Prototype Vacuum Vessel Sector
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Modular Coil Manufacturing RD

• Scoping studies during conceptual design
• Multiple suppliers examined process issues.
• Alloy and casting options to minimize
  deformation.
• Identified lowest-risk acquisition strategy
• Winding forms cast and machined by industry.
• Coil fabrication by Laboratory staff.
• Winding form prototyping and supplier
• qualification during preliminary design.
• Two competing suppliers, cost-type contracts.
• Developed manufacturing and QA plans for NCSX
  specs.
• Built prototype castings.
• Submitted sound proposals for production order.
• Production Contract awarded Oct., 2004
• Energy Industries of Ohio, Inc.

Casting being poured.
Casting ready to be machined.
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Major Component Manufacture is Proceeding Well
Modular Coil Winding Form being machined
Vacuum Vessel sector fabrication
Manufacturing RD eliminated major technical
uncertainties for component production.
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Modular Coil Winding RD

• Flexible conductor handling / winding.
• Keystoning and insulation tests
• Vacuum pressure impregnation
• Process development
• Material properties
• Mechanical tests (tension, compression, flexure,
  fatigue)
• Thermal tests (CTE, conductivity)
• Electrical resistance
• Twisted Racetrack Coil(integrated demonstration)
• Developed efficient process for accurate coil
  manufacture.
• Improved the design for manufacturability.
• Tested at operating temperature, current, and
  pulse length.

VPI mold development.
Twisted RacetrackCoil
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Coil Fabrication is Ready to Start
Winding and Conductor Payout Fixtures
Modular Coil Mfg. Facility
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System Engineering Ensures Requirements Flow Down
to Finished Product.
Dimensional Control Metrology Strategies,
equipment, and procedures for realizing required
1.5 mm winding accuracy. ? Coil fabrication
(0.5 mm) Field period assembly (0.5 mm) Final
assembly (0.5 mm)
Analysis Dynamic CAD modeling verifies that coils
can be installed over vacuum vessel.
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Construction Will Be Completed in 2009.

• MCWFs delivered in FY06-07.
• Coil winding in FY06-07.
• Sub-assembly activities start when VV sectors
  arrive in FY06.
• Final assembly testing FY08-09.
• First Plasma July, 2009.

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Research Program Will Address Physics Issues for
Compact Stellarator Attractiveness.
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Summary

• Research on NCSX will test the expected physics
  benefits of compact stellarators.
• Steady state, no disruptions, compact,
  tokamak-like physics.
• Realization of required 3D component and assembly
  geometries is the main engineering challenge.
• Progress in NCSX construction project indicates
  no obstacles to engineering realization of
  compact stellarators.