Presented by Brad Nelson Tom Brown, Mike Cole, Paul Fogarty, Paul Goranson, Phil Heitzenroeder,...
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Transcript of Presented by Brad Nelson Tom Brown, Mike Cole, Paul Fogarty, Paul Goranson, Phil Heitzenroeder,...
Presented by Brad Nelson
Tom Brown, Mike Cole, Paul Fogarty, Paul Goranson, Phil Heitzenroeder,
Wayne Reiersen, Dave Williamson, and others
NCSX PAC Meeting
August 2, 2000
Stellarator Core Engineering
Presentation Outline
• Review of original option, “saddle coils in PBX-M”– Vacuum vessel and PFCs– Coil / structure design– Access for heating and diagnostics
• Development of winding design criteria
• Design solutions for “out-of-PBX” options– modular options– Saddles with new 1/R coils
• Plans for design development for CDR and PVR.
Vacuum Vessel
• Vessel is stand-alone structure bake-able to 350C
Parameters
Material Inconel 625
Weight 8300 lbs
Outer radius ~ 2 m
Height ~ 1.7 m
Wall thickness ~ 1 cm
Contour tolerance +/- 5 mm
Inside surf area ~ 37 m2
Enclosed volume ~ 6 m3
Vessel fabrication options
• Press-forming is preferred option–Only 3 segment shapes required–Explosive forming a possible variant
•Brake-bending (ala W7-AS) possible but requires too much welding
PFC requirements• Carbon-based material, bake-able to 350C
• Neutral beam armor– Protect VV from NBI shine-through and during beam calibration– Peak power density ~ 800 W/cm^2
• Limiters / Divertor– Task force developing options for September– Limiters may be adequate for initial operation
• Vessel coverage– Coatings (eg boronization) may be acceptable initially– Full coverage may be required ultimately– Avg. heat flux ~ 30-40 W/cm^2 for 12 MW heating
• Geometry: PFCs fit within 25 mm envelope inside VV
NBI armor• Assume graphite tiles attached to VV, inertial cooling• Temperature < 700 C, well below 1200 C limit
PFC coverage
• Plan staged approach, with limiters and coatings for initial operation
• Preferred approach is full graphite tile coverage, but:
• Total coverage of wall with conformal tiles is costly– major cost driver, equal to VV cost– large number of tile shapes
• Options under study– coatings on low heat flux regions– simplified tile design– conformal blankets
• Cast Nickel-Al-Bronze structure, 48 segments, ~0.5-in wide x 3.5-in deep slots
Typical Coil Cross-SectionCore Assembly
VacuumVessel Helical
Coils
StructuralShell
Saddle coils wound on shell
Outboard shell subassembly
Vessel sector
Inboard shell subassembly
Shell / VV assembly
Leads and thermal insulation
Saddle coils wound on shell
coaxial lead for each coil installed
Thermal insulation sprayed over shell
(7 cm polyurethane with butyl rubber vapor barrier)
What are the issues?
• Access for Heating and Diagnostics
• Allowable winding parameters : Design Criteria
–Current density –Bend radius–Shell groove dimensions
Access requirements
• Heating Systems–4 NBI injectors: adapt existing
PBX-M systems–6 MW ICH (4 antennas)
• Diagnostics–Ports with correct size and view
for initial set of diag. (83 listed)–Spare ports for upgrades (20)
• Fueling/pumping
• Man access
Access for NBI
• Workable solutions found
• Beams tangent at 1.5 m
• Slight interference between beam boxes and with TF coils will require modifications
• No symmetry with 3 field periods and 20 TF coils
Access for RF heating
• Launcher envelope is 400x440x240 mm
• 4 launchers will fit within the large ports
MJC 20000713- 8
Access for diagnostics• Access solutions identified
for nearly all diagnostics
• Access ports must avoid saddle coils, shell parting lines, and external coils
Vacuum pumping on NBI duct
Winding design criteria
• Current density is the primary issue- LN2 cooling required for J up to ~20 kA/cm2
- Room temperature cooling possible for J < 10 kA/cm2
• Current density is limited by a number of factors- material temperature limits - thermal stress due to temperature rise- power consumption- cooldown and pulse repetition rate- fatigue, other effects
• The issues, then, are:- how hot does the conductor get during a pulse? - how hot can the conductor get before it reaches a limit?
Temp. depends on J in copper
How hot is too hot?
–Thermal stress in shell depends on winding spacing, bolt spacing and stiffness of winding
–Stiffness of winding is the primary factor, “stiff” conductor would limit temp rise to < 20K current density to < 10 kA/cm2
Outboard Flange
Bolt Pocket
Top/Bottom Interface
Coil Slot
• Thermal stress was considered primary limit
•Tests show cable soft enough to allow 250K rise
Conductor Sample
4-in dia
13-in
Plunger
R&D shows cable is soft
•Current density target set at <20 kA/cm2 in copper considering all factors
• The cable conductor is made from very fine (36 Gage) wire
• Even after compaction, this cable is very flexible, and can be readily wound on a radius of 1.5 times the conductor thickness
• Recommend bend radius of 3 times the thickness to avoid excessive key-stoning and bunching
Beforecompaction
Aftercompaction
What is minimum bend radius?
Design criteria summary
• “In-PBX” studies provided insight for design saddle coil windings
–Current density limit is 22 kA/cm2 in copper–Bend radius limit is 3 x conductor width–Winding groove > 13 mm for machining–Winding spacing depends on current in winding
(ie, loads on ligament)
• Criteria used to develop / optimize new options
2 options now being studied
Saddle coils plus 1/R (TF)
background coilsand PF/OH set
Modular coils
Plus weak 1/R
background coils
and PF/OH set
Coil option studies
• Design concepts being developed for both the saddle and modular coil options
–Vacuum vessel and PFCs–Winding (including conductor, leads, etc.)–Structure (including field/force/stress analysis)– Integration with background PF/TF coils
• Design evaluation process has begun
3 period modular coils
Modular coil winding pack
Parameter
Major radius, m 1.70
No. of modular coils 21
Coil to plasma distance, cm 21.7
Coil to coil distance, cm 15.0
Nominal cross section, cm 11 x 20
Current / Coil, kA 810
No. of Turns / Coil 40
Structure thickness, cm 1.6
Epoxy fill, cm 0.3
Winding pack dimensions, cm 4 x 16.2
Turn insulation thickness, mm 0.8
Ground wrap, mm 0.8
Turn dimensions, mm 14.4 x 17.6
Hole diameter, mm 5
Cable packing fraction, % 75
Current density in Cu, kA/cm2 11.5
A
B
C
Lateral force direction is away from structure
• EM Force (lb/in) for Coil #1 in Coil Local Coordinate System
Winding forces are toward web
• I-beam casting supports two winding packs per coil• Coil radial forces reacted by inner cylinder - tabs part of casting• Vertical tabs extend to surface at +/- 1-m for coil-to-coil support• Additional shear structure required
Alternate Concepts
Structure concepts
Coil Structure, Windings, and Side Plates
Assembly Sequence based on QOS Study
Figures are for QOS design
Modular coil fab and assy.
Modular coil issues
• Coil winding trajectory–Bend radius– twist
• Access for heating and diagnostics
• Current density–Thermal insulation of modular coils difficult
Minimum bend radius
• Bend radii should be on the order of 10 cm
• Initial coil cases only 4 cm, but optimization has produced ~9 cm minimum radius
• W7-AS and HSX coils have 11.5 and 8.1 cm minimum bend radii
• Twist must also be addressed
Design Evaluation ProcessParameter Analysis planned or in progress
Access Access will be evaluated against requirements
Design margin Compare calculated response to allowables for range of operating parameters
Cost (initial and oper.) Algorithms being developed to evaluate all costs
Risk (e.g., fab. errors cause bad surfaces)
Risk will be evaluated based on experience, discussions with vendors
Maintainability Feasibility and ease of maintenance activities (eg, tile replacement) will be evaluated
Fabrication and assembly schedule
Flow charts of fab and assy steps will be developed and durations will be estimated
Other differentiating parameters TBD
Plans for PVR, CDR
• Evaluate and select best option for chosen plasma(Saddles + 1/R, Modular + weak TF coils,)
• Optimize geometry– Iterate winding aspect ratio, twist, bend radius, etc.–Configure ports
• Continue R&D (primarily CDR)–Small coil winding test–Small structural casting test–Vacuum vessel pressing
Summary• The stellarator core design effort has included several different
magnetic configurations, but only two are now candidates
– Saddle coils plus background TF and PF coils (includes “In-PBX” option)– Modular coil option with “weak” 1/R coils and PF coils
• Concepts for vacuum vessel, saddle coils, and modular coils have been developed
• Access for heating and diagnostics evaluated in detail for C82, tools in place for detailed look at other specific configurations
• Plans in place to reach the PVR and CDR, most R&D is pending selection of configuration option