Engineering Design Status of the Quasi-Poloidal Stellarator, QPS

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Engineering Design Status of the Quasi-Poloidal
Stellarator, QPS

• Presented by B. Nelson for the QPS Team
• SOFE 05
• September 28, 2005
• Knoxville, TN

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QPS team

• ORNL Lee Berry, Mike Cole, Paul Fogarty, Kevin
  Freudenberg, Paul Goranson, Steve Hirshman, Jim
  Lyon, Don Spong, Dennis Strickler, Dave
  Williamson, Gary Lovett, Tom Hargrove, Martin
  Brown, John White, Jim Tsai
• PPPL Phil Heitzenroeder, Hutch Neilson, Larry
  Sutton, Frank Malinowski, Jim Chrzanowski
• Univ. of Tennessee Bob Benson, Tom Shannon,
  Arnold Lumsdaine, Madhu Madhukar, Masood Parang,
  Anut Chaudhri, Shankar Narasimhaswami, S.
  Sridharan, Shing-Jia Tang
• J.P. Pattern John Puhl, Gary Puhl
• Waukesha Kramer Foundry Bill Norris
• New England Wire Technologies Lana Superchi,
  Clayton Elliot

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Presentation outline

• Introduction
• What is QPS?
• Basic device description, for each element
• What is the baseline design?
• What are the issues?
• What RD is planned or underway?
• Assembly
• Summary

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What is QPS?

• QPS is a compact stellarator to be built at ORNL
  by a consortium including ORNL, the University of
  Tennessee, and PPPL.
• Compact stellarators have tremendous promise,
  combining the best features of tokamaks and
  stellarators
• High beta (gt4) stability
• No tokamak-like disruptions (no VDEs, zero or
  small plasma current)
• No current drive required for steady state
  operation
• Vertical and kink stability without a conducting
  wall or feedback system, even in highly elongated
  plasma configurations
• Low aspect ratio compared to more conventional
  stellarators
• QPS will study new physics regimes, complement
  NCSX
• Quasi-poloidal symmetry allows low damping for
  poloidal flows that disrupt turbulent eddies
  causing anomalous transport
• Extends stellarator physics to very low aspect
  ratio

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QPS device
OH Solenoid Inner TF Coil Legs
Inner Poloidal Field Coil
Outer Poloidal Field Coil
Outer Toroidal Field Coil Leg
Shell
Plasma
Modular Coil
Vacuum Vessel
Divertor
Outer VF Coils
Diagnostic or Pumping Port
Support Posts
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Baseline parameters for QPS design
Average major radius Average plasma radius Plasma aspect ratio Plasma volume Average field on axis from the set of modular coils Auxiliary toroidal field Ohmic current ECH power ICRF heating power 0.91 m 0.30.4 m 2.5 2-3 m3 B 1 T for 1.5-s pulse 0.15 T 0 to 100 kA 0.6-2 MW 24 MW
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QPS Coil Set
Coil Set Function, Coil set provides
Modular Coils Basic quasi-poloidally symmetric magnetic configuration
Vertical Field Coils Inductive current drive, plasma position control, plasma shaping
Toroidal Field Coils Addition or subtraction of toroidal field for control of magnetic transform
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Modular coil configuration has 20 coils, 5 shapes
1.78 m
1.46 m
Coil 1
Coil 2
2.12 m
2.08 m
2.02 m
Coil 3
Coil 4
Coil 5 Bean Section
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Continuous shell forms robust structure

• Shell consists of individual modular coil forms
  that are bolted together
• Penetrations for access are provided wherever
  needed
• Thickness can be optimized to reduce stresses,
  deflection
• Stellarator symmetry preserved, two toroidal
  electrical breaks

Electrical breaks
77
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Prototype winding form is in production

• Casting is almost complete
• Machined sand mold is accurate, cost effective
• Modified CF8M has low permeability, air quench
• Machining to start in November

M1
As cast wt. 7900 lbs
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Casting technique is ideal for prototypes

• Machined mold technique eliminates pattern
• Reinforced sand blocks are machined with router
• Mold cavity is very accurate compared to foam
  pattern technique
• No need to provide draft, other features related
  to conventional technique using hard patter

Density
Mold model
Pouring 15000 lbs
Machining mold part

• Flow solidification analysis, mold design require
  many iterations

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Conductor wound directly on winding forms
Winding form
Winding Pack
Current center, located within /- 1 mm
2 coils per form
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Flexible cable is used for the conductor

• Parameters
• Coil Envelope 6.1 x 2.7 inches
• Current / Coil 300 (nom) to
• 380-kA (max)
• Number of Elec. Turns 14
• Avg length per turn 120 in
• Nominal current / turn 21.4 kA
• Cable Size .44 x .44 in
• Heat removed via co-wound channels
• Net Current Density 5.1 6.5-kA/cm2
• Total peak power 40 MW
• Flexible cable used to wind coil

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Coil parameters, power supply, cooling temp.
determine pulse waveform and flat-top time
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Cooling water is distributed in winding pack

• Winding is cooled by conduction to cooling lines
  in winding pack

Electrical turn, ( 1 of 14)
Option 1
Option 2
Option 3
Each conductor has an imbedded cooling tube
Flexible SST tubing replaces conductor
Smaller copper tubing replaces conductor
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Option 1 has best cooling, opt. 2,3 would ratchet

Option 3
Option 2
Option 1
Ref K. Freudenberg, PIII.b-16,
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Conductor RD underway to select cable

• Issue
• Would like to use internal or co-wound cooling
  channels (to avoid cladding and chill plates)
• Progress
• Internally cooled cable shipped last week
• Flexible stainless tube on order
• Results
• Filling copper (or Teflon) tubes with Pb-Bi
  eutectic is feasible
• Emptying the eutectic cannot be accomplished with
  forced air only some residue remains
• Copper tubing work hardens, increasing winding
  difficulty

Cable with half-lapped fiberglass insulation
.425 in (10.8 mm)
Ref M. Madhukar, PI.a-4,
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We plan to wind the coils at Univ. of Tennessee

• Space has been prepared in the recently completed
  Magnet Development Laboratory (MDL), a UT
  facility.

• All winding/canning/potting processes are being
  developed through RD at this facility.

Ref P. Fogarty, PIII.b-10,
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Rolling cart fixture avoids handling issues

• Winding form shipped from vendor on cart, stays
  on cart for all winding, canning, VPI processing
  and shipping to ORNL

End View
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Winding RD

• Building on experience from NCSX, but
• Must modify technique to provide clamp-free
  condition to install vacuum can
• Investigating alternate methods to provide ground
  insulation
• Progress
• Practice coils wound using prototypical clamping
  techniques
• Twisted Tee winding form fabricated
• Results
• Cable easily positioned into winding form
• setting counteracted keystoning effects
• Clamps could be removed with virtually no
  conductor movement

NCSX Ref J. Chrzanowski, PIII.b-4,
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Cyanate ester system chosen over epoxy

• Coils must operate at elevated temperature (40-
  100 C goal) to maintain good vacuum properties
• Composite Technology Development (CTD) has
  developed high temperature cyanate ester material
  CTD 403
• Room temp processing (100 centi-poise), pot life
  several days
• Hydrophobic, may not be affected by water leaks
• Mechanical properties similar for both CTD 101K
  and CTD 403, but additional tests are planned for
  CTD 403
• Bakeout temperature will be limited by thermal
  stress and creep properties, but are much better
  for CTD 403

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Vacuum Pressure Impregnation (VPI)

• Progress
• VPI system set up at UT MDL
• Four turn racetrack coil VPI-ed

• Results
• Good wicking into cable
• Cyanate ester has very long pot life and is
  injected at room temperature
• Curing cycle easily achieved with temperature
  feedback system
• Next steps
• Measure mechanical and thermal properties
• Repeat twice and on twisted racetrack coil

Ref Univ. of Tennessee
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Vacuum canning is required for QPS coils
Winding Pack
Vacuum Weld
Vacuum Can
Seam Weld
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Vacuum canning RD distortion, temp. ok

• Mockup fabricated and welded
• Welds made w/o filler or special weld preps,
  trepans
• Distortion
• Calculation very localized, .002 in
• Measured very small, lt .002 in.
• Temperature
• Weld temperature at windings benign, glass
  insulation is not damaged

Ref A. Lumsdaine, PIII.b-12
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Castings are also o.k. in vacuum

• Vacuum testing performed on prototypical cast
  material
• Results
• Pressure continued to drop after several days
• No indication of connected porosity, virtual
  leaks, etc.
• Surface was as-cast, but will be polished on
  production article

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TF and VF coils
VF Coils

• Center Stack
• Includes
• TF Inner Legs
• Solenoid
• Vac. boundary

Outer TF Legs
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VF Coils / Solenoid

• 4 pairs of VF coils are included in design
• All but one VF coil pair already exist
• Inner VF PBX-DF-1 coil
• Inner VF PBX-OH5 coil
• Mid VF ATF mid coil
• Solenoid and outer PF pair would require new set
  of windings

Solenoid
ATF Coils
PBX Coils
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Limited room for Centerstack

• Centerstack includes TF coils, OH solenoid and
  vacuum casing
• Available clear vertical bore is 15 x 100 cm

Plasma
Centerstack
Midplane Cross section
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Centerstack integrates solenoid, TF coils
Bushings
Stays/Pins 0.5
Outer Shell (0.4)
TF Coil turns

• Forces require complex design with ties across
  winding
• Plasma current not needed for magnetic
  configuration, only used as knob
• VF coils can provide adequate flux swing to
  drive plasma current
• solenoid may be eliminated

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TF coils
Centerstack turns
Outboard legs

• 48 turns
• 1.5 x .75 in. centerstack turns
• 3.5 x .75 in. outboard
• /- 0.15 T (14 kA / turn)
• 2100 A/cm2 centerstack turns
• 850 A/cm2 outboard
• 12 return leg bundles
• Odd shape requires transition jumpers at center
  stack
• Stellarator symmetry is preserved

Transition jumpers
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QPS will use external vacuum vessel

• Eliminates complexity of internal vessel ,
  provides maximum envelope for plasma
• Good access with large (28 inch o.d.) ports
  around midplane, top and bottom
• PF, TF coils outside, modular coils inside
• Bakeout to 150C, operation RT 40C
• Good vacuum for plasma operation
• Parameters
• Material 316L ss
• Nominal outer radius 171 inches
• Maximum height 131 inches
• Inside surface area 56 m2
• Enclosed volume (with ports) 34 m3
• Time Constant - toroidal 10 ms - poloidal
  2 ms

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VV has good access for diagnostics, heating
(2 x 8) 2 diameter upper / lower ports
(2 x 12) 12 x 20 upper /lower vert. ports
(2 x 2) 2 x 4 upper /lower vert. ports
(12) 24 diameter radial ports
Views looking into radial ports
Ref M. Cole, PII.a-6
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Good access for maintenance
Access thru vertical ports
Access thru midplane ports
and Both vessel domes are removeable
Vessel spool piece supported from mod coils
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Core assembly sequence
Assemble mod coil / shell on support legs
Suspend vessel from mod coil shell
Install VV domes, TF and VF coils
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Summary

• QPS is a compact stellarator to be built at ORNL,
  and is currently in RD and prototyping phase.
• QPS represents a combined effort of ORNL, the
  University of Tennessee and PPPL
• The QPS design concept meets performance
  requirements
• 20 coil, 2 period modular coil set with
  integrated structure
• OH, VF, and TF coil sets
• External vacuum vessel
• Capable of 1.5 s flat-top at 1 Tesla
• Modular Coils are key element and subject of
  ongoing RD

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Backup
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Two compact stellarators planned for US program
NCSX (in fabrication) and QPS (design/RD phase)
National Compact Stellarator Experiment lt R0 gt
1.4 m, ltagt .33m Btor 2 T, A 4.3, Ip lt 350
kA
Quasi-Poloidal Stellarator lt R0 gt 0.9 m, ltagt
.34m Btor 1 T, A 2.7, Ip lt 150 kA
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Fabrication Plans and Options

• Most components built off-site and pre-assembled
  to the extent possible

System Fabrication By
Vacuum Vessel Commercial Tank manufacturer
Conventional Coils - TF, PF, Centerstack assy - PF coils exist, refurbish on site- Centerstack, TF similar to NSTX, (but integration by vendor)
Modular Coils Winding forms by qualified vendor Winding, VPI, canning by Univ. TN
Structures - connecting structures, base columns Commercial manf, same as VV if possible
Coil Services - electrical leads, cooling Commercial leads, piping on site
Assembly, incl. mod coil field period sub-assembly Assembly on-site by ORNL craft
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Cooling at exit
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Modular coil forces

• Minimum sheer case has highest normal operating
  loads
• Abnormal loading 40 higher (e.g. power supply
  sends max current)

Max centering load 116 kips
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Modular coil forces
()
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Modular coil forces
Almost no force away from ell
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Modular coil running load summary for all cases
shows only one with net force away from ell
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Stress in modular coil shell

• Stresses limited to 17 ksi