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Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
New Technology for Future Hadron Colliders
Peter McIntyreAl McInturff
Texas A&M University
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
Motto for high-field dipoles:keep it simple, stupid!
The problems for Nb3Sn high-field dipoles:• Conductor is fragile – wind & react,
degradation under Lorentz loading• Filaments are fat –persistent current multipoles,
snap-back• Preload is immense – how to assemble and apply
uniformly?• Conductor is expensive – 10 x NbTi
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
outer expansion bladders
inner expansionbladders
flux return steelaluminumcompression shell 12 Tesla central field
30 mm bore
29 cm2 Nb3Sn strand
13 kA coil current
108 MPa max coil stress
8 mH/m
740 kJ/m
21 MITs
12 Tesla block-coil dipole design
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
Block-coil designs enable us to address these problems
• Stress management: limit coil stress• Racetrack pancake coils
(bend ends up/down on center layers)• Close-coupled steel reduces amp-fac, suppresses
persistent-current multipoles• Simple assembly, preload using expansion bladders• Conductor cost optimization – least superconductor
of any high-field design!
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
Stress management• Each block within the coil controls stress so
that it cannot accumulate from inside blocks to outside blocks:
mica papershear release
laminar springs
inner coils:100% superconducting strands
outer coils: 50% copper strands
Kapton strain gages
coil housing expansionbladders
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
We have built a NbTi practice dipole to test fabrication, assembly issues
6.5 Tesla short-sample field6 layersSingle-block pancakesEnds planarRibs, plates, springs, shear
release, S-glass insulation, strain transducers as will be used in Nb3Sn models.
Vacuum-impregnated coil!
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
High-current testingTAMU-1 Quench History
0
2
4
6
8
0 5 10 15 20 25
Ramp #Iq
(KA
)
System
Training
Ramp-Rate
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
AC losses, splice resistance
0
2
4
6
8
10
1 10 100 1000 10000
ramp rate (A/s)
quen
ch c
urre
nt (k
A)
ramp-rate studiestraining
-1.5
-1
-0.5
0
0.5
1
1 2 3 4 5 5 6 7
Current (kA)
Volta
ge (
µV)
0.28 nΩ
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
Pancake coils are compartmentalized: easy to build, control axial stress internally
Center double pancake top/bottom single pancakes
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
12 Tesla Nb3Sn design
No axial Lorentz stress on center winding pair. Axial preload on outer windings locked into coil structure.
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
Provide overall preload using expansion bladders
• Flux return split vertically, serves as piston
• Bladders filled with low-melt Wood’s metal
• Bladders located between flux return and Al shell
• 2,000 psi pressure delivers full-field Lorentz load
• In cooldown, Al shell delivers additional preload
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
Optimize the conductor
• Quench stability – enough Cu to heal microquenches –much less Cu than…
• Quench protection – distribute the energy during a quench -- jCu ~ 2,000 A/mm2
• The expensive way: draw Cu into SC strand for both stability and protection.
• The optimized way:draw Cu into SC strand only for stability (~40%)cable pure Cu strands with SC strands for protection.
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
Half the outer coils are “free” Cu strands = half the cost!
0
10
20
30
40
50
0 5 10 15field strength (T)
coil a
rea
(cm
2)
NbTi Nb3Sn/NbTi
quadratic B dependence
RHIC
Tevatron
Pipe
SSC
LHC
VLHCblock-co il
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
Suppression of Persistent-Current Magnetization Multipoles
• Persistent-current fields are generated from current loops within the filaments, and also BIC’s.
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
There are only two techniques that can suppress snap-back in dipoles.• The flux plate: a planar steel sheet is imbedded within the coil.
It redistributes flux to suppress multipoles. At injection field the flux sheet is unsaturated, so it suppresses snapback.
• Persistent-mode superconducting windings on the beam tube: A sextupole (or decapole) winding on the beam tube will suppress multipoles throughout the excitation curve
• Schemes to cancel multipoles in cos θ dipoles by placement of steel shims can be used to cancel multipoles at one field value, but the shim steel is saturated even at injection so it cannot suppress snapback.
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
The steel flux plate redistributes flux to suppress multipoles
0.5 T 12 T
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
Multipoles with Persistent Currents
Curved Iron Boundary, w ith Sc magnetization
-4
-3
-2
-1
0
1
2
3
4
-12.5-11.5-10.5-9.5-8.5-7.5-6.5-5.5-4.5-3.5-2.5-1.5C e nt ra l F ie ld
b2b4b6b8b10b2b4b6b8b10
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
The flux sheet suppresses persistent-current multipoles 3x
-45
-40
-35
-30
-25
-20
-15
-10
-5
0-1.6-1.5-1.4-1.3-1.2-1.1-1.0-0.9-0.8-0.7-0.6-0.5-0.4-0.3-0.2-0.10.0
Central Field (Tesla)
b2(1
0^(-
4) u
nits
)
No_yoke
Planar_Iron
Curved_Iron
Planar_Sheet
Curved_sheet
Curved_thick_sheet
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
The Tevatron TriplerReplace the Tevatron ring with a single 12 T ring:
13.3 T @ 4.5 K
3 cm beam tube radius
single current coil
bn < 10-4 cm-n
Suppression of persistent current multipoles
TeVpp 6sat =
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
The Microbore Dipole
• At Snowmass, there was a constructive engagement between magnet builders, accelerator physicists
• The question: What is the physical aperture needed for a ~100TeV hadron collider?
• The answer: 3 cm horizontal, 2 cm vertical• The challenge: Can we design a dipole with this aperture
that is simpler, cheaper?
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
The Microbore Dipole2 layers, 3 cable segments, 2 splices!
11.6 Tesla central field
30x20 mm2 bore
8.6 cm2 Nb3Sn strand!
2,400 A/mm2 in Nb3Sn
16,500 A coil current
90 MPa max coil stress
2.5 mH inductance
340 kJ stored energy
35 MITs
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
True optimization of conductor
NbTi cable (B < 6.3 T)
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
Outer winding Center winding Inner winding
material NbTi (56% Cu) A: Nb3Sn (48% Cu)B: OFHC Cu
Nb3Sn (48% Cu)
# turns 12 14 3+1
# strands 48 48 12
strand diameter 0.68 0.65 1.35 mm
maximum field 6.3 11.2 12.2 T
Jsc 2200 3024 1846 A/mm2
JCu during quench 1700 1600 2000 A/mm2
maximum stress 5 90 70 MPa
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
Higher field can take less conductor!
0
10
20
30
40
50
0 5 10 15field strength (T)
coil a
rea
(cm
2 )
quadratic B dependence
RHIC (7 cm)
Tevatro n (5 cm)
Pip e (2 cm)
SSC (5 cm)
LHC (7 cm)
Trip ler (6 cm)
VLHC (3 x2 cm)
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
Photon stop can handle synchrotron radiation – but limits dipole length
P. Bauer et. al., FNAL TD-01-023
Dipole length < 22 m can accommodate full shadow with 3 cm bore width.
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
The microbore design takes the heat off Nb3Sn superconductor
• Use less of it: 8.6 cm2, one third of most designs• Suppress p.c. multipoles: can use fat filaments
The challenges:• want more jsc: 2,600 A/mm2 → 12 T• mixed-strand cable
– need to perfect cabling• develop coil winding for inner winding
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
There are a number of innovations in our designs that must be proven –
hence our R&D program:• Block-coil construction, stress management• Preload using pressurized bladders• Packaging the windings to control axial stress• Bending and fixturing the central windings• Mixed-strand cable to minimize Nb3Sn• Ti mandrel to eliminate loss of preload during cooldown• Suppression of snap-back using steel flux plate
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
Our group:
• Physicists: Al McInturff, Peter McIntyre, Akhdior Sattarov
• Technicians: Ray Blackburn, Tim Elliott, Bill Henchel, Andrew Jaisle
• Machinist: Nick Diaczenko
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
We are helping to train a new generation for accelerator physics and technologyPast MS and PhDs:• Mark Johnson – Agilent• Reza Kazimi – Jefferson Lab• Bo Lee – Cypress Semiconductor• Deepak Raparia – BNL• Weijun Shen – Cryomagnetics• Don Smith – Cypress Semiconductor• Rainer Soika – BNL • Chuck Swenson – NHMFL• Wu Yu – Cryomagnetics
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
Current Graduate Students• Burak Basaran (Mechanical Engineering)• Joong Byeon (Seoul Nat’l U., Hyundai Electronics)• Amit Gupta (Mechanical Engineering)• Hiroshi Ieechi (Honda)• Lucas Naveira (Florida State, NHMFL)• Patrick Noyes (Texas A&M)• Michael Poirier (Notre Dame)• Stephen Roberson (Michigan State)
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
Current Undergraduates
• Joe Brinkley (Physics) • Eric Casper (Physics)• Casey Deen (Physics)• Zane Goodwin (Physics)• Michael Hatridge (Physics) • Ryan Schmidt (Mechanical Engineering)
Texas A&M UniversityDOE AA R&D University Program ReviewMay 31, 2002
We continue to benefit greatly from collaboration with LBNL
• Cold testing of our model dipoles• Development of mixed-strand Nb3Sn cable• Pressurized bladder preload (Taylor)• Skinning of winding subassemblies
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