new technology for future hadron colliders

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


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


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


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!


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


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!


High-current testingTAMU-1 Quench History

0

2

4

6

8

0 5 10 15 20 25

Ramp #Iq

(KA

)

System

Training

Ramp-Rate


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


Pancake coils are compartmentalized: easy to build, control axial stress internally

Center double pancake top/bottom single pancakes


12 Tesla Nb3Sn design

No axial Lorentz stress on center winding pair. Axial preload on outer windings locked into coil structure.


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


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.


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


Suppression of Persistent-Current Magnetization Multipoles

• Persistent-current fields are generated from current loops within the filaments, and also BIC’s.


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.


The steel flux plate redistributes flux to suppress multipoles

0.5 T 12 T


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


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


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 =


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?


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


True optimization of conductor

NbTi cable (B < 6.3 T)


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


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)


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.


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


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


Our group:

• Physicists: Al McInturff, Peter McIntyre, Akhdior Sattarov

• Technicians: Ray Blackburn, Tim Elliott, Bill Henchel, Andrew Jaisle

• Machinist: Nick Diaczenko


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


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)


Current Undergraduates

• Joe Brinkley (Physics) • Eric Casper (Physics)• Casey Deen (Physics)• Zane Goodwin (Physics)• Michael Hatridge (Physics) • Ryan Schmidt (Mechanical Engineering)


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

new technology for future hadron colliders

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