Block-coil NbTi dipoles for 6 Tesla Rapid-cycling SuperSPS

Peter McIntyre

Dept. of Physics

Texas A&M University

p-mcintyre@physics.tamu.edu

The goal of our R&D: Dipoles for future hadron colliders

TAMU4: 14.1 T, 4 x 3 cm2 aperture28 cm2 superconductorCollider-quality field, suppress p.c. multipoles

LHC Tripler: 24 T, 56 mm apertureWindings = Bi-2212 inner, Nb3Sn outer

Designing dipoles with Nb3Sn

The challenges• The conductor is fragile – strain < 0.5%• High field limit would be imposed by Lorentz stress• Filaments are large – snap-back too large

The solutions• Block-coil geometry • Stress management• Hydraulic preload• Flux-plate suppression of snap-back

Stress management

Offload stress from windings to structure

stress (PSI) in structure @ 14 T

stress (PSI) in coils only @ 14 T

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

Suppression of multipoles from persistent current magnetization

• Persistent magnetization is generated from current loops within the filaments,

• Magnetization relaxes via BIC’s, then snap-back

The steel flux plate redistributes flux to suppress multipoles0.5 T 12 T

Multipoles with Persistent CurrentsCurved Iron Boundary, w ith Sc magnetization

-4

-3

-2

-1

0

1

2

3

4

-12.5-11.5-10.5-9.5-8.5-7.5-6.5-5.5-4.5-3.5-2.5-1.5

Central Field

b2

b4

b6

b8

b10

b2

b4

b6

b8

b10

5x suppression of p.c. sextupole – compensates for larger filament size

The Texas A&M program

• TAMU1 (6.5 T)– evaluate block-coil geometry, winding and impregnation

strategies using NbTi model - tested to short sample

• TAMU2 (5.2 T)– single-pancake mirror magnet with ITER Nb3Sn

conductor - completed, ready for testing

• TAMU3 (13.5 T) – double-pancake model with 2.4 kA/mm2 conductor -

beginning fabrication

• TAMU4 (14.1 T )

– complete Nb3Sn dipole with 4x3 cm bore

TAMU1

• Model dipole to study block coil geometry: cable preparation, winding techniques, impregnation: treat exactly according to the design for Nb3Sn.

Testing of TAMU1

TAMU-1 Quench History

0

2

4

6

8

0 5 10 15 20 25

Ramp #

Iq (K

A)

QH tests

Training

Ramp-Rate

Winding voltages during quench

AC losses

TAMU1 is the first fully impregnated NbTi dipole made in modern times.

It operated to short sample without training and exhibits good AC performance.

This result demonstrates that the helium access thought essential for NbTi stability is not necessary, provided that stress is managed so as to prevent conductor motion and friction heat.

1 T/s

1.5 T/s

TAMU2: our entry into Nb3Sn technology

TAMU2: 1 single-pancake windingmirror geometry, ITER superconductor5.6 T short-sample bore field

Coil winding

Ti mandrel to preserve preload through cooldown.

Inconel ribs, laminar springs transfer stress between windings.

Inject to LHC from SuperSPS

• For luminosity upgrade of LHC, one option is to replace the SPS and PS with a rapid-cycling superconducting injector chain.

• 1 TeV in SPS tunnel 1.25 T in hybrid dipole: flux plate is unsaturated, suppression of snap-back multipoles at injection.

• SuperSPS needs 6 T field, ~10 s cycle time for filling Tripler >1 T/s ramp rate

In block-coil dipole, cables are oriented vertically:

Result: minimum induced current loop, minimum AC losses

Again block-coil geometry is optimum!

nB ˆ

In cos dipole, cables are oriented on an azimuthal arch:

Result: maximum induced current loop, maximum AC losses

nB ˆ

Preliminary design for Super-SPS dipole

6 T short-sample field (to allow for AC loss degradation)

LHC NbTi strand (wider cable to optimize geometry, minimize inductance)

We are modeling AC losses, expect to be low.

Flux plate suppresses multipoles from persistent currents, AC-induced currents

(flux plate must be laminated)

Vertical cable orientation to suppress AC losses

Flux plate to suppress magnetization multipoles at injection