Optimizing Quadrupole Design for ILC Final Focus

Peter McIntyre and Akhdiyor Sattarov

Texas A&M University

Presented to ILC BDS Working Group7/19/2005.

e- e+

ILC Strawman BDS Layout

2 mrad IR, L* = 3.5 m

20 mrad IR, L*= 3.5 m

Challenges

• Maximize gradient

• Move as close as possible to IP – no steel

• Can Q0 be designed to tolerate heat, radiation damage from synchrotron radiation?

These are the same challenges that one faces in optimizing IR for LHC

IR

20 40 60

.02

.04

.06

.08

Q1340 T/m6 m long40 mm aperture

Q2450 T/m10 m long50 mm aperture

Q3450 T/m5 m long50 mm aperture

D18.0 T10 m long56 x 120 mm aperture

D28.0 T10 m long56 mm aperture

m

detector

Q1 is in harm’s way of particle lossesanalog effect for ILC is SR

D1

Q1

Multiplicity ~ f() e-bt Eparticle ~ pt /

So energy flow concentrates strongly down the beam direction.

Design Q1 using structured cable

6-on-1 cabling of Nb3Sn strand around thin-wall inconel X750 spring tube

Draw within a thicker inconel 718 jacket

Interior is not impregnated – only region between cables in winding

Volumetric cooling to handle volumetric heating from particle losses

3 mm

Stress analysis of structured cable

• Motivation, Design and Finite Element Analysis (FEA) of the 6-on-1 cable in conduit

• Nb3Sn: Heat treatment, properties, peculiarities, and how to work with it

• A few words about the conduit and Inconel X 750• Fabrication of the cable and coil• Testing of coils and short samples• Conclusion

Cable designSix strands of Nb3Sn are cabled around a hollow

Inconel X 750 tube

Then the assembly is sheathed in an outer armor that is drawn onto the 6-on-1 configuration

By virtue of its low effective Young’s modulus, the hollow inner tube protects the Nb3Sn wire from external loads

Mesh for FEAApply 100 MPa external load, look at how it distributes in the cable elements.

Strain (Von Mises)

Stress (Von Mises)

Zoom-in of von Mises strain on bottom middle wire

Ironless Quadrupole for Q1

20 mm bore radius, 340 T/m

4.5-6 K supercritical cooling

Impregnate rad-hard filler between cables, but leave interior of cables free for He flow

No insulation between cables

• During normal operation, current follows superconductor.

• During quench, current redistributes as necessary, no voltage can develop, coil quenches as if it were a single turn.

• Insulation is traditionally the weak link for radiation damage.

• No insulation what is next weak link?

Magnetics methodology

Placement of inner turns controls multipoles

Remove turns in regions of Bmax to enhance gradient

Place inner turns at smallest radius possible: G Bmax/R

Cryogenics

• All turns have jackets opened at ends• Liquid helium flows through hollow channels in

cables – superfluid or supercritical?• Zone flow in radial regions of similar Q• Probably can handle Q ~ 100 W/m cryogenic load

kerf cuts around end arcs of each turn

Voids between turns filled to seal He

Structured cable works nicely with BNL’s serpentine coil winding technique

by Brett Parker: 50 mm bore radius, 145 T/m gradient

Fabrication of structured cable

Prototype cabler used to make ~10 m piece lengths. Long lengths can be made at N.E. Electric.

Compressing Inconel sheath on cable

Short lengths prepared by drawing sheath onto cable.

For long lengths, compress sheath in hydraulic die.

Best is to compress to rounded hex final shape.

Bending cable on tight radius does not damage strands

Bending cable ovals outer sheath, ovals inner tube, but leaves the 6 strands round.0.8 mm strand, 1 cm radius OK.Important for small-bore quad!

Other special magnets for LHC IR-any use to ILC?

• block-coil Nb3Sn quads to 450 T/m

• Levitated pole dipole – 8 T bend, ~impervious to swept losses

Q2, Q3: push gradient usingblock-coil Nb3Sn quadrupoles

450 T/m @2 K superfluid cooling (w/iron)

D1: levitated-pole dipole

Cold iron pole piece, warm iron flux return.

Cancel Lorentz forces on coils, pole steel.

8.0 T

4.5 K

This is what optimized superconducting magnets can do for LHC IR

Comparison to baseline IR:

Reduce * 0.15 m

Reduce * 5 km

Reduce # of subsidiary bunch crossings 5

Reduce sensitivity to error fields and placements

Open space for another doublet to fully separate corrections in x, y.

Help me to optimize quads for ILC IRs

• Micro-lattice, what apertures are critical?• What is flux distribution in synchrotron

light, spent beam in first quad region?• How close into detector can an ironless

quad be placed?• Remember: for most optical effects of

multipoles, misalignments, etc., the closer Q0 is to the IP the less the impact on luminosity.