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Optimizing Quadrupole Design for ILC Final Focus
Peter McIntyre and Akhdiyor Sattarov
Texas A&M University
Presented to ILC BDS Working Group7/19/2005.
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e- e+
ILC Strawman BDS Layout
2 mrad IR, L* = 3.5 m
20 mrad IR, L*= 3.5 m
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Challenges
• Maximize gradient
• Move as close as possible to IP – no steel
• Can Q0 be designed to tolerate heat, radiation damage from synchrotron radiation?
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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
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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.
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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
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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
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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
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Mesh for FEAApply 100 MPa external load, look at how it distributes in the cable elements.
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Strain (Von Mises)
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Stress (Von Mises)
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Zoom-in of von Mises strain on bottom middle wire
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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
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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?
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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
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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
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Structured cable works nicely with BNL’s serpentine coil winding technique
by Brett Parker: 50 mm bore radius, 145 T/m gradient
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Fabrication of structured cable
Prototype cabler used to make ~10 m piece lengths. Long lengths can be made at N.E. Electric.
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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.
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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!
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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
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Q2, Q3: push gradient usingblock-coil Nb3Sn quadrupoles
450 T/m @2 K superfluid cooling (w/iron)
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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
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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.
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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.