1. LARP Collimation – Engineering & Analysis
Adapting the NLC Consumable Collimator to LHC Phase II Secondary Collimation
BEAM 2
BEAM 1
LARP Coll. Video-conf. May 12, '05
Phase II Collimator Engineering - E. Doyle

2. LARP Collimation – Engineering & Analysis
Overview
Review NLC consumable collimator
Compare NLC & LHC requirements
Conceptual design: NLC collimator as adapted to LHC
Thermal performance of candidate materials
Unresolved issues
LARP Coll. Video-conf. May 12, '05
Phase II Collimator Engineering - E. Doyle

3. NLC Consumable Collimator
BPMs (not shown) at inlet & outlet
Aperture is sole internal degree of freedom.
Movers align collimator to beam as sensed by BPMs
LARP Coll. Video-conf. May 12, '05
Phase II Collimator Engineering - E. Doyle

4. NLC Consumable Collimator
Heat dissipated by radiation. DT = 10W/jaw
Rigid datum structure aligned to beam by BPMs
Aperture control mechanism:
Thermal effects limited to small region
LARP Coll. Video-conf. May 12, '05
Phase II Collimator Engineering - E. Doyle

5. Phase II Collimator Engineering - E. Doyle
NLC Test Unit Cutaway
Aperture support one end of rotor only
Dual ball bearings
preloaded for tilt-stability
LARP Coll. Video-conf. May 12, '05
Phase II Collimator Engineering - E. Doyle

6. Phase II Collimator Engineering - E. Doyle
NLC Aperture-control Mechanism Located at one end of rotor only. Tilt–stability not well controlled in test unit.
LARP Coll. Video-conf. May 12, '05
Phase II Collimator Engineering - E. Doyle

7. Phase II Collimator Engineering - E. Doyle
NLC Aperture-Defining Geometry One independent variable (stop roller spacing) defines aperture.
s = stop roller spacing
LARP Coll. Video-conf. May 12, '05
Phase II Collimator Engineering - E. Doyle

8. Major Differences - NLC & LHC Specs
Specification
NLC
LHC
Comments
beam pipe ID
1cm
8.4cm
Spatial constraints due to beam spacing
jaw length
~10 cm
120 cm
jaw tilt-stability
gap range
0.2 – 2.0mm
0.5 – 60mm
Spatial constraints
SS power, per jaw
~1W – 10W
~1kW – 10kW (material dependent)
LHC requires water cooling
LARP Coll. Video-conf. May 12, '05
Phase II Collimator Engineering - E. Doyle

9. Phase II Collimator Engineering - E. Doyle
LHC Collimator Mechanism Concept Basic NLC design morphed to fit LHC constraints
Jaws hidden to show structure
1.2m long jaws, 150mm diameter
Helical coolant supply tubes flex, allow one rev of jaw
Aperture supported a both ends for stability, tilt adjustment
Also shown: aperture support at jaw center
thermal deflection away from beam
no tilt control
LARP Coll. Video-conf. May 12, '05
Phase II Collimator Engineering - E. Doyle

10. Thermal Distortion ANSYS Simulations
10 s apertures
beam
150mm OD, 25mm wall, 1.2m long
Simply supported
FLUKA heat generation for 10x10x24 rectangular grid mapped to similar area of cylinder
Steady state: 1hr beam lifetime
Transient:10 12 min beam lifetime
I.D. water-cooled 20C, h=11880 W/m^2/
Various materials: Al, 2219 Al, Be+Cu, Cu, Invar, Inconel
Ti, W rejected based on 2-D analysis
Variations
limit cooling to 45o arc
solid cylinder
jaw cut in two shorter pieces
Cu, 61C
support
dx=221 um
support
LARP Coll. Video-conf. May 12, '05
Phase II Collimator Engineering - E. Doyle

11. 360o cooling of I.D. 45o cooling arc
Note transverse gradient causes bending
Note axial gradient
61C
89C
Note more swelling than bending
support
dx=221 mm
Spec: 25mm
dx=79 mm
64% less distortion
support
LARP Coll. Video-conf. May 12, '05
Phase II Collimator Engineering - E. Doyle

12. Phase II Collimator Engineering - E. Doyle
Material Comparison for SS & Transient Thermal Deflection Green: meets alternative spec of 50um (SS) and 200um (transient).
Notes:
BeCu is a made-up alloy with 6% Cu. We believe it could be made if warranted
2219 Al is an alloy containing 6% Cu
Cu/Be is a bimetallic jaw consisting of a 5mm Cu outer layer and a 20mm Be inner layer
Cu – 5 mm is a thin walled Cu jaw
Super Invar loses its low CTE above 200C, so the 152um deflection is not valid
LARP Coll. Video-conf. May 12, '05
Phase II Collimator Engineering - E. Doyle

13. Jaw Materials - discussion
Only graphite meets the 25um deflection spec for both operating cases.
Be-containing jaws meet the spec for the SS case but not for the transient.
Be is unacceptable for environmental/safety reasons.
Al benefits from the reduced (45o) cooling arc.
nearly meets the spec for SS condition
Excessive deflection for the transient
What next?
Divide jaw in shorter sections
Use center-of-jaw aperture stops - jaw deflects away from the beam
Revisit materials not modeled in 3-D: W & Ti
LARP Coll. Video-conf. May 12, '05
Phase II Collimator Engineering - E. Doyle

14. Effect of shortened jaws, dense material, carbon pre-radiator
Notes:
Aperture transition from 10s to 7s
7s cases based on CERN ray files for interactions in TCPV
pre-radiator – Phase I carbon collimator concentrates energy deposition toward front of Phase II jaw.
LARP Coll. Video-conf. May 12, '05
Phase II Collimator Engineering - E. Doyle

15. Shortened jaws/dense material - discussion
Dividing jaws beneficial
Short front jaws more swelling than bending
Cu jaws nearly meet relaxed specs
W jaws look good, but:
temperatures and power densities very high (cooling system)
deflections much greater if referred to jaw centerline
What next?
Increase cooling arc in W jaws
Simulate single 48cm W jaw
Calculate cooling system loads
LARP Coll. Video-conf. May 12, '05
Phase II Collimator Engineering - E. Doyle

16. Conceptual design - coolant channels
Limited cooling arc: free wheeling distributor – orientation controlled by gravity – directs flow to beam-side axial channels regardless of jaw angular orientation. Far side not cooled, reducing DT and thermal distortion.
360o cooling by means of a helical channel. Lowers peak temperatures but, by cooling back side of jaw, increases net DT through the jaw, and therefore thermal distortion. Could use axial channels.
LARP Coll. Video-conf. May 12, '05
Phase II Collimator Engineering - E. Doyle

17. Conceptual design - Stop Roller Details
Ball nut (turned by actuator outside vacuum chamber).
Ball screw (stationary)
Thrust bearing
Hole for beam passage
As shown in current model: aperture range limited to ~ 10mm. This can be improved but this mechanism will not be able to produce the full 60mm aperture. Auxiliary jaw retracting mechanism needed. Also note vulnerability of mechanism to beam-induced heating.
LARP Coll. Video-conf. May 12, '05
Phase II Collimator Engineering - E. Doyle

18. Beam’s Eye View of Aperture Mechanism
Jaw retracted, aperture ~60mm
LARP Coll. Video-conf. May 12, '05
Phase II Collimator Engineering - E. Doyle

19. Geometrical limits due to 150mm rotor, 224 mm Beam Axis Spacing
30mm jaw travel (in red) causes jaw to intersect adjacent beam pipe. No space for vacuum chamber wall. Resolution: 1) smaller jaw diameter 2) vacuum envelope encloses adjacent beam pipe 3) less jaw motion 4) reduce diameter of adjacent beam pipe.
LARP Coll. Video-conf. May 12, '05
Phase II Collimator Engineering - E. Doyle

20. Alternate Stop-Roller Design
LARP Coll. Video-conf. May 12, '05
Phase II Collimator Engineering - E. Doyle

21. Status of Phase II LHC Collimator Concept
Deflection spec will be very hard to meet
Relax deflection spec
Allow use of Be
Reduce jaw length
Aperture stop mechanisms vulnerable to beam heating/damage
Relocate ball screw outside beam path – like NLC (jaw ends only)
Stop rollers unavoidably within region of beam pipe
Combine NLC rotary jaws with LHC positioning mechanism
Space limitations prevent 60mm max aperture with 150mm o.d. jaws
Reduce jaw diameter
Will likely increase deflection
Adversely affects aperture stop mechanism
Reduce opposing beam pipe diameter
Include a pass-through for the opposing beam in the collimator vacuum chamber
Reduce the maximum required aperture
LARP Coll. Video-conf. May 12, '05
Phase II Collimator Engineering - E. Doyle

22. Status of Phase II LHC Collimator Concept - continued
Cooling system loading is problematic for dense jaw materials
Other engineering issues
Jaws must fully retract in power-off condition
Spring load jaws outward. Inward-forcing springs (necessary in any case) sized to overcome outward-forcing springs and grounded on solenoid or pneumatic device which gives way when power is off.
Design of flexible coolant supply tubes
Manufacturability of jaws (material dependent)
How to apply heat loading for testing
Rotor indexing mechanism
LARP Coll. Video-conf. May 12, '05
Phase II Collimator Engineering - E. Doyle