1. LARP Collimation – Engineering & Analysis
Adapting the NLC Consumable Collimator to LHC Phase II Secondary Collimation
BEAM 2
BEAM 1
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

2. LARP Collimation – Engineering & Analysis
Overview
Review NLC consumable collimator
Compare NLC & LHC requirements
Conceptual design
NLC collimator adapted to LHC
NLC jaws in LHC mechanism
Thermal performance of candidate materials
Unresolved issues
LARP Collimation meeting June 15, 2005
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 Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

4. 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 Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

5. Phase II Collimator Engineering - E. Doyle
NLC Aperture-Defining Geometry One independent variable (stop roller spacing) defines aperture.
s = stop roller spacing
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

6. 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 problem; thermal bending problem
gap range
0.2 – 2.0mm
0.5 – 45mm *
Spatial constraints; NLC mechanism limited gap range
SS power, per jaw
~1W – 10W
~1kW – 15kW (material dependent)
LHC requires water cooling, possible power densities in boiling regime
* Original max gap was 65mm, revised 5/12/05
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

7. 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 (our first guess)
Helical coolant supply tubes flex, allow one rev of jaw
Aperture supported a both ends for stability, tilt adjustment
Alternative (also shown): aperture support at jaw center
thermal deflection away from beam
no tilt control
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

8. 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 45mm aperture. Auxiliary jaw retracting mechanism needed. Also note vulnerability of mechanism to beam-induced heating.
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

9. 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 (shown) 3) less jaw motion (45mm max aperture – agreed 5/12/05) 4) reduce diameter of adjacent beam pipe.
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

10. Phase II Collimator Engineering - E. Doyle
NLC concept - problems
Large jaw motions not possible
estimated max 15 – 20mm
Auxiliary mechanism to fully retract jaws
Gap-defining mechanism intrudes into beam-pipe stay clear
connect around outside of jaw => backlash, thermal sensitivity
move stops outward => lower sensitivity,poor mechanical advantage
Suitable only at ends of jaw – can’t prevent gap narrowing
Clearance problems with adjacent beam
Reduce jaw diameter => even less space for stop rollers
One solution: instead of auxiliary mechanism to fully retract jaws…why not just use LHC mechanism in the first place?
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

11. NLC-LHC Hybrid: Cylindrical jaws in LHC Mechanism
Jaw diameter 136mm
Maximum aperture 45mm
Jaw length 950mm (including end tapers) to fit existing mechanism
Tank widened & deepened
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

12. NLC-LHC hybrid configuration - problems
More thermal distortion with shaft support than NLC-type edge support
Additional thermal swelling
Tank and mechanism too short for full length NLC-type jaws
shorten jaws or expand mechanism
Jaws may be too heavy for LHC mechanism
.75m long x 136m diameter weighs 97kg (+) (limit = ?)
Solutions
Lighten jaws (how?), strengthen mechanism
Add rigid adjustable stop to limit minimum gap
spring loaded ends able to deform away from beam
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

13. Adjustable gap-defining stop
Stop prevents gap closing as jaw bows due to heat
Jaw ends spring-loaded to the table ass’y (not shown) … move outward in response to bowing
May use two stops to control tilt
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

14. NLC concept & Hybrid concept – shared problem
Jaw thermal effects / collimation efficiency tradeoff
Deformation
Swelling and bending
Structural failure or loss of properties due to temperature cycling
Heat removal
Control deformation by targeted heat removal
Potential for boiling
Dense materials
Pro: higher collimation efficiency
Con: higher temperature
increased deformation
Increased tendency to boil
higher heat flux density
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

15. Phase II Collimator Engineering - E. Doyle
Thermal Simulations
Water cooled
3-d model
FLUKA generated energy deposit mapped to blue area
Water cooling:
360o complete I.D.
~45o between arrows
3-d model
FLUKA generated energy deposit mapped to curved area
Water cooling: ~45o arc between arrows
2-d model
25 x 80mm grid
FLUKA generated energy deposit at shower max
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

16. 2-d simulation results – boiling considerations
80mm x 25mm rectangular section located at shower max
Water cooled back surface
TCSH1, 80% TCPV debris + 5% beam
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

17. 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 Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

18. 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 Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

19. 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
Heat flux to water of 10^6W/m^2 or greater is in regime of possible film boiling
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

20. 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.
environmental/safety issues, low collimation efficiency
Al benefits from the reduced (45o) cooling arc.
nearly meets the spec for SS condition
Excessive deflection for the transient case
Ti: excessive deflection
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
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

21. Phase II Collimator Engineering - E. Doyle
Effect of shortened jaws, dense material, carbon pre-radiator – deflections referred to jaw edge
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 Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

22. Phase II Collimator Engineering - E. Doyle
Effect of shortened jaws, dense material, carbon pre-radiator – deflections referred to shaft
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 Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

23. Shortened jaws/dense material - discussion
Dividing jaws beneficial
Short front jaws more swelling than bending
Cu jaws nearly meet relaxed deflection specs
W jaws look good, but:
temperatures and power densities very high (cooling system)
deflections much greater if referred to jaw centerline
What next?
Adopt and apply material damage criteria (short & long term)
Consider Glidcop
Increase cooling arc in W jaws
Other deflection reducing tricks (circumferential grooves)
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

24. Un-grooved 10kW evenly dist. Grooved 40% deep
Temperature
Vertical displacement
fixed
symm plane
symm plane
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

25. Grooved Cylindrical Jaw
ANSYS model – 150mm O.D., 25mm wall, 120cm long,
Two symmetry planes: mid-span; beam/jaw centerline
Grooves: 10mm deep, 50mm spacing
10kW heat, evenly distributed
45 deg cooling arc
Case
Power (kW)
Tmax (C)
Deflection - edge ref
(um)
Deflection - center ref (um)
Cu - 10s
mapped FLUKA 89 79
~130 Cu
even distributed
59.5 33
~100
Cu - grooved 15
~74
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

26. Status of Phase II LHC Collimator Concept
Deflection spec will be very hard to meet
Relax deflection spec
Allow use of Be or other light material
Reduce jaw length
Force deflection away from beam
Compensate for SS deflection in set-up, gauge transient relative to SS
NLC Aperture stops 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
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

27. Status of Phase II LHC Collimator Concept - continued
Cooling system loading is problematic for dense jaw materials
Suppress boiling by means of overpressure
Utilize boiling high heat transfer coefficient
Risk of film boiling and melt-down
Other engineering issues
Determining realistic failure criteria for jaw materials
Jaws must fully retract in power-off condition
NLC mechanism: 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.
LHC mechanism: includes this capability
Design of flexible coolant supply tubes
Manufacturability of jaws (material dependent)
How to apply heat loading for testing
Rotor indexing mechanism
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

28. LHC Phase II Collimation
BONUS SLIDES
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

29. Phase II Collimator Engineering - E. Doyle
Material Properties
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

30. Heat Transfer by Boiling Water
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

31. 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 Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

32. 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 Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

33. Beam’s Eye View of Aperture Mechanism
Jaw retracted, aperture ~60mm
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

34. Alternate Stop-Roller Design
LARP Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle

35. 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 Collimation meeting June 15, 2005
Phase II Collimator Engineering - E. Doyle