1. beam Rotatable Collimators as a Possible US Contribution to the LHC Luminosity Upgrade Project 24 April 2008 LARP CM#10 Tom Markiewicz/SLAC BNL - FNAL- LBNL - SLAC US LHC Accelerator Research Program

2. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 2 / 34 Vision DOE/LARP management perception is that rotatable copper collimators are relatively simple mechanical devices that could be offered as a low risk component of a US LHC Luminosity Upgrade Project, offsetting risk of not delivering Nb 3 Sn magnets, their main interest.

3. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 3 / 34 The Problem Suggesting that the US manufactures 36 of these devices for the 30 reserved Phase II secondary collimator lattice slots (plus 6 spares) Soft peddles fact that – 1 st single jaw has only now been brazed and still needs some weeks of work before thermal-mechanical tests can begin –SLAC has not begun, the “almost” fully defined, process of building the 1 st full beam testable double jaw collimator Ignores the CERN collimation “White Paper” plan calling for construction and mechanical, vacuum & beam testing of three “complementary” designs that can bring LHC luminosity from 10 34 to 10 35 before a production decision is made –The Cu secondary RCs do not give x10 improvement in luminosity –Destructive testing of the by-design damageable Copper may be prove extensive enough to remove RC from consideration Does not address adequately the quality control issues seen in CERN’s Phase I collimator production nor has there yet been any talk or agreement with CERN on interface, installation, or engineering support issues.

4. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 4 / 34 My Opinion LARP, through SLAC, is participating fully in the Phase II Collimation project as outlined in the CERN “White Paper” plan and any action on LARP’s part that looks, as this does, like it is circumventing the agreed to schedule damages our relationship with our colleagues and is doomed to failure. If, after the R&D process concludes in October 2010, a decision is made to produce some number of rotatable copper collimators, SLAC is ready to participate. This exercise should only be taken at the “CD-0” level: mission need and ballpark cost estimate, and is hopefully, laying the bureaucratic groundwork for eventual US participation in construction of collimators

5. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 5 / 34 References Executive Summary Second Phase LHC Collimators R. Assmann 2007-04 Description Phase 2 Collimator Project R. Assmann 2007-07-02 Collimation Issues for the Two LHC+ Scenarios and Future Plans R. Assmann Beam’07 2007-10-01

6. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 6 / 34 White Paper Plan 1.The R&D and prototyping of at least three different concepts for advanced collimation designs, each addressing different possible limitations to LHC luminosity. 2.Operational experience of the LHC with the Phase I collimation system to understand the nature of any luminosity limit and the best ways to ameliorate deleterious effects with already installed systems. 3.Testing of prototypes at CERN to their technological limits before any installation in the LHC 4.Installation and testing of qualified Phase II prototypes in the LHC during the second full year of LHC operation with a decision on phase II design and production, which may require more than one technology, at the end of the year. 5.Production of the collimators during years 3-4 of LHC operation, installation during regularly scheduled shutdowns and use beginning with year 5 of LHC operation.

7. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 7 / 34 White Paper Schedule

8. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 8 / 34 CERN Phase II R&D Budget

9. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 9 / 34 CERN Pre-Production Manpower vs. Time

10. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 10 / 34 Production Estimated at 8M CHF

11. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 11 / 34 NLC Consumable Collimator rotatable jaws – 500 to 1000 hits 6.0 Note short high-Z material. radiative cooling! Aperture control mechanism – 5  m accuracy & stability Alignment BPMs upbeam & down Movers align chamber to beam based on BPMs

12. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 12 / 34 LHC Phase II Base Concept physical constraints current jaw design beam beam spacing: geometrical constraint Length available 1.47 m flange - flange Jaw translation mechanism and collimator support base: LHC Phase I >10 kW per jaw Steady State heat dissipation (material dependent) Cu coolant supply tubes twist to allow jaw rotation Hub area Glidcop Cu Mo Cantilever Mo shaft @ both ends Helical cooling channels 25mm below surface 20 facets

13. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 13 / 34 Cu Jaw-Cu Hub-Mo Shaft Design 2mm shaft-jaw gap gives x5 improvement in thermal deformation over solid shaft-jaw design 1260 um  236 um (60kW/jaw,  12min) 426 um  84 um (12kW/jaw, t=60min) Rather than Cu, Moly shaft improves Gravity sag x3: 200 um  67 um Thermal bulge 30%: 339 um  236 um

14. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 14 / 34 Brazing Each Moly Shaft End to a Central Copper Hub After much R&D, developed method to braze Molybdenum to Copper for inner shaft

15. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 15 / 34 Three Braze Cycles Three main brazing steps. Brazing materials set to melt at gradually lower temperature. 1.) Braze each shaft end to a central half-hub 2.) In one go: Braze shaft hubs to Mandrel 25% Gold, 75% Copper Braze copper cooling coil to Mandrel 35% Gold, 65% Copper 3.) Braze jaw quadrants to mandrel surface 50% Gold, 50% Copper

16. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 16 / 34 Inserting Molybdenum Shaft Ends into Mandrel then Wind Coil Around Mandrel with Ends of Coil Protruding Out Each End

17. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 17 / 34 Braze Step#1 Shaft Assembly & Coil to Mandrel On support stand and ready for insertion in baking oven Carbon block used to hold thermally expanding copper against central hub and shaft (moly and copper) Next time may use carbon block full length of mandrel

18. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 18 / 34 Filling Coil-Mandrel Keystone Gaps Three brazing cycles needed before coil- mandrel ‘keystone’ gaps filled adequately On 3 rd cycle excess braze material attaches support stand to mandrel, which warps Pix of 2nd braze cycle

19. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 19 / 34 Recovery after Excess Braze Material Attaches Mandrel & Shaft to Inox & Inconel Braze Supports

20. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 20 / 34 Measure & Machine Quadrants to Mandrel. Assemble & Braze Using 50-50 Au-Cu brazing material ($$)

21. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 21 / 34 Results of Jaw Brazing 22 April 2008 Looks good! QA measurements will be done 23-Apr Next step is machine flat facets and grooves for heater tests and thermocouple holes.

22. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 22 / 34 Internally actuated drive and jaw mount for rotating after beam abort damages surface Completed 27 May 2007 Rotation drive with “Geneva Mechanism” Universal Joint Drive Axle Assembly Thermal expansion Gravity sag Differential transverse displacement

23. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 23 / 34 Up Beam end detail beam side view of Current Idea for RF Transition to Beam Pipe LCR meter, Contact Resistance, Trapped Mode Calculations Spiral style backing springs reside inside “Sheath” (sheath not shown) Round to Square Transition Thin sheet metal RF “Curtain”

24. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 24 / 34 Summary of Mechanical Design Complete braze procedure developed, but want to look at… Full length graphite choke when brazing coil to mandrel Keystone reduction –Blowing up coil with compressed air –Wedging copper between mandrel between coil slots to drive it towards coil Using 360 quarter length jaws with braze wire rings cut on ID rather than 90 quarter length jaws Anything to reduce number surface prep requirements for brazes Support & rotation done Well developed ideas on RF features that (in principle) are far from critical path

25. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 25 / 34 Performance Risks Will thermal-mechanical testing of the first jaw validate the shaft-hub- jaw design that should limit maximum jaw deflection into the beam area to 230 microns for 10 second bursts of 60kW beam absorption Will the mechanical accuracy of the device be adequate (40 um) Will the basic jaw-adjustment and jaw-rotation work as planned Will the effective impedance and RF characteristics of the jaw and the transition to the vacuum tank aperture be adequate Will the device vacuum be sufficiently low When damaged by an aborted beam, will the extent of damage be sufficiently localized to allow rotation to a clean surface, as planned

26. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 26 / 34 Exact Nature & Extent of Damaged Region Thin Cu sample in FFTB electron beam at SLAC Hole = Beam Size 2000um 500 kW 20 GeV e- beam hitting a 30cm Cu block a few mm from edge for 1.3 sec (0.65 MJ) FNAL Collimator with.5 MJ

27. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 27 / 34 Accident Case: Permanent deformation AND Molten copper Case: beam abort system fires asynchronously, 8 full intensity bunches into jaw Model: - increased resolution 3-D ANSYS & FLUKA models - Thermal heating/cooling analysis followed by quasi-static stress analysis - Jaw ends constrained in z during 200 ns, released for 60 sec cool-down - 0.27 MJ deposited in 200 ns - Molten material removed from model after 200 ns Result: - 57e3 peak temperature (ultra fine model) - 54  m permanent deformation (concave) 5mm melt 2.5mm x 2.5mm elements T max = 57 e3 Shower max – extent of melted zone 3.3mm Cooling tubes Shaft Jaw facets

28. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 28 / 34 Braze Test #3: Vacuum tests: No improvement 3rd Jaw Braze Test Assembly has been vacuum baked at 300 degrees C for 32 hours. Results in slightly lower pressure. Inclusion of longitudinal grooves in the inner length of jaws for better outgasing Test Chamber setup similar to previous test. OldNew Baseline3.2E-9 Torr2.4E-9 Torr?? w/ jaw assy.3.7E-9 Torr3.4E-9 Torr Presumed jaw assy. pressure 4.5E-10 Torr10E-10 Torr?? LHC requirement 7.5E-10 Torr

29. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 29 / 34 Efficiency Studies Chiara Bracco (CERN) Performance (Efficiency) of collimation system depends on # particles getting into the cold aperture (>10  ) per unit length as a function of location around the LHC given the optics model AND an aperture model 500E6 Halo protons tracked over 200 turns in 10cm steps by Bracco et al to get loss maps for each magnet Beam intensity limitations are due to losses in the dispersion suppressor above the quench limit. Phase I to II Global Improvement Phase I Beam Intensity Limit

30. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 30 / 34 Intensity Limit at “Dispersion Suppressor” with Phase II at Nominal Collimation Settings Losses due to particles that hit primaries but that do not see the secondaries While philosophy is every bit helps (take the x3.6) “ultimate” luminosity may require different collimation settings or completely different collimators (crystals as primaries?)

31. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 31 / 34 Graphite -> Copper Switching to copper will decrease the imaginary part of the impedance but increase the real part This is either good or bad depending on how you want to damp beam instabilities (Landau Damping versus Feedback) So, impedance still dominated by copper collimators

32. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 32 / 34 Unscrubbed Unit Cost Based on work done to date: $250k

33. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 33 / 34 Project Cost “x2 Estimate” Unit Cost for Tank, 2 jaws, rotation & support, RF$250k Unit Cost for Rack & pinion, motors, LVDTs$50k These are probably underestimates: Assembly, test & qualification at SLAC4 FTEs 36 units over 2 years$200k EDI&A6 FTE Lab overhead42%

34. LARP CM#10 - 24 April 2008Rotatable Collimator CP Proposal - T. MarkiewiczSlide n° 34 / 34 Project Schedule Sure to be dominated by braze operations and braze oven cycles 72 jaws with 3 braze cycles per jaw –imply that while not excluded 2 years of production is aggressive –1 year construction seems impossible