1. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Status Report on the Introduction/Reminder Improved mechanical design Wake fields Vacuum system design Cooling system for Si detectors Summary and outlook Introduction/Reminder Improved mechanical design Wake fields Vacuum system design Cooling system for Si detectors Summary and outlook Geneva, 23-2-2001 Massimiliano Ferro-Luzzi, CERN/EP Vertex

2. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP LHCb VD - LHC machine integration issues The LHCb Vertex Detector system should not hamper LHC operation Address: vacuum issues  static and dynamic vacuum see Adriana Rossi’s presentation  calculations and test measurements radio-frequency issues  high frequency modes, coupling impedance Z || / n  calculations and test measurements safety issues  define level of acceptability  perform risk analysis

3. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Side flange with feedthroughs Bending hinges Support frame Si detector Detector support and cooling Bellows (22000 signal wires) moves by 30 mm only two positions: open or closed !! “TP” Design presented at LEMIC February 2000 Si encapsulation and center frame are not shown ! see LHCb note 99-042/VELO

4. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Difficulties with TP design FEA displacement studies led to a rather bulky center frame  poor sideways accessibility for(a) wake field suppressors (b) Ti evaporator insertion System was not bakeable (the reverse was under study)  base primary vacuum pressure p 1 ~ 10 -8 mbar  aging of NEGs due to gas flow from VDS (?)  dynamic vacuum: struggle to get I crit > 3.4 A Communicating 1 ary and 2 ary volumes  NEGs must be regenerated after every access to Si detectors limited to ~10 cycles (?)

5. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP TP design center frame Desired situation Side wake field suppressors Ti evaporator No room on the sides ! Si detector box

6. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Optimized System Decouple access to Si detectors from access to 1 ary vacuum Use ultrapure neon venting NEGs need not be baked after access to Si detector Baking up to 150 o C is possible Mount two detector halves independently use of non-standard, large- size, rectangular bellows M. Doets, NIKHEF air 2 ary vacuum 1 ary vacuum

7. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP bellows chain/belt cooling/bake out gearbox 1:40 ball spindle 16x2 10 mm linear bearing 2x 30 mm motor Detectors halves opened/closed in steps (remote-controlled) vert. = 10 mm, horiz. = 2x30 mm Microswitches at out position LVDTs Steel frame Alignment: –2 planes –3 points each –define IP All motors, bearings, gearboxes, etc., are outside vacuum Support and motion mechanics 30 mm

8. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Support system Alignment pins for reproducible coupling Reproducible positioning Outer switch positions aligned to nominal beam axis

9. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Vessel installation Move bellows and couplings to “closed” position Install vessel from top Align vessel to beam line Fix vessel to frame Attach bellows

10. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Install detector housings Remove upstream flange (need 2 m access) Rectangular bellows –60 mm stroke –normal 30 mm –lateral 6 mm –need not withstand atmospheric differential pressure Fabrication –difficult and costly! –Palatine, Bird, Calorstat, MB, VAT,... = 2 ary vacuum vessel Install wake field suppressors and close upstream spherical flange

11. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Complete installation of 2 ary vacuum system Detector system separated from vacuum system functionality Connect inner system (detector housing) to motion drives via side flanges Install –pump-out, valves –turbo pumps, damping Seals: –1 ary / air: all metal –1 ary / 2 ary : viton & metal –2 ary / air: viton & metal

12. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Detector installation Install detector halves from sides Decouple detectors from flange box Tooling needed Detector half can be replaced by a dummy flange box Detectors Flange box

13. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP VELO assembly

14. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Install wake field suppressors after mounting 2 ary vacuum container Mount through top flanges –seal with view ports ? Upstream is easier: mounted with large flange off WF screens 420 910 IP Wake field suppressors

15. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Current design: Up/downstream suppressors are identical Material: CuBe Length: 179 mm Thickness: 100  m 16 segments Mounting to detector box is non-trivial Wake field suppressors

16. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Wake field suppressors …continued: Segments deform differently during movement Coating needed on suppressors (?) Press-fit to beam pipe structure Anneal CuBe, deform, harden at 400 o C

17. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Wake field simulations Performed MAFIA simulations: full tank model and smaller models detector halves in position open and closed compared various detector encapsulations with different corrugation shape and depth complex non-symmetric structures! LHCb-99-041 “A first study of wake fields in the LHCb VD” LHCb-99-043 “W. f. in the LHCb VD: strip shielding” LHCb-99-044 “W. f. in the LHCb VD: alternative designs for the w. f. suppr.” Conclusions: Frequency domain: no problematic resonant effects for corrugated encapsulation with corrugation depth < 20 mm Time domain: losses are acceptable Under study: low frequency slope of Im(Z || ) Time-consuming and CPU intensive (ABCI & MAFIA) N. van Bakel VU Amsterdam Thanks to: O. Brüning D. Brandt L. Vos

18. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP RF tests at NIKHEF First 3 measured eigenmodes of empty tank: 220, 270, 320 MHz Compare to simulation with MAFIA Study: Eigenmodes, short range effects, Z || Effect of WF screens, open/close halves RF fields inside secondary vacuum (pick-up) Use: Wire method Multiple (rotatable) loop antennas Reference LHC pipe F. Kroes, NIKHEF

19. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Vacuum system layout Main changes since last LEMIC (february 2000): removed conductance between 1 ary and 2 ary volumes conductance: 1 l/s  10 -5 l/s  reduced contamination of 1 ary vacuum and NEGs development of gravity-controlled safety valves used in addition to pressure-switch electrically activated valves  intrinsically safe solution decoupled air exposure of 1 ary and 2 ary volumes (see mech. design) use of ultrapure neon venting procedure to preserve NEGs  bakeable system (T  150 o C) reduces effect of several (static & dynamic) vacuum phenomena!

20. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP …continued Unchanged since last LEMIC (february 2000): thin separation foil between 1 ary and 2 ary vacuums which does not withstand atmospheric pressure  performed extensive MC physics simulations (assess effect of material)  investigated feasibility of Beryllium option (Brush Wellman)  performed extensive FEA calculations for Al and Be  developed a gravity-controlled safety valve to protect against differential pressure increase mixed-phase CO 2 cooling system for Si detectors in 2 ary vacuum Vacuum system layout

21. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Beryllium (1 mm thick): FEA: max  p  500 mbar* ~500 kUS$ per container if at all feasible! safety issues Aluminum (0.25 mm thick): FEA: max  p  15 mbar* NIKHEF: successfully welded 100  m on 300  m press-shaping being developed at NIKHEF “cheap & readily” available (compared to Be) * means: irreversible deformation, no safety factor included Thin vacuum foil

22. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP FEA for Al foil 0.25 mm Assumed annealed Al yield strength of 40 MPa (typical Al ~ 40…250 MPa) Max  p  15 mbar (irreversible deformation no safety factor included) By Marco Kraan, NIKHEF many more results at http://www.nikhef.nl/pub/departments/mt/projects/lhcb-vertex/ Displacement [mm]

23. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP FEA for Be foil 1.0 mm Assumed S-200F hot pressed block with a yield strength of 270 MPa (SR-200 cross rolled sheet: yield strength = 340 Mpa) Max  p  500 mbar (irreversible deformation no safety factor included) By Marco Kraan, NIKHEF many more results at http://www.nikhef.nl/pub/departments/mt/projects/lhcb-vertex/ Displacement [mm]

24. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Multiple scattering Main Problem: trigger decision based on tracks displaced from primary vertex no momentum information at this trigger stage low-momentum particles undergo more multiple scattering  fake signatures of a displaced secondary vertex  performed extensive Monte Carlo simulation and analysis Result: Increasing thickness of Al foil (100  250mm) reduces vertex trigger efficiency by factor ~1.2 (20% loss of good events) Other Problems: increased background rates increased occupancies 0.08 0 0 0.4 Signal efficiency Minimum bias retention 0.2 0.04 III, 250  m foil II, 250  m foil TP, 250  m foil III, 100  m foil II, 100  m foil TP, 100  m foil

25. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Labour intensive: –manufacture moulds –make foils: ~12 press/anneal cycles, etc. Extensive prototyping program Chiel Bron CP?! Thin vacuum foil

26. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Increase radius (10  20 mm) to avoid folding Crystal structure seems affected Development tests: –Employ Al alloy with Mg –Deform at higher temperature: 150 - 200 o C Later, vacuum tests: –microscopic holes ? (leaks) –mechanical properties: deformation pressure, rupture pressure, etc. Thin vacuum foil

27. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Mixed-phase CO 2 Cooling system Advantages: Radiation hard (used in nuclear power plants) Non toxic (conc. < 5%), non flammable Low pressure drop in microchannel tubes Good thermodynamic properties Widely available at low cost No need to recover or recycle Principle of operation: CO 2 is used in a two-phase cooling system. The coolant is supplied as a liquid, the heat is taken away by evaporation. LHCb VD: in total, ~ 54  40 W of heat, each cooled by a pipe of OD=1.1mm/ID=0.9 mm. Tested at NIKHEF: See LHCb 99-046/VELO capacity of cooling pipe > 50 W heat transfer coefficient between pipe and coolant > 2 W cm -2 K -1 Phase diagram CO 2 1 10 100 -80-70-60-50-40-30-20-1001020304050 Temperature [°C] Pressure [bar] vapor liquidsolid gas critical point triple point

28. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP CO 2 Cooling system layout Standard refrigerator unit Behind shielding wallHall area2 ary vacuum Storage vessel Liquid CO 2 pump Heat exchanger Restriction (  0.85*40 mm) Needle valve(sets total flow) Pressure regul. valve (70 bar) Shutter valve Cooling tubes (  0.9/1.1 mm) Gas return (  12mm) ~ 60 m Liquid supply (  6mm) H. Boer Rookhuizen, NIKHEF

29. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP CO 2 Cooling Tubes Total amount of CO 2 in the system  6 of liquid  3 m 3 of gas at STP In the 2 ary vacuum volume:  100 m  100 g of liquid  30 of gas at STP  50 mbar in 600 at T room Total amount of CO 2 in the system  6 of liquid  3 m 3 of gas at STP In the 2 ary vacuum volume:  100 m  100 g of liquid  30 of gas at STP  50 mbar in 600 at T room ID = 1.1 mm, OD = 0.9 mm vacuum brazed (no flux, no fittings) can sustain p > 300 bar (CO 2 : p equilib = 72 bar at 30 o C) ID = 1.1 mm, OD = 0.9 mm vacuum brazed (no flux, no fittings) can sustain p > 300 bar (CO 2 : p equilib = 72 bar at 30 o C) Flow restrictions

30. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Vacuum System Controls By NIKHEF group (from former NIKHEF accelerator) in close collaboration with LHC-VAC group. Meeting in Amsterdam on 11+12 Jan. 2001 Towards a detailed description of the vertex detector system: –detailed layout of vacuum system –monitoring and safety equipment –control system (PLC based) –describe static and transient modes –etc. Risk assessment L. Jansen, J. Kuyt NIKHEF

31. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Gravity-controlled valve weight ~ few grams, area ~ few cm 2 reacts to differential pressure ~ few mbar no electrical power no pressurized air intrinsically safe solution to 1 ary vacuum to 2 ary vacuum to auxiliary pump Use tandem valve to protect against both possible signs of differential pressure

32. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Spurious conductance in normal operation, i.e. molecular flow regime Dynamic response to sudden pressure change System behaviour during pump down Tests of gravity- controlled valve Sander Klous, NIKHEF

33. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Test setup

34. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP First Measurement Results Conductance (for H 2 O in range 10 -3…7 mbar): –1  10 -3 liter/sec without auxiliary pump  10 -7 mbar liter/sec –1  10 -5 liter/sec with auxiliary pump  10 -9 mbar liter/sec Expected leak rate for nominal 2 ary vacuum pressure (10 -4 mbar) Reaction to abrupt leak:  p maintained < 6 mbar Pump-down time through a restriction: preliminary, –3 hours for p < 1 mbarapproximate –3 hrs more for p < 10 -5 mbar results

35. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Risk Analysis Purpose: To provide an objective basis for a constructive and methodical evaluation of the VDS design. comprehensive overview of all (major) risks involved what risk scenarios, what consequences, what probabilities to occur ? requirements/recommendations for a given design choice what tests should be performed and what results obtained to make the chosen option acceptable ? basis for a later, more detailed risk analysis f.i. risk of “injuries to personnel” are not assessed in details, but believed to be  downtime and equipment loss risks

36. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Framework of Risk Analysis Use same model as for CERN Safety Alarms Monitoring System (CSAMS) (1) Identify undesired event (UE) (2) Determine the consequence category of UE (3) Use predefined table to fix maximum allowable frequency (MAF) (4) Determine required frequency by reducing MAF by factor 100

37. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Framework: frequency categories Indicative frequency CategoryDescription level (per year) Frequent Events which are very likely to occur > 1 in the facility during its life time Probable Events which are likely to occur 10 -1 - 1 in the facility during its life time Occasional Events which are possible and expected 10 -2 - 10 -1 to occur in the facility during its life time Remote Events which are possible but not expected 10 -3 - 10 -2 to occur in the facility during its life time Improbable Events which are unlikely to occur in the 10 -4 - 10 -3 facility during its life time Negligible Events which are extremely unlikely to < 10 -4 occur in the facility during its life time

38. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Framework: consequence categories Equipment CategoryInjury to personnelloss in CHFDowntime (indicative)(indicative) (indicative) CatastrophicEvents capable of resulting> 10 8 > 3 months in multiple fatalities Major Events capable of resulting10 6 - 10 8 1 week to 3 months in a fatality Severe Events which may lead10 4 - 10 6 4 hours to 1 week to serious, but not fatal injury Minor Events which may lead 0 - 10 4 < 4 hours to minor injuries Turns out to be the dominant criterium

39. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP FrequencyConsequence category category Catastrophic Major Severe Minor Frequent I I I II Probable I I II III Occasional I II III III Remote II III III IV Improbable III III IV IV Negligible IV IV IV IV Framework: risk classification table max allowable frequency required frequency Legend:I = intolerable risk II = undesirable but tolerable if risk reduction is out of proportion III = tolerable if risk reduction “exceeds” improvement gained IV = negligible risk

40. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Functional Analysis Within context of risk analysis, consider 3 STATIC modes of operation: Normal ring valves open full aperture of VD < 54 mm normal running mode for LHCb physics Standby ring valves open full aperture of VD > 54 mm e.g. beam filling/tuning, scheduled dump (in some cases LHCb might take data) Isolated ring valves closedfull aperture of VD is any e.g. hall access, remote-controlled or in-situ maintenance

41. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP TRANSIENT states: NEG-preserving vent procedure and subsequent pump-down use ultrapure Ar/Ne 1 ary and 2 ary volumes are separated monitor |p 1 -p 2 | and |p 1 -p air |, control p 1 (pump/inject) NEG-saturating vent procedure and subsequent pump-down use clean gas 1 ary and 2 ary volumes are communicating followed by a bake-out of VDS and LHCb pipe Functional Analysis

42. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Assumptions If the NEGs are exposed to ambient air (even if via a leak)  baking is needed after the subsequent pump-down ! if beam-induced desorption properties of a saturated (but not “air- vented”) NEG are good enough, this constraint could be relaxed If primary vacuum system vented with ultrapure Ar/Ne  baking is not needed standard procedure used at CERN (EST/SM, LHC/VAC,...)

43. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Downtime estimations Needed to assess gravity of a given undesired event! Tasks: obtain access to VD restricted area1 shift ? bring VDS to 1 atm (and T room )1 shift prepare LHCb beam pipe for bake-out of NEGs2 days remove or install a detector half 1 / 2 shift remove or install detector encapsulations1 day ? replacement of LHCb beam pipe section2 weeks ? pump down to p 1,2 < p crit (  5 mbar) 1 shift bake out VDS and pump down to p < p activateNEG 1 day bake out NEGs 1 day pump down to p < p beamfilling (assuming active NEGs)1 day ? reverse of “prepare … for bake-out of NEGs” 2 days evacuation and closing of experimental zone 1 hour ? (some tasks can proceed in parallel !) 1 day = 3 shifts = 24 hours 10 -4…5 mbar 10 -7…8 mbar ?

44. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Undesired Events UE-1: Damaged feedthrough pin on secondary vacuum a)  p remains <  p crit : safety valves remain closed b)  p exceeds  p crit : safety valves work properly c)  p exceeds  p crit : all safety valves fail UE-2: Loss of electrical power UE-3: CO 2 cooling system goes down UE-4: Leak of CO 2 cooling pipe UE-5: Uncontrolled beam displacement UE-6: Ion-getter pump goes down UE-7: Turbomolecular pump station goes down UE-8: Bellow between 1 ary & 2 ary vacuums breaks UE-9: Jamming of detector halves motion mechanics UE-10: Bellow between air & primary vacuum breaks.

45. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Sample Undesired Event UE-1a: Damaged feedthrough pin on secondary vacuum Assumptions: due to human action  mode Isolated (ring valves closed) leak rate into 2 ary vacuum small enough that safety valves stay closed leak rate to 1 ary vacuum small enough that NEGs are negligibly affected  NEG-preserving venting procedure with Ar/Ne (1 shift) Estimated damage: 1 ary vacuum not exposed to air  baking-out NEGs not needed replace feedthrough flange ( 1 / 2 ) and pump down (7)  LHC downtime < 3 days  category: Severe Requirements/remarks: required frequency: Remote (see experience with LEP/SPS/... ?) demonstrate that breaking of feedthrough pin will in most cases: (a) not cause a  p increase which triggers safety valves to open (b) negligibly affect the NEGs precautions: countersink flange connectors, tighten cable connectors, tighten cables, mount protective cage around feedthroughs,...

46. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Sample Undesired Event (continued) UE-1b: as UE-1a but differential pressure triggers safety valves to open Assumptions: as in UE-1a except that leak rate into 2 ary vacuum is such that safety valves open leak rate to 1 ary vacuum  substantial fraction of leak rate to 2 ary vacuum  vent procedure with clean gas or Ar/Ne (1 shift) Estimated damage: (compare to UE-1a) 1 ary vacuum was exposed to air  NEG bake-out needed 1. replace detector half with flange ( 1 / 2 )2. prepare beam pipe for baking (6) 3. pump down to p 1,2 < p crit (1)4. bake VDS + pump down to p < p activateNEG (3) 5. bake out NEGs (3)6. pump down to p < p beamfilling (3) service/inspect pumps, … (3 more shifts)  LHC downtime  1 week  category: Severe (but downtime is longer for LHCb !) Requirements/remarks: required frequency: Remote this is automatically fulfilled if actual frequency of UE-1a is Remote

47. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Sample Undesired Event (continued) UE-1c: as UE-1b but all safety devices fail to protect the thin-walled box Assumptions: as in UE-1b except that electrically activated valves and gravity-controlled safety valves fail to protect the thin-walled box  vent procedure with clean gas or Ar/Ne (1 shift) Estimated damage: (compare to UE-1b) as in UE-1b, but the thin-walled box (and perhaps some Si modules ?) must be replaced replace thin boxes, debris (if any) must be collected, replace detector LHCb beam pipe must be checked (and replaced ?) (2 weeks ?) If agreed by other parties: after bake out, install (new) vertex detector and move in all other LHCb detectors (additional 1 week) If not agreed: LHCb waits for next opportunity, but LHC is up !  LHC downtime = 1... 4 weeks  category: Major Requirements/remarks: required frequency: Improbable demonstrate that probability for coincidental failure is < 0.1, if actual frequency of UE-1b is Remote

48. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP Design of LHCb VD is based on 2 ary vacuum system –use thin separation foil protected by gravity-controlled and electrically controlled safety valves –First tests of gravity-controlled safety valves are positive –use 2-phase CO 2 cooling system in 2 ary vacuum –started risk analysis –needs formal agreement from LHC/VAC for TDR and further developments –allows baking up to T  150 o C –decouples access to Si detectors from access to 1 ary vacuum system –employs venting with ultrapure Ar/Ne Wake field effects under study Perform required tests before installation into LHC Full vacuum setup with wake field suppressors in LHC during single beam operation Summary and Outlook

49. Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP