LHCb Week, CERN, may ‘00M. Ferro-Luzzi LHCb Vertex Detector System: An Update Review of TP design mechanics, wake field suppression, vacuum system, cooling system. Difficulties with this design center frame stiffness, accessibility,... New requirements more cooling power, intermediate Y positions of two halves An (unfinished) improved design vacuum tank and flange, center frame Foil thickness what should we start with ? Milestones

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Mechanics: “TP” design Side flange Bending hinges Detector support and cooling Bellows (22000 signal wires) Support frame Si detector moves by 30 mm only two positions: open or closed !! See LHCb /VELO top half = bottom half

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Marco Kraan, Martin Doets FEA for TP center frame See The two detector support frames (for the Si detectors halves) are mounted on a “center frame” standing on three legs. FEA: deflection on center frame when loaded should be less than 0.1 mm. Materials used: Aluminum/Stainless Steel

LHCb Week, CERN, may ‘00M. Ferro-Luzzi FEA Model 1 Starting point. The maximum deflection is 0.7 mm

LHCb Week, CERN, may ‘00M. Ferro-Luzzi FEA Model 2 To decrease the deflection an open rib is added to the frame. The maximum deflection is 0.4 mm

LHCb Week, CERN, may ‘00M. Ferro-Luzzi FEA Model 3 Investigate deflection with a solid rib. The maximum deflection is 0.24 mm.

LHCb Week, CERN, may ‘00M. Ferro-Luzzi FEA Model 4 Stiffen frame with ribs under frame. The maximum deflection is 0.38 mm.

LHCb Week, CERN, may ‘00M. Ferro-Luzzi FEA Model 5 Decrease torsion with hollow box added at the rear of the frame and “more solid” ribs. The maximum deflection is: mm for Al, mm for SS. Conclusion: possible, but not very handy...

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Wake field suppression Performed set of MAFIA calculations Resonant effects  frequency domain (“E3”) Short range effects  time domain (“T3”) 1) complete VD with/without strip shielding ( mesh points, problems with disk space and CPU time) 2) reduced VD model (no strip shielding) a) position open/closed b) no strips, vary (reduce) cavity depth c) various designs See LHCb /VELO LHCb /VELO LHCb /VELO

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Reduced VD model d Without strip shielding: at what “depth” d of cavities does RF coupling become acceptable ? d varied: 160, 20, 5 mm

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Varying cavity “depth”: results E3 calculations show that cavity depth d of less than about 20 mm results in acceptable resonant losses (without strip shielding)  fine tune design Selected modes (those which exhibit significant losses): Almost ok ok

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Why not use wake field suppressor strips ? design very difficult (we could not find, so far, a satisfactory solution) Remember: four 130 cm long, very thin strips which must (a) be connected to exit foil (b) put under tension (thermal expansion and inward motion of exit foil, few mm) (c) be retractable (d) not touch the detector boxes even assuming unrealistic † thickness of 10  m (stainless steel), then  multiple scattering corresponds to about ( )  10  m  8.9/1.76   m of “perpendicular” Al foil † Due to resistive overheating. Compare to HERA-B case: current I herab = I lhcb /10 (and only one beam), resistance R herab = R lhcb  10  m/5  m  7mm/12.7mm  R lhcb  1.1  heat load P lhcb = P herab  10 2  2 / 1.1  180 (goes mostly to Si modules!) and HERA-B observed already a strip temperature increase. have to come closer to the beams than the detector boxes r  4 mm  more background, reduced efficiencies introduce a risk: what if the aperture requirements at startup are worse than currently assumed ? see e.g. HERA-B. WF calculations showed that, in “open” position, strips do not shield sufficiently (few kW of WF losses) what if one strip breaks at runtime? (and, in fact, strips did break at HERA-B)

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Foil design options Variant A Variant B

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Foil design options (continued) Away from beam region (both variants A and B) In beam region: variant A:12 mm clearance variant B: tapering as shown

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Various foil designs: E3 results E3 results: ok for both variants, with detectors closed and open. But... see T3 results.

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Various foil designs: T3 results T3 results: ok for position closed, not ok for open, but probably due to the fact that beam sees vacuum tank. Further calculations will be carried out with shielding around the detector boxes (hide tank from beam). Longitudinal loss factor

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Wake field suppression Criterium: losses < 100 W (time domain, or any resonant mode) Conclusions: 1) complete VD with/without strip shielding “deep” cavities require strip shielding 2) reduced VD model (no strip shielding) a) position open/closed requires shielding on sides of enclosures b) reduce cavity depth ok for depth of < 20 mm c) various designs ok, analog to b) tough with TP design! no space, no access!

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Si detector encapsulations Current solution: Al encapsulation. Try: Cu foil, Cu on Al, low-emission coatings (Ti, NEG),... Test setup needed ! System cannot (?) be baked out in-situ ! No valve to NEG-coated chamber ! 300  m 100  m Design must take into account: multiple scattering wake field effects vacuum compatibility

LHCb Week, CERN, may ‘00M. Ferro-Luzzi 2  z  15 cm Q b  2 × C r  6 mm Detector box E < 1V/m (?) Peak E-field on inside surface for moving bunch: E peak =  3.4 × 10 9 V/m E-field for fundamental harmonic (n=1, 40 MHz): E n=1  E peak / 21  1.6 × 10 8 V/m For condition E < 1 V/m we need skin attenuation of about In fact, about 19 skin depths !!  (Al, 40 MHz)  13.3  m  foil thickness > 250  m !! RF field attenuation  · Q b 2  3/2  0 ·  z ·r  For non-cylindrical complex geometry, EM fields will be even higher.   7500

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Vacuum constraints LHC: beam life time: static density of mbar  2 m (H 2 300K)  0.01 % of LHC limit for integrated density ( cm  molecules/cm 3 ) beam stability: dynamic effects must be taken into account LHCb: mbar  1.2 m (H 2 300K)  1.5 % of LHCb nominal luminosity Difficult to achieve with silicon detectors, electronics and signal wires directly in LHC vacuum !  differential pumping. (rough!) See LHCb /VELO

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Static pressure in VD Consider outgassing by: assuming outgassing rates of: (mbar l s -1 cm -2 )  11 m 2 Kapton (signal wires, pumped 40 hours) H 2 O  2.3 m 2 Al housing (per half) H 2  1.5 m 2 bellows (per half) H 2  8 m 2 SS vessel H 2 Pumps in detector volume:  140 l/s (per half) H 2 O Pumps in tank:  4000 l/s H 2 Bypass tube: 200 mm  4 mm pumped in the middle. Calculate using a static flow model. Result: mbar in detector volume mbar in VD tank mbar l s -1 from det. vol. to VD tank

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Aluminium exit foil 20 m beam pipe NEG Detector volume 1 Detector volume 2 Pump station 1 Pump station 2 Restriction Clean gas Reducing valve Overpressure safety Mechanical pump Ion-getter pump Penning gauge Ionization gauge Pirani gauge Electromechanical valve Self-opening valve  pressure sensor QMA

LHCb Week, CERN, may ‘00M. Ferro-Luzzi S ummary table: (Data are approximate. Q LHCb_total = estimate for the full vertex detector, i.e. both halves.) Item Outgassing rate of itemQ LHCb_total [mbar l s -1 ] Kapton foil, after 40 hrs pumping 1 E-7 mbar l s -1 cm -2 n/a sample Kapton flat cable QPI 3 E-5 mbar l s E-4 male/female pair of PEEK D-type 25-pin connectors6 E-6 mbar l s -1 / pair 50 E-4 male/female pair of stand. D-type 25-pin connectors1 E-5 mbar l s -1 / pair 100 E-4 Liverpool carbon-fiber Si support 1 E-8 mbar l s -1 cm -2 ~ 1 E-4 Outgassing measurements Continue: measure all unknown outgassing rates of components in a detector station

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Dynamic Vacuum Beam-induced particle bombardment  desorption, emission Ions, photons, electrons energies up to keV Local pressure runaway (ion/electron-induced desorption) Local static charge increase (electron multipacting) LHC beam instability See Adriana Rossi’s presentation

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Dynamic Vacuum (continued) Perhaps a solution: use coating of surfaces by Ti advantages: low  SEY, low , local pumping Design issues: better surfaces ? (NEG ?) in-situ coating required or not ? thickness of layer needed ? what re-coating rate ? affordable cathode temperature in-situ ? wake field / RF properties ? side effects ? (peeling,...) We need ,  for: different materials surface conditions (un)baked, saturated, activated, etc. different impact energy spectra Data available only in a few months ! (Mahner et al.)

LHCb Week, CERN, may ‘00M. Ferro-Luzzi New requirements on VD design Recent VELO workshop in Amsterdam (April ‘00): Top/bottom halves should have intermediate steps (not only open/closed), with “relaxed” overall position accuracy (0.3 mm). Only useful if we can acquire meaningful data in intermediate positions !  trigger algorithm Higher cooling power required (20 W/module  40 W/module) to accommodate for backup solution SCTA/velo. Should be no problem for CO 2 cooling system, but is it realistic at all ?  thermal modeling needed

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Summary of difficulties with TP design Recent FEA results: to obtain sufficient stiffness of center frame, a rather complex structure needs to be used  reduced space and accessibility MAFIA: WF suppressors on sides of the two detector boxes are needed  not easy to find a solution with current design because center frame is “in our way” and because of the fact that the two boxes are mounted separately into the tank Dynamic vacuum: we must have the option to insert a Ti evaporator  not easy with current design must enter from the front of tank and, again, center frame is “in our way”

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Towards a modified design in which difficulties become challenges.

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Vacuum tank new FEA required (probably additional ribs are needed) flange will be on inside of LHC ring solves lack of space issue on outside of ring all feedthroughs on the same big flange all cables and repeater cards on same side (present choice of feedthrough limits total number of pins to about !!)

LHCb Week, CERN, may ‘00M. Ferro-Luzzi optimally positioned short legs, no more problems of bending, stiff, stable structure xy-table can move down enough to allow insertion of complete detector (tilting mechanism no longer needed) frames not any longer “in our way” (more accessibility to critical items of VD) Support frames

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Detector and support frame both halves on same side VD easier to mount and position in the tank install complete VD at once the two halves are no longer interchangeable

LHCb Week, CERN, may ‘00M. Ferro-Luzzi TP design center frame New design Sideways accessibility (1) Side wake field suppressors Ti evaporator No room on the sides !

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Sideways accessibility (2) More access to critical WF suppressor Much room left on one side of the tank  2ary vacuum pumps (pumping on the detector boxes is more efficient)  if required, a Ti eva- porator with much more favorable design conditions

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Cooling system with mixed-phase CO 2 *

LHCb Week, CERN, may ‘00M. Ferro-Luzzi cool to 20  C CO 2 gas-liquid storage tank 57.3 bar at 20  C CO 2 supply line compresssor P [W] flow restrictions supply line expansion valve cooling lines gas only pressure (temperature) regulating valve heat to 20  C Mixed-phase CO 2 Cooling system See LHCb /VELO

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Report from LEMIC (LHC Experiment Machine Interface Committee) We presented the design of the Vertex Detector on (mechanics, vacuum, CO 2 cooling, wake field studies) Overall reaction was positive and constructive Major points of discussion: (a) foil resistance to differential pressure  test, add self-opening valves (b) dynamic vacuum issues  partial bake-out ? Ti coating ? (c) accuracy of WF calculations  test setup, compare (d) reliability of CO 2 cooling system (vac.)  demonstrate

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Set Si design parameters march 2000 (?) positions, materials, tolerable foil thickness,... Calculate dynamic pressure effectsmarch (?) desorption, multipacting Build 1-1 prototype summer test mechanics, RF, cooling, vacuum Formal approval of design from CERN/LHCsummer TDR ready december Outlook presented to LEMIC

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Why not start with 250  m Al foil ? Conservative approach, but, if physics permit, offers important advantages: RF penetration, pick-up E peak  1.3 × 10 9 V/m Easier to manufacture (more freedom in design) corrugation depth More resistance to differential pressure expect about ? mbar Continue developments to reduce foil thickness, while acquiring experience with this foil. Upgrade after some time of operation.

LHCb Week, CERN, may ‘00M. Ferro-Luzzi List of available LHCb notes LHCb , VELO, --- Heat dissipation studies for the LHCb microvertex silicon detector, N. van Bakel et al. LHCb , VELO, --- A first study of wake fields in the LHCb vertex detector, N. Van Bakel et al. LHCb , VELO, --- Mechanical design of the LHCb vertex detector : baseline solution, M. Doets et al. LHCb , VELO, --- Wake fields in the LHCb vertex detector : strip shielding, N. Van Bakel et al. LHCb , VELO, --- in preparation LHCb , VELO, --- Preliminary studies for the LHCb vertex detector vacuum system, M. Doets et al. LHCb , VELO, --- Preliminary studies for the LHCb vertex detector cooling system, M. Doets et al. LHCb , VELO, --- Geant description of the aluminum shielding of the vertex detectors T.J. Ketel

LHCb Week, CERN, may ‘00M. Ferro-Luzzi Topics for future LHCb notes (2000) Estimation of RF field attenuation through the Al shield Description of modified VD design FEA results for the VD vacuum tank and support frames Test of the VD CO 2 cooling system Measurements of outgassing rates for the VD components Measurements of the RF shield properties under differential pressure Test of self-opening valves Test of Ti evaporation on Al RF shield Measurements of RF properties of the VD Test of motion mechanics