grounding & shielding of the CMS Tracker

1. grounding & shielding of the CMS Tracker R. Hammarstrom (CERN EP/CMT) & W. Karpinski (RWTH AC I)

2. Outline • Overview of the CMS Tracker and its Readout electronics • Grounding and shielding policy • Cables and manifolds • Grounding schema of TOB • Grounding schema of TEC • Tracker shielding

3. Tracker Overview Endcap Pixel Outer Barrel Inner Barrel  ~ 2,4 meters L ~ 5,4 meters

4. Si – Module • Biasing 500V, I = 1.0 mA (after irrad.) • Front end • based on APV25 chips • supply voltage: • +2.5 V ; 0V I= 90 mA • +1.25V; 0V I= 80 mA • Optical hybrid • supply voltage: • +2.5 V ; 0V I =300 mA • Control system • based on DOH and CCU • supply voltage: +2.5 V ; 0V • CCU I =300 mA • DOH I =300 mA

5. Power supplies • Situated in counting room • PS modules power groups of ~60APV • I@2.5V =10A, I@1.25V =4A I@0V =14A • voltage drop = 5V • Cables 3 major sections • Patch Panel 3 (PP3) in USC55 – PP2 on balconies ~100m • PP2– PP1 on HCAL ~40m • PP1 - module groups ~2m-5m

7. Overall grounding and shielding strategy • Floating LV, HV power supplies of each detector group, their Return Lines • connected inside the detector to the Common Inter-Detector Ground • Shielded power cables with lowD.C. resistance and a low impedance • Shielded twisted pair cables for monitoring • Electrical isolation from other systems • Data transmission, clock and trigger distribution per optical link • Galvanic separation of tracker interior manifolds,as close as possible to • the detector,from the long distribution manifold outside the TK • Detector located inside a faraday cage

8. All subdetectors All shields, All manifolds will be electrically connected tothe 2 TK cylinder brackets A perfect and solid GROUND

9. Interconnection and Grounding of the cables • the individual shields remain insulated and interconnected at all three PP • Shields grounded at the common detector ground and floating at PP3

10. Cable inside the Tracker

11. Cable PP1 to PP2

12. Control Cable

13. Cable PP3 to PP2 Low impedance cable, Z ~2 Ohm -low inductance -high capacitance  -high immunity from E.M.I -minimize voltage overshoots due to current variations Prototype of the cable PP3 to PP2

14. Galvanic insulation, as close as possible to Tracker All manifolds will be connected to Tracker brackets

15. Grounding of TOB

16. TOB Ladder • 6 silicon detector modules • 6 front end hybrids • 6 optocal hybrids • 1 CCUM • 1 Interconnect bus • 1 Interconnect Card • Ladder is powered over one power cable • one floating LV channel • two HV bias channels

17. Grounding of TOB -The cooling pipes are used as LocalLadder Ground to which LV andHV supplies are referenced. -The CCUM Ground is connected to the TOBLocalLadder Groundinside each Ladder Local Ladder Ground

18. Grounding of TOB

19. Grounding of TOB - The Manifold pipes (Ø 8.0 mm) are used as part of the „TOB Common Ground“, to which all corresponding LV and HV supplies are referenced. - The Digital Control (CCUM + DOHM) power supply and Control Cable Shielding are automatically connected to the TOB Common Ground

20. Grounding of TOB Ground loops between Digital Control Cable and manifolds should be investigated

21. Grounding of TOB • manifolds are inter connected electrically in radial manner no loops inside the magnetic field and then tied to the TK brackets

22. Grounding of TEC

23. TEC: Services of 1/8 of the end cap

24. 28 Si-detectors • 28 FE hybrids • 28 Opto hybrids • 2 CCUM • 4 IC Boards

25. Grounding schema of TEC- Petals • The Si- modules on each petal are organized into three power groups with one multiservice cable serving each group • LV andHV supplies of all three group are referenced to the Local Petal Ground, which is distributed along the interconnect boards as a reference stub • The shields of the cables associated with the petal are tied to the Local Petal Ground

26. Grounding schema of one Power Group • The Local Petal Ground is insulated from the cooling system and petal CFK structure • The detector frames are insulated from the cooling system. • The CCUM Ground is not connected to theLocal Petal Groundinside petals

27. Grounding of the Control Link • Local Petal Grounds of all petals of one control link (3) are connected to • the TEC Common Ground • The Digital Control (CCUM + DOHM) power supply and Control Cable Shielding are • connected only once to the TEC Common Ground to avoid ground loops

28. TEC Common Ground could be realized using a thin Cu wire ( 2mm, R= 0.005/m)running in parallel in z direction or eventually cooling pipes ( 12mm, R= 0.034/m) • The Cu wires and all manifolds of one half of TEC will be connected (elec) together • at the end flange and tied to the 2 TK cylinder "brackets" at 3 and 9 o'clock positions End cap insulation disk

30. Shielding • Tracker Support tube and the tracker end flange covered by • 100 µm AL foil • Shields tied to TK brackets • No individual shielding of TOB • Shielding of TEC under discussion • - inner support tube, front and back terminating plates covered by • 50 µm Al-foils • - outer cylindrical skin made of metalized CFC or metalized kapton

31. TK Shielding