grounding & shielding of the cms tracker

W. Karpinski, Nov. 2001CMS Electronics week

CMS Microstrip Tracker

grounding & shielding of the CMS Tracker

R. Hammarstrom (CERN EP/CMT) & W. Karpinski (RWTH AC I)



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



L ~ 5,4 meters

Outer Barrel

Inner Barrel

Endcap

Pixel

~ 2

,4 m

eter

s

Tracker Overview



• Si – ModuleSi – Module• Biasing 500V, I = 1.0 mA Biasing 500V, I = 1.0 mA (after (after

irrad.)irrad.)

• Front endFront end based on APV25 chipsbased on APV25 chips supply voltagesupply voltage::

+2.5 V ; 0V I= 90 mA+2.5 V ; 0V I= 90 mA +1.25V+1.25V ; 0V ; 0V I= 80 mAI= 80 mA • Optical hybrid Optical hybrid

ssupply voltageupply voltage::

+2.5 V ; 0V I =300 mA+2.5 V ; 0V I =300 mA

• Control systemControl system bbased on ased on DDOH and CCUOH and CCU supply voltagesupply voltage: +2.5 V ; 0V: +2.5 V ; 0V

CCU CCU I =300 mA I =300 mA

DOH I =300 mADOH I =300 mA



Power suppliesPower supplies– Situated in counting roomSituated in counting room– PS modules powerPS modules power groups of ~60APV groups of ~60APV

[email protected] = =1010AA, , [email protected] = =4A 4A I@0V = =14A 14A

voltage dropvoltage drop = 5V = 5V

• Cables Cables 3 major sections3 major sections• Patch Panel 3 (PP3) in USC55 – Patch Panel 3 (PP3) in USC55 – PP2 on balconiesPP2 on balconies ~100m ~100m• PP2– PP1 PP2– PP1 on HCAL on HCAL ~40m ~40m• PP1 - module groups ~PP1 - module groups ~2m2m-5m-5m



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 low D.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



All subdetectorsAll shields,All manifolds will be electrically connected to the 2 TK cylinder brackets

A perfect and solid GROUND



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



Cable inside the Tracker



Cable PP1 to PP2



Control Cable



Prototype of the cable PP3 to PP2

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



Galvanic insulation, as close as possibleto Tracker

All manifolds will be connected to Tracker brackets



Grounding of TOB



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



-The cooling pipes are used as Local Ladder Ground to which LV and HV supplies are referenced.

-The CCUM Ground is connected to the TOB Local Ladder Ground inside each Ladder

Grounding of TOB

Local Ladder Ground



Grounding of TOB



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



Ground loops between Digital Control Cable and manifolds should be investigated

Grounding of TOB



Grounding of TOB

manifolds are inter connected electrically in radial manner no loops inside the magnetic field and then tied to the TK brackets



Grounding of TEC



TEC: Services of 1/8 of the end cap



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



•The Si- modules on each petal are organized into three power groups with one multiservice cable serving each group

•LV and HV 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

Grounding schema of TEC- Petals



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 the Local Petal Ground inside petals



•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

Grounding of the Control Link



End cap insulation disk

•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



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



TK Shielding

grounding & shielding of the cms tracker

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