TWEPP 2013 23-27 Sep 13

1. TWEPP 2013 23-27 Sep 13 • Detector Integration Issues in • High-Energy Physics S. Lusin CERN / University of Wisconsin

2. The Usual Method … • Three-phase process • Modeling • Integration • Implementation • HEP detector design starts with MC modeling • Design optimization driven by choice of target processes • Choice of detector technologies heavily influenced by performance targets, costs Higgs to 4-muon decay simulation in CMS detector

3. Making It Work … • Practical details of detector construction are addressed at a later stage • Conflicts inevitable -> Detector integration phase • Harmonize cable routing, cooling systems, power dissipation and interaction between subdetectors • Design changes can propagate back to subdetectors themselves • Can result in a further cycle of detector simulation • Services added later by different teams Implicit: Explicit: Detector Readout Cooling & Heating Hydraulics & Pneumatics Controls & Safety Alignment Radiation Shielding Mechanical Support Maintenance Access Survey Sealing & Isolation Lighting Ventilation • Services usually supplied as “standard” solutions • Use common industrial hardware • Installed in highly nonstandard environment

4. The CMS Detector • During Run 1 in CMS we have observed several instances of unexpected behavior • Attributable to the complexity of detector integration design • Issues that could be expected in any detector of comparable scale • Issues shared common features • CMS is segmented longitudinally into 13 sections • Central section holds cryostat containing solenoid, is fixed to cavern floor • Other sections are movable, allowing up to 10m free travel

5. CMS Underground Caverns CMS located in two adjacent caverns: Undergound Service Cavern (USC) Underground Experimental Cavern (UXC)

6. Connection Paths… • Power cabling paths between safe area and experimental cavern are shared with other detector cabling • Detector readout systems use fiber-optic cabling • Power system cables run through dedicated cable trays Experimental cavern Safe area electronics Far-side wall of experimental cavern

7. Connections- Near Wall Near-side wall of experimental cavern Safe area electronics Experimental cavern Connections to cable chains under detector

8. CMS VFD Installation • VFDs installed to power motors of C6F14 pumps inside experimental hall • Motivation was to reduce pressure excursions in the coolant • Noted experience of other LHC experiments with VFDs. Used extensive filtering on outputs • No galvanic connection through cabinet structure to any other cabinet or service cavern steel framework • Connections to outside world consist of: • 2 incoming cables from 18KV/400V transformer • 2 outgoing power cables to pump motors on opposite sides of experiment • 1 protective earth cable connecting to service cavern earth

9. VFD Connections to Cooling Plant

10. Common-Mode Currents

11. Discovered Earth Current Instead • Ch. 1: One phase of input to VFD at 50 A/div • Ch. 2: Current in protective earth wire to pump motor at 500 ma/div • 1A p-p current flowing on PE cable • Source unexplained • Spectrum from 0 to 5 kHz, expanded scale to 50 kHz

12. VFD Summary … • VFD tests showed: • Significant earth currents flowing through motor drive cabling • Source of currents not understood • But linked to motor operation- not external • HF noise from VFD switching present on input and output cabling • Interaction (“beating”) between VFDs running at different frequencies • Earth currents caused the most concern, since this was evidence of possible bearing currents in motors • Bearing currents are well-known effect exacerbated by use of VFDs, but this was something else • Turned out that earth current was the result of interaction between the filters themselves • A lesson in collective effects • Made easier to diagnose by fact of single earth connection to cabinet

13. Magnet Power Converter … • During monitoring of voltage across solenoid busbars in CMS service cavern, noticed some anomalies: • Objective had been to search for correlations with PLC communication failures • Instead, noted significant AC component at output of magnet power converter • Approx 500mV p-p on top of 1.4 VDC supply voltage • Such behavior is actually considered normal by power converter group which supplied converter • Large magnet series inductance suppresses AC currents • Magnet supply “deliverable” is stable magnetic field

14. CMS Magnet Common-Mode Voltage • AC component has a large common- mode contribution • Will not affect magnetic field • But concern is that CM currents could couple through CMS yoke • Ch.1 200 mV/div • Ch.2 200 mV/div • Red trace: sum @ 500 mV/div • 203 mV rms • Large 50 Hz component • Is there an AC component of current?

15. Current in Single Busbar • Indeed, there is: • Ch.3: current through + bus bar @ 1A / div • Current measurement through other busbar is similar • Currents are ~0.75A rms • Total current expected to be all common-mode: L(magnet)=14H • Where does this current go?

16. Current Accounting • Measuring net current (CM) into power converter • Made possible by the fact that converter is isolated from local structure • Evidence of circulating current through cavern metallic structures 380V 3ph. + P.E. 1.49A rms, 8.4A p-p

17. When life was simpler … • First CMS Endcap disk being lowered into cavern, 2005 • Balcony racks empty, most services not installed

18. How it’s different now … View of one half of CMS detector “Empty” space between blockhouse and detector disk reserved to allow for 10m opening between detector elements

19. Reasons that upgrading will be hard • We’ve built a ship in a bottle • Now we want a different ship • Upgrade plans have been all about the subdetectors so far • Sounds familiar … • Integration to come later once plans have gelled • Detector choices still being made • Electrical requirements specification will remain rough until final stages of prototyping • Same applies for cooling • Infrastructure design is not a line item in the schedule • Infrastructure will be expected instantly once detectors installed • But old infrastructure is already in place … • We’re already getting a taste of things to come

20. First Upgrade Experiences … Upgraded FE electronics took advantage of more powerful FPGAs But currents rose by factor of three. Incompatible with existing cabling Cabling cannot be modified on timescale of shutdown Required re-engineering of chamber power distribution system

21. Assembly of Outer Shielding Wall Providing a taste of operating in an installed environment Shielding wall to be assembled from sectors, in place H Gerwig & Crew

22. Situation - Specific Tooling Engineered for operation in as-built CMS environment Counterweighted installation fixture H Gerwig & Crew

23. Looking Ahead to Phase 2 Very preliminary study exploring the feasibility of removal of endcap calorimeters as a unit May be the only way to meet shutdown schedule constraints By H Gerwig & N Siegrist

24. Beam Collimator Removal TAS is actively-cooled copper beam collimator at each end of CMS Experimental Cavern Contained inside conical steel shielding structure Expect significant activation in Run 2 No one from original installation team is available at CERN Will need to replace for high-luminosity running Possibly the only choice will be to remove entire iron shielding nose

25. Lessons Learned … • Services are not engineered in .. • Necessary to validate them over time for compatibility with detector • Services may behave very differently once they’re installed in the experimental environment • Experiments are not always the prime customer of services • Power converters are specified for magnets • Standards specifications may not protect the secondary customer • Services change over time • As in proliferation of VFDs • Not all effects are immediately apparent • Have to anticipate them based on experience • Have to gauge potential for disruption • Assessment is informed by knowledge of the detector • Experiment changes over time • Late additions are arriving regularly • Upgrades will be extreme test of integration process