twepp 2013 23-27 sep 13

S. Lusin, TWEPP, 25 Sep 13 1

TWEPP 2013 23-27 Sep 13 TWEPP 2013 23-27 Sep 13

S. Lusin

CERN / University of Wisconsin

Detector Integration Issues in

High-Energy Physics


The Usual Method …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


Making It Work …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 teamsExplicit: Implicit:

Detector ReadoutCooling & HeatingHydraulics & PneumaticsControls & SafetyAlignmentRadiation Shielding

Mechanical SupportMaintenance AccessSurveySealing & IsolationLightingVentilation

Services usually supplied as “standard” solutions • Use common industrial hardware

• Installed in highly nonstandard environment


The CMS DetectorThe CMS Detector

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

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 Underground Caverns

CMS Underground Caverns

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


Connection Paths…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


Connections- Near WallConnections- Near Wall

Near-side wall of experimental cavern

Safe area electronics

Connections to cable chains under detector

Experimental cavern


CMS VFD InstallationCMS VFD InstallationVFDs 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


VFD Connections to Cooling Plant

VFD Connections to Cooling Plant


Common-Mode CurrentsCommon-Mode Currents


Discovered Earth Current Instead

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


VFD Summary …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


Magnet Power Converter …

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


CMS Magnet Common-Mode Voltage

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?


Current in Single BusbarCurrent in Single BusbarIndeed, 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?


Current AccountingCurrent AccountingMeasuring 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

1.49A rms, 8.4A p-p

380V 3ph. + P.E.


When life was simpler …When life was simpler …First CMS

Endcap disk being lowered into cavern, 2005

Balcony racks empty, most services not installed


How it’s different now …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


Reasons that upgrading will be hard

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


First Upgrade Experiences …First Upgrade Experiences …

Required re-engineering of chamber power distribution system

Upgraded FE electronics took advantage of more powerful FPGAsBut currents rose by factor of three. Incompatible with existing cablingCabling cannot be modified on timescale of shutdown


Assembly of Outer Shielding Wall

Assembly of Outer Shielding Wall

H Gerwig & Crew

Providing a taste of operating in an installed environment

Shielding wall to be assembled from sectors, in place


Situation - Specific Tooling

Situation - Specific Tooling

H Gerwig & Crew

Engineered for operation in as-built CMS environment

Counterweighted installation fixture


Looking Ahead to Phase 2Looking Ahead to Phase 2

By H Gerwig & N Siegrist

Very preliminary study exploring the feasibility of removal of endcap calorimeters as a unit

May be the only way to meet shutdown scheduleconstraints


Beam Collimator RemovalBeam Collimator RemovalTAS 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


Lessons Learned …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

twepp 2013 23-27 sep 13

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