CMS Tracker services

CMS Tracker services

Karl GillPH Dept, CERN

K. Gill, Mech. Forum 2013 2

Outline• Will focus on our recent main issues and lessons learned relating

to the Tracker services– illustrating main points via our present long-shutdown (LS1) activities– Brief look forward towards upgrades

• Work of a much larger group, particularly: D. Abbaneo, N. Bacchetta, C. Barth, G. Berruti, G. Bolla, E. Butz, E. Focardi, A. Gaddi, F. Hartmann, A. Kaminskiy, N. Lumb, A. Onnela, F. Palmonari, P. Petagna, H. Postema, P. Siegrist, P. Tropea, A. Tsirou, P-G. Verdini– Plus close collaboration with CERN groups PH/DT, EN/CV in LS1


Recap: CMS = Compact Muon Solenoid

ECAL

Tracker

HCAL

4T solenoid

Muon chambers

Total weight: 12,500 tOverall diameter: 15 mOverall length 21.6 mMagnetic field 4 T


Recap: CMS = Compact Muon Solenoid

CMS central Barrel wheel

YB0

4T solenoid

CMS Endcap


• Complex system of silicon sensors and related systems: Power, Cooling, Safety, Control, clock/trigger, Data acquisition.

• 10 years of R&D• 6 years construction and assembly• ~15yr operational lifetime

Recap: CMS Tracker

Excellent performance to date


Lifetime: Silicon radiation effects

• Pressing question in preparation of CMS upgrades– When do we need to replace the Tracker?

• Can it be done in stages?

• With 5 years of experience of running the Tracker– Radiation damage still expected to be the

main mechanism of module degradation

TDR projection of depletion voltage and leakage current density over 10 years running. 500fb-1 total, silicon at -10°C.Tracker TDR, CERN/LHCC 98-6


Models of Tracker damage

• We have a sophisticated radiation damage model

• Leakage current expected to be limiting factor

• Thermally activated, doubling every 7°C

• Good refrigeration needed to keep leakage current under control

Comparison of measured and modeled leakage currents per module

C. Barth


Temperatures on the silicon• Coolant at 4°C

– Limited by several reasons up until now

• Warm areas where we have poor cooling– Leaking lines

where cooling turned off

– or problems with thermal contacts

• We still run these parts today– They will likely be

switched off first

Cooling to -20°C we expect to be OK for almost all the Tracker. Lose few %, mainly the poorly cooled modules by 500fb-1 . Cooling to -25°C will give greater margin


CMS Tracker LS1 Challenge

• We have to improve several areas of the Tracker services during Long Shutdown #1 to achieve sustainable cold running in future (at least up to LS3):– Cooling– Sealing– Gas flushing– Instrumentation




Joint project with CERN PH/DT and CERN EN/CV




Joint project with CERN PH/DT and CERN EN/CV

“Tracker Humidity Improvement Project”}


The CMS fluorocarbon cooling system

Chilled water+12°C

Chilled water+6°C

USC55 - CV zone

Tunnel~ 150 m

TT

TT

Detectorcooling unit

(C6F14)

Chiller group(R507 A)

Brine group

TT

UXC55 - 1st floor balconies

• 7 liquid monophase detector cooling unit (2 for Silicon Strip Tracker, 2 for Thermal Screen, 1 for Pixels and 2 for Preshower)

TS/CV-Contract CMS-Contract x piping

3 cooling loops in cascade: chiller, brine (now C6F14 after important failure on heat exchangers), fluorocarbon



Chilled water+12°C

Chilled water+6°C

USC55 - CV zone

Tunnel~ 150 m

TT

TT


(C6F14)


Brine group

TT





Heat exchanger failures2007, 2008



Chilled water+12°C

Chilled water+6°C

USC55 - CV zone

Tunnel~ 150 m

TT

TT


(C6F14)


Brine group

TT





Increasing leaksin plant 2008



Chilled water+12°C

Chilled water+6°C

USC55 - CV zone

Tunnel~ 150 m

TT

TT


(C6F14)


Brine group

TT





Increasing leaks on detector side 2009-10


Cooling: issues since 2008**

• Heat-exchangers failure in 2007 in silicon strip (SS) plants– Replaced with double-wall HEx in 2008.– Switched to C6F14 in “Brine” circuit between primary and cooling plants to avoid contamination in event of another

failure• Have been running with compromised cooling capacity

• Leaks: in the silicon strip cooling plants– Led to complete refurbishment of silicon-strip cooling plants 2008/9 eliminating leaks in the plants

• Leaks: in the detector. – Grew at ~1kg/day per month in 2010– Extensive leak searches 2009-10. (Breaking some module thermal contacts along the way.)– Found and closed 5 most leaking lines

• Hypothesis that running pressure and particularly ON/OFF transitions were our enemy– 2011: Installed larger bypass valves and variable frequency drives on silicon strip cooling plants to smoothen

ON/OFF transitions.• Low leak rates have persisted through 2011 and 2012, ~1.5kg/day on SS2 circuits.

– No need to close further lines since.

** Report of issues and lessons learned to 2007: http://indico.cern.ch/conferenceDisplay.py?confId=41288


LS1 Tracker cooling improvements• With leaks suppressed we were able to

concentrate efforts on preparations for LS1

• System measurements 2011-12 to compare with requirements– Can only reach -3°C with 45kW load (spec is -

25°C) with nominal load on all cooling plants.

– With only one Si-Strips plant running at a time, -20°C reached with 20kW load. Still not enough!

– Other plants (pixel, preshower, thermal screen) meet requirements

• Pointed to several insufficiencies: – brine flow– brine circuit too warm– brine/primary HEx– brine/Silicon Strip plant HEx

Cooling system requirements

No great surprise after switch to C6F14 in brine circuit and the rapid selection of replacement HEx in 2008.


LS1 Tracker cooling improvements status

• A lot of work completed already:– Selection and procurement of new parts done in 2012:

• HExs, valves, cabling etc. – All mechanical work completed in first months of LS1

• Re-commissioning starting now– Next, validation tests of the system capacity planned

• To follow up with tackling issues with insulation of cooling pipe bundles – As well as better insulation of the cooling plant cabinets


Insulation of the cooling pipe bundles

What is the lowest coolant temperature without condensation on the outside of the cooling pipe bundles?

Aerogel Spaceloft 9251

Typically 2 layers used, 9mm + 6mm, but in some places only one layer possible.


Cooling pipe insulation tests

• In 2007, during pipe installation tests made with -20°C coolant at 16°C cavern temperature.

• +12°C measured on outside of the insulation layers on one bundle

• Cavern dewpoint can go as high as 13°C. – Usually in range -5°C (winter) to 10°C

(summer)

• No margin, especially if we hope to run colder still in future

13C

Note, only one data point, i.e. one bundle


Cooling pipe bundles

• (Only) one full sector pipe bundles (of 10) could be tested – Due to heat-exchanger failure and lack of

time no more measurements were done.

• Cannot test these bundles today (cooling/sealing issues) and still have time to react well inside the CMS LS1 schedule.

• Decided to be proactive and add heating wires onto all the cooling bundles.

Heater wires: E. Focardi, P. Siegrist

Heater wires• Wires running back and forth on

each cooling bundle– With temperature sensors along the

path

• Tests on mockup show that we can gain >10C margin

• 42 wires cover the full set of bundles– FLEXELEC (Lyon)– series resistors type, 20 W/m 60 V DC

• Preparations almost complete– Parts purchased and under test – Installation July and August


Recall: CMS Tracker LS1 Challenge

• We have to improve several areas of the Tracker services to achieve sustainable cold running in future (at least up to LS3):– Cooling– Sealing– Gas flushing– Instrumentation

“Tracker Humidity Improvement Project”

}Even if the cooling had been perfect, we were still blocked…


Tracker (and ECAL [HCAL]) services path inside CMS magnet


CMS inertion seals and flushing

Barrel - Endcap seal (Inflatable)

Gap between Barrel and Endcap flushed with nitrogen when CMS closed, air when open. 55m3/hr total for central detectors

Endcap ‘nose’ seal (silicone tubing)


Humid air penetration inside CMS

CMS cavern air.Dew point ≤ +13C

Hypothesis that humidity is bypassing CMS seals reaching eventually the Tracker bulkhead.

Estimate ~1m2 open behind YB-YE seal via ECAL/HCAL cable channelsAlso openings at ECAL/HCAL patch panels


Impact of humidity in the bulkhead

• The pixel volume is not well isolated from the Tracker bulkhead– Puts limits on the pixel

running temperature

• We have bare copper cooling pipes inside the Tracker bulkhead – not enough space to

insulate inside bulkhead

Volumes definition and dew point specs

28


Global sealing/flushing strategy to lower the dewpoint

(1) Global seal between beam pipe to the cryostate vessel. Must be sealed also when CMS is open.



(2) Stronger flushing of dry air or nitrogen at edge of Tracker bulkhead. Dew point to be kept well below temperatures of the coldest surfaces. Additional 350m3/hr now available


Global sealing/flushing strategy to lower the dewpoint

Sealing inside the vac-tank

K. Gill, Mech. Forum 201331

Install Aluminium tape / vapour barrier foils between neighbouring service channels

Here is shown one sealing set. Need for the two ends: 2 x 2 x 7 = 28 sets between channels 2 x 4 = 8 sets between channels and support rail sections

HCAL access HCAL access Materials to be used: Technonorm vapor barrier foil Aluminium plates Aluminium tape 2-sided (Kapton) tape

These small pieces shall be metallic, to allow to step on

Install vapour barrier foils on the Bulkhead closing panels

Metallic plates to be added here

Sealing: A. Onnela


• Greater gas supply now available from CMS. – ‘Membrane’ plant, purifying nitrogen from the

input air– Much greater dry gas supply to cavern

• 400 m3/hr air or “N2” ([O]~3%) – compared to ~60 m3/hr available previously

– Commissioned in May 2013. • Distribution underground almost complete.

• Additional 36 (copper, then multi-layer plastic pipes) tubes to distribute gas to Tracker bulkhead region– Installation in next 2 months

• Along with new humidity sniffer lines for bulkhead– Flow controls to Tracker bulkhead accessible

outside experimental cavern

Improved dry gas distribution

Dry gas: A. Gaddi, N. Lumb

Testing the sealing concept on mockup

K. Gill, Mech. Forum 201333

1.Dry vs. humid gas flows dictate the humidity inside a given volume.2.Diffusion is a weak mechanism for transporting humidity.3.Sealing is important but does not need to be 100% perfect everywhere inside YB0 A.Onnela


HS-2000, 8 per side; one inside, one outside the closed bulkhead volumeHMX + PT 4 per side; mostly inside the bulkhead volume

Z+

43-0176

43-0188

HS3HS4

HS7HS8

Instrumentation: Present sensors in bulkhead

• Several issues to deal with:– Limited number of

sensors– Results not in

agreement– HS not rad-hard– HMX obsolete

Present sensors: A. Tsirou, P. G. Verdini, P. Petagna


LS1 Instrumentation improvements: Sniffer• New baseline humidity

measurement – 26 Sniffer lines from bulkhead

region to service cavern– Accessible sensors: Vaisala

plus chilled mirrors– System ready for installation

Also a complex system, but all active parts will be accessible.

Sniffer: A. Tsirou, N. Lumb, R. Guida, L. Perrera and co.


LS1 Instrumentation improvements: FOS

• Fibre-optic sensors in Tracker bulkhead– Based on ongoing R&D on Fibre

Bragg Gratings, CERN PH/DT and Napoli

– Dewpoint to be determined by combination of FOS for temperature and humidity measurement

• Calibration ongoing • Aim to put 20 (RH+T) FOS per

side of CMS on 3 fibres Another relatively complex system, the active parts will be inaccessible.

FOS: G. Berruti, P. Petagna


LS1 Instrumentation Improvements: Arduino

• Additional large set of low cost, sacrificial sensors based on ‘Arduino’ product– >130 dewpoint sensors per end to

provide rapid and detailed feedback on the sealing

• Main aim is to validate the other sealing/instrumentation improvements– Not expected to be rad hard

• Untested and may fail quickly once LHC restarts

– Will remain good through LS1 as we gain experience

Arduino: F. Palmonari


Summary: running cold• All ingredients in place to correct past failures and weaknesses,

and bad luck– Main challenge for LS1. Lifetime of the present Tracker depends on a

positive outcome– The tasks of cooling, sealing, flushing and instrumentation were

underestimated previously– A large set of activities to remedy this in LS1, each seemingly relatively

simple, but overall it is a complex exercise with a lot of learning ahead

• LS1 work proceeding well so far– Busy months of installation and test ahead


Looking further forwards

• Tracker upgrades– “Phase 1”: Pixel detector

• ready for installation (E)YETS 2016/17

– “Phase 2”: Outer Tracker and pixel detector

• ready for installation LS3


Strategy for upgraded Tracker services• Up until recently we had intention to re-use

present services at Phase 1 and Phase 2– Even with likely greater need for power, cooling,

and bandwidth we expect that there would be enough capacity

• Thanks to recent advances in 2-phase cooling, front-end DC-DC conversion, optoelectronics

– An enormous effort to plan, prepare install and test the present pipes, cables, fibres

• Services on YB0 interleaved between sub-detectors• Costly, time consuming, with some risk of having similar

problems (e.g. sealing) as for present detector• 20MY and 1MCHF for Tracker fibre cables alone (own

experience)• Up to 100 people working on YB0 concurrently in 2007

– Due to time constraints, phase 1 pixel upgrade has limited options in any case


Pixel Ph1 cooling• Recent decision to use vacuum-

jacketed stainless steel concentric pipe instead of present copper tubes.

• Several advantages:– Natural material of choice given

concern over higher pressures– Optimal design for heat exchange

along transfer line– Full separation of pixel pipes

• Test in advance, Speed up detector replacement, Ability to run at lower T.

• On the other hand:– Cost, limited space for routing on YB0,

Access/schedule

Liquid supply

2 phase return

Insulating vacuum

Insulated junction boxes on YB0, enable installation of prefabricated pieces. Vacuum sections to be connected together with access at edge of YB0

Triax tube 6,12,28 mm ODs


Changing strategy for services on YB0• Good grounds to extend the arguments for putting new services for HL-LHC

Tracker, besides the obvious concern for longevity of parts – Remove constraints on our technology and design choices, as well as increase future

phase space for operational parameters– Remove constraints on detector geometry due to routing of services – Save substantial precious space in CMS for cooling tubes, power cables and optical fibres

• e.g. Optolinks– 50k+ single mode fibres presently installed, matched to edge emitting lasers at 1310nm

• well suited to analogue data transmission of present Tracker– New advances: could profit from availability of links with 10Gbit/s over 100m, using multi-

mode fibre, tuned to emitters at 850nm• Note, difficult to find very rad-hard lasers at 1310nm

– New cable choices are available with denser packing, reducing volume of space taken.

• Decision needed soon, and no going back either way!D. Abbaneo


Conclusion• Present Tracker services have all operated with very high reliability in general since

LHC started, generating very little downtime to CMS. – But, we were unable to run cold so far.

• We have to solve longstanding problems with cooling, sealing, flushing and instrumentation, areas that were underestimated previously.– Our main challenge for LS1

• Have to get this right first time for the upgrades.

• Looking forwards: considering services at P5 for Tracker upgrades– Pixels ‘phase 1’ upgrade: will re-use cables and fibres. whilst profiting from LS1 to install

optimal vacuum-jacketed concentric cooling pipes in LS1 instead of reusing the present copper pipes.

– ‘Phase 2’ Tracker for HL-LHC: We have the capacity for more power, cooling and bandwidth, but it is constraining our choices. Strategy moving towards installing all new services. Decision soon.

CMS Tracker services

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