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Tipp 2014 - Third International Conference on Technology and Instrumentation in Particle Physics Tipp 2014 - Th . . . / Report of Abstracts Cooling for the LHCb Upgrade . . . Abstract ID : 352 Cooling for the LHCb Upgrade Scintillating

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Tipp 2014 - Third International Conference on Technology and Instrumentation in Particle Physics

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Tipp 2014 - Th . . . / Report of Abstracts Cooling for the LHCb Upgrade . . . Abstract ID : 352

Cooling for the LHCb Upgrade Scintillating Fibre Tracker

Abstract content

As part of the LHCb Phase-II upgrade programme, the existing downstream tracking systems will be replaced by a new scintillating fibre tracker read out by multi-channel silicon photomultipliers (SiPM). To ensure high tracking performance over the entire experiment’s lifetime, the SiPMs will be operated at sub-zero temperatures, down to -40oC. This presentation outlines the proposed SiPM cooling system and describes the design considerations which led to the choice of the mono-phase liquid cooling solution. The requirements on the temperature uniformity and stability are discussed, along with the constraints which thermal considerations impose on the mechanical design of the tracker

  • modules. The prospective refrigerants (C6F14 and 3M Novec thermal fluids) are compared

with each other, including their effect on the environment. The SiPM cooling system consists of the remote cooling plant, insulated transfer lines, the local distribution pipework and the cooling structures inside 288 read-out boxes spread over twelve 5x6 m2 tracker planes. The main design challenges of this system are associated with its large extent (about 150 m of linear SiPM arrays to be cooled) and severe constraints on the geometrical envelope and, hense, insulation. Since the SiPM themselves produce very little heat, the estimated heat load of the cooling plant, 13 kW, is dominated by the heat influx through the insulation of read-out boxes, interconnection and transfer lines. Main system design parameters, as well as the latest results of the thermal mock-up tests, are summarised.

Summary

Primary author(s) :

GORBOUNOV, Petr (CERN and ITEP(Moscow))

Co-author(s) :

BLANC, Fred (Ecole Polytechnique Federale de Lausanne (CH))

Presenter(s) :

GORBOUNOV, Petr (CERN and ITEP(Moscow))

Track Classification : Emerging technologies: 4a) Cooling and cryogenics Contribution Type : Oral Comments: For the LHCb Upgrade SciFi Group Submitted by BLANC, Fred on Friday 28 February 2014

May 26, 2014 Page 1

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(SiPM) Cooling for the

LHCb Upgrade SciFi tracker(*)

Presented by Petr GORBOUNOV (CERN, Geneva and ITEP Moscow)

  • n behalf of the LHCb SciFi Tracker group

TIPP 2014, Amsterdam, 2 June 2014 ________________________

(*) SiPM = Silicon Photo-Multiplier(s); SciFi = Scintillating Fibres

  • P. Gorbounov

TIPP 2014, SiPM cooling for SciFi tracker 1

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SciFi Tracker

  • Motivation, design – covered by separate presentations at TIPP 2014:
  • B.Leverington, Experiments & Upgrades Session, 6 June – SciFi tracker, general
  • Z.Xu, Photon Detectors , 4 June – SiPMs
  • M. Deckendorff, Novel Technologies, 4 June – Scintillating Fibres
  • LHCb Tracker Upgrade TDR: CERN/LHCC 2014-001, LHCb TDR 15
  • P. Gorbounov

TIPP 2014, SiPM cooling for SciFi tracker 2

SciFi Tracker – by 2019

~32 mm

ROB: - fibre/photodetector interface (16 SiPMs)

  • SiPM enclosure and cooling structures
  • r/o electronics

r/o Rox (ROB)

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Why SiPM cooling ?

  • Small light yield (≤20 p.e./MIP)
  • decrease with time (fibres ageing)
  • Competing background hit rate: from dark noise
  • 50-100 fold rise by the end of LHC Phase II – due to radiation damage ( 6x1011 neq/cm2)
  • Solution: sub-zero cooling
  • (noise is suppressed by factor ~2/10C)
  • For satisfactory tracking performance after 50 fb-1 , the SiPMs have to operate at

down to -40C

  • The cooling system should permit to vary the SiPM temperature
  • Design challenges:
  • Large system extent (total length of SIPM arrays: ~150 m)
  • Tight space envelope : ΔZ ≤ 70 mm, no “guard” volume is possible
  • Potential condensation and frost formation issues
  • Difficult distribution/manifolding: 288 ROBs, over twelve 5x6 m2 planes, flexible sections
  • P. Gorbounov

TIPP 2014, SiPM cooling for SciFi tracker 3

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Other system requirements

  • Temperature uniformity in : ΔT<1°C per sub-array of four SiPM (~132 mm)
  • common gain and threshold adjustment for all channels in s/array
  • a gradient along the entire SiPM array is tolerable (up to 10°C over 3 m)
  • Temperature stability in time: ±1°C between calibrations (LHC fills?)
  • SiPM gain affects the detection efficiency (should be constant at 98-99%)
  • Can be relaxed for new generation of SiPMs
  • Modularity
  • To match the modular design of the FT: each ROB has its own cooling structure!
  • Safety
  • General LHC standards (flammability, toxicity etc); safe for detectors in case of

failure

  • Environment friendliness: ozone, GWP,…
  • Desirable features: simplicity, flexibility, performance margin, low cost
  • P. Gorbounov

TIPP 2014, SiPM cooling for SciFi tracker 4

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Choice of cooling technology

  • Observations:
  • External heat exchanger (discrete SiPMs, no internal cooling)
  • Expected heat load of O(10 W)/ROB is dominated by parasitic influx through

the insulation, flex PCB and fibres

  • No concerns about material budget (outside of acceptance) and radiation

resistance (~50 Gy, ~1012 neq/cm2 )

  • The cooling options considered at pre-TDR phase:
  • Thermoelectric, with low-temperature heat pipes
  • Chilled air, with local vortex tubes
  • 2-phase evaporative, C3F8, CO2, …?
  • Mono-phase liquid
  • P. Gorbounov

TIPP 2014, SiPM cooling for SciFi tracker 5

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Baseline cooling option

Mono-phase liquid cooling, with serial connection of ROBs in a branch (a branch=6 ROBs, ~3 m ) and low-GWP “Novec 649” refrigerant

+ No compelling reasons to use 2-phase cooling + Established technology, commercial components + Big reserve in cooling power, room for optimization + Probably, the simplest and least expensive option – Low-loss cold transfer lines (~100 + 100 m)

  • Serial connections:
  • “modularity” is slightly compromised, but…
  • pipework and overall system flow rate are reduced ~6-fold
  • optimal balance between ΔT and ΔP – to be further

studied in mock-up tests

  • P. Gorbounov

TIPP 2014, SiPM cooling for SciFi tracker 6 Branches 4 branches/layer 48 branches total

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Inside Read-Out Box (ROB)

  • P. Gorbounov

TIPP 2014, SiPM cooling for SciFi tracker 7

SiPM stiffener (low CTE alloy) SiPM chip

Cooling pipe, Cu, 7x7 mm bore 4 mm (smooth or grooved)

Cooling pipe stiffener In/outlet Thermal interface

11 mm

Refrigerant

7 mm

Flex PCB SiPM carrier SiPM assembly SciFi ribbon Heat Transfer Gap ≈4 mm “cold volume” flushed with dry gas 42-45 mm

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  • Direct heat load measurement

P=Mass flow rate x ΔT(inlet/oulet) x C(Tfluid)

  • ΔT (fluid/SIPM), cooling uniformity, ΔP and ΔT(in/out), external temperature distribution
  • Refrigerant flow optimization (currently, with C6F14)
  • Validation of predictions from CFD simulations
  • Input for engineering designs of the ROB and cooling plant

TIPP 2014, SiPM cooling for SciFi tracker 8

Mock-up = Cooling pipe + insulation + 10 cm of support plate + 4 dummy SiPM sub-arrays with flex cables and calibrated PT1000 sensors instead of SiPMs Chiller: down to -80°C, smooth flow control and monitoring (0-60 g/s for C6F14 and Novec)

  • P. Gorbounov

Single mock-up module under test

Mock-up tests

53 sm

ROB thermal mock-up, with front cover removed

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SLIDE 11

Mock-up tests, single module results

  • In agreement with simulations, at v > 1.0 m/s (>20 g/s), the flow becomes largely turbulent

(Re > 2300, secures a high HTC and small ΔT)

  • “Inlet/outlet effect” … still compatible with 1°C /sub-array requirement
  • ΔP(in-out) and ΔT(out-in) per module agree with simulation: ΔP = 0.2 bar and ΔT ≤ 0.3°C,

at -40°C and 1.5 m/s

  • Thermal load is largely compatible with 10…13 W/module. Measurements with 3…6 serially

connected modules will provide a more accurate estimate

TIPP 2014, SiPM cooling for SciFi tracker 9

  • P. Gorbounov

Preliminary design values: v=1.5 m/s, ΔP≈1.2 bar/branch, thermal load =20 W/module

Distance along the pipe, mm Distance along the pipe, mm ΔT, °C ΔT (SiPM – fluid inlet) vs T fluid ΔT (SiPM – fluid inlet) vs Flow Rate

  • 40°C
  • 20°C

0°C Flow, g/s v, m/s ΔT, °C

  • Theor. Re and ΔP(branch)

vs fluid velocity Velocity, m/s

Novec 649, ID 4 mm tube

laminar …………… turbulent

V= 1.5 m/s

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TIPP 2014, SiPM cooling for SciFi tracker 10

  • P. Gorbounov

IR images of the module, at Tfluid = -50°C (Troom = 23°C)

With extra

  • uter

Rohacell insulation sheets Front side Outlet edge No outer insulation (bare Alu sheets

Conclusions

  • Outer Alu heat spreader is effective, the surface T is well above dew point (≈10°C in cavern)
  • Extra outer insulation gives 10-15% reduction in heat load
  • Expected cold spots: module edges and lids having no internal insulation

~17.7°C ~17.5°C Back side Front side

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  • P. Gorbounov

TIPP 2014, SiPM cooling for SciFi tracker 11

Conceptual system design

Main cooling system design specifications (see TDR for more details):

  • Industrial chiller: cooling power ≥13 kW at -55°C, working T(fluid) ≤ -50°C
  • Refrigerant mass: 330 kg (~210 l at +40°C)
  • Pump: ΔP ≥ 3 bar, flow rate ≥ 3.3 m3/h
  • Transfer lines: ΔT = O(1°C), each way
  • Estimated cost (infrastructure only): 290-350 kCHF
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Refrigerant

  • Baseline choice: 3MTM NOVEC 649 thermal management fluid
  • fluoro-ketone, C6F12O
  • thermophysical properties similar to C6F14
  • volatile, dielectric, low viscosity
  • inflammable
  • low toxicity (widely used as a clean fire extinguishing agent in occupied

spaces, e.g. data centers)

  • GWP=1
  • Reactive with liquid water (not important for our application)
  • 3M positions Novec fluids as a replacement for pFC
  • Backup: C6F14 (3MTM FC-72)
  • very well studied, used in 13 LHC systems
  • deprecated, GWP=7400
  • P. Gorbounov

TIPP 2014, SiPM cooling for SciFi tracker 12

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Summary

  • Cooled SiPMs, in ~0.53 m arrays, T down to -40°C, combined L≈150 m
  • Mono-phase liquid cooling system, use of environment-friendly refrigerants
  • Design cooling power ~13 kW, dominated by heat leaks
  • Thermal mock-up tests (ongoing): general agreement with simulation
  • Issues to be further investigated:
  • NOVEC 649 validation
  • ROB edge insulation
  • Effect of warm electronics
  • Vapour barriers
  • Low-loss (flexible) interconnections
  • P. Gorbounov

TIPP 2014, SiPM cooling for SciFi tracker 13

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Backup slides

TIPP 2014, SiPM cooling for SciFi tracker 14

  • P. Gorbounov
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  • P. Gorbounov

TIPP 2014, SiPM cooling for SciFi tracker 15

SiPM details (see also Zhirui Xu’s talk)

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Why not “2-phase” (vapor compression)?

  • P. Gorbounov

TIPP 2014, SiPM cooling for SciFi tracker 16

Property Mono-phase Vapor compression

Well-tested, experience at CERN Yes Yes Temperature uniformity 4-5K / branch <1K / branch Refrigerant mass @ detector Heavy (C6F14) Light (C2F6, half-vapour) System pressure Low (2 – 4 bar max) High (>30 bar) Reversibility (cooling-heating) Yes No Thermal inertia Slow, easy to control Fast, more difficult to control Transfer lines Cold Warm (Inter-)connections at detector Cold Warm (in) / Cold (inter, out)

Local equipment, apart from cooling pipes (per branch)

Only on-off valves On-off, capillaries, HEX Cooling plant equipment Commercial chiller + pump Oil-free compressor, condenser Sensitivity to refrigerant choice Low Refrigerant is pre-defined Estimated infrastructure cost 290-350 kHF 300 KCHF + manifolding, capillaries, HEX = >400 CHF

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Cooling pipe fixation

  • Two basic designs for cooling pipe fixation (“vertical”≈ TDR and “horizontal”)
  • “Horizontal” design is better adopted for serial modules interconnection and

servicing SiPMs, potentially permits to decouple the cooling and SiPM structures

TIPP 2014, SiPM cooling for SciFi tracker 17

Vertical inlet/outlet

(“TDR design”)

SiPM assembly Fibre mat Pressing & retention force Cooling pipe with stiffener Spring-loaded plunger with a ball tip Retention force Horizontal inlet/outlet pipe is better positioned; can use thermal grease Thermal bridge SiPM s/modules can be removed without dismounting the pipe

  • P. Gorbounov
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Flow regime with round ID=4 mm pipe

  • P. Gorbounov

TIPP 2014, SiPM cooling for SciFi tracker 18

  • Pipe dimensions: 4 mm i.d. (round)
  • Refrigerant temperature: -50°C
  • Cooling load per module: 10 W
  • Fluid: NOVEC 649
  • Density: 1.7-2.9T(°C) g/cm3 (~1.8 at -50°C)
  • Viscosity: ~1.3 cSt, Thermal conductivity: ~0.075 W/mK (both at -50°C)

Velocity [ m s-1] Re [ -] ΔTw all-ref [ K] HTC [ W m -2 K-1] ΔT refout-in ( 6 m odules) [ K] Δp ( 6 m od & bends) [ bar] Flow Rate ( all system ) [ m 3h-1] 0.25 655 10.9 129 9.7 0.06 0.5 0.50 1310 8.6 178 4.8 0.14 1.1 1 2600 3.2 477 2.4 0.5 2.2 1.5 4000 1.6 937 1.6 1.1 3.3

  • Laminar flow (Re < 2300, v < 0.9 m s-1) is to be avoided;
  • Re ~ 3000 (v ~ 1.15 m s-1) could be risky: turbulent flow may not be achieved;
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CFD simulation

  • Simulation: joint project with

CERN EN-CV: “CFD studies for SiPM cooling”

  • Different module geometries

and heat transfer options

  • Heat load: < 10 W per ROB,

excluding connections

  • P. Gorbounov

TIPP 2014, SiPM cooling for SciFi tracker 19 CFD simulation for liquid cooling option

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  • P. Gorbounov

TIPP 2014, SiPM cooling for SciFi tracker 20 Calibrated PT1000 sensors Dummy flex PCB, with correct amount

  • f copper

Dummy SiPM sub-array with T-sensors at Si dye level SiPM assembly: ROHACELL insulation Heat exchanger (“cooling pipe”) Pressing bar

PT1000s