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BIC: Power Budget Estimation and Cooling Design Strategy

Mechanics and Integration: Barrel Imaging Calorimeter

Wouter Deconinck

University of Manitoba

on behalf of the BIC DSC

Mechanics and Integration

January 21, 2026

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ePIC Collaboration Meeting�January 20-23, 2026

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Most Significant Sources of Heat in BIC

AstroPix, End-of-Tray Cards (ETC), SiPM services, CALOROC

AstroPix sensors:

  • 2cm by 2cm chips at < 2mW / cm2 < 8 mW / chip heat dissipation
  • 4 instrumented trays ✕ 6 staves ✕ 218 chips = 5,232 chips / sector
  • Total of 42 W / sector, or 2 kW for entire BIC (48 sectors)

End-of-Sector Boxes (ESB), 96 ESBs total:

  • AstroPix End-of-Tray Cards (ETC):
  • 4 instrumented trays ✕ 1 ETC / tray / side, at 1W / ETC (FPGA)
  • Total of 4 W / ESB, or 384 W for entire BIC
  • SiPM services:
  • Scales per SiPMs, with 0.2 W / SiPM avg based on GlueX experience
  • Total of 12 W / ESB, 1.2 kW for entire BIC
  • CALOROC boards:
  • 1 CALOROC / side, at 8 W / CALOROC
  • Total of 8 W / ESB, or 768 W for entire BIC
  • Total of 24 W / ESB, or 2.3 kW for entire BIC (96 ESBs)

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Overall Heat Evacuation Strategy

Combination of conduction radially outwards, active cooling of ESBs

AstroPix sensors: passive cooling strategy

  • Large total heat load but small heat density and large conductive area radially
  • Thermal simulations indicate heat evacuation radially outwards through tray walls and through Pb/ScFi layers to 1” thick Aluminum plate is sufficient
  • Aluminum plate cooled from the back with room temperature cooling water

End-of-Sector Boxes: active cooling strategy

  • Higher heat density requires cooling with chilled water loop
  • Relative temperature stabilization of SiPMs to 7°C in each ESB with thermal mass of 0.5” Aluminum cold plate with embedded cooling loop (5°C water)
  • Metal-core PCB (1.7 mm) assumed for additional temperature stabilization and homogenization

The ESBs (and hence indirectly the AstorPix layers) will be slow flushed with nitrogen to prevent condensation.

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Cooling of AstroPix

All heat removal from AstroPix layers is transverse

Heat from AstroPix sensor is conducted through carbon fiber tray walls:

  • thin but long → surface area sufficient
  • heat conductivity of Carbon Fiber is�assumed to be identical to Aluminum

Temperature at inner layers is O(0.5°C)�above ambient (18°C cooling on outer Al�plate assumed; no cooling of inner plate�expected)

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ΔT<0.4°C

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Cooling of AstroPix

All heat removal from AstroPix layers is transverse

Heat from AstroPix sensor is conducted through carbon fiber tray walls:

  • Updated studies ongoing with�only only outer cooling, which�increases the ΔT to 1.4°C (for�4 layers and CF = Al k-factor)
  • Well within AstroPix tolerance

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Motivation of the ESB Cooling System

  • Required temperature stability of 7°C ±1°C, based on GlueX experience, to control both DCR (MIP detection) and gain (energy resolution).
  • Passive Bias Temperature Compensation (GlueX: 0.1 V bin SiPMs using Hamamatsu Vop data, jump-trim resistors) provides ~34 mV/°C correction to maintain SiPM gain within 5%

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SiPM noise and gain are a strong function of temperature!

*Operations in GlueX at 7°C for S10931-050 SiPMs

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Cooling of SiPMs

  • Factor of 2 difference in dark count rate between 5°C and 20°C
  • For BIC SiPMs at 1E9 1 MeV neq dose (~1 year at max. luminosity):
    • Pedestal 𝜎 of 2.1 p.e. @ 5°C vs. 3.3 p.e. @ 20°C
  • For the worst-case 8 p.e. MIP, noise rate is too high at 20°C to readout MIPs after a few years of running
  • Operating temperature chosen to enable MIP calibration well into EIC running

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SiPM noise is a strong function of temperature!

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Cooling of SiPMs

Aluminum cold plate, PCBs on both sides:

  • Side 1: ESB PCB with SiPMs
  • Side 2: CALOROC and AstroPix ETCs

Design dimensions:

  • Cu cooling lines ¼” OD
  • Aluminum cold plate thickness ½”

Production considerations:

  • clamped halves with ball milled channels
  • countersunk bolts around cooling lines
  • thermal interface materials to PCB boards
  • metal-core PCBs under consideration

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End-of-sector water-cooled cold plate

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Cooling of SiPMs

End-of-sector water-cooled cold plate: alternative designs

Aluminum cold plate, PCBs on both sides:

  • Side 1: ESB PCB with SiPMs
  • Side 2: CALOROC and AstroPix ETCs

Full cold plate design (based on experience�in fabrication of original design):

  • number of components and their�alignment proves challenging�(stress on metal-core PCB)
  • single cold plate with continuous�milled channel has some issues�fitting the bent pipe at corners

Long-drilled channel design which avoid�labor-intensive pipe bending operations

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Cooling of SiPMs

Cold plate, double-sided cooling:

  • Side 1: ESB PCB with SiPMs
  • Side 2: CALOROC and AstroPix ETC

Boundary conditions for CFD:

  • Water inlet temperature: 5°C
  • Volumetric flow rate: 0.3 gal/min�(negative pressure coolant)
  • Heat flux per SiPM: 0.046 W/cm²
  • Total power from CALOROC: 5 W
  • ESB metal core; CALOROC FR4

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End-of-sector water-cooled cold plate

Side 1

Side 2

Simulation shows ΔT ~0.5 °C at the SiPM side and a peak of ~3 °C at the CALOROC side.

*7°C chilled water anticipated

(see pre-brief)

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Cooling of SiPMs

End-of-sector water-cooled cold plate: CALOROC as metal core PCB

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  • reduction from 3.1°C over coolant to 0.2°C over significant thermal benefit variation of SiPM temps at the 0.2°C level
  • CALOROC board: FR4 PCB → metal-core PCB under consideration

Side 2

Side 1

Side 2

Side 1

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Cooling of SiPMs

End-of-sector water-cooled cold plate: Engineering first article

Ongoing: development and construction of PCB (thermal) test articles for validation of CFD calculations

  • resistive element array distributed at locations of SiPMs
  • no dedicated CALOROC thermal test articles
  • production of single (double-sided) cold plate
  • thermal diodes for temperature measurements

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BCAL-GlueX