NA62 Gigatracker cooling requirements

• Gigatracker (GTK) modules will operate in vacuum and under high radiation• Module has to be replaced on a regular basis• Cooling system required to avoid performance loss • The operation temperature for the frontend electronics will be 5°C or lower • Low material budget for the cooling system

Gigatracker Module

Cooling plate

Readout chip(12.5 x 20 mm), heat production ca. 3.2W per chip (2 W/cm2)

Sensor, silicon pixels(27 x 60 mm)

3D schematic drawing of the GTK module

support and alignement structure

beam direction

Component Material Thickness [μm] X0 [%]

Sensor Si 200 0.21

Bump Bonds Pb-Sn ~25 0.001

Readout Chip Si 100 0.11

Cooling Plate Si ~150 ~0.15

Sum ~0.47

Materials in the sensor areaThe total material budget (material in the beam) allowed for the GTK module is 0.5% X0(radiation length).

Cooling systems under investigation

• carbon plate, conductive cooling• convective cooling in a vessel• micro channels

Our proposal: Microchannel coolingGoals of development:1. Integration of micro channels into frontend electronics2. Cooling via an separate cooling plate with micro channels

a) 150mm thicknessb) 300mm thickness

Benefits:• Uniform temperature distribution in the area to be cooled• Small DT between coolant and readout chip => reduced thermal stress• Single-phase and two-phase cooling possible• Technology studied at EPFL with strong support of industrial partners• Mutual understanding to share knowledge (EPFL <> CERN)

Specifity of our application:• Very low material budget• Low heat flux

Tentative layout of micro channels for the Gigatracker

• area to be cooled ~40 x 60mm• channel length ~40mm • channel cross section 50mm x

50mm• separation walls 25mm thick• heat flux in the cooling region

2W/cm2 • Support and Connection of

services outside the sensor area and on one side

• Single-phase cooling

area to be cooled

Manifold

Open points for the prototype:• U-shaped channels or single line channels (pressure loss <> mass flow needed)• Thermal connection of the readout chip to the cooling plate

C6F14 cooling liquid of choice

C6F14 @ -20°C H2O @ +20°C

Density r [kg/m3] 1785 998

Viscosity n [10-7 m2/s] 8.2 10

Heat capacity cp [J/(kg K)] 976 4183

Thermal conductivity l [10-2 W/(m K)] 6.2 60

• radiation hard• thermally and chemically stable• nonflammable, nontoxic, nonconducting• known and used at CERN (CMS and Atlas Tracker)• used in liquid phase

More people for the GTK cooling1. Paolo Petagna, CERN PH-DT-PO, DT cooling Project Leader2. Alessandro Mapelli, EPFL Mircrosystems Laboratory, Microfabrication

technologies3. Piet Wertelaers, CERN PH-DT-PO, Consultant for design and layout of

cooling circuit4. Jerôme Daguin, PH-DT, Experience in C6F14 plants at CERN

Plans for the next monthsAugust/September:

• first layout for the micro channels• production of a prototype at the EPFL clean room • preparation teststand (cooling unit, instrumention …)• design of connecting component• development of a CFD-Model

Oktober/November:

• commissioning teststand• first test at room temperature• preparation of test at cold temperature, cryostat• assembly prototype and mockup chips

Thermal interface to be designed according to chip design and fabrication!!!