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

Sensor, silicon pixels(30 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).

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

a) 150m thicknessb) 300m thickness

Benefits:• Uniform temperature distribution in the area to be cooled• Small T 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 ~30 x 60mm• channel length ~40mm • channel cross section 50m x

50m• separation walls 25m 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

Open points for the prototype:•Thermal connection of the readout chip to the cooling plate •Total pressure in the channels

area to be cooled

Inlet manifold

Outlet manifold

silicon plate

silicon cover wh

Ll

hwLl

channel heightchannel widthhydraulic channel lenghtthermodynamic channel lenght

Production priciples• Micro channels etched in thin wafer• Cover wafer is bonded to channels• Cover contains holes for inlet and

outlet• Cover wafer will be thined by

etching in the critical beam area

C6F14 cooling liquid of choice

C6F14 @ -20°C H2O @ +20°C

Density kg/m3] 1785 998

Viscosity [10-7 m2/s] 8.2 10

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

Thermal conductivity [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• C3F8 is an option in case of to high pressure in the cooling plate for C6F14

Fluid temperature difference

Tf Tf

12bar pressure drop 2bar pressure drop

Temperature difference between inlet and outlet for channels of 50m x 50m

CFD model – boundary conditionsCooling platefixed temperature at the backside

Readout chip2 W/cm2, 12 x 20 mm

Sensor, silicon pixels30 x 60 mm

• all remaining walls are considered adiabatic, since the GTK will operate in vacuum

• heat source is the volume of the readout chip

Temperature distribution =70W/mK

Heat transfer coefficient between chips and cooling plate of =70W/mK, for a material thickness of 25 m

Temperature distribution =7W/mK

Heat transfer coefficient between chips and cooling plate of =7W/mK, for a material thickness of 25 m

Temperature distribution =0.7W/mK

Heat transfer coefficient between chips and cooling plate of =0.7W/mK, for a material thickness of 25 m

Plans for the next monthsSeptember:

• production of a prototype at the EPFL clean room • preparation teststand (cooling unit, instrumention …)• design of connecting component• further development of the 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!!!