Modules Cooling

for the Atlas Silicon Tracker barrel
at the Geneva University

A) Initial feasibility cooling studies using single phase liquid cooling in under-pressure mode (1996)

The cooling of the detectors and of the associated electronics is provided by a coolant in an alluminium tube. The cooling system consists of parallel alluminium tubes, one per module row, running along the z-direction of the barrel. A leakless cooling sistem is adopted, in which the fluid is below atmospheric pressure. A mixture of water and Glycol or water and Methanol is used.

Since the coefficient of thermal expension (CTE) of alluminium does not match that of the barrel structure, the tube is allowed to slide in order to avoid mechanical stress to be trasmitted on the structure. This is possible with a silicone compound joint between the cooling pipe and the modules.

In order to reduce the temperature gradient of the coolant, and to have a large and simple thermal contact area to the module, the tube is oval. The inner dimensions are 1.5 x 8.75 mm² and the wall thickness is 0.25 mm.

All thermal measurements are performed in a large freezer, 1.78m long, operating at nominally -10^oC air temperature. The aluminium pipe is equipped for measurements of the input and output liquid pressure and flow. Temperature measurements are performed with platinium resistors, PT100 (100 Ohm at 0^oC); the temperature dependent voltage is measured with a ADC in a MacIntosh.

Various thermal modules were built for thermal and metrology measurements. The modules have heater blankets to simulate the heat generated by the detectors, 1W per module, and chip resistors to simulate the heat from the electronics, 4W per module.

Z-module design:
- Thirteen simple modules were built with Aluminium plates, the thickness of which was designed to match the thermal conductivity of the silicon detectors and of the BeO Z-modules fan-in. The modules were built to test the reproducibility of the cooling joints.
- One module was built with fan-ins and boards made of Al₂O₃ and with the radiator in AIN. The module was built to test the assembly method and to perform initial thermal measurements.
- One module was built with fan-ins, boards and radiators made from AIN (CTE=3 x 10 ^-6 /^oC, close to that of Silicon)

Center-tap module design:
- One TPG module was built with a core of the high thermal conductivity TPG TC1050. See here a figure .

A two-module setup was built to perform initial thermal measurements using one or two modules. It consists of a small carbon sandwich plate with inserts, that support brachets for the mounting of modules on the barrel. It was mostly used for the TPG module.

A full length prototype was built with a large carbon fiber sandwich plate. It was equiped with 13 + 4 simple aluminium modules (figure). Tests of the reproducibility of the silicone compound joint were made, showing that within 0.4 degree, it is reproductible.