Thermal Properties of the LHCb VELO Silicon Sensors

This note reports on the thermal measurements performed on the first VELO production modules and on a test module with TPG inserts for improvement of the thermal coupling. The thermal behaviour of the modules and their cooling performance was tested in both dry air and under vacuum operation. The measurements showed that the CO_2 cooling system is able to provide the required operating conditions of the module (< 0 degrees Celsius). Thermal images of the VELO silicon showed a direct relation between the silicon temperature and the temperature sensors on the hybrid. A slight thermal improvement (1.6 degrees Celsius) was found when comparing vacuum operation of the test module with and without inserts.