  Silicon trackers at the SLHC will suffer high radiation damage from particles
produced during the collisions, which leads to high leakage currents. Reducing
these currents in the sensors requires efficient cooling to -30 C. The large
heat of evaporation of CO2 and the low viscosity allows for a two-phase cooling
system with thin and long cooling pipes, because the small flow of liquid
needed leads to negligible temperature drops. In order to reduce the material
budget a system is proposed in which a large scale tracker requiring ca. 50 kW
of power is powered via 1-2 mm diameter aluminum cooling pipes with a length of
several m. These long cooling pipes allow to have all service connections
outside the tracking volume, thus reducing the material budget significantly.
The whole system is designed to have negligible thermal stresses. A CO2 blow
system has been designed and first tests show the feasibility of a barrel
detector with long ladders and disks at small radii leading to an optimized
design with respect to material budget and simplicity in construction.
