LHCb is a flavour physics detector at the LHC, designed to detect decays of
b- and c-hadrons for the study of CP violation and rare decays. At the end
of Run-II the experiment will implement a major upgrade. The hardware
trigger will be removed and the entire experiment will operate at 40 MHz.
The Vertex Locator (VELO) is the silicon detector surrounding the
interaction region, responsible for reconstructing the primary collision
points and secondary decay vertices of long-lived particles. It will be
replaced with a new light weight pixel detector equipped with electronics
capable of providing 40 MHz readout.
The upgraded VELO modules will each host 4 silicon hybrid pixel tiles, each
read out by 3 VeloPix ASICs with a total power consumption of up to
30 W. The tiles will be subjected to significant
radiation damage and an efficient lightweight cooling solution is essential
to control reverse annealing in the silicon sensors. The solution adopted
is to mount the tiles on a cooling substrate composed of thin silicon plates
with embedded micro-channels that allow the circulation of evaporative
CO$_2$. This solution is highly efficient, has low and uniform mass, and is
radiation hard. Specific R/&D has resulted in a design which gives the
correct pressure-flow performance and allows the attachement of the
connector to the cooling substrate. The design has undergone robustness and
stability tests guaranteeing that the system level performance will function
correctly. The microchannels are currently in production and the cooling
status will be described.