The ATLAS Inner Tracker (ITk) is the phase-II upgrade of the current ATLAS tracking detector, meant to meet the challenges at the high-luminosity LHC.
The forward regions of the ITk silicon strip tracker (the "end-caps") will consist of six disks populated with wedge-shaped silicon micro-strip sensors, divided in "module" units containing the readout, power and control electronics.
The modules are directly glued on likewise wedge-shaped local support structures called petal cores, consisting of carbon fiber-based sandwich structures with embedded titanium cooling pipes as well as data and power buses. These support structures with 18 sensor modules in six different shapes glued on it are called petal. Each end-cap disk will be constituted of 32 petals.
The petal core structure provides mechanical stability for the glued on sensor modules while minimizing the amount of material. Evaporative CO2 cooling is used to allow for cooling of the sensors as well as the readout electronics.
A number of prototype petal cores have been constructed at DESY and IFIC. A variant of the process has been industrialised and additional prototypes have been produced to test the alternative to the baseline design. In addition, a thermo-mechanical petal prototype, fully loaded with dummy silicon modules emulating the heat sources of the real petals with the same geometry.
A whole set of measurements has been performed on these objects to validate the petal design. This extensive prototype testing consists of measurements to address their mechanical stability (e.g. bending and vibration tests), their thermo-mechanical behaviour using dual-phase CO2 cooling (e.g. infrared thermography) and their material properties (e.g. material budget measurements).
The experimental results have also been used to validate existing thermo-mechanical FEA simulations. The aim of this process is to validate a petal design as well as planning of QA and QC concepts for production.