Requirement:
The support structure should be made of a low radiation length material, so that the average radiation length of the complete device (including cable, connector, cooling) does not exceed 4%.
Justification:
Multiple coulomb scattering affects position and resulution.
Status:
After thorough evaluation of the possible materials we decided to design a Beryllium structure consisting of detector carriers (DC) and adjacent electronics carriers (EC). Two EC and one DC constitute one ladder. In three barrels we have 36 ladders. An alternative to the Beryllium structure would be a Graphite-Epoxy structure. The structure would be thicker which causes problems in determining the angle of incident for tracks. The ladders are held in place by two Beryllium endcaps. The endcap radiation length is also minimized to allow useful data taking in forward rapidities (XTPC, EMC endcap, forward calorimeter).
Requirement:
The support structure has to be removable without breaking vacuum.
Justification:
If the SVT is removed, running should be possible without extended down time.
Status:
The SVT group decided to design a clamp-shell design based on the ALEPH and DELPHI experience.
Requirement:
The structure should be deflection, displacement or sag should be less than the position resolution (below 20 micron)
Justification:
Physics simulations regarding matching efficiency and particle identfication via de/dx.
Status:
Finite element analysis (FEA) of all relevant parts was performed. None of the structural parts of the SVT fails to meet the requirement.
Requirement:
The structure should also host the first stage frontend electronics (FEE).
Justification:
This allows multiplexing on the detector to ease readout and integration, and makes it easier to meet noise and power requirements.
Status:
A hybrid structure was designed and is described in the hybrid system design chapter of this document.
Requirement:
The structure should also host the carrier interface and the HV interface.
Justification:
proper signal readout
Status:
Interfaces were designed and are described in the interface system design chapter of this document.