Draft: Update the VP modules geometry and materials

cc @tlatham

This merge request consists of improvements of the VP modules in DetDesc, with an equivalent merge request for DD4Hep in lhcb/Detector!406.

Both the changes here in DetDesc and in the DD4hep branch have been checked for overlaps and the geometry trees have been compared between DetDesc and DD4hep. The total mass of the VP module+supports is now within 0.5g of the measured mass.


  • Low-voltage cables are added to the modules support structure
  • The low-voltage transition PCB is added to the support
  • The HV wires and data interconnect cables are added (the same boxes as the LV cables, with appropraite density)
  • Mass for the copper plugs for the LV cables at the foot is added
  • VCR connectors added to the delivery pipes


  • The support foot is re-worked, in part to allow for the copper plug mass to be added in the correct location
  • The cooling clamp is removed (low mass and difficult to work in the LV cables with many overlaps)
  • Corrected lengths of the delivery pipes
  • Changed some parameterisation to ensure the braze sockets are located in the correct place
  • Some material editing to make sure masses are consistent with the measured mass of the modules
  • Some smaller corrections to fix overlaps in various parts of the modules

DD4hep Raditation length scans

Click to expand Below are some scans of the radiation length (as a percent of the material travelled through i.e. radiation length / thickness) of two modules to compare the changes proposed in this MR. Note that I could onl get the scans working with DD4hep! The scan of the "new" modules should be identical to the DD4hep ones, however the scan of the "old" module is not quite the same in DD4hep and DetDesc.

The scans were performed in 500 bins between x = -150mm to x = +150mm, 500 bins between y = -80mm to +80mm and from z = 290mm to z = 340mm i.e. modules 38 and 39. The RF foil has been ignored in these scans to make the module differences clearer. rad_scan_oldGeom_xy_noFoil


There is also a scan that is the difference between this MR and what is currently in master to show the changes. The difference as a result of the LV harness is clearly visible. However, the differences due to the GBTX hybrid thickness and the coolant delivery pipes is DD4hep specific and should be ignored in the DetDesc context. rad_scan_diff_xy_noFoil

Edited by Matthew David Monk

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