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icon9.gif  HCAL number of layers and yoke with plug [message #1500] Tue, 10 June 2008 03:30 Go to previous message
lucaci
Messages: 14
Registered: November 2007
Hello,
by default, the HCAL is build with 48 layers. However, in principle, it is possible to increase this number to 64. But this only in principle, since if one tries to increase it, when building the yoke, there is not enough place for building the plug. The error message that you get with:

/Mokka/init/globalModelParameter Hcal_nlayers 49

is:
==========> MOKKA ABORTING <============
Yoke03: Plug thickness negative or thinner then 5 layers of rpc !
Check the geometry! Sorry for abort :(


I've been looking around to see where this comes from. It seems that the z-start of the yoke endcap does not take into account if we increase the HCAL layers or not. It is set in SCoil01.cc to be:

zStartEndcap = z_limit = TPC_Ecal_Hcal_barrel_halfZ + Coil_extra_size + 350 = 4200

In my opinion, this z does not include the HCAL endcaps, which have the same number of layers as the barrel, that is Hcal_nlayers. For whatever reason (probably due to hardcode number of 350), this works for the default 48 layers, but not for more (or for less layers, but thicker).

As a consequence, the plug thickness, which is defined in Yoke03.cc as:

plug_thickness = zStartEndcap - HCAL_z - Hcal_plug_gap

is too thin (not enough for 5 layers).
zStartEndcap is set to 4200 in SCoil00.cc, whereas HCAL_z changes , as it should, with the number of HCAL layers, and Hcal_plug_gap is constant.

Can anybody tell me which is the correct solution for increasing the HCAL layers, such that the Yoke does not crash?

Thank you in advance,
Angela
 
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