A GEM Detector System for an Upgrade of the CMS Muon Endcaps

2. Pressure controllers, pre-distribution system (i.e. between negative and positive endcap) and pump compressor
(Fig. 71) are located in the UGC and therefore accessible anytime;
3. The manifolds for the final gas distribution and the flow meters are mounted in the distribution racks on the
detector.
The GEM gas system will re-use the pressure controllers, the pre-distribution system and the final distribution racks
already available since they were installed as a part of the RPC gas system. The amount of work needed to adapt
the present installation to the new system needs to be evaluated, but it is certainly a clear economical advantage.
The available distribution rack (Fig. 72) has 13 channels that can be used by the GEM detector. Each channel
is equipped with input and output flow-meter and a basic flow regulation system. Table 16 gives an overview of
the modules needed for a closed-loop gas system for the GEM detector. An approximate cost estimate for each
module is also given. The extra-cost due to the new modules needed for a closed-loop gas system with respect to an
open-mode gas system is about 70 kCHF and it will be easily recuperated during the first 6 months of operation. At
the present stage, the Purifier module remains as an option. Dedicated test during R&D and detector construction
phase will indicate if an extra module for O2 and H2O removal is really needed.
CF4 recuperation The CMS experiment will be soon equipped with a CF4 recuperation system. The advantage
of such a system is to allow controlling the N2 concentration in the detector since it is basically impossible to
filter N2 from the gas stream. Future test will be carried out in order to understand if the GEM gas system will
benefit from this plant that presently is under commissioning and, at the moment, it foreseen to be used only by
the CMS-CSC.
Conclusion The CMS-GEM detector will be equipped with a closed loop gas system as the extra-cost needed
for this solution will be easily recuperated during the first sixth months of operation. Table 16 gives an overview
of the price quotation for each module (material and manpower). The GEM gas system will also need two new
stainless-steel pipes from the SGX5 building to the UGC room. The cost for this item is not included in the present
evaluation. Also the piping on the disk needs to be verified if present and/or reusable.
Table 16: Summary of the new and existing modules needed for the CMS-GEM gas system.
Module Location Status Approximate price quotation (kCHF)
Primary supply SGX5 existing module -
Mixer SGX5 New module 30
Chamber pre-distribution system UGC55 existing module Minor modifications
Chamber distribution system UXC55 existing module Minor modifications
Pump UGC55 New module 25
Purifier (optional) SGX5 New module 35
Exhaust SGX5 New module 10
Connection to existing SGX5 existing module To be evaluated
CF4 recuperation plant
7.2 Cooling
This chapter discusses the needs and the foreseen solutions for the GEM cooling system. The GEMs only heat
source is the one dissipated by the electronics mounted on the detector surface. As in many other gaseous detectors,
the temperature of the chamber affects the operation of the GEMs and the optimal working conditions are met when
the chamber volume is kept between 18 and 24 ◦ C. As per design, the uniformity of such temperature shall be better
than ±1 ◦ C over the whole chamber volume. Stability of the temperature shall be kept below 1 ◦ C. For this reason,
the heat dissipated by the electronics shall be conveyed to an active cooling system and the transmission of such
heat to the chamber shall be as much as possible limited. The power dissipation depends on the electronics design
chosen. In case VFAT electronics is implemented, each one of the 72 chambers will dissipate 34W, for a total of
about 2.5kW. In case the GdSP electronics design is adopted, each chamber will dissipate 51W, for a total of about
3.7kW.
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