development of micro-pattern gaseous detectors – gem - LMU

32 Chapter 3 The Triple GEM Prototype 1.0
3.3.2 Gas Supply System
In the test stand assembly, a pre-mixed gas at a ratio of 93/7 is supplied to the detector via 3 mm
thick gas feeds. Two gas inlets are placed centrally with respect to the active detector area as can
be seen in Fig. 3.7, showing the whole detector setup. First measurements were done using the
pressure regulator on the gas bottle and a needle valve for pressure control. To guarantee more stable
operation conditions for further measurements, a flow and pressure control unit was implemented
between the detector and the gas supply, as can been seen in Fig. 3.8.
detector housing
Al Faraday Cage
gas exit
triggersystem
(scintillators)
HV : separate supply
for each electrode
active area
gas inlet
signal line
Figure 3.7: Top view of the closed prototype 1.0 triple GEM detector with connections to HV supply, gas
system and readout electronics. Trigger units are positioned above and beneath.
The mass flow controller (BROOKS 5850S), installed in the gas line between bottle and detector, is
adjusted to a constant gas flow of 0.900ln/h, which is implemented with the flow computer WMR
4000. A (MKS Baratron R○) is used to monitor the pressure at the exit line. In case the pressure
deviates from the nominal value, an electronically controlled regulation valve corrects for it. It was
found that, due to internal problems of the pressure control unit, the pressure could be stabilized only
in the range of ±10 mbar. It was decided to regulate the detector’s pressure to a mean value of 1020
mbar, keeping it independent of atmospheric influences.