development of micro-pattern gaseous detectors – gem - LMU

88 Chapter 9 Summary and Outlook
stable flow and pressure conditions in the detector. In this way efficiencies of εcorr > 95% could be
achieved. Furthermore, an influence of the temperature could be observed by cooling the detector
which results in a decrease of εcorr. Monitoring the temperature additionally to flow and pressure
control is thus recommended.
The triple GEM detector presented in this work is filled with Ar/CO2 in the ratio 93/7 and provides
an effective gain Ge f f = 10 4 . The applicable potential difference ∆UGEM is limited to approximately
350 V due to frequent discharges of O(discharge) ≈ 1min −1 at higher values.
The most stable working point of the triple GEM prototype 1.0 is:
Eind = 1.25 kV
for the electric fields in the gap regions and
cm , Etrans1,2 = Eind = 2.00 kV
cm
∆UGEM1 = 320 V, ∆UGEM2 = 340 V and ∆UGEM3 = 360 V at the GEM foils, respectively. With this
setup a stable operation of the detector in long term overnight-measurements is ensured.
Furthermore, the signal rise time was analyzed as a function of electric field in the induction gap,
Eind. In preparation for this analysis a GARFIELD / MAGBOLTZ simulation was implemented to
study the electron drift time in the drift region of the detector depending on the electric field. It was
found that the rise time by X-ray generated signals follows the drift time of electrons in the 3 mm
induction gap. This could be observed for 55Fe measurements in the range 0.1 kV
cm ≤ Eind ≤ 2.3 kV
cm as
well as for cosmic muons in the range 0.8 kV
cm ≤ Eind ≤ 2.0 kV
cm . This leads to the conclusion that the
signals in the triple GEM detector are dominated by electrons and not by ion induced pulses.
A prototype 2.0 with highly segmented strip anode is meanwhile realized. The active area of the
anode is divided in 150µm thick copper strips with 250µm pitch. In cooperation with the TU Munich
(E18) and HISKP Bonn a readout system is designed based on APV25 frontend modules. A first
prototype 2.0 setup including the APV readout is probably available in early 2011.
A complete readout system based on the GASSIPLEX frontend modules is implemented and data
are taken just now. Mounted in a table top tracking station, a first sample of 1083 muon events is
recorded. 90.6% of all tracks are considered for the fit that provides 79 ± 5µm spatial resolution of
the triple GEM detector.
In combination with MICROMEGAS detectors developed simultaneously to this work this setup
promises to be reliable for track reconstruction of cosmic muons with high resolution. Tests of the
triple GEM detectors’ tracking capability of 140 GeV muons at the H8 beam line at CERN and their
position accuracy of cosmic muon detection at increased background of gammas or neutrons are
foreseen.