development of micro-pattern gaseous detectors – gem - LMU

4
Triple GEM detectors
(100 x 100 mm²)
Figure 6: Schematic of the H8 beam setup with prototype of 15 mm drift tubes and reference chambers. A
tracking system by triple GEM detectors replacing the reference chambers is proposed.
new tracking system of four 10 × 10 cm 2 GEM detectors with a spatial resolution of approximately
50 µm. This is one motivation of this thesis.
With the implementation of the micro-pattern gaseous detectors developed in this thesis the problem
of space charge effects can be strongly reduced.
The present thesis deals with the construction of triple GEM detectors with active areas of
10 × 10 cm 2 . Principle, manufacturing and operation of the GEM foil are explained in Ch. 2.
The construction of a triple GEM ”prototype 1.0” with an unsegmented as well as with a five-fold
segmented copper anode is documented in Ch. 3. The description includes the monitoring of the HV
supply and the Ar/CO2 gas mixture at a ratio of 93/7.
Analog signals are recorded using a charge sensitive preamplifier followed by a 1 GHz flash ADC.
The analysis is based on an inverse Fermi-fit to the signals generated by cosmic muons or 5.90 keV
X-rays from a 55 Fe source.
After optimization of the voltage differences across the GEM foils or across the drift gap and induction
gap 18% FWHM energy resolution of the 5.90 keV Kα line is observed.
The energy resolution at the outer regions of the active area is 10% to 20% better compared to the
central source location indicating deformations of the GEM foils as discussed in Ch. 4.2.
Ch. 4.3 treats the analysis of cosmic muon signals. It is shown that the measured energy loss corresponds
to a Landau-like distribution. The mean energy loss agrees with the theoretical estimate
within 8% deviation.
Studies on the pulse height as a function of the induction field are presented in Ch. 4.4. An almost
linearly increase in the observed field range from 0.05kV/cm to 2.33kV/cm is measured as expected
by the charge transfer processes in a GEM detector.
Pulse height variations in dependence of the size of the readout plane are investigated using a fivefold
segmented anode. In Ch. 4.5 the pulse height is increasing at smaller size of the readout strips.
An explanation correlating the increasing signal with decreasing capacity describes data, but further
investigation is necessary for complete understanding.
The muon detection efficiencies are reported in Ch. 5. The implementation of stable gas flow and
pressure leads to an efficiency over 95%. Variations of the temperature are observed to worsen the