development of micro-pattern gaseous detectors – gem - LMU

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68 Chapter 6 Rise Time Studies 2 ns > 10 ns Channel 1) Preamplifier response to 2ns pulse Channel 4) Scintillator pulse exiting differentiating circuit Figure 6.7: Response of the CASTA82 preamplifier to a δ - shaped pulse of 2 ns width. for the CATSA82 preamplifier and 2 ns 10 ns Channel 1) Preamplifier response to 2ns pulse Channel 4) Scintillator pulse exiting differentiating circuit Figure 6.8: Response of the ELab preamplifier to a δ - shaped pulse of 2 ns width. τ = R · Ccoupl = 2.5Ω · 1.5 nF = 3.75 ns (6.3) regarding the ELab preamplifier. This estimation shows that the ELab preamplifiers rise time is negligible whereas the big coupling capacity of the CATSA82 preamplifier affects the rise time distribution significantly. In order to analyze the internal response time of the preamplifiers a δ-like pulse of 2 ns width and 10 mV maximum pulse height is fed to the input. Since the trigger scintillators provide a frequent signal we can use this as a pulse generator. Combined with a discriminator and dual timer as already used in the conventional readout, see Ch. 3.4.1, the resulting box-shaped pulse is fed to a differentiating circuit. This setup supplies the narrow pulse which can be seen in Fig. 6.7 and Fig. 6.8 together with the response of the two preamplifiers. In this manner the internal rise time of the preamplifiers is determined to approximately 10 ns for both (see channels no. 1 in the corresponding Fig. 6.7 and 6.8). The differentiating circuit transfers the scintillator pulse to a sharp negative pulse followed by a smaller overshoot that is repeated around 14 ns after the main pulse. The overshoot with 2 ns delay after the main pulse is not resolved by the preamplifiers. A plateau of the rise time is reached in 10 ns after the main pulse. The second small positive pulse of the test signal gives a second rise to the preamplifier response. The CATSA82 preamplifier shows a slightly faster response to the δ - shaped pulse than the ELab preamplifier whose amplitude is 50% higher, in contrast. This rise time is negligible in comparison to the 100 ns electron drift time and the 55 Fe induced rise times around 106 or 166 ns. 6.2 Rise Time Dependence on Induction - Field In order to understand the signal rise time formation, data were taken in dependence of the E-field on the induction gap with the X-ray source as well as with cosmic ray muons. This is motivated by the estimate that the detectable pulse begins with the presence of the amplified charges at the lower
6.2. Rise Time Dependence on Induction - Field 69 electrode of the undermost foil GEM1 resulting in an induced pulse on the anode. For these measurements the data was supplied to the flash ADC via the home-made ELab preamplifier since it shows less internal response time and higher gain than the CATSA82. 6.2.1 55 Fe Measurement with Eind- Field Variation The iron source was placed centrally on the active area of the detector and the induction field was varied in a range of 0.05 kV/cm ≤ Eind ≤ 2.33 kV/cm for each data sample of Nsample = 50 × 10 3 events (see Fig. 6.9). rise time [ns] 800 700 600 500 400 300 200 100 Edrift 55Fe Rise Time vs Eind cm kV = 1.25 Etrans1,2 = 2.00 Δ U = 360 V GEM3 Δ UGEM2 = 320 V Δ U = 320 V GEM1 cm kV TDet= 297 ± 4 K p = 1030 ± 10 mbar Det Cu anode seg preamp: ELab Ar:CO2 93:7 @ 1 bar Measurements MAGBOLTZ sim1 Ar/CO =93/7 p=1040mbar 301K 2 MAGBOLTZ sim2 Ar/CO2=93/7 p=1040mbar 298K MAGBOLTZ sim3 Ar/CO2=93/7 p=1040mbar 293K MAGBOLTZ sim4 Ar/CO =93/7 p=1030mbar 298K 2 0 0 0.5 1 1.5 2 2.5 Eind[kV/cm] Figure 6.9: 55 Fe signal rise time as a function of Eind. (Data is indicated by black dots and guiding line). MAGBOLTZ simulations for drift time of electrons in 3 mm induction gap are plotted (see legend). Concerning also the intrinsic rise time of the preamplifier results in a good approximation for the plateau at high fields (red crosses and green triangles). The accessible range is limited by frequent discharges at fields Eind > 2.33 kV/cm. A closer look at Fig. 6.9 shows that the signal rise time starts at approximately 650 ns (indicated by the black dotted data points in the figure). Increasing the induction field strength results in an exponential decrease reaching a plateau of 100 ns rise time at around 0.8 kV/cm. The rapid drop in signal rise time is due to the increase in drift velocity over one magnitude for at 0.05 kV/cm ≤ Eind ≤ 0.8 kV/cm (see Fig. 6.6). However, in the area of the plateau the variation of the drift velocity with field strength is no longer strong; it is only of about 10%. To illustrate this the drift times of electrons from the lowest foil GEM1 to the anode are simulated with MAGBOLTZ and additionally plotted in the figure. It is
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DEVELOPMENT OF MICRO-PATTERN GASEOU
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Dedicated to Engin Abat 29/09/1979
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Contents Introduction I 1 Interacti
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Introduction Our universe is moment
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is testing tubes with alternative d
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efficiency. Monitoring of this para
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8 Chapter 1 Interactions of Charged
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10 Chapter 1 Interactions of Charge
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Page 28 and 29: 18 Chapter 1 Interactions of Charge
Page 30 and 31: 20 Chapter 1 Interactions of Charge
Page 32 and 33: 22 Chapter 2 The GEM Principle doub
Page 34 and 35: 24 Chapter 2 The GEM Principle mobi
Page 36 and 37: 26 Chapter 2 The GEM Principle
Page 38 and 39: 28 Chapter 3 The Triple GEM Prototy
Page 50 and 51: 40 Chapter 4 Energy Resolution and
Page 68 and 69: 58 Chapter 5 Efficiency Determinati
Page 76 and 77: 66 Chapter 6 Rise Time Studies 3000
Page 80 and 81: 70 Chapter 6 Rise Time Studies obse
Page 82 and 83: 72 Chapter 6 Rise Time Studies
Page 84 and 85: 74 Chapter 7 Gas Gain Studies eff G
Page 86 and 87: 76 Chapter 7 Gas Gain Studies
Page 88 and 89: 78 Chapter 8 Implementation of High
Page 98 and 99: 88 Chapter 9 Summary and Outlook st
Page 100 and 101: 90 BIBLIOGRAPHY [Bieb 03] O. Biebel
Page 102 and 103: 92 BIBLIOGRAPHY [NIST 10] NIST. “
Page 104 and 105: 94 BIBLIOGRAPHY
Page 106 and 107: 96 Chapter A Assumptions for Effici
Page 108 and 109: 98 Chapter B Construction Drawings
Page 114 and 115: 104 Chapter C Design of Prototype 2
Page 121 and 122: Acknowledgements First of all I wou
Page 123: Selbständigkeitserklärung Ich ver
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