development of micro-pattern gaseous detectors – gem - LMU

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54 Chapter 4 Energy Resolution and Pulse Height Analysis Uin = Qdet Cdet = Qcoup Ccoup (4.11) where Qdet is the part of the total charge Qtot that remains on the anode. Therefore the total charge that was generated by primary ionizing particle and amplified by the three GEM foils, is divided in: Qtot = Qdet + Qcoup from these two equations one derives an expression for the charge on the coupling capacitor: Qcoup = Qtot Cdet Ccoup Uout = + 1 FCV (4.12) (4.13) The pulse height Uout is connected to the fraction of charges Qcoup via the charge-to-voltage conversion factor FCV of the charge sensitive preamplifier. The Canberra has a conversion factor of FCV = 1 V/pC and the conversion factor of the ELab preamp is 0.83 ± 0.04 V/pC (see Ch. 3.4.3). The amplification factor of the CATSA82 preamplifier has not been determined since its coupling capacity Ccoup = 50 nF results in less gain. As the flash ADC records data in a 12 bit range with an acceptance of ±0.5 mV one can identify a scaling factor mADC: mADC = 0.244 mV ADC channel Using this we transform from the recorded pulse height to the detected charges Qcoup. charge [pC] 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 Δ Ugem1= 315 V Δ Ugem2= 335 V Δ Ugem3= 355 V Qcoup cm kV Edrift = 1.25 cm kV Etran1,2 = 2.00 Eind vs # Strips cm kV = 1.67 χ 2 / ndf 2.842 / 3 p0 0.4629 ± 0.06472 p1 0.5055 ± 0.1228 Ar:CO2 93:7 @ 1 bar Canberra 2004 p0/(p1*x+1) 0 0 1 2 3 # strips 4 5 p0/(0.0876*x+1.124) (4.14) Figure 4.24: Amount of collected charge that reaches the preamplifier as a function of the number of readout strips being coupled together. The decreasing pulseheight is due to increasing detector capacity as a function of readout strips. In order to proof equation 4.13 the data taken with the Canberra2004 preamplifier is transformed as it is shown in Fig. 4.24. A fit function with two free parameters is applied to the data (red line in Fig. 4.24) and yields a strip capacity C PCB strip of:
4.5. Pulse Height Dependence on Strip Readout 55 Cstrip = p1 · Ccoup = 0.5055 · 970 pF = 490 ± 120 pF (4.15) assuming the detector capacity to be a multiple of its single strip capacity: Cdet = n · Cstrip , n ∈ [1, 5]. (4.16) Including the dimension of the readout plane, its thickness dPCB and the area Astrip of the readout strips as well as the dielectric constant of the PCB material, the theoretical capacity of a single strip with respect to the backplane is: C PCB strip = ε0 · εPCBAstrip dPCB = 8.85 · 10−12 (F/m) · 4.5 · 0.0035m 2 1.6 · 10 −3 m ≈ 85 pF . (4.17) Together with the coupling capacity of the Canberra preamplifier it is inserted as a fixed second parameter in the fit function: Cstrip Ccoup = 85 pF = 0.0876 (4.18) 970 pF Additionally, the capacity of one strip to its neighboring strips has to be taken into account. The capacity of two neighboring strips with length l, thickness b and distance d can be estimated to be [Nuhr 02]: Cneighbor ≈ 6.65 · 10 −2 b · l · εPCB · d pF = 6.65 · 10 −2 10 · 2 · 4.5 = 60 pF 0.1 . (4.19) This theoretically derived values are inserted in the fit function: Qcoup = Qtot n · Cdet 2·Cneighbor + Ccoup Ccoup = Qtot n · 0.0876 + 1.124 , n ∈ [1, 5] (4.20) with Qtot being the only free parameter. This fit is shown as dashed line in Fig. 4.24. From the fit functions’ first parameter p0 one derives a theoretical range of the total charge: This corresponds to an average gas gain G of: G := Ntotal Nprimary Qtotal ∈ [0.25, 0.46]pC (4.21) = Qtot/1.6 · 10 −19 C 223 = 1.0 ± 0.3 · 10 4 (4.22) which is in agreement with the measurements of the gas gain in Ch. 7. Concerning the active area of a single strip with respect to the lowest GEM foil as the responsible detector capacity Cdet one gets: C GEM strip = ε0 · Aactive strip dind gap = 8.85 · 10−12 (F/m) · 0.002m 2 3, 0 · 10 −3 m = 5.9 pF (4.23) which results in a constant Qcoup since CGEM strip ≪ Ccoup. The theoretical values for CGEM strip and CPCB strip , respectively, deviate from the experimental result at least by a factor of five. Further investigation of the involved capacities in the detector is needed. With the implementation of a highly segmented anode (“prototype 2.0”) the low capacity range can be studied and is in preparation.
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DEVELOPMENT OF MICRO-PATTERN GASEOU
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Dedicated to Engin Abat 29/09/1979
Page 9 and 10:
Contents Introduction I 1 Interacti
Page 11 and 12:
Introduction Our universe is moment
Page 13 and 14: is testing tubes with alternative d
Page 15: efficiency. Monitoring of this para
Page 18 and 19: 8 Chapter 1 Interactions of Charged
Page 20 and 21: 10 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 78 and 79: 68 Chapter 6 Rise Time Studies 2 ns
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
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104 Chapter C Design of Prototype 2
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Acknowledgements First of all I wou
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Selbständigkeitserklärung Ich ver
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