Stability study of gain and energy resolution for GEM detector

Accepted Manuscript Stability study of gain and energy resolution for GEM detector S. Roy, S. Rudra, S. Shaw, S. Chatterjee, S. Chakraborty, R.P. Adak, S. Biswas, S. Das, S.K. Ghosh, S.K. Prasad, S. Raha PII: DOI: Reference:

S0168-9002(18)31374-3 https://doi.org/10.1016/j.nima.2018.10.060 NIMA 61382

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Nuclear Inst. and Methods in Physics Research, A

Received date : 12 June 2018 Revised date : 9 October 2018 Accepted date : 9 October 2018 Please cite this article as: S. Roy, et al., Stability study of gain and energy resolution for GEM detector, Nuclear Inst. and Methods in Physics Research, A (2018), https://doi.org/10.1016/j.nima.2018.10.060 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Stability study of gain and energy resolution for GEM detector S. Roya , S. Rudrab,∗, S. Shawc , S. Chatterjeea , S. Chakrabortya , R. P. Adaka , S. Biswasa , S. Dasa , S. K. Ghosha , S. K. Prasada , S. Rahaa a Department

of Physics and Centre for Astroparticle Physics and Space Science (CAPSS), Bose Institute, EN-80, Sector V, Kolkata-700091, India b Santragachi, Jagacha, G.I.P. Colony, Howrah-711 112, West Bengal, India c Vidyasagar University, Vidyasagar University Road, Rangamati, Medinipur, West Bengal-721102, India

Abstract Study of the stability of gain and energy resolution for a triple GEM detector has been performed under continuous radiation of X-ray with high rate, using premixed gas of Argon and CO2 in 70/30 ratio and conventional NIM electronics. A strong 55 Fe X-ray source is used for this study. The novelty of this study is that for the stability test same source is used to irradiate the GEM chamber and to monitor the spectrum. The radiation is not collimated to a point but exposed to a larger area. Effect of temperature and pressure on these parameters are also studied. The detail method of measurement and the first test results are presented. Keywords: GEM, Gas detector, MPGD, Gain, Energy resolution, Rate

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1. Introduction 21 The stability test of a triple GEM (Gas Electron Multiplier) 22 detector has been carried out both for gain and energy reso- 23 lution from the 55 Fe X-ray spectrum with conventional Argon 24 based gas mixtures [1, 2]. The motivation of this work is to 25 study the performance of the GEM based detector operated at 26 high X-ray rate. The details of the experimental set-up, mea- 27 surement process and results are presented. This work has been 28 carried out as a part of R&D program for the ALICE TPC up- 29 grade at CERN [3, 4] and the Muon Chamber (MUCH) in the 30 31 CBM experiment at FAIR [5, 6]. 32 2. Experimental details A GEM detector prototype, consisting of three 33 10 cm × 10 cm double mask foils, obtained from CERN 34 has been used in this study with drift gap, transfer gaps and 35 induction gap of 3 mm, 2 mm and 2 mm respectively. The 36 summed up signal from all the readout pads are fed as a single 37 input to a charge sensitive preamplifier (VV50-2) [7] having 38 gain of 2 mV/fC and shaping time of 300 ns. A NIM based data 39 acquisition system is used after the preamplifier. The details of 40 41 42

∗ Now

at Seacom Engineering College, JL-2: Jaladhulagori (Via Andul Mouri), Sankrail, Howrah-711 302, West Bengal, India ∗∗ Corresponding author Email addresses: [email protected] (S. Rudra), [email protected], [email protected] (S. Biswas) Preprint submitted to Elsevier

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the electronic set-up is given in Ref [8]. Pre-mixed Ar/CO2 in 70/30 volume ratio has been used. A constant gas flow rate of 3 l/h is maintained using a V¨ogtlin gas flow meter. A particular circular patch of the detector is exposed with the X-ray of rate ∼ 350 kHz from 55 Fe source using a collimator of diameter 8 mm, corresponding to an area of ∼ 50 mm2 on the detector i.e. the equivalent rate per unit area is 0.7 MHz/cm2 . 3. Results Figure 1 (Top) shows typical energy spectra recorded with 55 Fe source at different ∆V. The main peak (5.9 keV full energy peak) and the escape peak are clearly visible for all the voltage settings. The gain of the detector has been calculated by measuring the mean position of 5.9 keV peak of 55 Fe X-ray spectrum with Gaussian fitting as described in Ref. [9]. For gain calculation the average number of primary electrons for each 5.9 keV 55 Fe X-ray photon fully absorbed in 3 mm drift gap in Ar/CO2 gas with 70/30 ratio is taken as 212. The % energy resolution of × 2.355 the detector is defined as sigmamean × 100% where the sigma and the mean are obtained from the Gaussian fitting of each spectrum. The gain and energy resolution have been measured, increasing the biasing voltage of the GEM detector and that as a function of ∆V across a GEM foil is shown in Figure 1 (Bottom). It is observed that the gain increases exponentially from a value of ∼ 3500 to 14000 whereas the energy resolution value decreases from 34% to 25% (FWHM) with increasing voltage. October 9, 2018

76 ∆V 371.4 V

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The stability test of the detector has been carried out uninterruptedly for a period of > 1200 hours after the initial conditioning time of 5 hours, at a ∆V ∼ 378.7 V keeping the drift, transfer and induction fields constant at 2.3, 3.4 and 3.4 kV/cm respectively. The spectra are stored automatically using the ORTEC MCA at an interval of 10 minute. The gain of gaseous detector depends significantly on the ratio of absolute temperature (T = t+273) and pressure (p) [10], according to the relation,

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G(T/p) = Ae(B p ) . (1) CuteCom software package is used for automatic and continuous monitoring of the t and p. The variation of the measured 87 gain and T/p are plotted as a function of time in Figure 2 (Top). 88 The gain vs. T/p correlation plot is fitted with the function given 89 by equation 1 and the values of the fit parameters A and B are 90 found to be 0.005 ± 4.11 × 10−5 and 0.047 ± 2.31 × 10−5 atm/K 91 respectively. The measured gain is normalised with the gain 92 calculated from the equation 1 and the normalised gain is plot- 93 ted as a function of the total charge accumulated per unit irra- 94 diated area of the GEM chamber, which is directly proportional 95 to time. The charge accumulated per unit area at a particular 96 97 time is calculated by dq r × n × e × G × dt 98 = (2) 99 dA dA where, r is the measured rate in Hz incident on a particular100 area of the detector, dt is the time in second, n is the number of101 102 primary electrons for a single X-ray photon, e is the electronic103 charge, G is the gain and dA is the irradiated area. In this study104 a total accumulation of charge per unit area ∼ 6.5 mC/mm2 is105 achieved. The normalised gain as a function of the total ac-106 107 cumulated charge per unit area is shown in Figure 2 (Bottom).108 The mean normalised gain has been found to be 1.054 with a109 110 rms of 0.15. 2

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Figure 1: (Top) Energy spectra of the GEM detector at different GEM voltage. (Bottom) The gain and the energy resolution as a function of the GEM voltage.

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(3) energy resolution = A0 e(B p ) The value of the fit parameters A0 and B0 are 1.33 × 108 ± 4.93 × 105 and -0.05 ± 1.29 × 10−5 atm/K. The measured energy resolution is normalised with the value calculated from the equation 3. The normalised energy resolution is plotted as a function of the total accumulated charge per unit area and shown in Figure 2 (Bottom). The mean normalised energy resolution is 1.063 with a rms of 0.21. T/p (K/atm)

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The energy resolution as a function of the time is shown in Figure 2 (Top) and in the whole period of measurement varied between 25% to 45% FWHM. The correlation curve between energy resolution and T/p is fitted with an exponential function:

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Figure 2: (Top) Variation of the measured gain, energy resolution and T/p as a function of the time. (Bottom) Variation of the normalised gain and normalised energy resolution as a function of dq/dA.

4. Conclusions A systematic study on stability of the gain and energy resolution of a triple GEM detector in long term operation under high rate of X-ray irradiation is performed with Ar/CO2 gas mixture in 70/30 ratio, using conventional NIM electronics. The prototype under test did not show any significant degradation in performances in a continuous operation of > 1200 hours under high rate of X-ray radiation. 5. Acknowledgements The authors would like to thank the RD51 collaboration for the support in building and initial testing of the chamber in the RD51 laboratory at CERN. References [1] F. Sauli, Nucl. Instr. and Meth. A 386 (1997) 531. [2] R.P. Adak et al., 2016 JINST 11 T10001 doi:10.1088/17480221/11/10/T10001. [3] Saikat Biswas, PoS(ICPAQGP2015)094 [arXiv:1511.04988]. [4] R. N. Patra et al., Nucl. Instrum. Meth. A 862 (2017) 25. [5] S. Biswas et al., Nucl. Instrum. Meth. A 718 (2013) 403. [6] S. Biswas et al., Nucl. Instrum. Meth. A 824 (2016) 504. [7] CDT CASCADE Detector Technologies GmbH, www.n-cdt.com. [8] S. Chatterjee et al., NIM A, doi.org/10.1016/j.nima.2018.08.068. [9] S. Roy et al., NIM A, doi.org/10.1016/j.nima.2018.08.056. [10] M.C. Altunbas et al., Nucl. Instrum. Meth. A 515 (2003) 249.