- Email: [email protected]
THGEM based photon detector for Cherenkov imaging applications
ARTICLE IN PRESS Nuclear Instruments and Methods in Physics Research A 617 (2010) 396–397
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
THGEM based photon detector for Cherenkov imaging applications M. Alexeev j, R. Birsa f, F. Bradamante i, A. Bressan i, M. Chiosso k, P. Ciliberti h, G. Croci a, M.L. Colantoni i, S. Dalla Torre f, S. Duarte Pinto a, O. Denisov i, V. Diaz f, A. Ferrero k, M. Finger e, M. Finger Jr.e, H. Fischer b, b ¨ , G. Giacomini g, M. Giorgi h, B. Gobbo f, F.H. Heinsius b, F. Herrmann b,, V. Jahodova c, K. Konigsmann b h i h f b j i L. Lauser , S. Levorato , A. Maggiora , A. Martin , G. Menon , F. Nerling , D. Panzieri , G. Pesaro , J. Polak c,f, E. Rocco k, L. Ropeleswki a, F. Sauli d, G. Sbrizzai h, P. Schiavon h, C. Schill b, S. Schopferer b, M. Slunecka e, F. Sozzi h, L. Steiger c, M. Sulc c, S. Takekawa h, F. Tessarotto f, H. Wollny b a
CERN, 1211 Geneva, Switzerland University of Freiburg, 79104 Freiburg, Germany Technical University of Liberec, 46117 Liberec, Czech Republic d TERA Foundation, 28100 Novara, Italy e Charles University, 18000 Prague, Czech Republic f INFN, Sezione di Trieste, 34127 Trieste, Italy g INFN, Sezione di Trieste and University of Bari, 70125 Bari, Italy h INFN, Sezione di Trieste and University of Trieste, 34127 Trieste, Italy i INFN, Sezione di Torino, 10125 Torino, Italy j INFN, Sezione di Torino and University of East Piemonte, 1500 Alessandria, Italy k INFN, Sezione di Torino and University of Torino, 10125 Torino, Italy b c
a r t i c l e in f o
a b s t r a c t
Available online 16 September 2009
We are developing a single photon detector for Cherenkov imaging counters. This detector is based on the use of THGEM electron multipliers in a multilayer design. The major goals of our project are ion feedback suppression down to a few per cent, large gain, fast response, insensitivity to magnetic fields, and a large detector size. We report about the project status and perspectives. In particular, we present a systematic study of the THGEM response as a function of geometrical parameters, production techniques and the gas mixture composition. The first figures obtained from measuring the response of a CsI coated THGEM to single photons are presented. & 2009 Elsevier B.V. All rights reserved.
Keywords: Micro-pattern gas detectors Single photon detectors THGEM
1. Introduction
2. The THGEM electron multiplier
The only available option to instrument at affordable costs large surfaces in Cherenkov imaging counters are still gaseous photon detectors. To optimise the photon detection process in timing, gain and overall stability, we are developing detector prototypes based on the THick GEM (THGEM) electron multiplier technology. The status of the project, development and first results of time resolution and gain capabilities of our THGEM detector prototype are given here.
THGEMs [1,2] are gaseous electron multipliers, which are based on the concept of the GEM technology. However, the physical dimensions of holes and pitch are up to one order of magnitude larger compared to GEM foil ones. Furthermore the production process of THGEMs differs from the production of GEMs. Instead of using foils with etched holes, THGEMs are printed circuit boards (PCB), and they can be manufactured by standardised industrial production processes. This manufacturing allows to create rims, which are copperfree rings around the drilled holes, with apertures of 0–0.1 mm. Other geometric dimensions of the PCB are 0.4–1.0 mm in material thickness, 0.2–0.8 mm in hole diameter and 0.7–1.2 mm in hole pitch. The industrial production allows series production of large quantities, even if some million holes per THGEM square meter are needed. The PCB material guarantees high mechanical stability and is also resistant against damages produced by electrical discharges.
Corresponding author.
E-mail address: fl[email protected] (F. Herrmann). 0168-9002/$ - see front matter & 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2009.08.087
ARTICLE IN PRESS M. Alexeev et al. / Nuclear Instruments and Methods in Physics Research A 617 (2010) 396–397
10000 best fit, exponential function, range 20−55 fC: slope: 113 000 slope: 110 000
1000 counts
THGEM-based detectors can be successfully used in magnetic field, because of the reduced gaps between the multiplication stages. The PCB production process allows an effortless variation of the production parameters. We produced more than 30 different types of prototypes in single layer configuration to determine the performance using a standard gas mixture of Ar : CO2 ¼ 70 : 30. For the characterisation of the detector prototype we measure the amplitude spectra of the anode signals and collect the absorbed currents from all electrodes. In the following we give a brief review of the attained results of these studies [3]. We group the detector variations in three types: One with large rim size (about 0.1 mm), the second without rims and a third group with very small rim size ð10 mmÞ. The results which we obtained show that large gains can be reached for the first group. At the same time these prototypes also show large gain variations of more than a factor of three over detector radiation history and time; the gain is also rate dependent. The second configuration of THGEMs, detectors which have no rim, show no such gain dependency. In particular, the gain is stable versus rate up to rates of at least 100 kHz=mm2 . However, the reached gains are smaller. Combining the advantages of the first and second group of prototypes, we defined the third group of THGEMs, detectors with very small rims of 10 mm. This kind of prototype shows overall gain variations below 20%. In addition small rims allow the THGEMs to stand higher bias voltages.
397
100
10 0
20
40 60 charge (fC)
80
100
Fig. 1. Amplitude spectra measured with a four-layer THGEM electron multiplier with CsI photocathode, illuminating the detector with 600 ps UV light pulses.
3. Single photon detection For our photon detector prototype, we have chosen a reflective photocathode architecture: the first THGEM layer is coated with a CsI film. The detector has a multilayer configuration and the first CsI coated layer is followed by three more THGEM layers and the anode layer. This design has the advantage to reach a larger photo conversion rate compared to architectures using a semi-transparent photocathode. Another clear advantage of using a reflective photocathode is that the thickness of the CsI coating layer is not critical which simplifies the production process. To determine gain and timing characteristics of a single photon detection process, laboratory studies have been performed by using 600 ps long light pulses. The UV photon sources were obtained by powering a LED with the PDL 800-B pulse controller by PicoQuant GmbH, Berlin, Germany. As photo conversion detector we were using a four layer THGEM with CsI coated surface. The physical dimensions of this prototype are 0.4 mm layer thickness, 0.8 mm pitch between holes, 0.4 mm hole diameter and 10 mm rim. The results in Fig. 1 show that gains larger than 105 have been achieved. The time resolution measurement was performed by using F1 TDC [4] with 108 ps bin size housed in the electronic readout environment described in Ref. [5]. A time resolution of 7.5 ns r.m.s. has been obtained (Fig. 2).
Fig. 2. Time spectrum measured with a four-layer THGEM electron multiplier with CsI photocathode, illuminating the detector with 600 ps UV light pulses.
Acknowledgements The authors are grateful to Prof. A. Breskin for his constant encouragement and many stimulating discussions. This work has partly been performed in the framework of the RD51 collaboration.
4. Outlook and conclusions We have characterised gain and time resolution of different kind of THGEM prototypes by changing production parameters and geometric dimensions. As a result we have determined an optimal set of geometrical parameters which benefit from overall stability versus time and high irradiation conditions. In the second stage of our research we have started characterising the single photon conversion process and achieved first results for a multilayer THGEM prototype with a CsI coated reflective photocathode.
References [1] R. Chechik, et al., Nucl. Instr. and Meth. A 535 (2004) 303; R. Chechik, et al., Nucl. Instr. and Meth. A 553 (2005) 35; C. Shalem, et al., Nucl. Instr. and Meth. A 558 (2006) 475. [2] J.M. Bidault, et al., Nucl. Phys. B (Proc. Suppl.) 158 (2006) 199. [3] M. Alexeev, et al., The quest for a third generation of gaseous photon detectors for Cherenkov imaging counters, Nucl. Instr. and Meth. A, in press, doi:10.1016/ j.nima.2009.05.069. [4] H. Fischer, et al., Nucl. Instr. and Meth. A 461 (2001) 507. [5] P. Abbon, et al., Nucl. Instr. and Meth. A 587 (2008) 371.
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
THGEM based photon detector for Cherenkov imaging applications M. Alexeev j, R. Birsa f, F. Bradamante i, A. Bressan i, M. Chiosso k, P. Ciliberti h, G. Croci a, M.L. Colantoni i, S. Dalla Torre f, S. Duarte Pinto a, O. Denisov i, V. Diaz f, A. Ferrero k, M. Finger e, M. Finger Jr.e, H. Fischer b, b ¨ , G. Giacomini g, M. Giorgi h, B. Gobbo f, F.H. Heinsius b, F. Herrmann b,, V. Jahodova c, K. Konigsmann b h i h f b j i L. Lauser , S. Levorato , A. Maggiora , A. Martin , G. Menon , F. Nerling , D. Panzieri , G. Pesaro , J. Polak c,f, E. Rocco k, L. Ropeleswki a, F. Sauli d, G. Sbrizzai h, P. Schiavon h, C. Schill b, S. Schopferer b, M. Slunecka e, F. Sozzi h, L. Steiger c, M. Sulc c, S. Takekawa h, F. Tessarotto f, H. Wollny b a
CERN, 1211 Geneva, Switzerland University of Freiburg, 79104 Freiburg, Germany Technical University of Liberec, 46117 Liberec, Czech Republic d TERA Foundation, 28100 Novara, Italy e Charles University, 18000 Prague, Czech Republic f INFN, Sezione di Trieste, 34127 Trieste, Italy g INFN, Sezione di Trieste and University of Bari, 70125 Bari, Italy h INFN, Sezione di Trieste and University of Trieste, 34127 Trieste, Italy i INFN, Sezione di Torino, 10125 Torino, Italy j INFN, Sezione di Torino and University of East Piemonte, 1500 Alessandria, Italy k INFN, Sezione di Torino and University of Torino, 10125 Torino, Italy b c
a r t i c l e in f o
a b s t r a c t
Available online 16 September 2009
We are developing a single photon detector for Cherenkov imaging counters. This detector is based on the use of THGEM electron multipliers in a multilayer design. The major goals of our project are ion feedback suppression down to a few per cent, large gain, fast response, insensitivity to magnetic fields, and a large detector size. We report about the project status and perspectives. In particular, we present a systematic study of the THGEM response as a function of geometrical parameters, production techniques and the gas mixture composition. The first figures obtained from measuring the response of a CsI coated THGEM to single photons are presented. & 2009 Elsevier B.V. All rights reserved.
Keywords: Micro-pattern gas detectors Single photon detectors THGEM
1. Introduction
2. The THGEM electron multiplier
The only available option to instrument at affordable costs large surfaces in Cherenkov imaging counters are still gaseous photon detectors. To optimise the photon detection process in timing, gain and overall stability, we are developing detector prototypes based on the THick GEM (THGEM) electron multiplier technology. The status of the project, development and first results of time resolution and gain capabilities of our THGEM detector prototype are given here.
THGEMs [1,2] are gaseous electron multipliers, which are based on the concept of the GEM technology. However, the physical dimensions of holes and pitch are up to one order of magnitude larger compared to GEM foil ones. Furthermore the production process of THGEMs differs from the production of GEMs. Instead of using foils with etched holes, THGEMs are printed circuit boards (PCB), and they can be manufactured by standardised industrial production processes. This manufacturing allows to create rims, which are copperfree rings around the drilled holes, with apertures of 0–0.1 mm. Other geometric dimensions of the PCB are 0.4–1.0 mm in material thickness, 0.2–0.8 mm in hole diameter and 0.7–1.2 mm in hole pitch. The industrial production allows series production of large quantities, even if some million holes per THGEM square meter are needed. The PCB material guarantees high mechanical stability and is also resistant against damages produced by electrical discharges.
Corresponding author.
E-mail address: fl[email protected] (F. Herrmann). 0168-9002/$ - see front matter & 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2009.08.087
ARTICLE IN PRESS M. Alexeev et al. / Nuclear Instruments and Methods in Physics Research A 617 (2010) 396–397
10000 best fit, exponential function, range 20−55 fC: slope: 113 000 slope: 110 000
1000 counts
THGEM-based detectors can be successfully used in magnetic field, because of the reduced gaps between the multiplication stages. The PCB production process allows an effortless variation of the production parameters. We produced more than 30 different types of prototypes in single layer configuration to determine the performance using a standard gas mixture of Ar : CO2 ¼ 70 : 30. For the characterisation of the detector prototype we measure the amplitude spectra of the anode signals and collect the absorbed currents from all electrodes. In the following we give a brief review of the attained results of these studies [3]. We group the detector variations in three types: One with large rim size (about 0.1 mm), the second without rims and a third group with very small rim size ð10 mmÞ. The results which we obtained show that large gains can be reached for the first group. At the same time these prototypes also show large gain variations of more than a factor of three over detector radiation history and time; the gain is also rate dependent. The second configuration of THGEMs, detectors which have no rim, show no such gain dependency. In particular, the gain is stable versus rate up to rates of at least 100 kHz=mm2 . However, the reached gains are smaller. Combining the advantages of the first and second group of prototypes, we defined the third group of THGEMs, detectors with very small rims of 10 mm. This kind of prototype shows overall gain variations below 20%. In addition small rims allow the THGEMs to stand higher bias voltages.
397
100
10 0
20
40 60 charge (fC)
80
100
Fig. 1. Amplitude spectra measured with a four-layer THGEM electron multiplier with CsI photocathode, illuminating the detector with 600 ps UV light pulses.
3. Single photon detection For our photon detector prototype, we have chosen a reflective photocathode architecture: the first THGEM layer is coated with a CsI film. The detector has a multilayer configuration and the first CsI coated layer is followed by three more THGEM layers and the anode layer. This design has the advantage to reach a larger photo conversion rate compared to architectures using a semi-transparent photocathode. Another clear advantage of using a reflective photocathode is that the thickness of the CsI coating layer is not critical which simplifies the production process. To determine gain and timing characteristics of a single photon detection process, laboratory studies have been performed by using 600 ps long light pulses. The UV photon sources were obtained by powering a LED with the PDL 800-B pulse controller by PicoQuant GmbH, Berlin, Germany. As photo conversion detector we were using a four layer THGEM with CsI coated surface. The physical dimensions of this prototype are 0.4 mm layer thickness, 0.8 mm pitch between holes, 0.4 mm hole diameter and 10 mm rim. The results in Fig. 1 show that gains larger than 105 have been achieved. The time resolution measurement was performed by using F1 TDC [4] with 108 ps bin size housed in the electronic readout environment described in Ref. [5]. A time resolution of 7.5 ns r.m.s. has been obtained (Fig. 2).
Fig. 2. Time spectrum measured with a four-layer THGEM electron multiplier with CsI photocathode, illuminating the detector with 600 ps UV light pulses.
Acknowledgements The authors are grateful to Prof. A. Breskin for his constant encouragement and many stimulating discussions. This work has partly been performed in the framework of the RD51 collaboration.
4. Outlook and conclusions We have characterised gain and time resolution of different kind of THGEM prototypes by changing production parameters and geometric dimensions. As a result we have determined an optimal set of geometrical parameters which benefit from overall stability versus time and high irradiation conditions. In the second stage of our research we have started characterising the single photon conversion process and achieved first results for a multilayer THGEM prototype with a CsI coated reflective photocathode.
References [1] R. Chechik, et al., Nucl. Instr. and Meth. A 535 (2004) 303; R. Chechik, et al., Nucl. Instr. and Meth. A 553 (2005) 35; C. Shalem, et al., Nucl. Instr. and Meth. A 558 (2006) 475. [2] J.M. Bidault, et al., Nucl. Phys. B (Proc. Suppl.) 158 (2006) 199. [3] M. Alexeev, et al., The quest for a third generation of gaseous photon detectors for Cherenkov imaging counters, Nucl. Instr. and Meth. A, in press, doi:10.1016/ j.nima.2009.05.069. [4] H. Fischer, et al., Nucl. Instr. and Meth. A 461 (2001) 507. [5] P. Abbon, et al., Nucl. Instr. and Meth. A 587 (2008) 371.