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Precision muon tracking detectors and read-out electronics for operation at very high background rates at future colliders
Nuclear Instruments and Methods in Physics Research A 824 (2016) 556–558
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Precision muon tracking detectors and read-out electronics for operation at very high background rates at future colliders O. Kortner, H. Kroha, S. Nowak n, R. Richter, K. Schmidt-Sommerfeld, Ph. Schwegler Max-Planck-Institut für Physik, Munich, Germany
art ic l e i nf o
a b s t r a c t
Available online 31 December 2015
The experience of the ATLAS MDT muon spectrometer shows that drift-tube chambers provide highly reliable precision muon tracking over large areas. The ATLAS muon chambers are exposed to unprecedentedly high background of photons and neutrons induced by the proton collisions. Still higher background rates are expected at future high-energy and high-luminosity colliders beyond HL-LHC. Therefore, drift-tube detectors with 15 mm tube diameter (30 mm in ATLAS), optimised for high rate operation, have been developed for such conditions. Several such full-scale sMDT chambers have been constructed with unprecedentedly high sense wire positioning accuracy of better than 10 μm. The chamber design and assembly methods have been optimised for large-scale production, reducing considerably cost and construction time while maintaining the high mechanical accuracy and reliability. Tests at the Gamma Irradiation Facility at CERN showed that the rate capability of sMDT chambers is improved by more than an order of magnitude compared to the MDT chambers. By using read-out electronics optimised for high counting rates, the rate capability can be further increased. & 2015 Elsevier B.V. All rights reserved.
Keywords: ATLAS HL-LHC FCC Drift-tube detectors Signal pile-up Baseline restoration
1. Introduction The ATLAS Monitored Drift Tube (MDT) chambers [1] account for the vast majority of precision tracking chambers in the muon spectrometer of the ATLAS experiment at the Large Hadron Collider (LHC), where they have to cope with unprecedentedly high background rates of photons and neutrons in the energy range around 1 MeV. With the upgrade of the LHC to High-Luminosity LHC (HL-LHC), which implies an increase of the background rate by a factor of 10, the rate capability of both the MDT detectors and their front-end electronics will be exceeded. Therefore, new detectors, so-called small-diameter Muon Drift Tube (sMDT) chambers with 15 mm tube diameter, half of the MDT diameter, have been developed. Under the same operating conditions and with the MDT read-out electronics the sMDT chambers have about an order of magnitude higher rate capability than the MDTs [2] (see Fig. 4). Because of the 3.8 times shorter maximum drift time of 175 ns and the smaller tube diameter, they have 8 times lower occupancy, can be operated at much shorter electronics dead time and are much less sensitive to space charge effects. The rate-capability of the sMDT chambers can be further improved with optimised signal shaping of the read-out electronics. The sMDT chambers are also a
n
Corresponding author. E-mail address: [email protected] (S. Nowak).
http://dx.doi.org/10.1016/j.nima.2015.12.018 0168-9002/& 2015 Elsevier B.V. All rights reserved.
cost effective solution for large area precision muon tracking at future hadron colliders (FCC-hh) up to the highest luminosities.
2. sMDT design and chamber construction The sMDT chambers consist of layers of industrial standard aluminium tubes with 0.4 mm wall thickness. Central to the design are the end-plugs (see Fig. 1a) which seal the tubes operated at 3 bar absolute gas pressure, insulate the sense wire against the tube wall, centre the wire in the tubes with a few micron precision and provide an external reference surface for tube positioning during the chamber assembly. The tube materials have been selected to prevent outgassing and cracking. No aging effects have been observed up to 9 C=cm charge accumulation on the wire corresponding to 15 times the ATLAS requirement. Semi-automated assembly and test stations are used for tube production with a rate of 100 tubes per day at each station. The tubes are assembled to a chamber using precise jigs (see Fig. 1b) on a flat granite table in a temperature controlled clean room. The overall wire positioning accuracy with a chamber was found to be better than 10 μm. The individual wire positions are measured with a coordinate measuring machine via the end-plug reference surfaces with an accuracy of better than 3 μm. A chamber can be assembled within one working day. Two sMDT chambers are already operational in the ATLAS detector, further 28 chambers are planned to be installed until 2018 [3].
O. Kortner et al. / Nuclear Instruments and Methods in Physics Research A 824 (2016) 556–558
557
Fig. 1. (a) Cross-section of an sMDT end-plug. (b) Precise jigs for chamber assembly with grids of holes for the end-plug surface at each chamber end.
Fig. 2. (a) Illustration of the signal pile-up effects (see text). (b) Principle baseline restoration circuit using on a diode.
Fig. 3. Unshaped (gain 10 000) and bipolar shaped pulse of bandwidth).
137
Cs γ-rays in sMDT tubes without (left) and with (right) baseline restoration (BLR, 200 MHz measurement
3. Improved read-out electronics The present read-out chip used both for ATLAS MDT and sMDT chambers uses bipolar shaping, which has the advantage of baseline stability at high counting rates, but introduces an undershoot below the baseline of the same charge after the signal pulse (see Fig. 2a). At high counting rates and minimum programmable dead time of 220 ns as used for the sMDT chambers,
signal pulses can overlap with the undershoot of preceding background pulses leading to reduced signal amplitude and jitter in the threshold crossing time depending on the signal charge and, therefore, to a degradation of the single-tube muon efficiency and spatial resolution (signal pile-up effects see Fig. 2a). The pile-up effects can be suppressed using baseline restoration (BLR). Fig. 2b shows a simple baseline restoration circuit following the bipolar shaper. A diode with working point set by the bias current IBase is
558
O. Kortner et al. / Nuclear Instruments and Methods in Physics Research A 824 (2016) 556–558
In order to investigate the effect of baseline restoration on sMDT signals at high background counting rates, a discrete amplifier and bipolar shaping circuit with optional BLR has been designed and built. Fig. 3 shows unshaped (amplifier gain 10 000) and shaped pulses of 137Cs γ-rays in sMDT tubes read out using the discrete electronics. The baseline restoration circuit strongly suppresses the undershoot as expected and reduces the full baseline restoration time by about a factor of two. Fig. 4 shows the MDT and sMDT single-tube resolution and muon efficiency depending on the photon flux and hit rate with and without baseline restoration for different dead time settings. The measurements performed at the CERN Gamma Irradiation Facility show vast improvement of the rate capability of sMDT compared to MDT tubes. Furthermore, full simulation of the drift tube and electronics response to the γ-rays (see Fig. 4) shows that baseline restoration successfully suppresses signal pile-up effects and, therefore, leads to further improvement of resolution and efficiency at high counting rates.
4. Summary sMDT chambers are well suited for large area high-precision muon tracking at the high background rates expected at maximum luminosity at FCC-hh. The rate capability of the sMDT chambers can be further improved by optimised shaping of the read-out electronics.
References Fig. 4. MDT and sMDT single-tube resolution and muon efficiency depending on the background photon flux and hit rate with and without baseline restoration (BLR) for different dead time settings compared to a full simulation of the drift tube and electronics response.
used following Ref. [4]. While for positive input signals the diode is non-conducting leaving the input signals unchanged, negative signals (undershoot) are shorted to ground leading to a fast restoration of the baseline.
[1] G. Aad, et al., ATLAS Collaboration, Journal of Instrumentation 3 (2008) S08003. [2] H. Kroha, et al., Nuclear Instruments and Methods in Physics Research Section A 718 (2013) 427. [3] C. Ferretti, H. Kroha, for the ATLAS Muon Collaboration, Proceedings of the 13th Pisa Meeting on Advanced Detectors La Biodola, Isola d'Elba, Italy, 24–30 May 2015. [4] L.B. Robinson, Review of Scientific Instruments 32 (1961) 1057.
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Precision muon tracking detectors and read-out electronics for operation at very high background rates at future colliders O. Kortner, H. Kroha, S. Nowak n, R. Richter, K. Schmidt-Sommerfeld, Ph. Schwegler Max-Planck-Institut für Physik, Munich, Germany
art ic l e i nf o
a b s t r a c t
Available online 31 December 2015
The experience of the ATLAS MDT muon spectrometer shows that drift-tube chambers provide highly reliable precision muon tracking over large areas. The ATLAS muon chambers are exposed to unprecedentedly high background of photons and neutrons induced by the proton collisions. Still higher background rates are expected at future high-energy and high-luminosity colliders beyond HL-LHC. Therefore, drift-tube detectors with 15 mm tube diameter (30 mm in ATLAS), optimised for high rate operation, have been developed for such conditions. Several such full-scale sMDT chambers have been constructed with unprecedentedly high sense wire positioning accuracy of better than 10 μm. The chamber design and assembly methods have been optimised for large-scale production, reducing considerably cost and construction time while maintaining the high mechanical accuracy and reliability. Tests at the Gamma Irradiation Facility at CERN showed that the rate capability of sMDT chambers is improved by more than an order of magnitude compared to the MDT chambers. By using read-out electronics optimised for high counting rates, the rate capability can be further increased. & 2015 Elsevier B.V. All rights reserved.
Keywords: ATLAS HL-LHC FCC Drift-tube detectors Signal pile-up Baseline restoration
1. Introduction The ATLAS Monitored Drift Tube (MDT) chambers [1] account for the vast majority of precision tracking chambers in the muon spectrometer of the ATLAS experiment at the Large Hadron Collider (LHC), where they have to cope with unprecedentedly high background rates of photons and neutrons in the energy range around 1 MeV. With the upgrade of the LHC to High-Luminosity LHC (HL-LHC), which implies an increase of the background rate by a factor of 10, the rate capability of both the MDT detectors and their front-end electronics will be exceeded. Therefore, new detectors, so-called small-diameter Muon Drift Tube (sMDT) chambers with 15 mm tube diameter, half of the MDT diameter, have been developed. Under the same operating conditions and with the MDT read-out electronics the sMDT chambers have about an order of magnitude higher rate capability than the MDTs [2] (see Fig. 4). Because of the 3.8 times shorter maximum drift time of 175 ns and the smaller tube diameter, they have 8 times lower occupancy, can be operated at much shorter electronics dead time and are much less sensitive to space charge effects. The rate-capability of the sMDT chambers can be further improved with optimised signal shaping of the read-out electronics. The sMDT chambers are also a
n
Corresponding author. E-mail address: [email protected] (S. Nowak).
http://dx.doi.org/10.1016/j.nima.2015.12.018 0168-9002/& 2015 Elsevier B.V. All rights reserved.
cost effective solution for large area precision muon tracking at future hadron colliders (FCC-hh) up to the highest luminosities.
2. sMDT design and chamber construction The sMDT chambers consist of layers of industrial standard aluminium tubes with 0.4 mm wall thickness. Central to the design are the end-plugs (see Fig. 1a) which seal the tubes operated at 3 bar absolute gas pressure, insulate the sense wire against the tube wall, centre the wire in the tubes with a few micron precision and provide an external reference surface for tube positioning during the chamber assembly. The tube materials have been selected to prevent outgassing and cracking. No aging effects have been observed up to 9 C=cm charge accumulation on the wire corresponding to 15 times the ATLAS requirement. Semi-automated assembly and test stations are used for tube production with a rate of 100 tubes per day at each station. The tubes are assembled to a chamber using precise jigs (see Fig. 1b) on a flat granite table in a temperature controlled clean room. The overall wire positioning accuracy with a chamber was found to be better than 10 μm. The individual wire positions are measured with a coordinate measuring machine via the end-plug reference surfaces with an accuracy of better than 3 μm. A chamber can be assembled within one working day. Two sMDT chambers are already operational in the ATLAS detector, further 28 chambers are planned to be installed until 2018 [3].
O. Kortner et al. / Nuclear Instruments and Methods in Physics Research A 824 (2016) 556–558
557
Fig. 1. (a) Cross-section of an sMDT end-plug. (b) Precise jigs for chamber assembly with grids of holes for the end-plug surface at each chamber end.
Fig. 2. (a) Illustration of the signal pile-up effects (see text). (b) Principle baseline restoration circuit using on a diode.
Fig. 3. Unshaped (gain 10 000) and bipolar shaped pulse of bandwidth).
137
Cs γ-rays in sMDT tubes without (left) and with (right) baseline restoration (BLR, 200 MHz measurement
3. Improved read-out electronics The present read-out chip used both for ATLAS MDT and sMDT chambers uses bipolar shaping, which has the advantage of baseline stability at high counting rates, but introduces an undershoot below the baseline of the same charge after the signal pulse (see Fig. 2a). At high counting rates and minimum programmable dead time of 220 ns as used for the sMDT chambers,
signal pulses can overlap with the undershoot of preceding background pulses leading to reduced signal amplitude and jitter in the threshold crossing time depending on the signal charge and, therefore, to a degradation of the single-tube muon efficiency and spatial resolution (signal pile-up effects see Fig. 2a). The pile-up effects can be suppressed using baseline restoration (BLR). Fig. 2b shows a simple baseline restoration circuit following the bipolar shaper. A diode with working point set by the bias current IBase is
558
O. Kortner et al. / Nuclear Instruments and Methods in Physics Research A 824 (2016) 556–558
In order to investigate the effect of baseline restoration on sMDT signals at high background counting rates, a discrete amplifier and bipolar shaping circuit with optional BLR has been designed and built. Fig. 3 shows unshaped (amplifier gain 10 000) and shaped pulses of 137Cs γ-rays in sMDT tubes read out using the discrete electronics. The baseline restoration circuit strongly suppresses the undershoot as expected and reduces the full baseline restoration time by about a factor of two. Fig. 4 shows the MDT and sMDT single-tube resolution and muon efficiency depending on the photon flux and hit rate with and without baseline restoration for different dead time settings. The measurements performed at the CERN Gamma Irradiation Facility show vast improvement of the rate capability of sMDT compared to MDT tubes. Furthermore, full simulation of the drift tube and electronics response to the γ-rays (see Fig. 4) shows that baseline restoration successfully suppresses signal pile-up effects and, therefore, leads to further improvement of resolution and efficiency at high counting rates.
4. Summary sMDT chambers are well suited for large area high-precision muon tracking at the high background rates expected at maximum luminosity at FCC-hh. The rate capability of the sMDT chambers can be further improved by optimised shaping of the read-out electronics.
References Fig. 4. MDT and sMDT single-tube resolution and muon efficiency depending on the background photon flux and hit rate with and without baseline restoration (BLR) for different dead time settings compared to a full simulation of the drift tube and electronics response.
used following Ref. [4]. While for positive input signals the diode is non-conducting leaving the input signals unchanged, negative signals (undershoot) are shorted to ground leading to a fast restoration of the baseline.
[1] G. Aad, et al., ATLAS Collaboration, Journal of Instrumentation 3 (2008) S08003. [2] H. Kroha, et al., Nuclear Instruments and Methods in Physics Research Section A 718 (2013) 427. [3] C. Ferretti, H. Kroha, for the ATLAS Muon Collaboration, Proceedings of the 13th Pisa Meeting on Advanced Detectors La Biodola, Isola d'Elba, Italy, 24–30 May 2015. [4] L.B. Robinson, Review of Scientific Instruments 32 (1961) 1057.