16 Integration of Detectors into a Large Experiment: Examples from ATLAS. . .
737
The final alignment values will clearly be obtained with the large statistics of
muon tracks traversing the muon chambers (rates of about 10 kHz are expected at a
luminosity of 10 33 cm −2 s −1 for muons with p T > 6 GeV).
16.5.2 Construction Experience and Measured Performance in
Laboratory and Test Beam
The muon chambers are based on technologies, which were used in previous experiments: drift tubes and CSCs have been used widely in the past; RPCs were used in
the L3 and Babar experiments, while TGCs were used in OPAL. Nevertheless, large
R&D efforts have been necessary to address the special requirements of the LHC
environment.
The high particle fluxes (mainly photons and neutrons) have necessitated
searches for the right type of materials and gases, which prevent wire deposits
in the case of drift tubes, while new operational modes were developed for
the RPCs (proportional regime instead of the streamer regime used in previous
experiments) and the TGCs (quasi-proportional mode instead of saturated mode),
with the corresponding required changes in the front-end electronics.
In the case of the ATLAS muon spectrometer, the requirement of a precise standalone measurement limits the amount of material in order to minimise multiple
scattering. This has led to the development of thin but precise Aluminium tubes,
which are mounted on very light structures. The deformations of these structures
can be monitored by a sophisticated alignment system, as well as the extensive use
of paper honeycomb in the trigger chambers to limit the contribution of the detectors
in the material description.
Beyond this, the greatest challenge came mostly from the very large, unprecedented areas that the muon chambers had to cover and the correspondingly large
numbers of electronic channels. The ATLAS muon system contains approximately
25,000 m 2 of active detection planes, and roughly one million electronic channels.
The main parameters of the muon chambers are listed in Table 16.11.
The requirement of achieving all this within ‘reasonable cost’ was actually one
of the biggest issues encountered. In terms of lessons learned from the construction
process; beyond the general observations made in Sect. 16.2.3, three issues emerge
as the most important ones:
• Putting in place, right from the beginning, very tight procedures for quality
assurance/quality control (QA/QC). Given the enormous number of elements
(wires, strips, tubes, supports) involved, the presence of well-defined and complete QA/QC systems was of the utmost importance. Any and all issues which
went unnoticed sooner or later resulted in time and energy-consuming corrective
procedures being taken.
• Planning for services. Despite all initial designs and tolerances and safety factors,
the cabling procedures always turn out to be more complicated, more time-
737
The final alignment values will clearly be obtained with the large statistics of
muon tracks traversing the muon chambers (rates of about 10 kHz are expected at a
luminosity of 10 33 cm −2 s −1 for muons with p T > 6 GeV).
16.5.2 Construction Experience and Measured Performance in
Laboratory and Test Beam
The muon chambers are based on technologies, which were used in previous experiments: drift tubes and CSCs have been used widely in the past; RPCs were used in
the L3 and Babar experiments, while TGCs were used in OPAL. Nevertheless, large
R&D efforts have been necessary to address the special requirements of the LHC
environment.
The high particle fluxes (mainly photons and neutrons) have necessitated
searches for the right type of materials and gases, which prevent wire deposits
in the case of drift tubes, while new operational modes were developed for
the RPCs (proportional regime instead of the streamer regime used in previous
experiments) and the TGCs (quasi-proportional mode instead of saturated mode),
with the corresponding required changes in the front-end electronics.
In the case of the ATLAS muon spectrometer, the requirement of a precise standalone measurement limits the amount of material in order to minimise multiple
scattering. This has led to the development of thin but precise Aluminium tubes,
which are mounted on very light structures. The deformations of these structures
can be monitored by a sophisticated alignment system, as well as the extensive use
of paper honeycomb in the trigger chambers to limit the contribution of the detectors
in the material description.
Beyond this, the greatest challenge came mostly from the very large, unprecedented areas that the muon chambers had to cover and the correspondingly large
numbers of electronic channels. The ATLAS muon system contains approximately
25,000 m 2 of active detection planes, and roughly one million electronic channels.
The main parameters of the muon chambers are listed in Table 16.11.
The requirement of achieving all this within ‘reasonable cost’ was actually one
of the biggest issues encountered. In terms of lessons learned from the construction
process; beyond the general observations made in Sect. 16.2.3, three issues emerge
as the most important ones:
• Putting in place, right from the beginning, very tight procedures for quality
assurance/quality control (QA/QC). Given the enormous number of elements
(wires, strips, tubes, supports) involved, the presence of well-defined and complete QA/QC systems was of the utmost importance. Any and all issues which
went unnoticed sooner or later resulted in time and energy-consuming corrective
procedures being taken.
• Planning for services. Despite all initial designs and tolerances and safety factors,
the cabling procedures always turn out to be more complicated, more time-