16 Integration of Detectors into a Large Experiment: Examples from ATLAS. . .
709
the experiments and those planned 9 years ago, it is important to remember the
prominent events, at CERN and within the collaborations, which happened during
these years:
• at the time of the submission of the various TDRs for ATLAS and CMS,
the construction and installation schedule was worked out top-down, based
on a ready-for-operation date of summer 2005 for the LHC machine and the
experiments;
• in 1999, the CMS collaboration decided to replace the micro-strip gas chamber
baseline technology for the outer part of their Inner Detector by “low-cost”
silicon micro-strip detectors. This is probably the most outstanding example of
decisions, which the collaborations had to take after the TDRs were submitted
and which have affected the construction schedule in a major way;
• in 2001, when the CERN laboratory management announced significant cost
overruns, mostly in the machine, but also in the ATLAS and CMS experiments,
it also announced a 2-year delay in the schedule for the machine, which
obviously led to a readjustment of the construction and installation schedule of
the experiments. By that time, both in ATLAS and CMS, the Technical Coordination teams had worked out a realistic installation schedule, which still
needed to be fleshed out substantially in areas such as services installation,
commissioning of ancillary equipment for operation of the huge devices to be
operated underground, etc.;
• the ATLAS experimental cavern was delivered more or less on time in spring
2003, whereas the CMS experimental cavern suffered considerable delays and
was delivered only towards the end of 2004.
16.2.3.2 Physicists and Engineers: How to Strike the Right Balance?
This is a very delicate issue because there exists no precise recipe to solve
this problem. The ATLAS and CMS experiments were born from the dreams of
physicists but are based today on the calculations and design efforts from some
of the best teams of engineers and designers in the world. One should not forget
that, originally (in 1987), even the physicists thought that only a muon spectrometer
behind an iron dump was guaranteed to survive the irradiation and that most tracking
technologies were doomed at the highest luminosities of the LHC [16].
Although a strong central and across-board (from mechanics to electronics,
controls and computing) engineering effort would have been desirable from the
very start (i.e. around 1993), a standard centralised and very systematic engineering
approach alone, as is frequently used in large-scale astronomy projects, could not
have been used for several reasons:
• the cost would have been prohibitive;
• only the physicists can actually make the sometimes difficult choices and
decisions when faced with problems requiring certain heart-wrenching changes
in the fundamental parameters of the experiment (number of layers in the
709
the experiments and those planned 9 years ago, it is important to remember the
prominent events, at CERN and within the collaborations, which happened during
these years:
• at the time of the submission of the various TDRs for ATLAS and CMS,
the construction and installation schedule was worked out top-down, based
on a ready-for-operation date of summer 2005 for the LHC machine and the
experiments;
• in 1999, the CMS collaboration decided to replace the micro-strip gas chamber
baseline technology for the outer part of their Inner Detector by “low-cost”
silicon micro-strip detectors. This is probably the most outstanding example of
decisions, which the collaborations had to take after the TDRs were submitted
and which have affected the construction schedule in a major way;
• in 2001, when the CERN laboratory management announced significant cost
overruns, mostly in the machine, but also in the ATLAS and CMS experiments,
it also announced a 2-year delay in the schedule for the machine, which
obviously led to a readjustment of the construction and installation schedule of
the experiments. By that time, both in ATLAS and CMS, the Technical Coordination teams had worked out a realistic installation schedule, which still
needed to be fleshed out substantially in areas such as services installation,
commissioning of ancillary equipment for operation of the huge devices to be
operated underground, etc.;
• the ATLAS experimental cavern was delivered more or less on time in spring
2003, whereas the CMS experimental cavern suffered considerable delays and
was delivered only towards the end of 2004.
16.2.3.2 Physicists and Engineers: How to Strike the Right Balance?
This is a very delicate issue because there exists no precise recipe to solve
this problem. The ATLAS and CMS experiments were born from the dreams of
physicists but are based today on the calculations and design efforts from some
of the best teams of engineers and designers in the world. One should not forget
that, originally (in 1987), even the physicists thought that only a muon spectrometer
behind an iron dump was guaranteed to survive the irradiation and that most tracking
technologies were doomed at the highest luminosities of the LHC [16].
Although a strong central and across-board (from mechanics to electronics,
controls and computing) engineering effort would have been desirable from the
very start (i.e. around 1993), a standard centralised and very systematic engineering
approach alone, as is frequently used in large-scale astronomy projects, could not
have been used for several reasons:
• the cost would have been prohibitive;
• only the physicists can actually make the sometimes difficult choices and
decisions when faced with problems requiring certain heart-wrenching changes
in the fundamental parameters of the experiment (number of layers in the