CMS might provide valuable lessons for future ILC detectors.

The MDI panel about to visit ATLAS.

These air pads are used to move the slices of the CMS detector around.

The ILC detectors come with many question marks attached. What will they look like? Will they be permanently installed or rolled into the beam with a system that lets one take data while the other enjoys a maintenance makeover (called "push-pull")? Despite all these questions, a group of experts on machine-detector interface, the MDI panel, is already thinking about cavern size, heavy-load cranes and cable leads in the return yokes. With the detectors for the LHC nearing completion, the MDI panel visited CERN in October to find out about the dos and don'ts of detector integration.

Norbert Meyners

One of these experts is Norbert Meyners. Employed as a physicist at DESY in the early nineties, he quickly became an expert on machine and detector assembly, especially at DESY's ZEUS experiment and in the planning for the TESLA detector. "Experimental physicists sometimes forget their basic physics laws - gravity, conservation of energy and things like that. That means they forget to think about holes for the cables or fixtures and generally underestimate the logistic needs such a detector has," says Meyners. People like him are involved at this stage already so that planning stays realistic and detector assembly feasible.

The MDI panel looked at the different ways the LHC detectors are assembled. "We poked our noses into every hall, cavern, tunnel and crane to learn as much as possible from our CERN colleagues," explains Wolfgang Lohmann, organiser of the meeting together with Ariella Cattai from CERN. "The ILC detector community faces similar challenges as the LHC and is a point right now where they have to take important decisions," says Cattai, who has been involved in integrating detectors for many years. She was on the team that put Delphi underground and is currently working on CMS. "With all the expertise and experience we're making with the LHC, we thought it would be nice to share facts to speed things up and make our colleagues avoid mistakes."

Tall as a five-storey building and a great deal more complicated, ATLAS, the largest of the four LHC experiments, is assembled in its underground cavern. Each end is served by separate shafts, each of which with a 65-ton crane in place. The group also visited ALICE and CMS, the second largest but heaviest of the four experiments. Unlike ATLAS, it is assembled in a huge hall at the surface, tested and then lowered down by 2000-ton cranes in eleven slices. Airpads are used to move each of the slices into their final position.

The ILC detectors are more likely to look and work like CMS, so the MDI-experts are seriously considering above ground assembly options. "Of course each concept has advantages and disadvantages," says Meyners. Assembling the detector above ground lets scientists put it together and test it while civil engineering goes on underground, which saves a lot of time. The size of the yoke and the need to be able to open the detector by at least three metres on each side will determine the cavern measurements. To save cost, the scientists are striving to keep it as small as possible, but make it as large as necessary. The final focus magnets of the beam delivery system determine the position of the high-tech 'microscope.' The experts also have to consider leaving room for shielding and to allow enough space for infrastructure - electronics, cooling, cables, shafts, lifts and hopefully a visitor facility (something very dear to hearts of the ILC communicators).

The organisers were pleased with the great interest from their Japanese members of the panel, and impressed with their determination to document every detail. "My personal favourite was a presentation on radiation protection and the state-of-the-art radiation monitoring system that was installed and tested in the CMS magnet," recounts Lohmann. "The CERN people certainly know their stuff!"

View the slides.

-- Barbara Warmbein