CERN Accelerating science

A new home for GEM detectors at CERN

by Rui De Oliveira (CERN)

Since the beginning of  2019, a new building at CERN is ready to house ongoing R&D activities that will push the performance of detectors to cope with the high performance of the LHC.

Building No.107 (replacing the building 102) offers a brand new laboratory with sophisticated equipment, needed to advance key detector technologies. It houses three main activities: the TE / VSM service, the EP / DT / MPT service and finally the TE / MPE service.

The main activities on the so-called Saleve side of the building is the "TE/VSM service, also known as the surface treatment workshop”, it includes the galvanic deposition of many metals and advanced surface cleaning to reach extreme vacuum condition for the LHC.

The MPT "Micro Pattern Technologies" service, is housed in the centre of the building, offering the manufacturing of printed circuits boards of all complexities as well as the design and production of a large number of detectors type MPGD (Micro Pattern Gas Chamber). Finally, coming to the Jura side, “TE / MPE service” is the official CERN PCB design office mainly involved in the electronic component assembly workshop (fig.1).

Fig. 1: Bird’s eye view of the activities in building 107

The TE/VSM and EP/DT/PMT services are physically linked because they share the same water treatment plant, they also use similar chemical processes. On the other hand, EP/DT/PMT and TE / MPE services are strongly linked due to the nature of the ongoing activities around the manufacture of PCBs. This was also the original motivation for ​​grouping these activities in the same building.

The first suggestion that the building 102 should be drastically renovated to meet modern requirements came in 2006. After studying many scenarios, the decision was made in 2011 to construct a new building. A period of approximately one year has been assigned to the drafting of the specifications while the construction site started in 2012 and was officially finished at the end of 2017.

The ergonomics of building 107 now meet the latest standards foreseen also space for future expansion of the ongoing activities. As far as safety is concerned, the building fully satisfies current legislation, often exceeding legal requirements and has been cited as an example by many delegations that visited CERN during audits. Thanks to the new equipment, the new laboratory meets the most stringent standards in the field (fig.2).

Fig. 2: New chemical processing lines in the room 107 RA 27

Another motivation for the construction of this building was the ability to provide correct production infrastructure for LHC upgrades and experiments. Many are currently in progress but we will quote two as an example: the modification of ALICE TPC detector, and the increase of Muon detector performance for CMS. In both cases, it has been chosen to introduce gas particle detectors based on GEM (Gas Electron Multiplier).

The EP / DT / MPT workshop have constantly improved this technology (GEM), which began more than 20 years ago and was invented by Dr Fabio Sauli in 1997, and is now a very reliable component allowing its integration into large scale experiments.

 Fig. 3: GEM production team handling different type of GEMs

To achieve these two detectors improvements (ALICE TPC and CMS GE1/1) the amount of GEM to produce required going beyond the stage of a simple laboratory producing prototypes to a quasi-industrial production.

It should be pointed out that this technology is still quite recent and despite many technology transfer attempts, it was impossible at the production start date to find an industrial with this ability. Today the situation is different; some companies now have the capacity to mass-produce.

More than 1400 GEMs have been produced in the EP/DT/MPT service with formats up to 1.5m x 0.6m. This production was spread over a period of 2 years and required the constant effort of a team of five people, up to seven at the peak of production. The production yields of about 70% initially, reached 90% in average at the end of production, with peaks at 100% for some batches. The deadlines imposed by the machine stops have been fully respected.

Many other experiments have chosen this technology and the EP/DT/MPT workshop for the production of their detector components, including COMPASS, LHC-B, KLOE, CBM @FAIR, BM @ N, Phoenix TPC, SBS tracker to name some of them.

Fig. 4: First large production of Micromegas detectors for T2K experiment

Other technologies developed at CERN such as Micromegas detectors (fig. 4) and THGEM detectors have been the subject of numerous productions at CERN for T2K, Compass tracker, Compass RICH, ILC TPC prototypes, ILC Calorimeter prototypes, ATLAS NSW and many others.

Institutes around the world have adopted these technologies for a simple reason: the majority are transferable or have already been transferred to industry. This allows imagining serenely large-scale manufacturing at competitive costs.

The exploration and development of these new technologies has shown that other new, more efficient or economical structures are feasible and are within the reach of any reasonably equipped institute. One of the common features of these new structures is the use of resistive electrodes. Many of these institutes are at work on this topic, they promise bigger, cheaper, extremely light, flexible, faster detectors, with temporal resolutions rivaling the best solid detectors. The range is very large.

Thanks to the quality and the diversity of its equipment, the EP/DT/MPT workshop can play an active role in these developments and in fact it is regularly contacted for the materialization of new concepts in the field of MPGD detectors.

Fig. 5: Detailed layout of the Micro Resistive Well detector

For one of them, namely the Micro Resistive Well detector (Fig. 5), the new EP/DT/MPT workshop can have a bigger impact. This protected version of the Micro Well detector was originally invented in 1998 but soon neglected because of stability problems. However, this concept is back thanks to the addition of the latest concepts of resistive protections.

The first test results show that this detector is endowed with great versatility. It allows realizing large detectors (theoretically up to 2m x 0.5m), it is insensitive to discharges, and it can work at high flux (greater than 10 MHz / cm2) with an excellent spatial resolution (less than 50um) while is very light (with a material budget of less than 0.2% X0). Moreover, it can adapt mechanically to many applications (planar or cylindrical) since it is flexible and finally it is within reach, in terms of production, of many companies producing PCBs.

All in all, the new facility offers a unique equipment that will allow further R&D to be pursued on special detector technologies both for future HEP experiments but also for many other applications outside particle physics. The completion of this building adds to CERN’s excellent infrastructure and strengthens the laboratory’s role as a hub for collaborative R&D efforts.