AIDA-2020 upgrades RPCs for new high-energy accelerators
Daniela Antonio (CERN), 26/11/2018
AIDA-2020 team resposible for the RPC upgrade. Image credit: Giulio Aieli
Resistive Plate Chamber (RPC) technology has been largely used as a gas detector in particle physics for many decades, allowing for cost-effective instrumentation of large areas in the detection of charged particles. For new future accelerators, such as the High-Luminosity LHC and the Future Circular Collider, RPC detectors require an upgrade to meet the demands of the higher particle rates. RPC detectors should have a higher rate capability, better space and time resolution, low noise and occupancy, supported by faster and more sensitive front-end electronics. To satisfy these needs, RPCs have undergone a technological upgrade, defining a new standard of RPC detectors at hadron colliders.
“There are two main differences,” explained Giulio Aieli, from the Istituto Nazionale di Fisica Nucleare (INFN). “We increased the amplifier sensitivity in about a factor of 10 and we halved the gas gap and electrode thickness.”
The higher amplifier sensitivity allows for the detection of smaller electron avalanches, thus increasing the detection rate capability and the longevity of the detector; on the other side, the halved thickness for the gas gap and electrode produces faster electron avalanches, increasing the time resolution from 1ns to 0.4ns on a single measurement. In short, the detector has become more sensitive, thinner and lighter.
Of course, a more senstive detector implies a number of other changes to efficiently exploit the detector’s higher sensitivity, since a more sensitive electronics would be pointless without a correspondingly grounding and noise-rejecting layout. Some other upgrades were made to improve the noise rejection and protection from external mechanical stress. They affected the readout strip-line systems and included the installation of a faster and more sensitive front-end. The re-designed readout strip-lines allow for the increase of mechanical precision.
Since the higher front-end sensitivity allows the RPCs to operate at a regime that allows smaller electron avalanches, it makes them compatible with a wide selection of more ecological gas mixtures. “As a crucial side benefit of the smaller avalanche charge, we enabled the RPC to use gas mixtures with a lower global warming potential (GWP),” adds Aieli.
The upgrade took place in the context of AIDA-2020, by the team of Work Package 13 – Innovative Gas Detectors, as part of the project’s Join Research Activities. The WP13 works included the performance measurement of all the components on real-size prototypes, with a muon beam and intense gamma source, at CERN’s Gamma Irradiation Facility (GIF++).
The first prototype
A first prototype of the upgraded RPCs, with 1mm gas gap and 1.2mm electrodes, consists of two singlet RPC detectors 100x50 cm2 in size. Each detector is read by two orthogonal sets of strips, reading both coordinates, 40 and 20 strips respectively. The strip pitch is 2.5cm. The new highly sensitive front-end electronics readout, operating with just 1000 electrons of noise, was embedded inside the RPC Faraday cage.
The new RPCs and related electronics allowed to set a new record in large dimension single gap RPCs: a time resolution of 0.35 ns a space resolution of 1 mm and a rate capability above 10 kHz/cm^2. Other test indicate that a micrometric resolution is achievable by optimizing the readout strip layout.
Optimised engineering design and production protocols
These upgrades also relate to other works in WP13, namely the optimisation of the engineering design and production protocols for gaseous detectors based on the RPC technology, of which results have also been published recently. The production processes were validated with quality control and assessment on a statistically significant number of industrially-produced detectors. These protocols guarantee a high and uniform quality production of RPC detectors, in view of its large-scale application on scientific applications, such as high performance muon triggers, next generation hadron calorimeters, very large volule time of flight scanners, and life-science applications, such as medical diagnostic investigation and muon tomography for geological volcanology studies, for archeological research and for homeland security.