Technological Aspects and Developments of New Detector Structures,
Common Characterization and Physics Issues
Contacts: P. Colas, F. Resnati, P. Wintz, I. Deppner, M. Tygat, L. Moleri
Contact email: DRD1-WG1-convenors@cern.ch
WG1 Indico category: https://indico.cern.ch/category/16507/
A large variety of technologies have to be developed to cover the needs of future experiments with cost-awareness and sustainability concerns. Improving existing detectors to make them larger, working at higher rates or lower backgrounds, with better stability and improved performance, will require new technologies and development. Working group 1 will study and monitor the progress in wire, RPC, MPGD and TPC technologies.
Wires
Since the invention of the Multi-Wire Proportional Chamber (MWPC) at CERN by Charpak et al. in 1968, the technology of wire-based gaseous detectors has been continuously developed and further improved to achieve new capabilities. The MWPC technology led to the development of Drift Chambers (DC, 1973) for higher-resolution particle tracking, Cathode-Strip Chambers (CSC, 1977) and Thin-Gap Chambers (TGC, 1983) for tracking with much shorter timing, and (Muon-) Drift Tubes (DT, 1980) or Straw Tube Chambers (1989) with robust mechanical and electrostatic shielding of the anode wire in the center of the cathode tube. All listed technologies, with substantial and continuous technical improvements and enhancements since their invention, are to date widely used in current state-of-the-art HEP and non-HEP experiment installations.
tRPC and RPC
Introduced in 1981 by Santonico and Cardarelli, Resistive Plate Chambers (RPCs) are parallel-plate counters consisting of a thin (about 1-2 mm) gas volume at near-atmospheric pressure, enclosed by two electrodes made of high-resistive materials (orders of 10^9 to 10^13 Ωcm bulk resistivity), such as glass or High-Pressure Laminate (HPL), across which a high voltage is applied up to about 50 kV/cm. RPCs are characterized by an excellent spatial resolution of the order of a few 100 μm, a good time resolution of the order of 1 ns, a high detection efficiency (more than 95%) and rate capability up to about 1 kHz/cm^2. Double-gap configurations exist to enhance detection efficiency. In the 90s, timing-RPCs, in literature also referred as Multigap RPC (MRPC) have been developed by Fonte, Smirnitsky and Williams, where the active volume consists of multiple (up to more than 20) small size (about 100-300 μm) gas gaps, leading to superior time resolutions down to 20-150 ps.
MPGD
The concept of Micro-Pattern Gaseous Detectors (MPGDs) was born with the Micro-Strip Gas Chambers (MSGS) in 1988 to cope with high particle fluxes. The micro-electrodes used to multiply charges in gas were created on different substrates, exploiting technologies from the semiconductor industry (e.g. Photolithography, Etching, etc.). From the MSGC developments, a number of new structures were conceived with amplification around micro-electrodes (e.g. MicroGap, MicroDot, Micro-Groove, Micro-WELL) and with amplification in semi-uniform electric field (e.g. MicroMegas, GEM, THGEM). The R&D done in the last years, in particular within the framework of the RD51 Collaboration, aimed to develop MPGDs for applications in High Energy Physics (HEP) and Nuclear Physics ex- periments. Some notable examples of the employment of MPGDs are the ATLAS New Small Wheel and the CMS forward muon detector systems, and ALICE TPC. MPGDs are also largely exploited in non-collider physics experiments, such as neutrino oscillation experiments, and direct Dark Matter searches, as well as for applications beyond particle physics. For instance, MPGDs are used in X-ray polarimetry experiments, and muography. The popularity of MPGDs is due to some intrinsic qualities of the technology, like the high spatial resolution, high particle-flux capability, large active area with small dead surfaces, and resilience to radiation. Operating MPGDs with stable and uniform gain in certain conditions (e.g. highly ionizing environment, variable irradiation fluxes) remains a challenge to be addressed by future developments.
TPC
TPC A Time Projection Chamber (TPC) is a drift chamber where the timing of the events is used to reconstruct one of the spatial coordinates. The TPC concept was introduced in 1974 by David Nygren and it finds nowadays application in Particle Physics at Colliders, fixed-target experiments, Nuclear Physics, Non-accelerator physics and societal applications (e.g. muography). Until the end of the 1990s TPCs at colliders were read out exclusively by multi-wire chambers (e.g. DEL- PHI and ALEPH TPCs at LEP, the first ALICE TPC at LHC, NA61). Since the invention of MPGDs, many projects focused on their application as a TPC readout. Some of the advantages could be an improved spatial resolution, reduced ion backflow and mechanical robustness of large detectors. In 2009 the T2K/ND280 TPC was read out by Micromegas, and in 2023 the ALICE readout was changed DRAFT into 4-GEMs. Additional TPCs for T2K/ND280 under construction apply the ERAM technique with a resistive anode invented for ILC. As an alternative to the standard charge readout, optical readout of TPCs is developing rapidly, thanks for example to the R&D for CYGNO, DUNE and MIGDAL experiments. Optical readout can also find application in polarimetry.
Challenges
Wires
Future experiments require smaller wire cell sizes, with high mechanical precision (<50 μm) over large wire and detector lengths up to 5 m. Specific R&D topics for large-volume drift chambers with orders of 10^5 anode and field wires are new wiring systems (robots) and the design of modular units of drift cells to facilitate the detector assembly. The technique of ion cluster counting for higher-resolution PID has to be exploited with single-cluster sensitive readout electronics. Straw tube developments include smaller diameter (5 mm), shorter time range (less than 80 ns) for event timing, ultra-thin straw films (15 μm) with minimal radiation length (comparable to the gas volume), and long straw lengths with precise wire centering. Operation in vacuum is a unique application of straw detectors and will be extended to ultra-long straws up to 5 m and large detector gas volumes of 25 m^3. R&D goals include a higher flux capability (of the order of 100 kHz/cm^2) and extending longevity up to charge loads of the order of 10 C/cm, both being a factor of ten higher than current standards. Research on new wire materials, e.g. new alloys or metallized carbon monofilaments with higher strength (Young’s modulus) to reduce sagging and electrostatic deflection is needed. Wire and cathode-coating studies to further improve resistance against high irradiation and extend operation to higher charge loads are continuously needed.
tRPC and RPC
The possible usage of RPCs in high luminosity / high background-rate environments (e.g. the HL-LHC, FAIR and other future facilities) has triggered a number of new efforts to improve the tRPC and RPC rate capability and to extend detector longevity. Those include searches for new electrode materials with lower (compared to regular float glass or HPL) or tunable resistivity such as Fe-doped glass, vanadate-based glasses, ceramics, DLC, or Si-GaAs wafers; the development of low noise, i.e. low threshold, readout electronics (yet keeping a few ps time resolution at high bandwidth); studies of outgassing and material ageing. In addition, following European regulations which increasingly ban the emission of greenhouse gasses, RPCs are facing an important challenge to replace the standard, tetrafluoroethane-based gas mixture with a more eco-friendly alternative. Parallel efforts to limit gas consumption or emission using recirculation and recuperation systems are ongoing. Closely related are the studies to operate RPCs with low flow or even in sealed mode, which is of particular interest also for non-HEP applications. Finally, new chamber geometries such as cylindrical or single-electrode RPCs are being developed to enhance specific performance features.
MPGDs
The next generation of MGPD will have the challenge of operating at high speeds, in stable conditions, covering large surfaces and offering time resolutions ranging from nanoseconds to tens of picoseconds. The typical sturdiness of the MPGD amplification structures makes them appealing for environments with harsh conditions (high irradiation, cryogenics, high and low pressures). The studies of new materials opens up the doors to new fabrication techniques, like 3D printing and additive fabrication, which in turn will enable unprecedented structure geometries.
TPCs
To extend the use of TPCs to higher luminosity and in more noisy environments (e.g. FCC and BELLE II), ion backflow must be minimized. Moreover, electric field distortions created by the space charge of drifting ions have to be mitigated and corrected in real-time. Low-radioactivity materials will be needed in TPCs DRAFT for rare events and negative-ion TPCs. The latter also require solutions for the environmental consequences of using electro-negative gases (with high GWP, like SF6) for rare events and negative-ion TPCs. The latter also require solutions for the environmental consequences of using electro-negative gases (with high GWP, like SF6). To help tackle these challenges, WG1 plans to have regular meetings with representatives from all the communities working with different technologies, where new ideas, new structures, goals, challenges and realizations will be presented, favouring cross-fertilization. This will allow a follow-up of the projects, from their start-up to several years of operation, paying particular attention to the feed- back from experience.