High-rate irradiation of 15mm muon drift tubes and development of an ATLAS compatible readout driver for micromegas detectors

摘要

The upcoming luminosity upgrades of the LHC accelerator at CERN demand several upgrades to the detectors of the ATLAS muon spectrometer, mainly due to the proportionally increasing rate of uncorrelated background irradiation.ududThis concerns also the "Small Wheel" tracking stations of the ATLAS muon spectrometer, where precise muon track reconstruction will no longer be assured when around 2020 the LHC luminosity is expected to reach values 2 to 5 times the design luminosity of $1 imes 10^{34} ext{cm}^{-2}ext{s}^{-1}$, and when background hit rates will exceed 10 kHz/cm$^2$. This, together with the need of an additional triggering station in this area with an angular resolution of 1 mrad, requires the construction of "New Small Wheel" detectors for a complete replacement during the long maintenance period in 2018 and 2019.ududAs possible technology for these New Small Wheels, high-rate capable sMDT drift tubes have been investigated, based on the ATLAS 30 mm Monitored Drift Tube technology, but with a smaller diameter of 15 mm.ududIn this work, a prototype sMDT chamber has been tested under the influence of high-rate irradiation with protons, neutrons and photons at the Munich tandem accelerator, simulating the conditions within a high luminosity LHC experiment. Tracking resolution and detection efficiency for minimum ionizing muons are presented as a function of irradiation rate. The experimental muon trigger geometry allows to distinguish between efficiency degradation due to deadtime effects and space charge in the detectors. Using modified readout electronics the analog pulse shape of the detector has been investigated for gain reduction and potential irregularities due to the high irradiation rates and ionization doses.udThis study shows that the sMDT detectors would fulfill all requirements for successful use in the ATLAS New Small Wheel endcap detector array, with an average spatial resolution of 140 $mu$m and a track reconstruction efficiency of around 72% for a single tube layer at 10 kHz/cm$^2$ irradiation rate.ududA second proposal for a New Small Wheel detector technology are Micromegas detectors. These highly segmented planar gaseous detectors are capable of very high rate particle tracking with single plane angular resolution or track reconstruction. The ATLAS community has decided in 2013 in favor of this technology for precision tracking in the New Small Wheels.ududA prototype Micromegas detector will be installed in summer 2014 on the present ATLAS Small Wheel to serve as test case of the technology and as template for the necessary changes to the ATLAS hardware and software infrastructure.udTo fully profit from this installation, an ATLAS compatible Read Out Driver (ROD) had to be developed, that allows to completely integrate the prototype chamber into the ATLAS data acquisition chain. This deviceudcontains state-of-the-art FPGAs and is based on the Scalable Readout System (SRS) of the RD51 collaboration.udThe system design, its necessary functionalities and its interfaces to other systems are presented at use of APV25 frontend chips. Several initial issues with the system have been solved during the development.udThe new ROD was integrated into the ATLAS Monitored Drift Tube Readout and into a VME based readout system of the LMU Cosmic Ray Facility. Additional successful operation has been proven meanwhile in several test cases within the ATLAS infrastructure. The whole data acquisition chain is ready for productive use in the ATLAS environment.