Precision tracking at high background rates with the ATLAS muon spectrometer

Since start of data taking the ATLAS muon spectrometer performs according to specification. End of this decade after the luminosity upgrade of LHC by a factor of ten the proportionally increasing background rates require the replacement of the detectors in the most forward part of the muon spectrometer to ensure high quality muon triggering and tracking at background hit rates of up to 15,kHz/cm$^2$. Square meter sized micromegas detectors together with improved thin gap trigger detectors are suggested as replacement. Micromegas detectors are intrinsically high rate capable. A single hit spatial resolution below 40,$mu$m has been shown for 250,$mu$m anode strip pitch and perpendicular incidence of high energy muons or pions. The ongoing development of large micromegas structures and their investigation under non-perpendicular incidence or in high background environments requires precise and reliable monitoring of muon tracks. A muon telescope consisting of six small micromegas works reliably and is presently used as precision tracker with position resolution better 20,$mu$m to study a 0.5,m$ imes$,0.5,m large micromegas with novel floating strip anode.\ Micromegas using resistive strip technology have been successfully operated unter $10^7~ rac{neutrons}{cm^2,s}$ of 11,MeV at our irradiation facility at the Garching tandem accelerator laboratory. Using the facility with 20,MeV protons we could show that the track reconstruction efficiency and spatial resolution of 15,mm drift-tube detectors is robust against up to 20,kHz/cm$^2$ highly ionizing background hits. No ageing was observed after accumulating an irradiation dose corresponding to ten years of high luminosity LHC operation.\ In ATLAS most of the 30,mm diameter monitored drift-tube detectors will remain in place. They may be operated using a considerably faster and more linear drift-gas mixture. Such gas mixtures have been shown to be marginally sensitive to high photon fluences and not to age due to ionizing radiation.