Electronics design and system integration of the ATLAS New Small Wheels

The upgrades of the Large Hadron Collider (LHC) at CERN and the experiments in 2019/20 and 2024/26 will allow to increase the instantaneous luminosity to L =2× 10³⁴ cm⁻² s ⁻¹ and L =5−7× 10³⁴ cm⁻² s ⁻¹, respectively. For the High Luminosity (HL) HL-LHC phase, the expected mean number of interactions per bunch crossing will be 55 at L =2× 10³⁴ cm⁻² s ⁻¹ and 140 at L =5× 10³⁴ cm⁻² s ⁻¹. This increase drastically impacts the ATLAS trigger system and trigger rates. For the ATLAS Muon Spectrometer, a replacement of the innermost endcap stations, the so-called ''Small Wheels', which are operating in a magnetic field, is therefore planned for 2019/20 to be able to maintain a low pT threshold for single muons and excellent tracking capability in the HL-LHC regime. The New Small Wheels will feature two new detector technologies: resistive Micromegas and small strip Thin Gap Chambers comprising a system of 2.4 million readout channels. Both detector technologies will provide trigger and tracking primitives fully compliant with the post-2026 HL-LHC operation. To allow for some safety margin, the design studies assume a maximum instantaneous luminosity of L =7× 10³⁴ cm⁻² s ⁻¹, 200 pile-up events, trigger rates of 1 MHz at Level-0 and 400 KHz at Level-1. A radiation dose of 1700 Gy (innermost radius) is expected. The on-detector electronics will be implemented on some 8000 boards; four different custom ASICs will be used. The large number of readout channels, high speed output data rate, harsh radiation and magnetic environment, small available space, poor access and low power consumption all impose great challenges for the system design. The overall design and first results from integration of the electronics in a vertical slice test will be presented.