Speaker
Mikel Eukeni Pozo Astigarraga
(CERN)
Description
ATLAS is a Physics experiment that collects high-energy particle collisions at the Large Hadron Collider
at CERN. It uses tens of millions of electronics channels to capture the outcome of the particle bunches
crossing each other every 25 ns. Since reading out and storing the complete information is not feasible
(~100 TB/s), ATLAS makes use of a complex and highly distributed Trigger and Data Acquisition (TDAQ)
system, in charge of selecting only interesting data and transporting those to permanent mass storage (~1 GB/s) for later analysis.
The data reduction is carried out in two stages: first, custom electronics performs an initial level of
data rejection for each bunch crossing based on partial and localized information. Only data corresponding
to collisions passing this stage of selection will be actually read-out from the on-detector electronics.
Then, a large computer farm (~17 k cores) analyses these data in real-time and decides which ones are
worth being stored for Physics analysis. A large network allows to move the data from ~1800 front-end
buffers to the location where they are processed, and from there to mass storage. The overall TDAQ system
is embedded in a common software framework that allows to control, configure and monitor the data taking process.
The experience gained during the first period of data taking of the ATLAS experiment (Run I, 2010-2012) has inspired a number of ideas for improvement of the TDAQ system that are being put in place during the
so-called Long Shutdown 1 of the Large Hadron Collider (LHC), in 2013/14.
This paper summarizes the main changes that have been applied to the ATLAS TDAQ system and highlights the
expected performance and functional improvements that will be available for the LHC Run II. Particular
emphasis will be put on the evolution of the software-based data selection and of the flow of data in the
system. The reasons for the modified architectural and technical choices will be explained, and details
will be provided on the simulation and testing approach used to validate this system.
Primary author
Dr
Fabrizio Salvatore
(University of Sussex (GB))
