The module, which was produced in collaboration with STFC's Particle Physics Department (PPD), was installed in ATLAS in 2022 and, as of May 2023, has taken over from the legacy Cluster Processor Module as the primary electron trigger for the ATLAS detector.

Since the success of this collaboration, Technology and PPD have been working closely with Brookhaven National Laboratory in the US to specify, design, assemble and test a new Global Common Module (GCM).

The GCM, as one of the ATLAS experiment's Phase-II upgrades, represents another step towards CERN's goal of a High-Luminosity LHC (HL-LHC).

Supporting the success of the Hi-Lumi Upgrade

The GCM is a state-of-the-art high-speed, high-density, and high-power module created to enable the complex global trigger algorithms that ATLAS requires in the HL-LHC era.

ATLAS generates an enormous amount of raw data at approximately 1 million gigabytes per second.

The experiment's trigger system must wade through this sea of data to identify a (comparatively) small number of interesting physics events.

This is not an easy task. The trigger system is incredibly complex and is implemented in a hierarchical structure, with the first level based on custom hardware and the rest based on software.

The upgrades outlined by the HL-LHC project, which seek to boost the LHC's performance to increase the potential for discoveries after 2029, will make the ATLAS event selection process even more challenging.

To meet those challenges, ATLAS' first-level hardware trigger must be upgraded again to keep its event selection process efficient.

This will be achieved by concentrating all the detector data pertaining to the same bunch collisions into a single hardware processing node, providing the hardware trigger algorithms with a “global view" of physics events.

The GCM is the hardware platform upon which the ATLAS Global Trigger will be running and is a pioneering example of high-energy physics data processing technology.

A single GCM board features more than 200 high-speed serial links (each running up to 25 Gbps) and consumes up to 400W of power.

Extensive computer simulations have been employed to guide the GCM Printed Circuit Board (PCB) layout design, achieving signal integrity, power integrity, and thermal reliability.

In February 2024, the team assembled the first fully functional GCM prototype module, and all power circuits and high-speed links were tested successfully.

A total of around 60 GCM boards will be needed for the ATLAS Global Trigger System and the Technology Department will be responsible for producing approximately half of them.

Doctor Weiming Qian, Principal Design Engineer in STFC Technology Department's Electronic System Design team, said:

"The Global Trigger is of utmost importance to ATLAS. If it doesn't function correctly, the ATLAS experiment won't work and there is no plan B. The STFC Technology Department has first-class engineers and a proven record in high-speed complex digital system design. I'm very proud that we have been entrusted by the ATLAS experiment to develop this critical part of the Phase-II Upgrade together with BNL. I'm also pleased to see that our collaboration with BNL is going well and the test results of the first GCM prototype are very promising. “

Interested in learning more about ATLAS' trigger system? Read our previous blog on Technology's work on the ATLAS eFEX module.

​Written by Cat Lewin-Williams and Weiming Qian.​​