Cooling and Timing tests of the ATLAS Fast Tracker VME boards

TL;DR

This paper details the integration, cooling, and testing of the ATLAS Fast Tracker VME boards, focusing on power management, thermal stability, and system performance in a high-energy physics trigger upgrade.

Contribution

It presents the design, implementation, and testing of a custom cooling system for the high-power VME boards in the ATLAS FTK system, ensuring stable operation.

Findings

Successful integration of 32 PUs and 8 SSBs in the FTK system.

Effective cooling system maintains temperature stability under high power load.

System achieves the required processing rate for ATLAS trigger upgrade.

Abstract

The Fast Tracker (FTK) is an ATLAS trigger upgrade built for full event, low-latency, high-rate tracking. The FTK core, made of 9U VME boards, performs the most demanding computational task. The Associative Memory Board Serial Link Processor (AMB) and the Auxiliary card (AUX), plugged on the front and back sides of the same VME slot, constitute the Processing Unit (PU), which finds tracks using hits from 8 layers of the inner detector. The PU works in pipeline with the Second Stage Board (SSB), which finds 12-layer tracks by adding extra hits to the identified tracks. In the designed configuration, 16 PUs and 4 SSBs are installed in a VME crate. The high power-consumption of the AMB, AUX and SSB (respectively of about 250 W, 70 W and 160 W per board) required the development of a custom cooling system. Even though the expected power consumption for each VME crate of the FTK system is high compared to a common VME setup, the 8 FTK core crates will use $\approx$ 60 kW, which is just a fraction of the power and the space needed for a CPU farm performing the same task. We report on the integration of 32 PUs and 8 SSBs inside the FTK system, on the infrastructures needed to run and cool them, and on the tests performed to verify the system processing rate and the temperature stability at a safe value.