Sep 22 – 26, 2014
Centre des Congrès - Aix en Provence, France
Europe/Zurich timezone

Upgrade of the ATLAS Central Trigger for LHC Run 2

Sep 24, 2014, 2:50 PM
Centre des Congrès - Aix en Provence, France

Centre des Congrès - Aix en Provence, France

14 boulevard Carnot 13100
Oral Trigger Trigger


Kristof Schmieden (CERN)


This talk focuses on the upgrades of the ATLAS central trigger processor (CTP) during the past year. The increased energy and luminosity of the LHC in the next run period requires a more selective trigger menu in order to satisfy the physics goals of ATLAS. Therefore the electronics of the CTP is upgraded and the commissioning status will be presented. In addition, the CTP software has been extended to allow the CTP to be partitioned into three freely configurable and separately operating sets of sub detectors. This new approach and its operational advantages are discussed as well.


In the Run 2 period the LHC will increase the instantaneous luminosity and the center-of-mass energy up to 14 TeV, while providing collisions every 25ns. This effectively doubles the collision rate and luminosity compared to Run 1 and requires the ATLAS trigger to be more selective. Overall, reducing the 40 MHz
collision rate to a recording rate of about 1 kHz, while retaining
events of interest for the physics program, is
putting stringent requirements on the ATLAS trigger system hardware,
software, network, and operational resources.

In particular this motivated several upgrades of the Level-1 trigger, the first step of the trigger system,
which needs to reduce the collision rate by a factor 400 down to 100 kHz
with a decision latency of less than 2.5 us. It is primarily composed
of the Calorimeter Trigger, the Muon Trigger, and the Central Trigger
Processor (CTP) which are all implemented in custom-built
electronics. The CTP collects trigger information from all Level-1
systems and forms a Level-1 trigger decision, which, if positive,
initiates the readout of all ATLAS sub-detectors.

Due to the increased instantaneous luminosity in the next run period of the LHC
the first level trigger is required to provide more trigger items, make use of topological trigger information which requires more inputs, and provide a larger flexibility to be overall more selective while satisfying the physics goals of ATLAS.
As a result several components of the CTP and its interfaces have been upgraded, using new electronic, firmware and software.
The new firmware for the CTP input modules operates the trigger path backplane of the switch matrix with double data rate (80 MHz), which doubles the number of usable inputs to 320. Upgraded core modules of the CTP provide twice as many trigger conditions as the previous ones and additional direct inputs to receive information from the topological calorimeter trigger. In order to process topological information from the muon system the firmware of the Muon-CTP
interface is upgraded as well. Also the CTP output modules are upgraded. The new hardware modules also provide extended monitoring capabilities and more flexible configuration options.
The upgraded system is installed and currently tested. Both, system and commissioning progress, will be discussed in the talk.

Additionally the control software system of the CTP has been upgraded, introducing a new approach of managing the CTP which allows a much more flexible use of the hardware. The new CTP can be logically split into three partitions. Each is freely configurable and independently using almost the full functionality of the CTP hardware with a configurable set of subdetectors. This approach is feasible due to the upgraded CTP core and CTP output hardware and firmware and gives clear operational advantages, e.g. allowing for concurrent
calibration runs of several sub-detectors. The design and advantages of this new approach as well as the implication for the system operation will be discussed together with first experiences from the commissioning phase.

Primary authors

Denis Oliveira Damazio (Brookhaven National Laboratory (US)) Francesca Pastore (Royal Holloway, University of London)

Presentation materials