Status and Performance of the ALICE Trigger Electronics David Evans The University of Birmingham, UK School of Physics and Astronomy, The University of Birmingham, Birmingham, UK L. Barnby, M. Bombara, D. Evans, G.T. Jones, P.G. Jones, P. Jovanovic, A. Jusko, R. Kour, M. Krivda, C. Lazzeroni, R. Lietava, Z. Matthews, S. Navin, A. Palaha, P. Petrov, O. Villalobos-Baillie The Institute of Experimental Physics of Slovak Academy of Sciences, Košice, Slovakia I. Králik, L. Šándor P.J. Šafárik University, Faculty of Science, Košice, Slovakia J. Urbán

Layout of Talk Introduction ALICE Physics Running Conditions Overview of the Central Trigger Processor (CTP) Trigger classes Sub-detector clusters Past-future protection The Local Trigger Unit Emulation of the CTP Error generation Current status of the project

ALICE Physics Study of the strong interaction (QCD) at LHC energies In particular, the quark-gluon plasma (QGP) and its properties Collide Pb-Pb at LHC energies to form QGP Also collide p-p as reference. In addition, ALICE has extensive p-p physics programme.

Running Conditions 1 month per year – lead-lead collisions at 5.5 TeV per nucleon (1.2 PeV per Pb-Pb collision) L ~ 1027 cm-2 s-1 Interaction rate ~ 8 kHz Event size ~ 86 MB 7 months per year – proton-proton collisions at 7 TeV L ~ 2x1033 cm-2 s-1 Interaction rate ~ 200 kHz Event size ~ 2.5 MB

The ALICE Experiment Central Trigger Processor Size: 16 x 26 metres Weight: 10,000 tonnes Detectors: 18 Central Trigger Processor

Highlights of the ALICE CTP Three levels of hierarchical hardware triggers: L0 (1.2µs after beam interaction) → L1 (6.5µs) → L2 (88 µs) At any time, 24 ALICE sub-detectors dynamically partitioned in up to 6 clusters. Cluster configuration arbitrary and fully programmable – could be exclusive, more likely to overlap. Past-future Protection logic selects events with either no pile-up, or a number of pile-up interactions up to a programmable limit. Independent protection for each cluster; operates on all three trigger levels. High data traffic over the TTC system Channel A: L1 signal Channel B: Orbit, Pre-pulse But also, for each trigger: L1 Data Message - 5 16-bit words RoI Message - 4 words L2a Message - 8 words Upgrades: L0 can be transmitted over TTC (as well as LVDS cable). Status of trigger inputs now transmitted to DAQ at time of L0 trigger.

Position of TTC crate in ALICE Racks are located below the Di-Muon magnet in cavern. short latency for L0 – 1.2µs, but… stray magnetic field radiation no access when beam is on TTC crate supplies LHC clock direct to CTP and to Time-of-Flight detectors. CTP sends L0, L1, L2 signals and messages to sub-detectors via individual TTC partitions.

Context diagram of the Central Trigger Processor (CTP) CTP inputs LHC timing – BC, Orbit 60 trigger inputs 24 L0 24 L1 12 L2 24 BUSY inputs CTP outputs 24 independent sets 7 outputs per sub-detector 168 signals total CTP readout Trigger data for events accepted at L2 level Interaction Record CTP interface ECS, DAQ, RoIP

Block diagram of the CTP Synchronous, pipelined processor 40.08 MHz bunch-crossing clock (BC) Modularity and scalability Logic blocks designed as individual VME boards 6U form-factor 8 PCB layers moderate density

CTP boards in a VME crate Front panel connections Timing inputs Trigger inputs BUSY inputs CTP outputs Interface links Internal connections Custom backplane

L0 Processor board - layout example - VME interface VME Controller FPGA Flash memory Trigger input LVDS receivers L0 Logic FPGA ADC, phase measurement Snap-shot memory (1M x 32) Backplane LVDS transceivers ADC, supply monitor (I2C)

CTP board gallery L0 processor BUSY processor FAN-OUT board In a VME crate …

Trigger (Physics) Classes Trigger class - a basic processing structure throughout the CTP logic There are 50 independently programmable “physics” classes An additional test class - software-triggered, configured “on the fly” (application: calibration trigger, etc.) “Rules of engagement”: A cluster can be associated with an arbitrary number of trigger classes A trigger class, on the other hand, affects only a single cluster The associations are programmable

Generation of the Class L0 Trigger Trigger input selection: fully programmable Shared resources: 2 Scaled-down BCs (1 – 109) 2 Random triggers (1 – 109) 4 BC Masks (1 bit per bunch) Reduction of the class-trigger rate trigger pre-scalers (1 – 106) Cluster selection: Cluster BUSY (1 out of 6) Mandatory global vetoes: DAQ BUSY (trigger enable) CTP BUSY (CTP readout) CTP Dead Time (1.5µs)* All/Rare: boosts the acquisition of rare events * Practically has no effect on trigger efficiency

Past-future Protection circuit 4 independently programmable circuits at each trigger level (+1 for Test Class) 2 identical blocks, based on dual-port memory Sliding time-window during which the interaction signal (INTa/b) is counted Programmable parameters: Protection interval (ΔTa/b) 2 Thresholds (THa1/2, THb1/2) Output delay (a/b) Output logic function Delay and alignment of output signals

Local Trigger Unit (LTU) Uniform interface between the CTP and sub-detectors: easier control easier mods/upgrades Unique features: Full CTP emulation (stand-alone mode) Error emulation (front-end tests) VME, 6U form-factor Similar to other CTP boards

Context diagram of the LTU Front panel connections: Inputs from CTP (LVDS) Outputs to TTCvi, TTCex L0, BUSY – sub-detector TTCvi functionality now incorporated in upgraded LTU firmware (LTUvi) Hence no longer used.

Block diagram of the LTU LTU modes: Global (run) mode - propagates CTP signals Stand-alone mode - provides full CTP emulation

Switchboard CTP designed to handle up to 24 simultaneous L0 inputs Recent hardware upgrade CTP designed to handle up to 24 simultaneous L0 inputs covered all known L0 inputs plus gave 6 spare at time of construction. Explosion of possible L0 inputs in last 2 years 18  >40 (although not all needed in single run) Solution: make Switchboard from programmable fan-in/out boards. 25 L0 inputs can be chosen from 50 at any time. All 50 switchboard inputs can be monitored – even if not included in trigger.

CTP - September 2008 Beam pick-up T0 SPD V0 CTP in stable operation with up to 12 sub-detectors in single cluster and with multiple clusters. (i.e. several hours at a time of stable running). During brief period of circulating beams: Timing measurements for trigger inputs made and corrected in software. Trigger on pixel detector (SPD) & trigger detectors. Also triggers on bunch crossings Trigger timing (before alignment) versus bunch number single shot for SPD, V0, beam-pickup BPTX, T0 triggers

Summary ALICE Trigger electronics installed and successfully commissioned with all major sub-detectors and control systems. Several upgrades to hardware, firmware and software made since installation. The ALICE trigger system provided stable operation during several months of cosmic ray running and during first beam from LHC in Sept 2008. We are ready for looking forward to first collisions later this year. Many thanks to the RT2009 organisers and thank you for listening.