Speaker
Description
Summary
The ALICE Central Trigger processor and its requirements have been in development
over a period of about ten years. The present trigger concept dates from 2001.
ALICE expects to take data in a number of different running configurations, using
various ion-ion beams and also using pp collisions, the latter at a significantly
lower luminosity than the other LHC experiments. The principal design aim for the
experiment has been to choose detectors that allow the measurement of very high
multiplicities (up to 8 000 tracks in the main detector), and this has led us to a
set of detectors with somewhat inhomogeneous intervals for detection and readout of
signals. These range from a large Time Projection Chamber (TPC), which is
sensitive
for a period of 88 μs and which reads out throughout this interval, to triggering
detectors (T0 and V0) sampling forward multiplicities, which are able to resolve a
single bunch crossing. The ALICE trigger addresses these problems by implementing
partitioning of the detector, so each partition has an independent dead time, and
through the imposition of a “past-future protection” interval, related to the
sensitive time of the detectors, during which only a programmable restricted number
of additional collisions can take place.
The trigger handles combinations of up to 50 trigger inputs and runs up to 50
triggers in parallel; these are mediated through the trigger class, a trigger
specification combining trigger inputs, trigger output detectors (the detector
cluster) past-future protection requirements and certain other flags.
The Central Trigger Processor (CTP) is implemented using 6 different types of 6U
VME board, together making up eleven active boards for the CTP. In addition, for
each detector there is a Local Trigger Unit (LTU) which receives trigger
information for the specific detector from the CTP and provides the interface to
the detector, where appropriate through the RD-12 TTC system. The LTU can also be
used in standalone mode as a generator of simulated trigger signals. The LTU boards
for ALICE have now been produced, and the production of CTP boards will have been
completed by the end of September 2005.
