Speaker
Mrs
Alexandra Oltean
Description
The electromagnetic Photon Spectrometer (PHOS) of ALICE measures electromagnetic
showers up to 100 GeV with PbWO4 crystals and APD's placed a cold zone of -25 C.
Readout regions of 448 crystals are combined as coherent trigger regions via analog
signals which are processed by one FPGA-based, Trigger Region Unit (TRU). The
signals are 2*2 analog sums with 100 ns shaping time, connected over equal length
flat cables from 14 FEE digitizer boards to a centrally placed TRU board with an
FPGA which receives all signals from the trigger region after 8 bit, 40 MHz
conversion. Both level-0 and level-1 trigger algorithms are executed within the
FPGA, consisting on charge summing over sample times and over 4*4 crystal windows.
Due to external latencies, the level-0 decision is due after 300 ns processing time,
whilst 5 us are available for more refined level-1 decisions. The trigger outputs
are transmitted as 40 MHz Yes/No signals to the central trigger processor. The 10
layer TRU cards have been designed around a 50 kilogate Xilinx VirtexPro FPGA, with
external reconfiguration logic, allowing to detect and correct single event upsets
during operation. In view of further applications in Alice, the TRU is equipped with
a level-0 multiplicity input and 1 Gbit/s serial outputs for building hierarchies of
TRU triggers. Eight TRU cards are embedded together with 112 FEE cards inside the
closed PHOS modules, necessitating water cooling for both TRU and FEE cards via
surrounding copper cassettes.
Author
Dr
Hans Muller
(CERN)
Co-authors
Prof.
Bernhard Skaali
(University of Oslo, Physics Department)
Prof.
Dieter Rohrich
(University of Bergen, Physics Institute)
Rui Pimenta
(CERN)
Xi Cao
(HUST Wuhan, China)
