Diapositiva 1

1

The trigger system of the ICARUS Experiment
A.G. Cocco, M.Della Pietra, A.Di Cicco, P.Di
Meo, A.Ereditato, G.Fiorillo, P.Parascandolo,
R.Santorelli, P.Trattino, B.Baboussinov,
S.Centro, F.Pietropaolo, S.Ventura Università
Federico II and INFN, Sezione di Napoli Via
Cinthia, I-80126 Napoli, Italy Università degli
Studi di Padova and INFN, Sezione di Padova Via
Marzolo,8 35131 Padova, Italy
INTRODUCTION AND OBJECTIVES
THE SECOND TRIGGER LEVEL -TRIGGER CONTROL UNIT-
The ICARUS detector is a very massive liquid
Argon Time Projection Chamber aimed at the study
of some of the fundamental issues of
astroparticle physics such as solar and
atmospheric neutrino interactions, neutrinos
following a Supernova explosion, neutrino
oscillations with beams from particle
accelerator,nucleon decay for some channel
predicted by GUTs. The main challenge of the
ICARUS trigger system is to be able to detect the
events induced in the detector by rare
phenomenon such as the Supernova explosions. For
this purpose we have designed a segmented trigger
system. The proposed design is based on three
trigger levels. The first one has been tested on
a small LAr TPC detector, the architecture and
the design of the other two levels are presently
being defined.
The Trigger Control Unit, which is a VME module,
performs coincidences amongst the fired wires
from the different planes and with PMTs and
validates the trigger proposals passing their
addresses to the next trigger level. It provides
analysis of each incoming event distinguishing
between global and local ones. It determines the
nature of the event on the basis of the energy
deposition, the detector occupancy, the 2D/3D
pattern of fired pixels. The second trigger level
is preliminarily implemented on the UNIBOARD.
En11 MeV
En12 MeV
En900 MeV
Em10 GeV
DATA ACQUISITION OVERVIEW
The picture includes simulated neutrino
interactions and passing muons. The energy
releases in the detector as seen in the two
projections (top) and as reconstructed by the
trigger (bottom) are shown. The fired pixels are
displayed in red.
The chamber readout scheme consists of three
parallel wire planes the first facing the drift
region, with horizontal wires (Induction I
plane) the other two with the wires at 60 from
the horizontal direction (Induction II and
Collection planes). The 3D image reconstruction
of the event is provided by the signal of the
electrons crossing the three wire planes,
together with the measurement of the drift time
(performed using a photomultiplier system).
THE THIRD TRIGGER LEVEL -TRIGGER SUPERVISOR-
TRIGGER ARCHITECTURE
The Trigger Supervisor which is a VME module,
validates the trigger request according to the
DAQ status, performs the trigger distribution and
monitoring. In addition it performs statistical
computations such as the number of valid
triggers, the number of global triggers, the
number of local triggers, etc.

• The trigger scheme is based on three levels
• the Local Trigger Control Unit (LTCU) which is
  remotely controlled by RS232, receives the
  Analogue Wire Sums from the CAEN V791 (front end
  board serving 32 input channels) and from PMTs
  and provides the first trigger level proposals.
  Each analogue crate can host one LTCU
• the Trigger Control Unit (TCU) implements the
  actual trigger logic. It performs a topological
  analysis of each event distinguishing between
  local and global ones on the basis of number and
  pattern of fired pixels. The whole detector can
  be handled by four TCU modules
• the Trigger Supervisor (TS) provides the trigger
  signal distribution (sending the trigger requests
  to the V783), control, analysis and statistical
  monitoring of the system.

TEST PERFORMANCE OF THE LTCU WITH A PROTOTYPE
DETECTOR
We measured the LTCU efficiency on a LAr TPC
detector exposed to cosmic-rays, using a PMT
viewing the LAr scintillation and working in
high efficiency conditions. It is used to provide
the external trigger. The trigger proposals from
the LTCU have been recorded by the DAQ. The
efficiency has been evaluated as the fraction of
trigger proposals generated wrt the total number
of detected events as a function of the tracks
incidence angle. The maximum measured efficiency
is around 80. This result can be ascribed to the
noise of the board, estimated around 20 mV and
due to the absence of a ground plane. The new
board version, which will be soon available is
based on eight layers layout and additional
shielding against environmental noise.
THE FIRST TRIGGER LEVEL -LOCAL TRIGGER CONTROL
UNIT-
PHYSICS MOTIVATIONS AND SEGMENTATION

• The digital stage provides
• masking of the noisy inputs
• setting of the comparators threshold
• test pulsing
• setting of the time windows for rate
  measurements.

The Trigger system has been designed to be able
to detect some of the most interesting, but
extremely rare, events such as those induced by
Supernova explosion. Due to the high rate, such
an event could not be handled if one aims at
storing for each event the whole detector image.
However, the events induced by a Supernova
explosion are low energy events which have a
little occupancy of the detector, as shown by
Montecarlo Simulations. The proposed design has
the capability to select the volume around the
event and only readout the few corresponding
channels (local events), leaving the other
unaffected channels free to record further
events, thus reducing the global dead time.
The elementary unit which contributes to define
the picture of the event is called pixel and it
is defined by the coincidences between 9 AWS from
the Collection plane and 9 AWS from the Induction
II plane.
CONCLUSIONS

• The Trigger system of the ICARUS experiment is
  based on three levels and a segmented
  architecture.
• The LTCU, that processes the signals from
  readout wire planes of the detector has been
  prototyped and tested on a TPC detector in order
  to evaluate the noise conditions and fake trigger
  rate due to electronic noise. A new version of
  the LTCU is presently being mounted.
• The architecture of the two higher trigger
  levels are presently being defined.

The analogue stage provides filtering and
discrimination.
14th IEEE-NPSS Real Time Conference 2005, June
4-10 2005, Stockholm-Sweden
Presented by Adele Di Cicco