Etude et impact du bruit de fond corrélé pour la mesure de l'angle ...

52 3. The Double Chooz experiment
tel-00821629, version 1 - 11 May 2013
channels sampling signals at 500 MHz, with 8 bit resolution and 1 V dynamic
range.
The FADC are designed to deal with signal from SPE/channel level up to
about 50 MeV, without saturation. The 40 mV SPE pulse correspond to
> 6 ADC counts. Energies up to the GeV level are covered with amplitude
saturation, which leads to some degree of non-linearity above 100 MeV. The
non-linearity is estimated up to 40 % above 500 MeV.
Every FADC channel has 2 MB of memory bu↵er, holding up to 1024 waveform
of 4 µs length. The memory bu↵er is split into pages with adjustable
size (i.e., read-out window length). Upon a trigger is received, the waveform
is stored and the memory page is changed, giving the possibility to read-out
the memory and continue to sample data without introducing dead times.
The read-out window is set to 256 ns, which contain > 90 % of the scintillation
light emitted. Each waveform consists then in 128 samples of 2 ns
each.
Every PMT (390 from ID, 78 from IV) and FEE output (26 from ID and
18 from IV) are connected to a FADC channel, for a total amount of 512
FADC channels.
3.2.4 Trigger system
DC implements a custom trigger system which relies on the estimation of
the deposited energy in the detector based on the analog sum of the signals
provided by the FEE. There are four units: three trigger boards (TB) and
one trigger master board (TMB). One TB is dedicated to trigger on the
energy in the IV, the other two are dedicated to the ID.
ID trigger boards
ID PMTs are divided in 12 sectors containing 32 PMTs each. Half of the
PMTs from a given sector are connected to the first trigger board TB-A
while the others are connected to the second one TB-B. The FEE sums
signals from a sector, by group of 16 PMTs, and sends it to the trigger
boards. The PMTs are connected to the TBs in such a way each PMT
connected to the TB-A is surrounded by PMT connected to TB-B and vice
versa. Each TB looks at the same detector volume, so the trigger decision
should be always the same among the two boards. This allows an intrinsic
trigger e ciency monitoring (Sec. 4.4.1).
The trigger is made if the detector energy satisfies one of the two configurable
thresholds: pre-scaled (E & 0.2 MeV) and neutrino-like (E & 0.35 MeV).
In case one trigger condition is fulfilled, the TB form an eight bit word
containing the trigger decision and sends it to the TMB.