Speaker
Description
Summary
An Underwater Neutrino Telescope uses large area PMTs
inside OMs to detect the Cherenkov light from the muons
generated by neutrinos in the seawater. The PMTs are put in a
17” glass sphere capable to stand at more than 350 Atm
external pressures. The signals at the output of PMTs must be
suitably coded and sent on-shore. The OM contains the PMT
and its power supply board, the front-end electronics, the data
pack and transfer electronics, the slow control interface and a
set of environmental sensors.
The work described in this paper is aimed at the
development of the low-power front-end for the Optical
Modules (OM) of the NEMO submarine neutrino detector
[2,3,4,7]. A mini-tower equipped with 16 OMs (NEMOPhase1
MiniTower) has been successfully deployed in
December 2006 in front of the Catania harbour as a first
prototype. It uses the front-end electronics described in [1].
The technological solutions adopted for the NEMO
MiniTower provide results well in agreement with
expectations. In the meantime, we have proceeded in our
development of a solution which can fulfil all requirements of
a km3-scale detector, in particular for what concerns power
consumption, PMTs aging and signal dynamics.
Our work is based on the design of an Application
Specific Integrated Circuit (ASIC) for the development of the
Trigger, the PMT signal classification and fast sampling of
the PMT signal, which is performed according to the signal
classification. Moreover, commercial ADCs and a Field
Programmable Gate Array (FPGA), provide digital encoding,
data packing and then data transfer towards the shore station
for acquisition.
A board containing the PMT interface electronics, the
ASIC, the ADC and the FPGA constitutes the OM front-end.
By means of the FPGA, this board receives the slow control
and transmits the measurements of environmental parameters
such as temperature, humidity etc., together with the data.
The final version of the chip, named LIRA05, has been
tested and the single blocks, constituting its architecture, that
is, the analog memory, the trigger and single photon classifier
and the clock frequency multiplier, have been characterised.
The board to test the whole front-end together with the PMT
is being prepared.
The design of the front-end board and of the chip, in
particular, are based on parameters and specifications that in
some cases are not yet definitive, for the performance of the
whole detector.
We have used the most recent data coming from
simulations of high energy neutrino events produced in a
submarine detector in order to define the specifications of the
front-end electronics that optimise the detector performance.
These simulations describe the signals collected by each PMT
in the apparatus in response to particle events, taking into
account the optical background due to 40K, the optical
properties of the sea water, the orientation and position of the
PMTs.
As a result a new architecture has been defined for the
chip that performs the sampling.
This new device, called Smart Auto-triggering Sampler
(SAS), will consist of functional blocks very similar to those
already designed and successfully tested.
