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MODULAr: concept design of internal detector mechanics


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Title: MODULAr: concept design of internal detector mechanics

MODULAr concept design of internal detector
A. Menegolli, University and INFN Pavia
Basic Considerations
  • The basic requirements of a large LAr detector
    like MODULAr are
  • precision in wires positioning (100 µm)
  • uniform purification of the full Argon volume.
  • The ICARUS-T600 mechanics successfully fulfills
    the above requirements if evacuated before
  • Scaling the T600 detector to significant larger
    sizes requires a relatively small revision of the
    design the main new task is to preserve the LAr
    purity even in case of a filling procedure
    without previous dewar evacuation.

MODULAr structure
The structure of the MODULAr detector has been
considerably streamlined in order to reduce the
number of components, their cost and increase the
reliability of the system.
The modular structure allows to repeat the
initial engineering design of the prototype to a
series of several subsequent units, reducing
progressively their cost and their construction
time the basic unit is a 10 kton sensitive LAr
The main aim of MODULAr detector is the one of
filling and maintaining over many years a very
large amount of ultra-pure LAr in stable
conditions inside a dedicated underground cave,
within very rigid safety conditions.
Under such conditions, a 20 kton sensitive volume
modular detector might be operative in 4 years,
and additional clone units of 10 kton each could
be built during the years depending on the
physics requirements.
Geometry of an ICARUS-T600 half-module (T300)
cloned into a larger detector scaled by a
factor 8/3 2.66 the cross sectional area of
the planes is 8 x 8 m2 rather than 3 x 3 m2. The
length of such a detector is 50 meters.
3 m
3 m
ICARUS-T600 mechanics review
LAr containers solution with Aluminum honeycomb
panels 150 mm thick the total internal volume of
a cryostat is (3.9 x 3.6 x 19.6 275) m3.
Perforated 142 mm aluminum honeycomb
Each of the two T300 half-modules hosts a
stainless-steel mechanical structure that
sustains the different inner detector subsystems,
in particular way the TPC wire planes.
Inner detector
Horizontal beams
Stainless-steel structure (beams and pillars)
Peek supports
Mechanical precision achieved for all the inner
detector parts 100 mm
Event images are not distorted by misalignment
of wire planes.
MODULAr mechanical structure
MODULAr mechanical structure has been studied in
order to be highly streamlined, taking as a
reference the work done for the T600. It is
essentially made of only three main mechanical
  1. an external insulating vessel
  2. a linear supporting and holding structure
  3. the liquid Argon and Nitrogen supply and

The external insulating vessel is made of two
metallic concentric volumes with the inter-space
filled with perlite as a thermal insulation.
Perlite insulation
Low conductivity foam glass light bricks for the
bottom support layer
Perlite mineral vastly used industrially easily
available at low cost.
A 1.5 m thickness of perlite corresponds to a
specific heat loss of 3.86 W/m2, significantly
smaller than the specific heat loss of
ICARUS-T600 (7 W/m2). Taking into account the
dimensions of the vessel, the total heat loss is
8.28 kW three units of 4 kW (cold) power should
be adequate to ensure cooling of the walls of
the vessel during normal operation (the plant of
ICARUS-T600 consists of 10 units).
Evacuation of the perlite is unnecessary
Like ICARUS-T600, MODULAr wire frame design is
based on the concept of the variable geometry
design beams of the wire frames are movable.
Frame beams are connected by a set of calibrated
springs compensating for tension increase on
wires possibly occurring during cooling and
filling phases.
T600 tensioning system (springs and movable frame)
The wire mechanical tension is kept constant
HV system
The HV system produces a stable and uniform field
over the 4 m maximum drift length. The cathode is
biased with negative voltage (-200 kV for a
nominal drift field of 0.5 kV/cm) the field is
kept uniform by means of a series of equally
spaced field shaping electrodes (race tracks)
surrounding the active volume voltage on the
race tracks is distributed from the cathode by
means of a resistive divider chain.
To reduce the noise induced by the power supply
ripple, in ICARUS-T600 a highly efficient
rejection two-stage RC filter has been designed
and implemented.
Nominal HV for a T300 half-module 75 kV for 1.5
m drift (E 0.5 kV/cm). HV system operated in
steady conditions up to 150 kV.
HV feedthrough
The refrigeration with N2 circulation, provides
cooling of the Argon volume ensuring that the
Argon properties (drift velocity) are uniform all
over the active volume the whole
liquid is moving orderly inside the vessel
volume also the free electrons lifetime is kept
MODULAr wire arrangement
Like ICARUS-T600, a MODULAr LAr TPC is composed
of two read-out wire planes (three orders of wire
planes at 60 and 0 each) with a HV cathode in
The MODULAr read-out wires are also scaled out by
a factor 8/3 2.66 with respect to the existing
ICARUS-T600 wires.
Three orders wire planes
Longer MODULAr wires have a higher capacitance
and the S/N ratio is significantly decreased
(wires 10 pF/m cables 50 pF/m).
This factor is compensated widening the pitch
from the 3 mm of ICARUS-T600 to the 6 mm of
MODULAr, doubling the dE/dx signals therefore we
expect S/N ratios similar to the ones of the T600
( 10/1).
The average LAr mass observed by each read-out
wire is about 200 Kg/channel a 20 kton sensitive
volume will then require a number of channels of
the order 100,000.
MODULAr wire features
  • For each 10 kton modular unit, about 50,000
    stainless-steel wires of several lengths will be
  • 10 m for 60º wires
  • - 25 m for 0º wires (2 coplanar, adjacent sets
    per wire plane)
  • 1301014 cm for corner wires.
  • Because of the 50 m length of the MODULAr
    detector, the horizontal (0º wires) read-out
    plane will be subdivided in two sub-planes
    hosting 25 m wires.

MODULAr wire production, holding, tensioning and
storing make use of the technologies already
developed and tested for the ICARUS-T600 wires.
ICARUS-T600 9 meter wire
Peek comb
Slipknots at both ends
Printed board
Golden stainless-steel ferrule
Peek shell
The wires are held in place by winding over
themselves (like guitar chords) after having
passed them around a golden stainless steel
sleeve. The wires are fixed in position by
inserting the sleeves into the pins of 32 wire
holding combs.
Stainless steel comb holder
The 32 wire modules are fixed on the high
precision supporting and holding frames.
Wire tension T 1169 4 g
Wire holdings
T (g)
Breaking tension B 2923 98 g
T (g)
Wiring devices
Wire module rolling around a PVC spool
Tensioning group to fix and tension the wires
Wiring table
Wiring could begin at any time and the wire
modules can be cleaned and stored until
PVC spools after washing and during drying
Wire production speed for T600 wires 1 hour
for the assembly of a 32 wires module
PMTs for light collection
As for ICARUS-T600 a number of photomultipliers
located behind the read-out wire planes are used
to provide a t 0 trigger.
This is important for the cosmic rays and proton
decay events (no starting signal provided), but
could as well very useful in order to tag events
coming from CNGS beam.
The technique consists in glass 8 PMTs with a
thin deposit of wavelength shifter in order to
record the prompt (µs) VUV scintillation light
from the LAr.
New 8 PMTs are being developed with about twice
the Quantum Efficiency of the PMTs originally
used in ICARUS-T600, that was around 10.
The minimal requirement for MODULAr PMT trigger
is the detection of 10 MeV signals (SuperNova
neutrinos) in such case about 100 PMTs for
read-out plane are needed (minimum signal 8
Summary (1)
  • The mechanical structure of the MODULAr detector
    will use as a starting point the ICARUS-T600
    geometry, which is taken as a reference design.
  • The structure of the detector will be
    considerably streamlined in order to reduce the
    number of components, the cost and the
    construction time a modular detector of 20 kton
    sensitive volume could be operational in 4 years.
  • The geometry will be a clone of an ICARUS-T600
    half-module into a larger detector with linear
    dimension scaled by a suitable factor.

Summary (2)
  • The basic module is a 10 kton sensitive volume
    ICARUS-T600-like detector (2 x 5 kton) insulated
    by a vessel made of two metallic concentric
    volumes with the inter-space filled with perlite
    as a thermal insulation.
  • The detector clone modules will be located in a
    new experimental area, now under consideration,
    to be realized about 10 Km off-axis from LNGS,
    tailored specifically to the MODULAr experiment.
  • Further 10 kton modular units can be added in
    the course of the years, provided experimental
    halls are realized, depending on the physics
    requirements the engineering of the modular
    units would strongly reduce the cost and the time
    for the realization of a LAr detector of several
    tens of kton.