LNGS Scientific Committee
03/05/2010
STATUS REPORT OF ICARUS T600 AT LNGS
We apologize for the late submittal of the paper, but these are truly exceptional times
for ICARUS.
A few days ago the detector’s vacuum has been broken, the volume has been filled
with ultra-pure Argon gas at a slight overpressure. The liquid Nitrogen cool-down of
the ICARUS walls has been started on Friday 16th of April, and filling with liquid
Argon started on the 29th of April.
Then Argon in its liquid form (about 50 truck sized batches!) is transferred firstly at
each time in a large buffer tank to ensure its adequate purity and then, after
verification with an appropriate purity monitor, introduced in the final LAr volume.
We estimate the duration of the process in about two weeks, at the end of which the
HV will be turned on and presumably early tracks detected. At this stage purity will
be eventually improved and maintained both with the gas and liquid purifiers.
Therefore the commissioning of the ICARUS detector is now proceeding smoothly
toward its final phase with 600 tons of ultra pure liquid Argon.
All the safety and technical requirements have been fulfilled.
Hopefully the experiment should be operational both for cosmic beam neutrinos by
the second half of May 2010.
In the following, a summary of the accomplished and on-going activities is presented
in more detail.
1. Cryogenic Plant
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In January, sensors for the measurement of the thermal insulation and lateral
panel deformations were installed, following the request coming from the
Laboratories. This measurement was requested after the partial collapse of the
T600 thermal insulation North panel happened in April 2009. Sensor outputs
have been inserted in the overall Process Control of AEI and are continuously
monitored.
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AEI and LNGS Process Control were aligned from 15th of January to 22nd of
February. A review of the two systems has been held directly in Hall B, jointly
by AEI and LNGS, starting from 7th of April.
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During the second half of March, the ICARUS Collaboration installed forty
temperature sensors, in order to monitor the temperature in several points of
the thermal insulation lateral panels. Temperature measurements will be
compared with the simulations done by Air Liquide, which foresees a
difference from ambient and panel temperatures variable from 3 to 7 degrees.
The thermal losses on the panels will also be compared with the calculation
done by Air Liquide (AL).
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At the end of March, the procedures for the start-up of the T600 have been
delivered and signed by the ICARUS Collaboration.
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LNGS Scientific Committee
03/05/2010
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From 29th of March to 3rd of April, filters of the gaseous and liquid purification
systems of both cryostats, and their relative dewars, have been evacuated. The
vacuum tightness of the dewars has been tested with helium leak detector.
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In the same week, Air Liquide prepared the four packs of bottle of ultra-pure
Argon for the gas return inside the cryostats, following the end of the vacuum
phase. AL also realized and helium-tested the gas return circuit.
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After Easter, from 7th of April to 13rd of April, liquid nitrogen pumps were
turned on, in view of the beginning of the cooling foreseen for the 14th of
April. In the meantime, on 10th of April, a successful cryogenic emergency test
programmed by AL was held in Hall B, at the presence of LNGS personnel.
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On 14th of April vacuum phase ended, and ultra-pure Argon was pumped
inside the two cryostats, bringing them to an over-pressure of +100 mbar, in
order to prevent the residual out-gassing from the inner walls of the detector.
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On Friday 16th of April the cool-down has started and it proceeds smoothly.
2. ICARUS T600 Vacuum phase
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December 2009: following the signal feed-throughs replacement in the whole
detector, over pressure tests have been performed on both cryostats by
injecting Argon gas. Leaks of ~ 0.4 mbar/h for p = +50 mbar were measured.
Detailed inspections allowed spot out a wrong tightening of the large flanges
of the manholes. Therefore these flanges have been welded to the cryostats,
resulting in an overall leakage reduced by a factor three.
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January 2010: initial vacuum test on both modules (P1 = 580 mbar, P2 = 450
mbar). Leak rate allowed extrapolating the reachable primary vacuum value
compatible with the switching-on of the turbo molecular pumps (~ 0.1 mbar).
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On the 9th of January: start of vacuum phase for Cryostat 1.
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On the 15th of January: Start of vacuum phase for Cryostat 2.
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The target vacuum value of 10-4 mbar was reached in a couple of weeks in
both cryostats; see fig. 1 and fig. 2.
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During the whole vacuum phase the mechanical deformations of the inner
walls were monitored remotely from the Control Room, see fig. 3. As
expected, a linear displacement was found with decreasing pressure
difference.
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On the 14th of April the residual vacuum pressure in the detector was P =
4.5*10-5 mbar in Cryo n.1 and P = 3.8*10-5 mbar in Cryo n.2. This
corresponds to a residual vacuum loss of Cryo n.1: L = 4 · 313 l/s · 4.5 · 10-5
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mbar = 0.06 mbar l/s; Cryo n.2: L = 3 · 313 l/s · 3.8 · 10-5 mbar = 0.04 mbar
l/s. As a comparison, 0.3 mbar l/s at P = 10-4 mbar was reached in 2001 in
Pavia. However, a large fraction of this out-gassing yield is due to water,
which is however expected to freeze on the internal walls during cooling down
phase, not affecting at all the LAr purity. Finally a mass-spectrometer residual
gas analysis fixed the Oxygen contribution to at most 10% of the total
pressure; see fig. 4.
Fig. 1: Pressure as a function of the effective pumping time inside cryostat n.1.
Fig. 2: Pressure as a function of the effective pumping time inside cryostat n.2.
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Fig. 3: Inner wall deformation as a function of the pressure measured by one of the
sensors installed inside the T600.
Fig. 4: Residual gases measured by the mass-spectrometer, showing that the strongest
contribution to the out-gassing comes from water.
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3. ICARUS Cryostats cooling
On the 14th of April the vacuum inside the detectors was broken with pure Argon gas.
Afterward also the dewar walls were filled with Argon at atmospheric pressure.
On the 16th of April the cooling of cryostats started with 10 Stirling compressors fully
operative and with the addition of liquid Nitrogen from the 30 cubic meter storage.
The vapor not managed by Stirling compressors was exhausted in hall B through a 50
kW electrical heater and safely evacuated from hall B via the ventilation system.
During the cooling process all the parameters were monitored:
-Internal pressure controlled at +100mbar above ambient pressure;
-Temperature gradients on the wire chambers, measured on 6 verticals with 5 probes
each, kept within 50 °C;
-Displacements and temperature of the external wall.
Fig. 5: Temperature evolution in Cryo 1 in the center column, left and right side.
Fig. 6: Temperature evolution in Cryo 2 in the center column, left and right side.
During the first phase (from 16th to 22nd April) the cooling was stopped during the
night to minimize the internal temperature gradients.
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From the 17th to 19th of April the cooling was operated without pumps using the
natural circulation of the boiling Nitrogen (so called thermosiphon operation).
From the 20th to 22nd of April the cooling was operated with liquid Nitrogen
circulated with one pump.
Since the 23rd of April the cooling was continuously operated, day and night, with one
pump, reaching 90 K on the 24th of April.
The efficiency of the Stirling compressors has been remarkable as only 5 liquid
Nitrogen refill were required.
4. ICARUS Cryostats Argon filling
On the 29th of April the cooling of the transfer lines was performed via a second
Nitrogen pump and the liquid Argon filling, 10,000 liters, started initially (30 April)
in Cryostat West and next day the same amount of Argon was transferred into cryostat
East.
Since the 3rd of May, three transports of liquid Argon per day are foreseen (~20 tons
each).
5. ICARUS Read out
Measurement campaign have been performed in December 2009 and in March 2010,
injecting test pulse signals into the decoupling boards, to check the electronic chain,
measure the electronic noise, get a first calibration of the channels and test the
response linearity. About 60 crates have been acquired together for different
amplitudes and durations of the test pulse signal.
Due to the ongoing activities on the detector commissioning, the top floor was not
accessible to close the Faraday cages screening the signal cables from detector flanges
to the decoupling boards. Different sources of electrical noise present on the top of the
detector, related to the vacuum activities (vacuum pumps, UPS and different electrical
equipments) prevented the realization of the needed low noise environment.
However tests allowed checking the automatic algorithms to analyze the acquired data
and extract the calibration constants.
As an example, fig. 7 shows the interpolated amplitude of the response to a test pulse
of about 70 fC for the 32 channels collection boards of three consecutive crates, while
fig. 8 shows an example of linearity of a board as a function of the amplitude of the
test pulse signal.
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LNGS Scientific Committee
03/05/2010
Fig. 7: interpolated amplitude (~70 fC injected charge) for the collection boards of
three adjacent crates.
4. Status of the event reconstruction software.
The present software is an evolution of the code developed and used to analyze the
cosmic ray data collected with the T600 on surface in Pavia. Developments completed
or being validated are:
-Full coupling within the Root framework;
-Full coupling with the mysql package, to handle on- and off-line databases;
-Decoding of compressed data;
-3D track reconstruction;
-Automatic algorithms to reconstruct tracks and vertexes;
-Automatic analysis of calibration runs;
-Muon momentum reconstruction with multiple scattering;
-LAr purity estimation with muon tracks;
-Photo-multiplier signal analysis;
-Reconstruction of the electromagnetic showers: shower axis, longitudinal and
transverse profiles.
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Fig. 8: recorded charge as a function of the test pulse height averaged over a single
board of 32 channels; the linearity fit is also shown.
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