M.Ameri1, M.Anghinofi1,
P.Cocconi1, S.Cuneo1, R.Papaleo2, F.Parodi1,
G.Raia2 and A.Rottura1
1 I.N.F.N.- Sezione di Genova, Via Dodecaneso 33, GENOVA I-16146
2 I.N.F.N.- Laboratori
Nazionali del Sud, Via S.Sofia 44, CATANIA
Abstract
The
Junction Box is the part of the ANTARES project where the main electro
optical cable from the shore is splitted to the 13 stings of the detector.
The different active components housed inside will produce a total amount
of heat greater than 1 Kwatt; it is therefore important to guarantee a
good heat dissipation in order to avoid damages to the instrumentation
due to local overheating. This report describes the test performed in our
laboratory using the titanium box equipped withdifferent
heaters and merged on a water bath at constant temperatureto
simulate thereal conditions. The
result have defined the optimal configuration in order to guarantee a safe
margin with respecttothe
maximum temperature allowed by the instrumentation; simulations performedwith
the FEA code show good agreement with the measured temperatures.
The
aim of theinternational ANTARES
collaboration is the realization of an undersea detector to measure high
energy neutrinos. The detector, ready to take data starting from the year
2003, will be located on the bottom of in the Mediterranean sea at2500
mdepth , close to the town of Toulon
in
France.
When completed, the effective area of the detector will be 0.1 Km2 , sufficient
to measure fluxes of cosmic neutrinos.The
configuration of the detector is shown in fig.1: 13 flexible strings support
different optical modules (OM) to form anarray
ofa total of 1000 PMTs to sense
the Cherenkov light produced by the muons on the sea water.Starting
from the bottom each string includes:
-a
socket with the electro optical connection to anchor the string in the
sea bed (BSS).
-100
m of electro mechanical cable.
Fig.1: The ANTARES undersea detector
-30
segments each composed by a frame to supportthe
three PMTs , a local control module (LCM) to house the read out electronics
and 12 m of electro mechanical cable.
-a top buoy
to keep the string in the vertical position.
Each string
is then connected by an electro optical cableto
a junction box (JB) which ensure the link to the shore station via a 40
Km long cable containing a 5 K Volt line and 24 opticalfibers.The
JB is a component extremely important: it represents, in fact,the
‘ single point failure’ of the apparatus and a
Fig. 2: The Junction Box and the
frame
possible
malfunctioning would compromise the result of all the experiment. The JB,
represented in fig. 2, is composed by a container and a frame for support
and handling. The design and the realization of the JB has been performed
by our group using two titanium hemispheres available from the Moscow University
collaborators. In particular, the volume inside the two hemispheres was
found to be largely insufficient to house the required instrumentation
and cable connections (penetrators): the final design includes therefore
a specially machinedtitanium spacer,
the two hemispheres, a small box for the plug-in of the main cable and
a large number of seals; a detailed description of the mechanical executive
design can be found in ref ().
Table1
designation
|
quantity
|
total
dissipation (W)
|
main
transformer
|
1
|
1000
|
clock+ROR
module
|
1
|
10
|
output
breaker
|
7
|
50
|
output
breaker/switch
|
16
|
50
|
low
voltage supply
|
1
|
50
|
JB
control module
|
1
|
50
|
timed
relay
|
2
|
2
|
short
mode relay
|
1
|
2
|
The
JB will contain different items including a transformer to lower the 5
K Volt AC from the shore down to 1 K Volt AC and 25 Volt DC, the splitter
to supplythe 13 strings with the
possibility to switch off a single line, different optical connections
for data transmission and multiplexing, an intelligent unit to drive the
slow controls and to generate a fast trigger to the DAQ. For the purpose
of this note, themain issue is
the total amount of power dissipated by these components listed in table
1: 900 mWatts by the transformer and 250 m Watts from the rest.
The
JB , in fact, is expected to continuously operatefor
a nominal 10 year period and any local overheating of the electronics should
be carefully avoided.We have therefore
decided to perform some measurements on the heat transmission using the
JB in the configurationdescribed
in section 2; the results of these tests confirm that the total power listed
in table 1 can be safely dissipated provided that thegeometrical
configuration where the main transformer is located in the top region of
the JB is chosen. The successful comparison to the simulations using a
xxx program are finally discussed in section 3.
2.
The experimental apparatus and the measurements.
The
JB in its final configuration willbe
mounted by October 2000 since the titanium spacer needs a dedicated time
to be produced and machined while the inner components are expected to
come a bit later. We therefore decided to start our test for heat dissipation
using the JB in its simplest configurationwhere
the two available hemispheres are separated by a stainless disk to generate
two regions: region A to house the transformer and region B for the electronics.
The general layout of the apparatus which has been mounted in our laboratory
in Genova is shown in fig 3 and includes:
Fig. 3: The experimental apparatus for the test
-a box of 30x30x50 cmmade by a 0.3 cm thick copper sheet with dimension very close tothe real transformer. Six flat heater resistors ofdimension 2x20x0.1 cm (mod xxxx)are located in the inner part of each side of the box; each resistor is supplied with 250 V AC to give a power of 150 mWatts: the total amount of heat released in the box is therefore 900 mWatts as in the 40 Kvolt amp transformer. The box is fixed 5 cm. from the disk by a support; this clearance is necessary to insulatethe transformer from metallic components surrounding it.Both the inner part of the box and the volume of region are filled with xxx liters ofmineral oil ( sigla)using an external tube connected to one oh the three holes already present in the top of thehemisphere.The remainingtwo holes are used for exhaust and to drive the supply to the heaters;
-
a stainless (tipo) disk of 80 cm diameter and 1.5 cm thickness to separate
the two regions. The disk is sandwiched between the 2.5cm large flangespresent
in thehemispheres; only the flange
of region A has a slot carved on it: to ensure sealing we used an o-ringwhile
a glue xxxx was used for region B;
-two
cylindrical heaters 1cm diameter, 20 cm length located in region B. The
heaters are located in the central region with a support fixed in the disk
and produce 250 mWatt to simulate the heat from the electronics of table
1.Region B is filled with air at
atmospheric pressure; however a tube connects this region with a pumping
system located outside which can be used to make a low vacuum before filling
with another gas.
In
order to be able to monitor the temperature at different locations, 8 platinum
resistors are located in the system as shown in fig 3 :3 on the oil bath(PT6,PT8,PT4),
1 on the surface(PT7) and 1 on the inner part of the copper box(PT5), 2
on the air of region B(PT2, PT3) and 1 in the stainless disk (PT1).The
sensors (PT100 mod) are read out by a xxxx which scans up to 8 different
channels.
In
this configuration, the system was located in the middle of a big cylindrical
tank containing 1500 liters of tab water maintained at constant temperature
in the range 14 +/- 1.5 degree Celsius by a chiller mod xxxx.The
same temperaturewas measured in
the sea water at 2500 m depth in the location where the JB will be positioned:
we are therefore confident to realistically simulate the real conditionsof
the experiment.
When all the parts of the system had reached the temperature of the water, we switched on the power and recorded the 8 temperatures in 5-30 minutes intervals up to the equilibrium value. This procedure was repeated in three different conditions:
(a)the
transformer is in the upward region ; region B is filled with air at 1
atm
(b)the
transformer is in the downward region; region B is filled with air at 1
atm
(c)the
transformer is in the downward region; region B is filled with helium at
1 atm
The
temperature Tn of the nth sensor was fitted as a function of the time t
from the initial temperature T0=14 degree, using the following expression:
Tn=Te-(Te-T0)*exp(-t/A) (1)
where
Te and A are free parameters representing, respectively, the final temperature
and the half time need to reach it.The
values of Te and An for the (a), (b) and (c) conditions are listed in table
2
Table
2
sensors
|
PT1
|
PT2
|
PT3
|
PT4
|
PT5
|
PT6
|
PT7
|
PT8
|
Te
(a)
|
36
|
30
|
30
|
39
|
58
|
28
|
49
|
34
|
A(a)
|
18
|
12
|
10
|
70
|
88
|
90
|
30
|
92
|
Te
(b)
|
55
|
42
|
42
|
17
|
70
|
57
|
54
|
42
|
A(b)
|
70
|
12
|
11
|
|
74
|
73
|
41
|
100
|
Te
(c)
|
50
|
35
|
32
|
17
|
73
|
60
|
55
|
44
|
A(c)
|
125
|
8
|
18
|
|
100
|
96
|
53
|
145
|
The
fit is generally goodas shown in
the example of fig 4.
These results clearly indicate that in condition (a) where the transformer is in the upper region of the JBthe heat exchange with respect to the water is optimized and the temperature of both the oil and air areminimized.Indeed we tested also conditions (b) since this geometry wouldavoid possible oil leakage from the transformer to the electronics in the downward region. However, the values obtainedin (b) are too close to the limit allowed by the instrumentation: xx deg for the transformer, yy for the optic fiber in region B and zz for the switches.An improvement is obtained in condition (c) where the helium is used to improve the thermal exchange with the titanium shell.
Of course the two heaters in region B are only a crude approximation of the real electronic configuration; in particular, being our empty volume much higher than the real conditions, it might be possible that our results for conditions (b) and (c) are optimistic;moreover it is not know the effect ofthe use of helium gas in electronic devices for a long period .All these considerations
Fig.
4: The fit of the temperature in the copper box in condition (a) as
a function of time
support
our decision to choose configuration (a) for the JB; of course a lot of
attention will be paid for the design and choice of the feed through to
be located in the separation disk to allow the transmission of the voltage
and anode cable connected to the transformer.