Maintenanceof the ANTARES
deep-sea neutrino telescope
1
Marco Circella --- INFN [email protected]
on behalf of the ANTARES Collaborationhttp://antares.in2p3.fr
VLVnT11, Erlangen, 13 October 2011M. Circella, INFN Bari: Maintenance of ANTARES
Contents
1. ANTARES apparatus (brief introduction)2. Construction and maintenance operations3. Experience gained during the process (key points)
2VLVnT11, Erlangen, 13 October 2011M. Circella, INFN Bari: Maintenance of ANTARES
M. Circella, Apparatus status and plans 3ANTARES ERC/FRB meeting, Paris, 8 March 2010© F. Montanet
• 12 detection lines
• 25 storeys / line• 3 PMTs / storey• ~900 PMTs
~70 m
100 m
350 m
14.5 m
Submarine links
JunctionBox
40 km cable to
shore
Anchor/line socket
a storey
~2500 m depth
The ANTARES apparatus
Hydrophone Rx
(5 RX + 1 RxTx/line)
Local Control Module (inside a titanium cylinder)
Optical Beacon
for timing calibration (blue LEDs)
17” glass sphere10” PMT Ham. R7081-20
(14 stages)
Basic detector element: storey
4
(4 beacons/line)
VLVnT11, Erlangen, 13 October 2011M. Circella, INFN Bari: Maintenance of ANTARES
The apparatus: key numbers and features
• 12 detection lines + instrumentation line
• 25 storeys/line, each with 3 optical modules and an electronics container (Local Control Module-LCM or Master Local Control module, MLCM)
• 5 sectors, each with up to 5 storeys, in each detection line---sectors are the basic functional units (for power, clock, data transmission) of the lines
• 885 optical modules installed in total for data acquisition, + acoustic positioning system and an optical beacon time calibration system, + AMADEUS (a prototype system for neutrino “acoustic detection”), + various devices for site monitoring and/or environmental sciences
• Original design: each line is connected to the underwater junction box by means of its own interlink cable---modified design for last lines: two lines are connected to the same junction box output by means of a y-shaped interlink cable
5VLVnT11, Erlangen, 13 October 2011M. Circella, INFN Bari: Maintenance of ANTARES
Construction of the apparatus• Junction Box and long-distance electro-optical cable
installed in 2001-2002 – Junction Box in operation for almost 10 years!
• Various prototype lines operated in 2003-2005• The 12 detection lines were installed between 2006 and
2008 – first lines in operation for more than 5 years!
6
Line being loaded on the ship
Line deployment
Line connection
VLVnT11, Erlangen, 13 October 2011M. Circella, INFN Bari: Maintenance of ANTARES
Line recovery• The automatic release of the anchor can be activated from
the surface - no need to prior disconnect the line from its cable
• After release, the line will float up to the surface • Line recovery is very similar to a time-inverted deployment
operation
7VLVnT11, Erlangen, 13 October 2011M. Circella, INFN Bari: Maintenance of ANTARES
Non-standard recovery of line 9 (hooked-up from the ship)
The speaker on the ship after a line recovery
– or was it before a line deployment?
Maintenance operations of the past 3 years
• Repair of the main electro-optical cable in summer 2008
• Replacement of a few interlink cables, installation of new-design cables (y- and x-shaped)
(remark: wet-mateable cables and connectors are among
the most critical items in the apparatus)
• 3 lines (lines 12, 6, and 9) recovered, upgraded and reinstalled in 2009-2010
8
Not discussed in this talk
VLVnT11, Erlangen, 13 October 2011M. Circella, INFN Bari: Maintenance of ANTARES
• ~90% of optical modules operational• a few sectors h.s.
Apparatus status at end of construction
• Line recovered on March 12 2009
• At time of recovery, 3 sectors out of 5 were not operational
• A leak was suspected in LCM6
• During line recovery one OM reached the sea surface free…
• It was a faulty OM which had got free from storey 6 (due to failure of one screw)
• A leak was detected on LCM6, which contained about 1.2 l of water.
• The microleak (1.2 l in ~4 months @ 230 bars!) was located on the connector for the faulty OM
• Power problems developed inside the module
• Moral: without precautions, one faulty screw can lead to a failure of one complete line
Line 12 investigations
9
Solution implemented in all recovered lines
VLVnT11, Erlangen, 13 October 2011M. Circella, INFN Bari: Maintenance of ANTARES
10
Line 6 and 9 investigations• Power box of MLCM of sector 5 of line 6 found faulty (no operation of the full
sector)• Problem on one output of the power module of line 9 (no operation of one
sector)• Both problems above showed up shortly after installation of the line =>
procedures modified so that more extended tests are performed onshore before deployment
• A small amount of water was found in LCM of storey 5; the leak seem to have taken place under low pressure, at the interface between the titanium cylinder and the top flange---the module had been re-opened and re-sealed soon before the first deployment (in non-optimal conditions)
• Moral: stick to the procedures!
Water marks…
VLVnT11, Erlangen, 13 October 2011M. Circella, INFN Bari: Maintenance of ANTARES
Flooded Optical Modules
• About 3% of the OMs installed are flooded, in most cases from the very beginning
• The recovery of line 9 allowed us to inspect two of them: the problem is due to a failure of the vacuum valves
11VLVnT11, Erlangen, 13 October 2011M. Circella, INFN Bari: Maintenance of ANTARES
(One flooded OM recovered on line 9)
On the HV re-tuning procedure
12
• Change of HV settings can compensate for OM gain drifts (at the cost of a full calibration for threshold settings, charge conversion parameters, time offsets)
• Most of the channels show a negative gain drift, hence they need a HV increase• Typical HV change is in the range of a few tens of volts (see plot below for the
very first tuning); for a small fraction of channels a change larger than 100 V is required
• The HV range of the PMT bases allow us to repeat this procedure at least for ~10 more times in the future
• Implication: no significant biofouling on the OMs!
VLVnT11, Erlangen, 13 October 2011M. Circella, INFN Bari: Maintenance of ANTARES
Experience gained (management point of view)
13
• Maintenance of deep-sea structures is possible, if it is well prepared (spares, facilities, expertise)
• A good Quality System is vital for construction as well as for apparatus operation and maintenance
• A detailed Analysis Risk has to be performed before finalizing the design, and then constantly revised – beware: this can be a very tricky business!
• Stick to the (carefully defined) procedures!
• Extensive tests have to be performed on everything; precautions against failure of anything should be adopted
VLVnT11, Erlangen, 13 October 2011M. Circella, INFN Bari: Maintenance of ANTARES
14
Upgrades
• Nanobeacons installed on 3 OMs of one line
• Modified LED beacons installed on two lines
• Next: laser beacon and acoustic emitter installed on the instrumentation line; prototype KM3NeT DOM(s) proposed to be installed as well
VLVnT11, Erlangen, 13 October 2011M. Circella, INFN Bari: Maintenance of ANTARES
Conclusions
15
• ANTARES shows that construction AND maintenance of a large apparatus in the deep sea is possible
• After the long maintenance campaign of the past 2 years (3 lines recovered, upgraded and reinstalled) the apparatus is again in stable data taking conditions, in the full 12-line configuration, since November 2010 – remark: 3 lines in 2 years was just the level of maintenance expected.
• Line problems due to old failures. Rest of the apparatus is stable. The loss of OMs is at the level of 1.5% of available channels per year => Data taking extended to 2016
• Some KM3NeT-oriented upgrade performed on the recovered lines + plan to install prototype(s) of KM3NeT DOM on the instrumentation line
• Secondary Junction Box of Ifremer installed for associated science purposes
• Important experience gained during these activities, useful for KM3NeT design
VLVnT11, Erlangen, 13 October 2011M. Circella, INFN Bari: Maintenance of ANTARES