Maintenance of the ANTARES deep-sea neutrino telescope 1 Marco Circella --- INFN Bari [email protected] on behalf of the ANTARES Collaboration

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)


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


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


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


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


• ~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


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…


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


(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!


Experience gained (management point of view)

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• 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


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


Conclusions

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• 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


Documents

Maintenance of the ANTARES deep-sea neutrino telescope 1 Marco Circella --- INFN Bari [email protected] on behalf of the ANTARES Collaboration