Maintenance of the ANTARES deep-sea neutrino telescope 1 Marco Circella --- INFN Bari on behalf of the ANTARES Collaboration VLVnT11, Erlangen, 13 October 2011M. Circella, INFN Bari: Maintenance of ANTARES

Contents 1.ANTARES apparatus (brief introduction) 2.Construction and maintenance operations 3.Experience gained during the process (key points) 2 VLVnT11, Erlangen, 13 October 2011M. Circella, INFN Bari: Maintenance of ANTARES

M. Circella, Apparatus status and plans 3 ANTARES 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 Junction Box 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 sphere 10” PMT Ham. R (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 5 VLVnT11, Erlangen, 13 October 2011M. Circella, INFN Bari: Maintenance of ANTARES

Construction of the apparatus Junction Box and long-distance electro-optical cable installed in – Junction Box in operation for almost 10 years! Various prototype lines operated in 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 7 VLVnT11, 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 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 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 ~4 230 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 See this slide in presentation-mode with “animations on”! 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 11 VLVnT11, 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