Stato del sistema di raffreddamento del rivelatore SPD di ALICE Rosario Turrisi

Cooling: working principle PP1 PP3 Joule-Thomson cycle sudden expansion + evaporation at constant enthalpy Fluid C4F10: dielectric, chemically stable, non-toxic, convenient eos Nominal evaporation: 1.9 bar, 15°C now: difficult procurement PP4 PP=patch panel heaters ~35m gas pipes 12/10-10/8 mm ~40m liquid pipes 6/4 mm capillaries liquid pump condenser pressure cooling tube compressor Filters (60μm) p, T two ‘knobs’: liquid-side pressure flow gas-side pressure temperature enthalpy

The issue Performance worsening in time Minimum acceptance reached: 62.5%, most because of cooling failure Start of LS1  <45% extrapolation from last year assumes constant trend

Critical components X T D Capillaries (CuNi, 550 mm long, 0.5 mm i.d.) Cooling pipes Phynox, 40 μm wall thickness Round 2.8 mm pipes squeezed to 0.6 mm inner size Inline filters Fundamental to protect previous items, 60 μm porosity 1 accessible during beam stop 1 accessible dismantling part of ALICE (~6 months job) (Missing) filter at the plant added after 1 year run a 2 μm filter at the liquid outlet SEM picture of the filter (orange square=1mm2) no access PP=patch panel X T D = 5.6 mm T = 11.8 mm X = 0.7 mm (~1 mm in the filtering area) D

poor cooling performance & local inefficiencies Chase the guilty Search and confirm the cause has been a long and painful process, 4 years long All procedure tested on a dedicated test bench set up by our team with CERN Many tests performed SEM analysis of PP4 filters enlightening… many particles of several materials, possible origin: graphite from pumps, weldings, plant’s hydrofilter 20 μm The filters mesh has 60 μm size in average smaller sized particles can be stopped and bigger can go through! some pollution can pass the first filter and stop on the second Once clogged, the second (PP3, not reachable) filter causes: pressure drop lower flow rate Add the heat-up of the fluid along the supply line, and you have: poor cooling performance & local inefficiencies

The hard way: drilling TESTED BY DRILLING > 100 FILTERS ! After several (unsuccesful) attempts (solvents, ultrasounds) we went ‘’the hard way’’ with the following procedure: drilling: tungsten carbide tip welded on 5 m long twisted ss cable, rotated by a drill counter-flow at 200 mbar w/manometer to detect the presence of the hole (~50 mbar drop) takes 2-3’ cleaning: rilsan pipe connected to a rotary vane vacuum pump to aspire the drilling debris walk inside the pipe with a twisted ss cable with a magnetic tip fixed at the end cleaning machine to force counter-flow wise a cleaning fluid repeat several times the previous steps last, let the cleaning machine run overnight (or more) with a 60 m filter to collect particles analyze this filter with an optical microscope and (if needed) the SEM redo the cleaning procedure if not happy TESTED BY DRILLING > 100 FILTERS !

Access point Target point Fiberscope L=5 m, Ø=1.5 mm magnet Edwards RV3 rotary vane 2-stage pump Fiberscope L=5 m, Ø=1.5 mm magnet tungsten carbide 5-faces tip cleaning machine Access point Ø 2.5 mm ss twisted cable Target point 4.5 m of ss pipe 4mm i.d.

The drill team Yannick Lesenechal Andrea Francescon Samuel Rambaut Claudio Bortolin Rosario Turrisi Royal straight: five nice cards but the strength is the team! And we’re well backed by the whole SPD team!

200 μm

Clean it! Sector #9 drilled on Feb 14 Material collected by vacuum cleaning after drilling Material collected after the cleaning procedure Analyses by Norberto Jimenez Mena and Maud Scheubel (EN-MME-MM)

Materials analyses stainless steel silicon compounds (a.k.a. ‘’dust’’…) fluorine compounds 100 μm 100 μm 100 μm Analyses by Norberto Jimenez Mena and Maud Scheubel (EN-MME-MM)

Interventions and results Drilled 5 filters: sectors 9 (Feb 14), 7 (Feb 27), 6 (Mar 6), 4 & 5 (TS Apr 23-27) Oldest flow rate values from last November 8 sectors above nominal value 5 drilled, 3 because of vacuum cleaning Last cleaning of sector 3 restored the possibility to turn it on completely! 12 12 11 hs on 11 11 10 12 12 11 10 1.8 g/s = nominal value new flow rate values old flow rate values drilled filters

snapshot from November 10, 2011 Recovered acceptance Acceptance changed from this …to this! 65/120 modules ‘’on’’ - 62.5% snapshot from November 10, 2011 112/120 modules ‘’on’’ - 93.3% NOW RUNNING cannot be recovered could be recovered hot 100% cooling efficiency !!!

Happy end! Recovered the cooling system to 100% efficiency no more ‘’special maintenance’’ until pPb run (unless needed) The plan for LS1 changed accordingly: no need to move TPC, ITS, etc. (>6 months job!) If needed could do the drilling of the 5 left filters Finally our soundtrack plays! …and the SPDer’s

Attività SPD @ CERN TS3 (17-21 Settembre 2012) Test in pressione delle vecchie linee di input (2 pp x 4gg) Durante LS1 (11 Febbraio 2013 – xx/xx/2014) Rimozione nuove linee input e subcooling (4 pp x 5gg) Ripristino vecchie linee (pulizia, connessioni, leak test) (4 pp x 10gg) Consolidamento rack impianto (CERN EN/CV/DC) Installazione filtro acqua (CERN EN/CV/DC) Ricalibrazione valvole sicurezza (CERN EN/CV/DC) Ricalibrazione sensori temperatura e pressione (2pp x 5gg) Foratura filtri di 5 settori (dipendente da andamento prestazioni, 1ppx15gg +pers. CERN)