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

2. Principle of cooling operation
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
PP=patch panels
PP3: close to the detector, not (immediately) accessible, PP4: ~6 m upstream SPD
PP4
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

3. Motivation Performance worsening in time
Minimum acceptance reached: 62.5%, most because of the cooling
Start of LS1  <45%
extrapolation from last year
assumes constant trend

4. Critical components X T D Capillaries Cooling pipes Inline filters
used to enter the coexistence phase by pressure drop
CuNi, 550 mm long, 0.5 mm i.d.
Cooling pipes
where evaporation, thus heat absorption, happens
Phynox, 40 μm wall
Round 2.8 mm pipes squeezed to 0.6 mm inner size
Inline filters
Fundamental to protect previous items, located in 2 patch panels
1 accessible during beam stop
1 accessible dismantling part of ALICE (~6 months job)
SEM picture of the filter
(orange square=1mm2)
no access
PP=patch panel X T
D = mm
T = mm
X = 0.7 mm (~1 mm in the filtering area) D

5. 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

6. 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 !

7. Access point Target point Fiberscope L=4.5 m, Ø=1.5 mm magnet
Edwards RV3 rotary vane 2-stage pump
Fiberscope
L=4.5 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.

8. 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!

9. 200 μm

10. 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)

11. 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)

12. 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

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

14. 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!)
Finally our soundtrack plays!
…and the SPDer’s

15. First application Flow= 2.0 g/s @ 4.75 bar Modules on= 100%
First sector treated: #9
It never worked properly
First one to be turned on for some time: 12/12/2007, h 15:13, for 41’
Pre-cleaning:
4 cycles
vacuum cleaning + 3 magnet sweeps + vacuum cleaning + counterflow
last counterflow left running overnight
flow: from 0.27 to 0.46 g/s
Cleaning: 5 cycles (overnight counterflow between cycle 3 and 4)
Results:
Was: bar
Flow= bar
Was: 0%
Modules on= 100%

16. Sector 4 drilling First try gave no clear drilling signal
Had to check with the fiberscope  critical
so we could skip a long test step…
Second try had the right outcome

17. Efficiency history
DSF status (tests pre-installation): efficiency = 100%
First switch on after installation: efficiency = 87%
Long stop (you know why…) – minor rerouting of return pipes
Restart after long stop: efficiency = 71%

18. Efficiency history Interventions in fall 2009
Start of LS1  <45%
Interventions in fall 2009
Stable after interventions: efficiency = 83%
Last resume after tech stop: efficiency = 64%
extrapolation from last year
assumes constant trend

19. Possible solutions
Essential for any intervention of this kind: first, try in the lab!
We build a test bench to reproduce the issue and test any possible of solution
setup to reproduce fluid conditions on a replica of detector’s hydraulics
the problem has been reproduced using calibrated carbon powder
the possible solutions have been tested on this setup
Be open-minded: solution can come from whatever technology, e.g. …
solvents… ultrasounds… drill…

20. Attività SPD @ CERN Pianificate per il 2012 TS2 (June 25-29 Giugno)
Prova funzionamento sistema senza subcooling (1 pp x 3gg)
TS3 (20-24 Agosto)
Test in pressione delle vecchie linee di input (2 pp x 4gg)
TS4 (22-26 Ottobre)
Nessuna attività – stabilizzazione del sistema pre-run pPb
Durante LS1 (24 Novembre 2012– metà 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)
10 settimane-uomo OFFICINA MECCANICA