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1 Results on glass timing RPC aging P. Fonte LIP/ISEC Coimbra, Portugal. 15 October 2002 GSI Darmstadt/Germany.

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Presentation on theme: "1 Results on glass timing RPC aging P. Fonte LIP/ISEC Coimbra, Portugal. 15 October 2002 GSI Darmstadt/Germany."— Presentation transcript:

1 CB1@GSI 1 Results on glass timing RPC aging P. Fonte LIP/ISEC Coimbra, Portugal. 15 October 2002 GSI Darmstadt/Germany

2 CB1@GSI 2 Aging in streamer mode glass RPCs (BELLE) [Kubo et al, RPC2001, H.Sakai et al.,NIM A484, 153 ] Problem water+freon+streamers  Fluoridric acid   Deposits Glass corrosion   Dark current  Inefficiency Freonless gas Freon gas Efficiency (%) Singles rate (Hz/cm 2 ) Days Wet (1000ppm) Dry

3 CB1@GSI 3 Aging in streamer mode glass RPCs (BELLE) [Kubo et al, arXiv: hep- ex/ 0211020 v1] AnodeCathode Freon Freonless New glass Deposits may be removed by scrubbing with alcohol AFM pictures ~ 50 nm  ~80 nm  ~ 5 nm 

4 CB1@GSI 4 Aging in avalanche mode glass RPCs 6 counters with single 0.3 mm gap, irradiated with an UV lamp. One glass electrode and one aluminium electrode. 3 glass-cathode and 3 aluminium-cathode counters. Gas: (85% C 2 H 2 F 4 +10% SF 6 +5%C 4 H 10 ) + 10% rel. humidity. Currents measured continuously + temp., press. and lamp intensity. 20 hours irradiation + 2 hours rest  for dark current measurement. Test in progress UV lamp Aluminium Glass

5 CB1@GSI 5 Glass cathode Aluminium cathode Dark current (nA) Days Integrated charge (mC  10 8 avalanches) Chambers 2 and 6 cleaned Corrected for temperature variations Aging in avalanche mode glass RPCs Results after 200 days Equivalent to ~900 days @ 200Hz/cm 2. No measurable aging, but...

6 CB1@GSI 6 Ageing in avalanche mode glass RPCs After 180 days Glass: SCHOTT Athermal (dark glass for welding masks) Aluminium electrodes absolutely clean! Localised dry deposit Removable by scrubbing Diffuse dry deposit Diffuse wet deposit (anode only) Anode Cathode UV Hypothesis: Polymerisation from gas? Ion extraction from glass? Elemental analysis soon (glass  heavy elements)

7 CB1@GSI 7 Bad news There is some material deposition after an equivalent of 900 days of operation at 200 Hz/cm 2 (but only 18 days @ 10 kHz/cm 2 ). Good news The deposit seems have no influence so far on the chamber operation (but at high rates situation may be worse due to Malter effect). The gas was heavily polluted with water + other stuff (glues, rubbers, etc.)  very unfavourable situation Further research Origin of deposit? Gas: unavoidable at high rates  gas must be cleaner. Glass: probably absent in electron-conductive materials  may not appear in low resistivity materials/high-rate counters. Repeat in reasonably clean conditions. (but present test should progress until chambers show measurable effects) Conclusions


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