Presentation Transcript
Slide1 : Results on glass timing RPC aging P. Fonte LIP/ISEC
Coimbra, Portugal. 15 October 2002
GSI Darmstadt/Germany
Aging in streamer mode glass RPCs (BELLE) : 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/cm2) Days Wet
(1000ppm) Dry
Aging in streamer mode glass RPCs (BELLE) : Aging in streamer mode glass RPCs (BELLE) [Kubo et al, arXiv: hep- ex/ 0211020 v1] Anode Cathode Freon Freonless New glass Deposits
may be removed
by scrubbing with
alcohol AFM pictures ~ 50 nm ~80 nm ~ 5 nm ~5 nm
Aging in avalanche mode glass RPCs : 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% C2H2F4+10% SF6 +5%C4H10 ) + 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
Aging in avalanche mode glass RPCs : Aging in avalanche mode glass RPCs Results after 200 days Equivalent to
~900 days @
200Hz/cm2.
No measurable
aging, but...
Ageing in avalanche mode glass RPCs : 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 Hypothesis: Polymerisation from gas?
Ion extraction from glass? Elemental analysis soon
(glass heavy elements)
Conclusions : Bad news
There is some material deposition after an equivalent of 900 days of operation at 200 Hz/cm2 (but only 18 days @ 10 kHz/cm2).
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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