CB1@GSI 1

Results on glass timing RPC aging

P. FonteLIP/ISEC

Coimbra, Portugal.

15 October 2002GSI Darmstadt/Germany

CB1@GSI 2

Aging in streamer mode glass RPCs (BELLE)

[Kub

o et

al,

RP

C20

01, H

.Sak

ai e

t al.,

NIM

A48

4, 1

53]

Problemwater+freon+streamers

Fluoridric acid

DepositsGlass corrosion

Dark current

Inefficiency

Freonless gas

Freon gasEff

icie

ncy

(%)

Sin

gles

rat

e (H

z/cm

2 )

Days

Wet (1000ppm)

Dry

CB1@GSI 3

Aging in streamer mode glass RPCs (BELLE)

[Kub

o et

al,

arX

iv: h

ep-

ex/ 0

2110

20 v

1]

Anode Cathode

Freon

Freonless

New glass

Depositsmay be removed

by scrubbing with alcohol

AFM pictures

~ 50 nm ~80 nm

~ 5 nm ~5 nm

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% 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

CB1@GSI 5

Glass cathode

Aluminium cathode

Da

rk c

urr

ent (

nA)

Days

Integrated charge (mC108 avalanches)

Chambers2 and 6cleaned

Corrected fortemperaturevariations

Aging in avalanche mode glass RPCsResults after 200 days

Equivalent to ~900 days @200Hz/cm2.

No measurable aging, but...

CB1@GSI 6

Ageing in avalanche mode glass RPCsAfter 180 days Glass: SCHOTT Athermal (dark glass for welding masks)

Aluminium electrodes absolutely clean!

Localiseddry

deposit

Removable by

scrubbing

Diffuse dry

deposit

Diffusewet

deposit(anode only)

Anode Cathode

UVUV

Hypothesis:Polymerisation from gas?Ion extraction from glass?

Elemental analysis soon(glass heavy elements)

CB1@GSI 7

• 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