September 9, 2003A. Cardini / INFN Cagliari1 M. Alfonsi 1, G. Bencivenni 1, W. Bonivento 2, A.Cardini 2, C. Deplano 2, P. de Simone 1, F. Murtas 1, D. Pinci 3, M. Poli-Lener 1, D. Raspino 2, B. Saitta 2 Aging Test at Casaccia 1.Laboratori Nazionali di Frascati - INFN, Frascati, Italy 2. Sezione INFN di Cagliari – Cagliari, Italy 3. Sezione INFN di Roma 1, Roma, Italy

September 9, 2003A. Cardini / INFN Cagliari2 Aging at Casaccia-1 PC 60 Co BOTTLES HV CONTROL ROOM 4.5 m Casaccia GEM A,B,D P GEM-C GEM-E  Ar/CO 2 /CF 4 = 45/15/40,  200 cc/min  Module 0.1 (chambers A e B) + chamber D (10x10 cm 2 16 Gray/h  Chamber C (old 20x24 cm 2 ) as a 0.5 Gray/h  Chamber E (very old 20x24 cm2) equipped with ASDQ ( Gray/h  HV(“reference”) = 1280 V, G ~ 6x10 3 ;  Monitor H 2 O, T e P: ± 1ppm, ± 0.1 ° K, ± 0.1mb (Panametrics/MKS)

September 9, 2003A. Cardini / INFN Cagliari3 exhaust MKS mixer Ar CO 2 CF 4 C B A D E CO 60 not in scale T, RH probe P atm probe Polypropilene-gas pipes Stainless steel-gas pipes Gas mixture supply & P,T,RH monitoring

September 9, 2003A. Cardini / INFN Cagliari4 We used the knowledge of dependence of the gain on V(t)*T(t)/P(t) to correct and normalized the detector current T ( o K) P (mb) T/P ( o K mb -1 ) Time (days) Temperature and Pressure in the gas mixture

September 9, 2003A. Cardini / INFN Cagliari5 Results from Casaccia-1 Current decrease rate seems proportionalto gas water content Below a few water ppm currents seems not to vary too much No changes in current for the monitor chamber (“C”) in the whole period Normalized Currents (  A) Water (ppm) Time (days) A B H20H LHCb years 8.5 LHCb years  i tot /i  -67 %  i tot /i  -60 % 2 C/cm C/cm 2

September 9, 2003A. Cardini / INFN Cagliari6 Aging Mechanism ? Even if we are not yet completely sure (surface chemical analysis is currently in progress) we believe that the current decrease is related to the etching of the copper on the GEM foils due to hydrofluoric acid (HF). HF is produced in the reaction F - + H 2 0  HF + OH -, and this could explain the large current decrease rate when water content in the gas mixture is above 10 ppm. It should be noted however that local aging tests we performed in the past, both with X-rays (~ 1cm 2, 10 LHCb year with  G/G < 5%) and at PSI (hadronic 300 MHz per at least 5 days on ~15 cm 2, for a total of ~ 5 years at LHCb with NO variations in detector efficiency), did not show such a large gain variations. We suspect that the reduced gas flow – which could not be increased by 20 as the accelerating factor – could be partially responsible of these high current reductions.

September 9, 2003A. Cardini / INFN Cagliari7 Aging Mechanism ? New GEM foilAged GEM foil Copper etched away close to the GEM hole ? 50  m

September 9, 2003A. Cardini / INFN Cagliari8 To check if the current reduction rate depends on the gas mixture water content we built 2 new 10x10 cm 2 detectors These detectors were dried in an oven at 50 ºC and then exposed to gammas in Casaccia at 16 Gray/h for a week The Casaccia-1 large detectors (A and B) and the monitor chamber (C) were irradiated as well To control the gas contamination possibly generated by radiation we supplied the gas to the two new detectors with an independent gas line We did not start the aging test until the gas water content was below 0.5 ppm V The Casaccia-2 Aging Test

September 9, 2003A. Cardini / INFN Cagliari9 T, P and H 2 O Always below 0.5 ppm V ! Temp. Press. T/P H2OH2O  (T/P)  -1.6% !

September 9, 2003A. Cardini / INFN Cagliari10 A B Raw (no T/P correction) currents 0.35 C/cm 2 ~ 2 LHCb y 0.13 C/cm 2 ~ 0.75 LHCb y

September 9, 2003A. Cardini / INFN Cagliari11 C new D new E Raw (no T/P correction) currents  i tot /i  -10 % (Only due to T/P variations) 0.45 C/cm 2 ~ 2.6 LHCb y 0.35 C/cm 2 ~ 2.0 LHCb y Voltage change

September 9, 2003A. Cardini / INFN Cagliari12 A B Normalized currents 0.35 C/cm 2 ~ 2 LHCb y  i tot /i  -20 %  i tot /i  -8 % 0.13 C/cm 2 ~ 0.75 LHCb y

September 9, 2003A. Cardini / INFN Cagliari13 Normalized currents 0.45 C/cm 2 ~ 2.6 LHCb y 0.35 C/cm 2 ~ 2.0 LHCb y  i tot /i  -20 %  i tot /i  -35 % Very Preliminary new D new E

September 9, 2003A. Cardini / INFN Cagliari14 It seems that there is a small effect due to the water content of the gas mixture, but this is important only at very high radiation rates. It also seems that there is a dependence of the current reduction rate on the gas flow. This is suggested by the local aging tests (X- rays and PSI). For these reasons we believe that the Casaccia test is much more destructive than a non-accelerated test. This is also suggested by the behavior of the monitoring chamber, where we do not see any gain reduction in 1 LHCb equivalent year, while we clearly see for example a –8% current reduction in 0.75 LHCb years for chamber B at Casaccia-2. Preliminary conclusions on aging

September 9, 2003A. Cardini / INFN Cagliari15 Gas flows during various tests Aging TestGas (cc/min)Current (uA)Current/flow Standard100~ ~ 0 X-rays  .004 PSI200~ Casaccia big   2.9 Casaccia small   0.75 Casaccia mon Sauli (Hamburg) 803   0.15 M1R1 estimation ~ 100 (?)12~ 0.12 (?)

September 9, 2003A. Cardini / INFN Cagliari16 What’s next? Chemical surface analysis on GEM foils Local gain measurement on aged detectors Efficiency measurement on aged detectors X-rays detector aging at various gas flows