september 9, 2003a. cardini / infn cagliari1 m. alfonsi 1, g. bencivenni 1, w. bonivento 2,...

September 9, 2003 A. Cardini / INFN Cagliari 1

M. Alfonsi1, G. Bencivenni1, W. Bonivento2, A.Cardini2,

C. Deplano2, P. de Simone1, F. Murtas1, D. Pinci3,

M. Poli-Lener1, D. Raspino2, B. Saitta2

Aging Test at Aging Test at CasacciaCasaccia

1. Laboratori Nazionali di Frascati - INFN, Frascati , Italy

2. Sezione INFN di Cagliari – Cagliari, Italy

3. Sezione INFN di Roma 1, Roma, Italy


Aging at Casaccia-1

PC

60CoB

OTTLES

HV

CONTROLROOM

4.5

m

Casaccia

GEMA,B,D

P

GEM-CGEM-E

Ar/CO2/CF4 = 45/15/40, 200 cc/min

Module 0.1 (chambers A e B) + chamber D (10x10 cm2) @ 16 Gray/h

Chamber C (old 20x24 cm2) as a monitor @ 0.5 Gray/h

Chamber E (very old 20x24 cm2) equipped with ASDQ (96 ch.) @ 0.1-0.2 Gray/h HV(“reference”) = 1280 V, G ~ 6x103;

Monitor H2O, T e P: ± 1ppm, ± 0.1°K, ± 0.1mb (Panametrics/MKS)


exhaust

MKSmixerAr

CO2CF4

C

B

A

D

E

CO 60

not in scale

T, RH probePatm probe

Polypropilene-gas pipes

Stainless steel-gas pipes

Gas mixture supply & P,T,RH monitoring


tp

TtV

norm eiti

0

We used the knowledge ofdependenceof the gain on

V(t)*T(t)/P(t)

to correct and normalized the detector current

T (

oK

)P (

mb)

T/P

(oK

mb

-1)

Time (days)

Temperature and Pressure in the gas mixture


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

Norm

aliz

ed C

ur r

ent s

( A

)W

ate

r (p

pm

)

Time (days)

A

B

H20

11.4 LHCb years

8.5 LHCb years

itot/i -67 %

itot/i -60 %

2 C/cm2

1.5 C/cm2


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- + H20 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 (~ 1cm2, 10 LHCb year with G/G < 5%) and at PSI (hadronic beam @ 300 MHz per at least 5 days on ~15 cm2, 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.


Aging Mechanism ?New GEM foil Aged GEM foil

Copper etched away close to the GEM hole ?

50 m


To check if the current reduction rate depends on the gas mixture water content we built 2 new 10x10 cm2 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 ppmV

The Casaccia-2 Aging Test


T, P and H2O

Always below 0.5 ppmV !

Temp.

Press.

T/P

H2O

(T/P) -1.6% !


A

B

Raw (no T/P correction) currents

0.35 C/cm2 ~ 2 LHCb y

0.13 C/cm2 ~ 0.75 LHCb y


C

new Dnew E

Raw (no T/P correction) currents

itot/i -10 %(Only due to T/P variations)

0.45 C/cm2 ~ 2.6 LHCb y

0.35 C/cm2 ~ 2.0 LHCb y

Voltage change


A

B

Normalized currents

0.35 C/cm2 ~ 2 LHCb y

itot/i -20 %

itot/i -8 %

0.13 C/cm2 ~ 0.75 LHCb y


Normalized currents

0.45 C/cm2 ~ 2.6 LHCb y

0.35 C/cm2 ~ 2.0 LHCb y itot/i -20 %

itot/i -35 %

Very Preliminary

new D new E


• 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


Gas flows during various tests

Aging Test Gas (cc/min)

Current (uA) Current/flow

Standard 100 ~ 0.01-0.05 ~ 0

X-rays 100 0.2 0.4 .002 .004

PSI 200 ~ 50 0.25

Casaccia big 350 800 1000 2.3 2.9

Casaccia small

200 100 150 0.5 0.75

Casaccia mon.

350 60 0.17

Sauli (Hamburg)

80 3 12 0.04 0.15

M1R1 estimation

~ 100 (?) 12 ~ 0.12 (?)


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

september 9, 2003a. cardini / infn cagliari1 m. alfonsi 1, g. bencivenni 1, w. bonivento 2,...

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