1. Un Rivelatore a Tripla-GEM per le Camere a Muoni di LHCb
M. Alfonsi1, G. Bencivenni1, W. Bonivento2,
A. Cardini2 , P. de Simone1, F. Murtas1, D. Pinci3,
M. Poli-Lener1, D. Raspino2 and B. Saitta2
Laboratori Nazionali di Frascati - INFN, Frascati , Italy
Sezione INFN di Cagliari – Cagliari, Italy
Sezione INFN di Roma 1, Roma, Italy

2. A. Cardini / INFN Cagliari
M1R1
Rate Capability up to 0.5 MHz/cm2
Station Efficiency >96% in a 20 ns time window (*)
Cluster Size <1.2 for a 10x25 mm2 pad size
Radiation Hardness C/cm2 in 10 years (**)
Chamber active area x24 cm2
(*) A station is made of two detectors “in OR”. This improves time resolution and provides some redundancy
(**) Estimated with 50 e-/particle at 184 kHz/cm2 with a gain of ~ 6000
CSN1, 5 aprile 2004
A. Cardini / INFN Cagliari

3. A. Cardini / INFN Cagliari
A Triple-GEM detector is built by inserting three GEM foils between two planar electrodes, which act as the cathode and the anode.
The volume between the cathode and the first GEM is usually referred to as the DRIFT gap. This is also the sensitive gap in the detector.
Conversion &
The TRANSFER gaps are the volumes between the GEMs.
The volume between the last GEM and the anode is usually called the INDUCTION gap.
The anode is segmented in pads to provide the spatial information and these electrodes are readout with charge/current preamplifiers.
CSN1, 5 aprile 2004
A. Cardini / INFN Cagliari

4. A. Cardini / INFN Cagliari
Large (20x24 cm2) GEM foils, divided in 6 sectors, are stretched with the tool shown above and then glued on frames.
CSN1, 5 aprile 2004
A. Cardini / INFN Cagliari

5. A. Cardini / INFN Cagliari
M1R1 Full Size Prototype
ASDQ FEE
Boards
Sensitive gaps
CSN1, 5 aprile 2004
A. Cardini / INFN Cagliari

6. A. Cardini / INFN Cagliari
9.7 ns
5.3 ns
4.5 ns
Considerable improvement with respect to the Ar/CO2=70/30 gas mixture, which exhibits a poor time resolution of about 10 ns RMS, is obtained with the new CF4 and iso-C4H10 based gas mixtures, which allow to reach time resolutions better than 5 ns RMS
Our Choice:
Ar/CO2/CF4 45/15/40
Fast & Non-flammable
Single Chamber Time Spectra
CSN1, 5 aprile 2004
A. Cardini / INFN Cagliari

7. A. Cardini / INFN Cagliari
Working region, upper limited by Cluster Size = 1.2, is found to be V wide, a large plateau for a micro-pattern gaseous detector!
OR Efficiency in 20 ns
Working
region
2.0 fC
Cluster Size
3.0 fC
G~4000
G~20000
CSN1, 5 aprile 2004
A. Cardini / INFN Cagliari

8. Discharge probability per incident particle
Recenti misure suggeriscono che un rivelatore possa tollerare fino a circa 1000 scariche/cm2
P <
G <
CSN1, 5 aprile 2004
A. Cardini / INFN Cagliari

9. A. Cardini / INFN Cagliari
Local Aging Test
high intensity X-rays detector active area 10х10 cm2 irradiated area ~1mm2
Ar/CO2/CF4 (60/20/20)
Ar/CO2/CF4 (45/15/40)
Ar/CF4/C4H10 (68/25/7)
ΣVGEM= 1230 V
ΣVGEM= 1280 V
ΣVGEM= 1030 V
G=2.5·104
G=6·103
G=104
IG3_Dw+IPad ~270 nA
IG3_Dw+IPad ~160 nA
IG3_Dw+IPad ~160 nA
Φgas=166.6 cc/min
Φgas=200 cc/min
Φgas=154 cc/min
ΔG/G < 5%
ΔG/G < 5%
ΔG/G ~10%
10 LHCb
Years
6.6 C/cm2
10 LHCb
Years
1.8 C/cm2
10 LHCb
Years
3 C/cm2
CSN1, 5 aprile 2004
A. Cardini / INFN Cagliari

10. Aging set-up at CasacciaPC
60Co
25 kCi
GAS BOTTLES HV
4.5m
GEM
A,B,D
GEM-C
GEM-E
Gas mixture:Ar/CO2/CF4 = 45/15/40;
Large chamber A, B + small D in test
position ~ 16 Gy/hour;
Large chamber C in monitor
position ~ 0.5 Gy/hour;
Large chamber E in low irradiation
position ~ Gy/hour;
HV(“reference”) = 1280 V, G ~ 6x103;
H2O/T/ P = ± 1ppm / ± 0.1°K / ± 0.1mb
(Panametrics/MKS probe systems)
CSN1, 5 aprile 2004
A. Cardini / INFN Cagliari

11. A. Cardini / INFN Cagliari
PSI
Normalized Currents (%)
Casaccia / Big Detector A / 16 Gy/h
Casaccia / Big Detector B / 16 Gy/h
Casaccia / Big Detector C / 0.5 Gy/h
Casaccia / Small Detector D / 16 Gy/h
X-Ray / Small Detector / Local Aging
H2O injection
CO2 problem
2 clearly different trends !
11 LHCb years
CSN1, 5 aprile 2004
A. Cardini / INFN Cagliari

12. A. Cardini / INFN Cagliari
Casaccia / Big Detector A / 16 Gy/h
Casaccia / Big Detector B / 16 Gy/h
Casaccia / Big Detector C / 0.5 Gy/h
Casaccia / Small Detector D / 16 Gy/h
X-Ray / Small Detector / Local Aging
Normalized Currents (%)
G/G ~ 0
G/G ~ -10%
for 0.15 C/cm2
Integration time: 3  35 days
1.2 LHCb years
2 clearly different trends !
CSN1, 5 aprile 2004
A. Cardini / INFN Cagliari

13. A. Cardini / INFN Cagliari
@ Settembre 2003
Clarify aging mechanism:
Physical/Chemical analysis of irradiated detectors
Understanding different chamber behavior:
Investigation on the Gas-flow effect
Absolute Gain Measurement
Gain Uniformity
Gain/Efficiency Recovery by voltage increase:
A gain recovery by a factor 2 has already been performed during the Casaccia test
CSN1, 5 aprile 2004
A. Cardini / INFN Cagliari

14. W.Witzeling (Tech. Coord.) in the Zürich Sept. ’03 LHCb-week:
“Ageing is a delicate issue in this region and recent ageing results on the GEM require further clarification before a final decision can be taken.”
“The TB congratulates the GEM team to the results achieved and encourages them to pursue the work with the aim of coming to a positive decision in March 04.”
CSN1, 5 aprile 2004
A. Cardini / INFN Cagliari

15. X-ray test : Uniformity (Pad Current)
Chamber A (nA/pad)
Chamber B (nA/pad)
Good uniformity on the chambers
CSN1, 5 aprile 2004
A. Cardini / INFN Cagliari

16. Aging induced by low gas flow
We tried to reproduce the Casaccia test results, irradiating with X-rays a 10x10 cm2 chamber (total current ~2 mA on ~ 1 cm2 irradiation spot) flushed with a low gas flow (20 cc/min).
A current drop of ~ 40% for a 0.55 C/cm2 integrated charge (~3 LHCb years) is found on the low gas flow measurement.
NO current drop is observed on the high gas flow measurement.
High gas flow
Low gas flow
CSN1, 5 aprile 2004
A. Cardini / INFN Cagliari

17. SEM analysis on Casaccia chambers
No damage on gold-plated drift cathode and Pad PCB. They are perfectly clean.
Fluorine found on G2 and G3 could be present as Cu-F compound,
forming a thin insulating layer (no carbon deposits observed on the
surfaces).
G1: No fluorine No etching
G2:Small fluorine,etching started
G3:Large fluorine etching
Ch A G1 down sample 5
Inner → 44 µm
 Outer → 76 µm
Ch A G2 down sample 9
Inner → 47 µm
 Outer → 79 µm
Ch A G3 down sample 11
Inner → 64÷65 µm
 Outer → 77÷78 µm
CSN1, 5 aprile 2004
A. Cardini / INFN Cagliari

18. SEM analysis on Casaccia chambers
The fluorine strongly etched the third GEM, not only widening the
copper holes but also etching the kapton inside hole (from the bottom to
the top), changing the hole shape. The effective inner hole diameter,
from the standard mm becomes mm.
Cross section of the first GEM foil
of the aged chamber A.
Cross section of the third GEM foil
of the aged chamber A.
CSN1, 5 aprile 2004
A. Cardini / INFN Cagliari

19. Gain and rate capability on aged chambersV A B
Reference Xray LNF
6.103
Casaccia MHz/cm2
-89% (11.5 Y)
-80% (8.5 Y)
X-Ray MHz/cm2
-55%
-32%
Gain
Rate Capability
Casaccia B
Casaccia A
~50%
~30%
X-Ray
LHCb
Rate capability reduced due to charging down
Chamber A current drop (~89%) ~ gain drop(~55%) + rate capability (~30%)
CSN1, 5 aprile 2004
A. Cardini / INFN Cagliari

20. Beam test results on aged chambers
After Casaccia, chambers A and B were tested at CERN PS-T11.
Time and efficiency performances are similar to those found before Casaccia
aging test, except for a V shift in the working point, and practically
unaffected working regions.
96%
old new
old new
CSN1, 5 aprile 2004
A. Cardini / INFN Cagliari

21. A. Cardini / INFN Cagliari
Conclusioni
Casaccia results seem to be understood : the etching observed is correlated with bad gas flow rate condition;
No corrosion effect observed on the cathode and anode;
Etching effects mainly on the third gem with fluorine deposits near the copper holes edges;
No aging occurs if the gas flow is properly set, as in the LHCb running condition;
Detectors, even after a severe irradiation in bad conditions, exhibit good time and efficiency performances.
CSN1, 5 aprile 2004
A. Cardini / INFN Cagliari

22. Conclusion of the Muon Group on the M1R1 Technology (Feb. ’04)
“We are satisfied with the understanding of the ageing process in GEM detectors and recommend them to be adopted for M1R1.”
Addendum-2 to the Muon TDR is under preparation
CSN1, 5 aprile 2004
A. Cardini / INFN Cagliari

23. Technical Board on 25 February ’04
Final approval of the GEM chambers for Region 1 of the Muon Station 1 (Cagliari+LNF)
“After the preliminary decision in September 03, more studies on ageing were performed, the effects seen in the Casaccia tests are now understood (gas flow). TB supported proposal by Muon group to adopt GEM chambers for the M1 R1 region.” (W. Witzeling)
CSN1, 5 aprile 2004
A. Cardini / INFN Cagliari

24. A. Cardini / INFN Cagliari
Cosa viene ora?
Maggio 2004: programma dettagliato sulla costruzione e costi
M1R2: ci è stato chiesto di studiare la fattibilità
Ci sono indicazioni che sia una scelta “saggia”
Problemi di manpower: necessari almeno 2 tecnici a tempo pieno
Costi da valutare
Sistema GAS da studiare …
CSN1, 5 aprile 2004
A. Cardini / INFN Cagliari