Un Rivelatore a Tripla-GEM per le Camere a Muoni di LHCb M. Alfonsi 1, G. Bencivenni 1, W. Bonivento 2, A. Cardini 2, P. de Simone 1, F. Murtas 1, D. Pinci 3, M. Poli-Lener 1, D. Raspino 2 and B. Saitta 2 1. Laboratori Nazionali di Frascati - INFN, Frascati, Italy 2. Sezione INFN di Cagliari Cagliari, Italy 3. Sezione INFN di Roma 1, Roma, Italy
M1R1 Rate Capability up to 0.5 MHz/cm 2 Station Efficiency >96% in a 20 ns time window (*) Cluster Size <1.2 for a 10x25 mm 2 pad size Radiation Hardness 1.6 C/cm 2 in 10 years (**) Chamber active area 20x24 cm 2 (*) 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/cm 2 with a gain of ~ 6000 CSN1, 5 aprile 2004 A. Cardini / INFN Cagliari 2
A Triple-GEM detector is built by inserting three GEM foils between two planar electrodes, which act as the cathode and the anode. Conversion & 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. 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 3
Large (20x24 cm 2 ) 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 4
M1R1 Full Size Prototype ASDQ FEE Boards Sensitive gaps CSN1, 5 aprile 2004 A. Cardini / INFN Cagliari 5
9.7 ns 5.3 ns 4.5 ns 4.5 ns Considerable improvement with respect to the Ar/CO 2 =70/30 gas mixture, which exhibits a poor time resolution of about 10 ns RMS, is obtained with the new CF 4 and iso-c 4 H 10 based gas mixtures, which allow to reach time resolutions better than 5 ns RMS Our Choice: Single Chamber Time Spectra Ar/CO 2 /CF 4 45/15/40 Fast & Non-flammable CSN1, 5 aprile 2004 A. Cardini / INFN Cagliari 6
Working region, upper limited by Cluster Size = 1.2, is found to be 70-80 V wide, a large plateau for a micropattern gaseous detector! Cluster Size OR Efficiency in 20 ns 2.0 fc 3.0 fc Working region G~4000 G~20000 CSN1, 5 aprile 2004 A. Cardini / INFN Cagliari 7
Discharge probability per incident particle Recenti misure suggeriscono che un rivelatore possa tollerare fino a circa 1000 scariche/cm 2 P < 5.4 10-11 G < 2.7 10 4 CSN1, 5 aprile 2004 A. Cardini / INFN Cagliari 8
Local Aging Test high intensity X-rays detector active area 10х10 cm 2 irradiated area ~1mm 2 Ar/CO 2 /CF 4 (60/20/20) ΣV GEM = 1230 V Ar/CO 2 /CF 4 (45/15/40) ΣV GEM = 1280 V Ar/CF 4 /C 4 H 10 (68/25/7) ΣV GEM = 1030 V G=2.5 10 4 G=6 10 3 G=10 4 I G3_Dw +I Pad ~270 na I G3_Dw +I Pad ~160 na I G3_Dw +I Pad ~160 na Φ gas =166.6 cc/min Φ gas =200 cc/min Φ gas =154 cc/min G/G < 5% G/G < 5% G/G ~10% 10 LHCb Years 6.6 C/cm 2 10 LHCb Years 1.8 C/cm 2 10 LHCb Years 3 C/cm 2 CSN1, 5 aprile 2004 A. Cardini / INFN Cagliari 9
Aging set-up at Casaccia Gas mixture:ar/co 2 /CF 4 = 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; GAS BOTTLES GEM-E GEM A,B,D GEM-C Large chamber E in low irradiation position ~ 0.1-0.2 Gy/hour; PC HV 4.5m HV( reference ) = 1280 V, G ~ 6x10 3 ; H 2 O/T/ P = ± 1ppm / ± 0.1 K / ± 0.1mb (Panametrics/MKS probe systems) 60 Co 25 kci CSN1, 5 aprile 2004 A. Cardini / INFN Cagliari 10
Normalized Currents (%) PSI 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 H 2 O injection CO 2 problem 2 clearly different trends! 11 LHCb years CSN1, 5 aprile 2004 A. Cardini / INFN Cagliari 11
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 G/G ~ 0 G/G ~ -10% for 0.15 C/cm 2 Integration time: 3 35 days 2 clearly different trends! 1.2 LHCb years CSN1, 5 aprile 2004 A. Cardini / INFN Cagliari 12
@ 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 13
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 14
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 15
Aging induced by low gas flow We tried to reproduce the Casaccia test results, irradiating with X-rays a 10x10 cm 2 chamber (total current ~2 µa on ~ 1 cm 2 irradiation spot) flushed with a low gas flow (20 cc/min). A current drop of ~ 40% for a 0.55 C/cm 2 integrated charge (~3 LHCb years) is found on the low gas flow measurement. High gas flow Low gas flow NO current drop is observed on the high gas flow measurement. CSN1, 5 aprile 2004 A. Cardini / INFN Cagliari 16
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 17
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 45-50 µm becomes 60-65 µm. Cross section of the first GEM foil of the aged chamber A. CSN1, 5 aprile 2004 Cross section of the third GEM foil of the aged chamber A. A. Cardini / INFN Cagliari 18
Gain and rate capability on aged chambers Gain Gain @ 1280 V A B Reference Xray LNF 6. 10 3 6. 10 3 Casaccia drop @ 15-20 MHz/cm 2-89% (11.5 Y) -80% (8.5 Y) X-Ray 1.6 MHz/cm 2-55% -32% Rate Capability Casaccia B ~30% X-Ray Casaccia A ~50% 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 19
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 20-25 V shift in the working point, and practically unaffected working regions. 96% old new old new CSN1, 5 aprile 2004 A. Cardini / INFN Cagliari 20
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 21
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 22
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 23
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 Problemidimanpower: necessarialmeno2 tecnici a tempo pieno Costi da valutare Sistema GAS da studiare CSN1, 5 aprile 2004 A. Cardini / INFN Cagliari 24