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Aging Studies of CMS Muon Chamber Prototypes
T.Ferguson†,G.Gavrilov,A.Korytov††,A.Krivchitch,E.Kuznetsova,E.Lobachev,G.Mitselmakher††,L.Schipunov.
Petersburg Nuclear Physics Institute,188350 Gatchina, St.Petersburg, Russia
† Carnegie Mellon University, Pittsburgh, PA, 15213, USA†† University of Florida, Gainesville, FL, 32611, USA
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• The CMS Endcap Muon System consists of 540 cathode strip chambers(CSCs) of 6 different kinds
• All chambers are made of 7 cathode panels separated by six 1 cm gaps:– panels of copper-clad FR4 interleaved with 16 mm honeycomb– wire plane of 50 µm Au+W wires spaced 3.2 mm apart• Overall area covered by the chambers is more than 1000 m2 corresponding
to 6000 m2 for the separate planes• The amplitude from m.i.p. particle ~1pC which corresponds to a gas gain
6×104
� The LHC counting rate at the worst CSC spots ~ 130 Hz/cm per wire or2MHz per plane (typical area S = 3m × 1m)
� The maximal accumulated charge in 10 LHC years per unit wirelength
Qwire= 0.08 [C/cm] and per unit area Qwire= 0.04 [C/cm2]
CMS Endcap Muon System and LHC conditions
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Chamber prototypes• Three prototypes were fabricated
using materials intended forchambers production. The activearea each of prototypes 175××××240 mm2
• Three gas mixtures were usedAr(30%)+CO2(50%)+CF4(20%)Ar(30%)+CO2(70%)Ar(40%)+CO2(50%)+CF4(10%)
• Two different versions of the gassealing design were used.a A bead of RTV is placed along a
panel perimeter before the chamberwas closed.
b The chamber was first closed andtighten then a bead of RTV wasapplied.
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Aging settings• Sealing design a. the obvious
drawback is direct contact of RTVwith gas mixture.
• The CF4 in gas mixture compensatesthe Si influence from the RTV
(J. Kadyk, J. Wise), preventing anodeaging.
• The goal to study the scale of cathodeaging using baseline gas mixtureAr(30%) + CO2(50%) + CF4(20%)
• An accumulated 13 C/cm at the wireirradiated zone is needed to becomparable with LHC conditions.
• This dose may be obtained in a fewmonth with a quick aging test.
• The nominal gas gain 6××××104 wasreduced by a factor of ~1.5. Due tothe space charge effect caused by thehigh intensity irradiation.
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Test setup• Collimated 90Sr ββββ-source (2Ci)
was used for irradiation.• Total counting rate is ~13 MHz/cm; Rate of charge accumulation is
0.3 C/day.• To have the gas refreshing rate
for the test and the final LHCSCS’s equal, the refreshingtime was evaluated as :Ttest= TLHC ×××× Vtest / VLHC = 20 min
Gas flow 75 Vtest/ Day• During the aging test were
monitored:− gas gain as a peak position of
55Fe amplitude spectra;− dark current;− count rates with 55Fe and
noise.
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Aging test resultsAr(30%) + CO2(50%) + CF4(20%) gas mixture
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Aging test results (SEM/XEM analysis)Ar(30%) + CO2(50%) + CF4(20%) gas mixture
Anode wire surface in
irradiated zoneCathode surface coveredby the silicon deposits
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SEM/XEM analysis of the cathode surface
EDAX B
Zone n°1
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Aging test results (SEM/XEM analysis)Ar(30%) + CO2(70%) gas mixture
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Aging test resultsAr(40%) + CO2(50%) + CF4(10%) gas mixture
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Aging test resultsAr(40%) + CO2(50%) + CF4(10%) gas mixture
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Aging test results (SEM/XEM analysis)Ar(40%) + CO2(50%) + CF4(10%) gas mixture
Anode wireirradiated zone
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Ar+50%CO2+10%CF4
Oxygen content
0
20
40
60
80
100
120
140
160
180
200
0 2 4 6 8 10 12
Wire length, cmO
xyge
n co
nten
t, m
onol
ayer
s
wire#1wire#2wire#3
Ar+50%CO2+10%CF4
Oxygen and carbon penetration into the wire#2
0,0E+00
5,0E+20
1,0E+21
1,5E+21
2,0E+21
2,5E+21
3,0E+21
0 0,5 1 1,5 2 2,5 3 3,5Depth, mg/cm2
Con
cent
ratio
n, a
t/cm
3
X = 6.5 cmX = 11 cmX = 6.5 cmX = 11 cm
oxygen
carbon
Nuclear Reaction Method Analysis
14
Aging test results (SEM/XEM analysis)Ar(40%) + CO2(50%) + CF4(10%) gas mixture
d
c
b
a
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Conclusion• A Nuclear reaction method of
analysis demonstrates the increaseof the oxygen in the irradiatedzone.
• Changing the amount of CF4 in thegas mixtures from 20% to 10%altered the character of the wiresurface aging. The ablation of thegold surface was replaced bycracking.
• The accumulated dose forAr(30%)+CO2(50%)+CF4(20%)Ar(40%)+CO2(50%)+CF4(10%)gas mixtures is ~13 C/cm of anodewires length and ~ 0.21 C/cm2 forthe cathode plane, which is 5 timesmore of 10 LHC years.
• Both gas mixtures showed littlesigns of aging in prototypes besidesof dark current increase. The gasgain remained stable up to the endof the tests.
• Sealing design b. demonstratedless coating of the cathode despitediminished CF4 content in the gasmixture.
