10.10.01 G. Gavrilov 1

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.