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[email protected] MPGD. R&D Collaboration, CERN – September 10, 2007

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Micromegas Micromegas Performance and Performance and Ageing studiesAgeing studies

David Attié

MPGD. Towards an R&D Collaboration, CERN – 10 September 2007


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Summary

• Gain measurements

• Energy resolution

• Ion feedback

• Ageing

• Conclusion


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Gain measurements

Description:

• “Standard” 50 m mesh of 10 cm x 10 cm size

• Gas mixing system with triple mixture available

Goals:

• find a gas mixture with comfortable gain margin • know as much as possible the maximum gain (to avoid spark)


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100

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100000

50 55 60 65 70 75 80 85 90 95 100

Field (kV/cm/atm)

Ga

in

Iso : 1%

Iso : 2%

Iso : 3%

Iso : 4%

Iso : 5%

CF4 : 3%, Iso : 1%

CF4 : 3%, Iso : 2%

CF4 : 3%, Iso : 3%

CH4 : 6%

CH4 : 7,5%

CH4 : 9%

CH4 : 10%

CH4 : 5%, CF4 : 3%

CH4 : 5%, CF4 : 5%

CH4 : 5%, CF4: 10%

CH4 : 10%, CF4 : 3%

CH4 : 5%, CO2 : 3%

CH4 : 10%, CO2 : 10%

CO2 : 10%

CO2 : 20%

CO2 : 30%

CO2 : 10%, Iso 2%

CO2 : 10%, Iso 5%

CO2 : 10%, Iso 10%

CF4 : 3%, CO2 : 1%

CF4 : 3%, CO2 : 3%

CF4 : 3%, CO2 : 5%

Iso : 2%, CH4 : 10%

Iso : 5%, CH4 : 10%

Iso : 10%, CH4 : 10%

Ethane 10%

Ethane 5%

Ethane 3,5%

Ethane 2%

Ethane 3,5% - CO2 10%

Ethane 3,5% - CF4 3%

Ethane 3,5% - CF4 10%

Ethane 3,5% - Iso 2%

Mixtures of gases containing argon: gain curves

iC4H10

CO2, CH4C2H6

Micromegas Mesh : 50 m gap of 10x10 cm² size


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Ar/CH4: simulation vs. measurements

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E/P (V/cm/atm)

Gai

n

ArCH4 10% : Mea.

ArCH4 9% : Mea.

ArCH4 7,5% : Mea.

ArCH4 6% : Mea.

ArCH4 10% : Sim

ArCH4 9% : Sim

ArCH4 7,5% : Sim

ArCH4 6% : Sim

Good agreement:measurements are consistent with simulations


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50000 55000 60000 65000 70000 75000 80000 85000

E/P (V/cm/atm)

Ga

in

ArIso 1% : Mea.

ArIso 2% : Mea.

ArIso 3% : Mea.

ArIso 4% : Mea.

ArIso 5% : Mea.

ArIso 1% : Sim

ArIso 2% : Sim

ArIso 3% : Sim

ArIso 4% : Sim

ArIso 5% : Sim

Ar/iC4H10: simulation vs. measurements :

Penning effect

UV photons ?

Agreement with the slope at low fields but not with the absolute gain and the photons effects


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5%

10%

15%

20%

25%

30%

35%

40%

100 1000 10000 100000 1000000

Gain

RM

S

Iso : 1%

Iso : 2%

Iso : 3%

Iso : 4%

Iso : 5%

Energy resolution vs. gain

Argon/Isobutane

• Best RMS for a gain between 3.103 & 6.103

• Degradation increase in inverse proportion to the quencher


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00,

20,

40,

60,

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Energy resolution

Pressure = 1 atm, thickness = 10 μm

Photon energy (keV)

Tra

nsm

issi

on

(%

)

• Obtain easily a monochromatic source by filtering the Kβ line at 6,4 keV

• 10 μm of Chromium foil (Center for X-Ray Optics)

• Chromium K-edge (Center for X-Ray Optics)

• Micromegas standard 10 cm x 10 cm

• 55Fe source in Argon/iC4H10 (95:5)– Escape line at 3 keV– Kα at 5.9 keV– Kβ at 6.4 keV

σE/E = 8.0 %

FWHM = 18.8 %

2/ndf = 112

σE/E = 7.0 %

FWHM = 16.6 %

2/ndf = 19


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Energy resolution

source

Cr foil

Drift cathode

mesh


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Energy resolution

• Energy resolution using a « microbulk »

• Argon/Isobutane (95:5)

• Chromium foil

55Fe

σE/E = 5.7 %

FWHM = 13.5 %

2/ndf = 1.36


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Energy resolution

• Energy resolution using an Ingrid (gap: 50 μm; picth: 32 μm; Ø: 14 μm)

• Argon/Methane (90:10)

• Chromium foil

55Fe

σE/E = 5.0 %

FWHM = 11.7 %

2/ndf = 1.35


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Ion feedback

• Measurement concept:

meshdrift

0drift

II

IIf

-500 V

-300 V

IdriftI0

Imesh

• I0: primary current

• Idrift: cathode current

• Imesh: amplification current

X-rays generator


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Ion feedback

0,01

0,1

1

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10 100 1000

Field ratio (Ea/Ed)

Ion

fe

ed

ba

ck (

%)

0,01

0,1

1

10

10 100 1000

Field ratio (Ea/Ed)

Ion

fe

ed

ba

ck (

%)

- Pitch: 58 μm; Ø: 31 μm

- Pitch: 20 μm; Ø: 10 μm

a

d

E

Ef


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Ageing

• X-rays gun (40 kV, 20 mA)

• Micromegas “Bulk” (T2K-like)

• Gas mixture: – Argon/Isobutane (95:5)– Argon/CF4/Isobutane (95:3:2)


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1,0

13/04/07 14/04/07 15/04/07 16/04/07 17/04/07 18/04/07 19/04/07 20/04/07 21/04/07 22/04/07 23/04/07 24/04/07

AgeingN

orm

aliz

ed

unit

Time (d)

- Mesh current- Mesh current

Ar/CF4/Iso (95:3:2)

16,1 C / cm² ~ 20 LHC years


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Ageing

Time (d)

Norm

aliz

ed

unit

- Mesh current

- Temperature

- Pressure

- Mesh current

- Temperature

- Pressure


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Ageing

• Gain ~4000• Mesh current ~ 5 μA during 5 days inside 10 cm²• New measurement procedure with an other bulk:

11 cm

11 cm

Hole 2cm x 5cm

Absorber 200 m of Al 2cm x 2cm


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0

02/05/07 03/05/07 04/05/07 05/05/07 06/05/07 07/05/07 08/05/07

AgeingC

urr

ent

(mA

)

Time (d)

- Mesh current- Mesh current

Ar/Iso (95:5)

0,17 C/cm² ~ 2 LHC years


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Ageing

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Vmesh (V)

Gai

n

Before "cooking"

After "cooking"

After ageing

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Vmesh (V)

Gai

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Before "cooking"

After "cooking"

After ageing

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Vmesh (V)

Gai

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Before "cooking"

After "cooking"

After ageing


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Conclusion

•The choice of the gas mixture could be adapted to the needs

•The energy resolution can easily reach 5 % RMS (11,7 % FWHM)

•The ion feedback is depending of the geometry and achieve 10-3

•Until now, no ageing has been observed clearly

•The studies continue following the technology developments…