A new design of the Micro Pixel Chamber using DLC electrodes

Speaker: F. YamaneA

A. OchiA, Y. HommaA, T. KawamotoB, T. MasubuchiB, Y. KataokaB, H. HasegawaA, N. NagasakaA, K. MatayoshiA, K. OgawaA

Kobe Univ. A

Tokyo ICEPPB

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Outline• μ-PIC with resistive cathodes• The new design• First results of new μ-PICs

μ-PIC with resistive cathodes

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μ-PIC with resistive cathodes

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➢ Property of the μ-PIC• Made by PCB techniques• 2D readout with Anode/Cathode strips (400um

pitch)• Enough gas gain to detect MIPs

• Any floating structures are not needed• Arranging μ-PICs to tile form -> Large area

➢ The μ-PIC with resistive cathodes• Resistive material for cathodes (105~7Ω/sq.)• High tolerance of discharges compared to

standard μ-PICs (10-3~4)• Induced charges are read from resistive cathodes

• Any capacitors for readout are not needed• Diamond Like Carbon (DLC) (details in the backup)

• Noble material made by carbon sputtering• Fine patterning (

Design of the resistive μ-PIC

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25um

50umDF

FPC

↑Pickup Cathode

Resistive cathodeAnode➢ Production: RAYTECH Inc.➢ Carbon sputtering: Be-Sputter Co., Ltd➢ 256 channels -> 10cm x 10cm➢ The top layer: FPC (25um)

• Resistive & pickup cathodes are patterned each side on the FPC

➢ The bottom layer: Dry film (50um)• 256×256 pixels are well aligned

by photolithography. Anode strips are connected to the surface.

➢ 2 years ago (MPGD2015)• Anode strips were not connected

to the surface because of the remaining dry resist in the FPC layer.

• This problem has been solved by filling the holes with nickel pattern.

↑Anode Strip

MPGD2015Remaining dry resist

Black: DLCBrown: CupperGray: NickelRed: Sputtered nichrome

Operation tests

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100

1000

10000

540 560 580 600 620 640 660Anode Voltage [V]

Cathode signalAnode signal

➢ Gas gain measurement using 55Fe source• Gas mixture: Ar:C2H6=90:10• Preamp: ATLAS ASD (0.8V/pC, τ=16ns)• Gas gains of > 10000 were obtained by

both anodes and cathodes readout.

➢ Fast neutrons irradiation test• Tandem Van de Graaff facility in Kobe Univ.• Neutron energy: ~2MeV• Neutron flux: >1MHz/cm2

• The μ-PIC could be operated stably in the irradiation environment of fast neutrons.

Current monitor on anodes

Beam on Beam offA

no

de

curr

ent

[nA

]

The new design

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Problem for all channels readout

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➢ In the current design, 16 strips were united to 1ch for simplification

➢ In order to read signals from all 256 channels, 256 RC circuits are needed.

➢ However, the large board for putting 256 resisters and capacitors is needed like bottom left picture.

Inside of the gas package

Backside of the gas package

μ-PIC

10cm

Detector

x 256

Equivalent circuits by DLC & PCB technique

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Rigid Board↑Pickup Anode

Polyimide Gluing sheet

25um

50um

35um

DF

FPC

↑Pickup Cathode

↑Anode Strip

DLC CathodeAnode

➢ Bias resisters -> DLC• 400um pitch DLC bias resisters were

patterned on FPC➢ Capacitors -> Polyimide gluing sheet

• The μ-PIC were glued on the PCB which has readout strips correspond to anodes.

• The gluing sheet behaves as capacitors for respective strips (~22pF/strip)

DLC bias resisters x256

The new μ-PIC board

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μ-PIC

10cm

➢ DLC and PCB techniques have enabled all RC circuits to be put in the μ-PIC board (10cm x 10cm)

Detector

x 256

μ-PIC

PCB with anodereadout strips

First results of new μ-PICs

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The spectrum of 55Fe source

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➢ Gas mixture: Ar:C2H6=90:10➢ Preamp: ATLAS ASD(0.8V/pC, τ=16ns)➢ Noise level is very low. Clear signals of

5.9keV and 3.2keV could be seen. ➢ Energy resolution: ~20%(FWHM)@5.9keV

Anode signal Cathode signal

Gas gains of new μ-PICs

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Previous: 40umNew chambers: 75um

➢ Gas gains of >10000 were obtained on the anodes readout.

➢ New chambers could identify very small signals which have reached the lowest limit of MCA

➢ Difference of operation voltage is due to the size of anode diameter

➢ Difference of the anode diameter affects not only gas gains but also optimum drift field

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1000

10000

460 480 500 520 540 560 580 600 620 640

The gain map of resistive μ-PICs

New uPIC1

New Upic2

Previous uPIC

Performance test using cosmic muons

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➢ Last week, new μ-PICs have succeeded to detect cosmic muons• New μ-PICs are compatible with

SRS-APV readout• mmDAQ was used for data

aquisition

Hit map of cosmic muons

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Hit map Hit map Hit timingHit timing ADCADC

➢ Left: Hit map of anodes• Empty spaces are correspond to 32strips where voltage were not applied.

➢ Right: Hit map of cathodes• RC38 could not detect signals.• This inefficiency must be studied.

Anodes Cathodes

RC37

RC38

RC41

RC37

RC38

RC41

Position resolution (1D)

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➢ Position resolution (1D) of the μ-PIC was measured by the residual method.• Operation gas gain: ~4000• 1519 events were obtained in 12 hours run.• Building cluster by uniting hit strips.• Hit position -> Center of the cluster mass• Requiring 1 hit on each chamber ->

169events• Residual: x2 - (x1 + x3)/2• Position resolution: σ/√(1.5) = 133um• Theoretical value: 400um/√12 =115.5um• However statistics are little, new μ-PICs

have showed good value

➢ 2D readout operation (2FECs needed) will be performed in the near future.

RC37 RC38RC41

Cosmic muon

x1 x2 x3

Preliminary

Summary & Future prospects

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Summary➢ The μ-PIC with resistive cathodes has been developed.➢ Resistive cathodes were made by Diamond Like Carbon.➢ DLC and PCB techniques have enabled all RC circuits to be put in the μ-PIC

board (10cm x 10cm)➢ Operation test

• Gas gains > 10000• Energy resolution ~ 20%(FWHM) @ 5.9keV• Position resolution of 133um was obtained on anode direction using cosmic

muons which is consistent with the theoretical value (preliminary)

Future prospects➢ 2D resolution, 2D imaging, 3D tracking➢ Optimization of parameters (operation voltage, resistivity, anode diameter)

Backup

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Diamond Like Carbon

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➢ Diamond Like Carbon (DLC): Noble resistive material composed of sp2 & sp3 amorphous carbon.

➢ Made by sputtering technique.➢ Developed by Kobe Univ. from 2012➢ Property

• Fine patterning (

Comparison: Gas mixture

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100

1000

10000

400 450 500 550 600 650 700

Gai

n

Anode Voltage [V]

Ar:C2H6=90:10

Ar:C2H6=80:20

Ar:C2H6=70:30

➢ Drift field: 1kV/5mm = 2kV/cm➢ Gas: Ar:C2H6=90:10, 80:20, 70:30➢ The maximum gain was achieved at gas mixture of Ar:C2H6 = 90:10

Comparison: Anode or Cathode

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100

1000

10000

440 490 540 590

Gai

n

Anode Voltage [V]

Anode Readout

Cathode Readout

➢ Drift field: 930V/3mm=3100V/cm➢ Gas: Ar:C2H6=90:10➢ The gain of cathodes became larger than that of anodes.➢ The gluing sheet (35um thickness, 22pF/strip) may not have enough capacitance.

カソード信号の位置依存

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1~8 9~16 17~24 25~32 33~40 41~48 49~56

65~72 73~80 81~88 89~96 97~104 113~120

129~136 137~144

57~64

145~152 153~160 161~168 169~176 177~184 185~192

121~128105~112

193~200 201~208 209~216 217~224 225~232 233~240 241~248 249~256

アノード電圧印加範囲: 33~64strip→各測定範囲: 32strips×8strips

Neutron irradiation test

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D+ beam

Discharges in the pixel

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➢ Carbon like deposits were seen between the anode and the cathode.➢ This deposits have thickness about 10um.➢ This deposits could be removed by blowing or wiping.➢ This deposition seems to be originated from quenching gas.

Conductive passage

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➢ High voltage was applied on the damaged pixel.➢ Compared to the left picture (before), the passage between the anode and

the cathode is clearly seen in the right picture (after).➢ This passage could not be removed.➢ This passage was made by carbonization of polyimide.

Cutting dead pixels

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➢ Cutting resistive strips around dead pixels (right pic)• This will not affect the readout

because readout strips are under the FPC layer.

• Thanks to the ladder connections, voltage can be applied to other pixels. (bottom pic)