Developments and tests of m-PIC with Resistive Cathode

Atsuhiko OchiKobe University

4/10/2012 10th RD51 collaboration meeting

A. Ochi, 10th RD51 meeting

More stabilities and robustness is needed for some application◦ Operation in high ionized particle (HIP)◦ Very high gain for detecting single electron◦ The electron density may excess the Raether limit (107-8)◦ Continuous sparks will destroy the electrodes easily because of

existence of substrates near electrodes.◦ Dead time due to resuming HV is also problem.

There are two approaches for stable operation◦ Reducing the spark◦ Making spark tolerant structure

Self quench mechanism for sparks will be added, using MPGD (m-PIC) electrodes

1st trial: Metal cathodes are covered by high resistivity material. This report: Cathodes are made from resistive material, and cathode

signals are read using induced charge.

Requirements for more stability

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A. Ochi, 10th RD51 meeting

Previous trial: m-PIC with resistive overcoat Resistive kapton is on

the cathodes of m-PIC. We can detect signals

using 55Fe, but there found no spark reduction

Gas gain < 10000 R

RR

+HV

100mm

25mm

CathodeResistive sheet

Anode 400mm

Drift plane-HV

~1cmDetection area: filled by gas

25μm

25μm

Anode

Resistivefilm

Cathode

E-field will be dropped by spark current.

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At January 2012 (have been reported at 9th RD51 meeting)◦ All cathodes are made from carbon-polyimide◦ Pickup electrodes are lied under cathodes

and insulator◦ We have two dimensional signals◦ However, it is difficult to operate in high gain

(> 10000), and there is no spark reductoin There are many extra holes, cause from the

miss alignment The connectivity of anode pixels were also

poor

m-PIC with resistive cathode and capacitive readout: First trial

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Cathode-pickup

Anode

Insulator (polyimide)Resistive cathode

Pickupreadout

Anode

Improvements for manufacturing

• Manufactured by Raytech Inc.

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Top pattern

Cathode pattern

Double side mask

Anode pattern

Anode pattern etching

Anode PI etching

Anode plating

Resistive PI baking

PI stacking

Anode drilling by laser

Cu spattering from rear

Anode plating

• Very good accuracy (compared with previous samples)

– Surface resistivity– About 50MW / strip

(10cm)

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Micro scope picture of a prototype (RC27)

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Signal of 55Fe　 (about 0.5V/pC)

Conditions：　Ar:C2H6=7:3 mixture gas　Drift field: 3.3kV/cm

Va = 660V, Gain ~ 20000

Cathode (pickup)

Anode

300mV

• Conditions– Drift field = 3.3kV/cm– 55Fe (5.9keV)– Using the signal from cathode

pickup electrodes• Results

– High gain (>60000) was achieved, and operation was stable (in case of Ar:C2H6=7:3)

– There found small discharges over the maximum gain in right figure. However, no big sparks have been found around maximum gain.

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Gain curve

460 500 540 580 620 660 7001000

10000

100000Ar:C2H6=7:3Ar:C2H6=9:1Ar:CO2=7:3Ar:CO2=9:1Ga

in

Anode voltage [V]

Potential of electrodes:◦ Cathodes (resistive): 0V

Negative HV◦ Anodes : Positive HV 0V

No HV on anodes◦ AC coupling capacitors

and HV resistors are not needed

Result:◦ High gain ( ~ 50000) was

achieved as well as previous setup

Novel Operation condition with applying HV to resistive cathode

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510 520 530 540 550 560 570 580 590 600 6101000

10000

100000

Gain

- Cathode voltage

(0V)

R+HV(~600V)

New operation-HV(~-600V)

Direct connection to readout

Previous operation

A few MeV – few tenth MeV neutron will produce recoiled nucleon inside detectors◦ That produce great amount of energy

deposit (a few MeV/mm2) in gaseous volume.

The concerned problem for gas detector◦ “Raether limit” … the electron cluster

more than 107-8 cause the detector to discharge.

We can evaluate the spark probability for HIP by measuring the spark rate dependencies on neutron irradiation

Neutron source◦ Tandem nucleon accelerator (3MeV

deuteron) + Beryllium target.(Kobe University, Maritime dept.)

◦ d+ 9Be n + 10B◦ Neutron energy: mainly 2MeV

Spark test using fast neutron

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HV current on anodes are monitored while neutrons are irradiated

We found strong spark reduction using resistive cathode !!

Spark probability measurements

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Normal m-PIC (metal cathodes)　 Gain = 15000　 Irradiation: 2.4×103 neutron/secResistive cathode m-PIC 　 Gain = 15000　 irradiation: 1.9×106 neutron/sec

[mA] 10

8

6

4

2

0

[mA] 10

8

6

4

2

0

neutronDrift

-HV(~1kV)

Cathode = 0V

A+HV(~600V)

AnodeVoltage recorder

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Spark probability for fast neutron (~2MeV)

• Conditions– Gas: Ar+C2H6 (7:3)– Drift field: 3.3kV/cm– Definition of the sparks:

– Current monitor of HV module shows more than 2mA or 0.5mA.

– Spark probability = [Spark counts] / neutron

– The spark rates on normal m-PIC are are also plotted as comparison (cyan, magenta plots).

• Results– Reduction of sparks are

obviously found. The rate was 103-5 times less than normal m-PIC case at same gas gain.

Spark reduction

m-PIC with resistive cathodes and capacitive readout is newly developed and tested.

More than 60000 of gas gain is achieved stably using 55Fe source under Ar(70%)+ethane(30%) gas.

Sparks are reduced strongly. ◦ The spark rate under fast neutron (2MeV) is suppressed 105

times smaller than that of normal m-PIC.◦ It can continue to run under intense (~106 n/cm2/s) neutron at

high gain (~104). More improvement of the production is needed.

◦ To operate it at all detection area in order to use as imaging devise.

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Conclusion and future prospects

These researches are supported by • Japan MPGD Basic R&D Team.• Grant-in-Aid for Scientific Research (No.23340072)• RD51 collaboration