Developments and tests of m -PIC with Resistive Cathode
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Transcript of Developments and tests of m -PIC with Resistive Cathode
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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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