Developments and tests of m -PIC with Resistive Cathode

1. Developments and tests of m-PIC with Resistive Cathode Atsuhiko Ochi Kobe University 4/10/2012 10th RD51 collaboration meeting

2. Requirements for more stability • 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. A. Ochi, 10th RD51 meeting

3. Previous trial: m-PIC with resistive overcoat Drift plane -HV E-field will be dropped by spark current. • Resistive kapton is on the cathodes of m-PIC. • We can detect signals using 55Fe, but there found no spark reduction • Gas gain < 10000 25μm ~1cm Detection area : filled by gas 25μm Resistive film Cathode Resistive sheet Cathode 25mm Anode +HV 100mm Anode 400mm R R R A. Ochi, 10th RD51 meeting

4. m-PIC with resistive cathode and capacitive readout: First trial Resistive cathode • 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 Insulator (polyimide) Pickup readout Anode Cathode-pickup Anode A. Ochi, 10th RD51 meeting

5. Improvements for manufacturing • Manufactured by Raytech Inc. Resistive PI baking Top pattern Cathode pattern PI stacking Double side mask Anode drilling by laser Anode pattern Cu spattering from rear Anode pattern etching Anode PI etching Anode plating Anode plating A. Ochi, 10th RD51 meeting

6. Micro scope picture of a prototype (RC27) • Very good accuracy (compared with previous samples) • Surface resistivity • About 50MW / strip (10cm) A. Ochi, 10th RD51 meeting

7. Signal of 55Fe(about 0.5V/pC) Va = 660V, Gain ~ 20000 Conditions： Ar:C2H6=7:3 mixture gas Drift field: 3.3kV/cm Cathode (pickup) 300mV Anode A. Ochi, 10th RD51 meeting

8. Gain curve • 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. Gain Anode voltage [V] A. Ochi, 10th RD51 meeting

9. Novel Operation condition with applying HV to resistive cathode (0V) Previous operation • 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 +HV(~600V) R -HV(~-600V) New operation Direct connection to readout - Cathode voltage A. Ochi, 10th RD51 meeting

10. Spark test using fast neutron • 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 A. Ochi, 10th RD51 meeting

11. neutron Spark probability measurements -HV (~1kV) Drift • HV current on anodes are monitoredwhile neutrons are irradiated • We found strong spark reduction using resistive cathode !! Cathode = 0V Anode +HV (~600V) Voltage recorder A [mA] 10 8 6 4 2 0 [mA] 10 8 6 4 2 0 Normalm-PIC (metal cathodes) Gain = 15000 Irradiation: 2.4×103 neutron/sec Resistive cathode m-PIC Gain = 15000 irradiation: 1.9×106 neutron/sec A. Ochi, 10th RD51 meeting

12. 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 A. Ochi, 10th RD51 meeting

13. Conclusion and future prospects • 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. • These researches are supported by • Japan MPGD Basic R&D Team. • Grant-in-Aid for Scientific Research (No.23340072) • RD51 collaboration A. Ochi, 10th RD51 meeting