1. Atsuhiko Ochi Kobe University 4/10/2012 10 th RD51 collaboration meeting

2.  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 (10 7-8 ) ◦ 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 (  -PIC) electrodes  1 st 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 meeting2012/10/42

3.  Resistive kapton is on the cathodes of  -PIC.  We can detect signals using 55Fe, but there found no spark reduction  Gas gain < 10000 R R R +HV 100  m 25  m Cathode Resistive sheet Anode 400  m Drift plane -HV ~1cm Detection area : filled by gas 25μm Anode Resistive film Cathode E-field will be dropped by spark current. A. Ochi, 10th RD51 meeting2012/10/43

4.  At January 2012 (have been reported at 9 th 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 2012/10/4A. Ochi, 10th RD51 meeting4 Cathode-pickup Anode Insulator (polyimide) Resistive cathode Pickup readout Anode

5. Manufactured by Raytech Inc. 2012/10/45A. Ochi, 10th RD51 meeting 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

6. Very good accuracy (compared with previous samples) – Surface resistivity – About 50M  / strip (10cm) 2012/10/4A. Ochi, 10th RD51 meeting6

7. 2012/10/4A. Ochi, 10th RD51 meeting7 Conditions ： Ar:C2H6=7:3 mixture gas Drift field: 3.3kV/cm Va = 660V, Gain ~ 20000 Cathode (pickup) Anode 300mV

8. Conditions – Drift field = 3.3kV/cm – 55 Fe (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. 2012/10/4A. Ochi, 10th RD51 meeting8 Gain Anode voltage [V]

9.  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 2012/10/4A. Ochi, 10th RD51 meeting9 - Cathode voltage (0V) R +HV(~600V) New operation -HV(~-600V) Direct connection to readout Previous operation

10.  A few MeV – few tenth MeV neutron will produce recoiled nucleon inside detectors ◦ That produce great amount of energy deposit (a few MeV/mm 2 ) in gaseous volume.  The concerned problem for gas detector ◦ “Raether limit” … the electron cluster more than 10 7-8 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+ 9 Be  n + 10 B ◦ Neutron energy: mainly 2MeV 2012/10/4A. Ochi, 10th RD51 meeting10

11.  HV current on anodes are monitored while neutrons are irradiated  We found strong spark reduction using resistive cathode !! 2012/10/4A. Ochi, 10th RD51 meeting11 Normal  -PIC (metal cathodes) Gain = 15000 Irradiation: 2.4×10 3 neutron/sec Resistive cathode  -PIC Gain = 15000 irradiation: 1.9×10 6 neutron/sec [  A] 10 8 6 4 2 0 [  A] 10 8 6 4 2 0 neutron Drift -HV (~1kV) Cathode = 0V A +HV (~600V) Anode Voltage recorder

12. 2012/10/4A. Ochi, 10th RD51 meeting12 Conditions – Gas: Ar+C 2 H 6 (7:3) – Drift field: 3.3kV/cm – Definition of the sparks: – Current monitor of HV module shows more than 2  A or 0.5  A. – Spark probability = [Spark counts] / neutron – The spark rates on normal  -PIC are are also plotted as comparison (cyan, magenta plots). Results – Reduction of sparks are obviously found. The rate was 10 3-5 times less than normal  -PIC case at same gas gain. Spark reduction

13.   -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 10 5 times smaller than that of normal  -PIC. ◦ It can continue to run under intense (~10 6 n/cm 2 /s) neutron at high gain (~10 4 ).  More improvement of the production is needed. ◦ To operate it at all detection area in order to use as imaging devise. 2012/10/4A. Ochi, 10th RD51 meeting13 These researches are supported by Japan MPGD Basic R&D Team. Grant-in-Aid for Scientific Research (No.23340072) RD51 collaboration These researches are supported by Japan MPGD Basic R&D Team. Grant-in-Aid for Scientific Research (No.23340072) RD51 collaboration