Measurements of Stability of Gas Electron Multiplier (GEM) Y.L. Yamaguchi, H. Hamagaki, K. Ozawa, S.X. Oda, M. Inuzukaa, S.Sanob CNS,Univ. of Tokyo, National Research Institute for Cultural Properties Tokyoa, Waseda Univ.b 9/21/2005 DNP/JPS meeting in Hawaii

DNP/JPS meeting in Hawaii Contents Introduction Gas Electron Multiplier (GEM) Characteristics of CNS-GEM and CERN-GEM Aim of the study Experimental setup for measurements Results P/T dependence of gain Gain stability CNS-GEM and CERN-GEM Ar-CH4 and Ar-CO2 Summary 9/21/2005 DNP/JPS meeting in Hawaii

DNP/JPS meeting in Hawaii Gas Electron Multiplier (GEM) GEM is originally invented by F.Sauli @CERN. Structure A metalized polymer foil with holes (Cu:5mm + Kapton:50mm + Cu:5mm ) Hole : pitch @　100mm f @ 50mm A photograph of GEM Insulator Mechanism of signal amplification A micrograph of GEM VGEM is applied between the metal layers. When an electron passes through the hole on GEM, strong electric field inside the hole induces the cascade of electrons. VGEM 50mm 100mm GEM can be an upgrade for a wire chamber. Electric field inside holes 9/21/2005 DNP/JPS meeting in Hawaii

DNP/JPS meeting in Hawaii Characteristics of CNS-GEM and CERN-GEM We succeeded in fabricating a new type of GEM (CNS-GEM) using a dry etching method. CERN-GEM CNS-GEM Etching method wet etching dry etching The cross section of a hole A hole with double-conical shape A hole with cylindrical shape 9/21/2005 DNP/JPS meeting in Hawaii

DNP/JPS meeting in Hawaii Aim of the study Measure basic properties of CNS-GEM. Gain P/T dependence Stability Known problem on gain stability It has been reported that gas gain of CERN-GEM increases (or decreases) as a function of illumination time. A. Orthen et al.,NIM A 512 (2003) 476 Possible reason Due to shape of holes of GEM Charge up of the Kapton surface inside the holes. CERN-GEM CNS-GEM CNS-GEM is expected to have better stability than CERN-GEM. 9/21/2005 DNP/JPS meeting in Hawaii

DNP/JPS meeting in Hawaii Experimental setup for the measurements 55Fe(X-ray,5.9 keV) HV1 Mesh P/T dependence of gain Gain stability CNS-GEM,CERN-GEM Ar-CH4 (Ar : CH4 = 90 : 10) Ar-CO2 (Ar : CO2 = 70 : 30) HV2 3mm 1MΩ 10MW GEM 3 10MW 1MΩ 2mm 1MΩ 10MW GEM 2 1MΩ 10MW 1MΩ 2mm GEM 1 10MW 2mm 10MW 1MΩ PAD VME ADC PreAmp 9/21/2005 DNP/JPS meeting in Hawaii

DNP/JPS meeting in Hawaii P/T dependence of gain (CERN-GEM) Gain is measured as a function of P/T. Pressure is manually changed during the measurement. Correlation function is evaluated as the formula below. CERN-GEM Ar-CH4 Assumed correlation function is good agreement with the measurements. 9/21/2005 DNP/JPS meeting in Hawaii

DNP/JPS meeting in Hawaii P/T dependence of gain (CNS-GEM) 0.1% fluctuation of P/T causes about 1% fluctuation of gain. The effect of P/T on gain is less than 1%. P/T is stable within 0.1% during our measurements. Ar-CH4 Ar-CO2 CNS-GEM CNS-GEM 9/21/2005 DNP/JPS meeting in Hawaii

Gain stability of CERN-GEM Gain stability of CERN-GEM is measured as a baseline. Increasing of gain as a function of illumination time is clearly seen. A difference of gain stability between Ar-CO2 and Ar-CH4 is observed. Further study is underway. 9/21/2005 DNP/JPS meeting in Hawaii

DNP/JPS meeting in Hawaii Gain stability of CNS-GEM (Ar-CH4) CNS-GEM shows very good stability!! CNS-GEM is stable within error of the measurement. 9/21/2005 DNP/JPS meeting in Hawaii

DNP/JPS meeting in Hawaii Gain stability of CNS-GEM (Ar-CO2) The case of Ar-CO2 is similar to that of Ar-CH4. The gain stability of CNS-GEM is better than that of CERN-GEM. The shape of holes in GEM significantly affect gain stability. 9/21/2005 DNP/JPS meeting in Hawaii

DNP/JPS meeting in Hawaii Summary P/T dependence and stability of gain have been measured. Assumed correlation function between gain and P/T is good agreement with the measurements. A difference of gain stability between Ar-CO2 and Ar-CH4 is observed. Further study is underway. The gain stability of CNS-GEM is better than that of CERN-GEM. The shape of holes in GEM significantly affect gain stability. 9/21/2005 DNP/JPS meeting in Hawaii