1. 1/18 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 東大 CNS における GEM の基本動 作特性の研究 Measurement of basic properties of GEM at CNS, Univ. of Tokyo Yorito Yamaguchi CNS, Univ. of Tokyo

2. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 2/18 Outline Introduction Setup for Measurements Basic properties of Standard-GEM −P/T dependence, Gain Stability, V GEM dependence Development of 150  m-GEM −Feature of 150  m-GEM −Electric field, Gain, Multiplication factor, Gain Stability Summary

3. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 3/18 Introduction A new type of GEM was successfully developed using a dry etching technique. CERN wet wet etching Bi-conical SciEnergy Co., Ltd dry dry etching Cylindrical Etching technique The cross section of a hole Hole shape Basic properties were measured to evaluate the performance of SciEnergy-GEM. P/T dependence, Gain Stability,V GEM dependence.

4. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 4/18 Setup for Measurements E D = 0.5kV/cm E T = E I  V T =  V I =  V GEM Moisture % < 10ppm

5. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 5/18 Measurement of basic properties −P/T dependence of Gain −Gain Stability −V GEM dependence of Gain

6. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 6/18 Ar/CO 2 Longitudinal axis : Gain Horizontal axis : P/T [Torr/K] Range : 2.50~2.65 It was observed that Gain decreases exponentially as P/T increases. A change of 1% in P/T value causes a gain variation of 9% (Ar/CH 4 ) and of 11% (Ar/CO 2 ). P/T Dependence of Gain ① Ar/CH 4

7. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 7/18 Base point in Gain P=760.0Torr T=300.0K →P/T=2.533 [Torr/K] Both results of SciEnergy-GEM and CERN-GEM are in good agreement with the unique exponential function. The results with different P/T can be normalized to the same condition using the obtained function. P/T Dependence of Gain ②

8. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 8/18 Gain Stability ① CERN-GEM It was reported that gain of CERN-GEM increases (or decreases) as a function of illumination time. A. Orthen et al., NIM A 512 (2003) 476 Known problem in gain stability 1.Due to shape of a GEM hole Charge up of the insulator surface inside the hole. 2.Due to nature of insulator 3.Due to surface conditions Possible reason Measurement condition V GEM is kept constant during the measurement. Rate of signals is 3Hz for all measurements.

9. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 9/18 Gain Stability ② All results are normalized to the condition of P/T=2.533 [Torr/K] using the obtained relation between Gain and P/T. Gain variation SciEnergy-GEM within 0.5% (both case) CERN-GEM Increase 15% (Ar/CH 4 ) Increase 45% (Ar/CO 2 ) Without charge-up

10. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 10/18 Gain Stability ③ SciEnergy-GEM has a much better gain stability than CERN- GEM. 10  m from hole edge SciEnergy-GEMCERN-GEM The electric field near the hole edge is distorted due to a bulge of a insulator for CERN-GEM. →Probability of charging-up is higher for CERN-GEM than SciEnergy-GEM. Drift direction of electron E [V/cm] Electric field inside a GEM hole V GEM =350V

11. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 11/18 V GEM Dependence of Gain SciEnergy-GEM can attain 20% (Ar/CH 4 ) and 50% (Ar/CO 2 ) higher gain than CERN-GEM at the same V GEM. →SciEnergy-GEM has larger effective area in multiplication than CERN-GEM.

12. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 12/18 Development of 150  m-GEM −Feature of 150  m-GEM −Electric field of 150  m-GEM −Gain of 150  m-GEM −Multiplication factor −Gain Stability

13. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 13/18 Feature of 150  m-GEM The dry etching technique can allow to fabricate a thicker GEM (Thick-GEM) than Standard-GEM (insulator thickness:50  m). −150  m-GEM is comparable to a triple layer structure of Standard-GEM with respect to the total length of a hole. Larger effective path length for multiplication Less effect of transmission efficiency Advantage of 150  m-GEM 150  m-GEM is expected to multiply electrons more effectively than triple layer structure of Standard-GEM. 150  m 70  m 140  m Cu(8  m) + LCP(150  m) + Cu(8  m)  = 70  m hole pitch = 140  m Structure of 150  m-GEM *LCP:Liquid Crystal Polymer

14. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 14/18 Electric Field of 150  m-GEM V GEM /50  m=250V/50  m  >0 The electric field of Thick-GEM is much stronger than that of Standard-GEM. →Especially, 150  m-GEM reaches plateau for about 50  m. 150  m-GEM should have a better multiplication ability than Standard-GEM. ● 150  m-GEM V GEM =750V ● 100  m-GEM V GEM =500V ● Standard-GEM (50  m) V GEM =250V Electric field through the hole center

15. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 15/18 Gain of 150  m-GEM Standard-GEM 100  m-GEM 150  m-GEM Gain at 300V/50  m Magnification Ratio 3.9 x10 4 1.0 x10 3 30 3.6 x10 2 1.3 x10 3 1.0 →(Gain 100  m-GEM ) 3/2 Tamagawa-san’s result 150  m-GEM had a continuous discharge at 270V/50  m.(Gain~4000) 150  m-GEM can attain much higher Gain than Standard- GEM at the same V GEM /50  m. Gain for Standard-GEM is obtained by triple GEM structure. Ar(70%)/CO 2 (30%)

16. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 16/18 Multiplication Factor Simulation results of the transmission efficiency is used. ■ 150  m-GEM (M 150 ):  T150 =0.17 ■ 100  m-GEM (M 100 3/2 ):  T100 =0.34 ■ Standard-GEM (M 50 3 ):  T50 =0.24 As expected from the electric field inside a hole, 150  m-GEM has the highest multiplication factor. E I is stronger than for Standard- GEM and 150  m-GEM.

17. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 17/18 Gain Stability of 150  m-GEM Ar(90%)/CH 4 (10%) The rate of signals = 2.5Hz V GEM =230V Gain of 150  m-GEM is stable within 1.0% for 9 hours. →150  m-GEM has a good gain stability as well as Standard-GEM

18. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 18/18 Summary The basic properties have been measured to evaluate the performance of SciEnergy-GEM. −Gain decreases exponentially as P/T increases. A change of 1% in P/T value causes a gain variation of 9% (Ar/CH 4 ) and of 11% (Ar/CO 2 ). −SciEnergy-GEM has a much better gain stability than CERN-GEM. Probability of charging-up is higher for CERN-GEM because of a distortion of electric field near the hole edge. −SciEnergy-GEM can attain higher gain than CERN-GEM at the same V GEM. 150  m-GEM has been fabricated successfully using dry etching. −Electric field of 150  m-GEM is much stronger than that of Standard-GEM. −150  m-GEM has much higher gain and multiplication ability with a good gain stability than a triple layer structure of Standard-GEM.

19. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 19/18 Back up

20. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 20/18 Applications We are developing some detectors using GEMs. GEM-TPC →S.X. Oda et al., NIM A 566 (2006) 312 Photon detector Hadron Blind Detector (HBD) installed in PHENIX@RHIC. →Please hear Ozawa-san’s talk (15:15~ in tomorrow session). Neutron Counter →Development is now on going.

21. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 21/18 From the equation of state, The expected relation between Gain and P/T should be exponential. Relation between Gain and P/T

22. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 22/18 Simulation of GEM structure Aim of study To understand the behavior of electrons inside a GEM hole qualitatively and quantitatively. To search for optimum GEM structure.

23. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 23/18 Potential Distribution of GEM hole The electric field inside the GEM hole was calculated using Maxwell 3D. Potential distributions are very similar in both cases. The calculation was carried out for two type of GEM. Bi-conical (CERN-like) Cylindrical (SciEnergy-like) V GEM =350V Bi-conicalCylindrical

24. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 24/18 Electric Field inside GEM hole Hole center 10  m from hole edge Drift direction of electron Although there is little difference between them at hole center, the electric field of Bi-conical near the hole edge is distorted due to a bulge of a insulator.

25. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 25/18 Simulation of Avalanche The avalanche inside a GEM hole was simulated using Garfield. The calculation results from Maxwell 3D are the inputs to Garfield. Avalanche simulation ware carried out with two methods. True path integration Projected path integration Ar/CO 2 (70:30) was used at P=760.0Torr, T=300.0K. ions electrons Gain can be defined as a following equation.

26. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 26/18 Behavior of Electrons Created point of electronNumber of created electronLost point of electron GEM There is a significant difference in multiplication near the hole edge. SciEnergy-GEM has better multiplication ability than CERN-GEM. More than 70% of secondary electrons are absorbed by the lower electrode of GEM. Gain

27. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 27/18 Gain Simulation results are qualitatively consistent with measured result, but they are quantitatively inconsistent. It is needed to improve the calculation method in multiplication inside a GEM hole. Most of electrons created near the hole edge are absorbed by electrode. →There is not a big difference in gain as seen in multiplication factor.

28. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 28/18 Setup for Measurements of 150  m-GEM E D = 0.5kV/cm  V I =  V GEM /3

29. 01/26/2007MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo) 29/18 Gain of 150  m-GEM (Ar/CH 4 )