1. Study of a charge distribution on a readout board with a triple GEM chamber MPGD group T. Uchida, M. Sekimoto, T. Murakami, M. Tanaka, S. Tanaka, N. Ujiie, and K. Nakayoshi (KEK) K. Kadomatsu and A. Sugiyama (Saga University ) E. Nakano and S. Nakagawa (Osaka City University) Shoji Uno (KEK) KEK Detector Technology Project October 31 st, 2006

2. Contents GEM foils made by Japanese company Effective Gas gain as a function of various parameters  V GEM, E D, E T,E I, g I Gas mixture: Ar-CH 4 (90/10) (P10) Ar-CO 2 (70/30) Charge distribution on a readout board

3. GEM foils made by Japanese company New method (plasma etching) was tried in a few years ago. –Not chemical etching (CERN) –M. Inuzuka, et al., NIM A 525(2004) 529-534 Plasma + Laser –To reduce sparks It is convenient for us to make new types of GEM foils. –Fine pitch/small hole : 50  m/30  m –Thicker/thinner : 100(150)  m/ 25  m –Other activities in Japan Univ. of Tokyo RIKEN etc Today, I will report on results with standard GEM foils. –50  m thick –140  m pitch 70  m diameter 10cm Scienergy Co., Ltd. (Japanese company) http://www.scienergy.jp/

4. Chamber Structure g I (1 mm) g D ( 4 mm) GEM1 GEM2 GEM3 g T2 (2 mm) g T1 (2 mm) 55 Fe (5.9 keV X-ray) Cathode Strip 0.5kV/cm 1.75kV/cm 3.5kV/cm Drift region Transfer1 region Transfer2 region Induction region Ar-CO 2 ΔV GEM ＝ 370V P10 ΔV GEM ＝ 330V

5. Effective gas gain vs ΔV GEM Ar-CO 2 P10

6. Gas gain vs various parameters P10 Ar-CO 2 P10 Ar-CO 2 EDED EIEI ETET EIEI

7. Readout strip –Strip pitch ： 200  m –width ： 100  m –gap ： 100  m –length : 50mm –Number of strips = 64 Zoom up view 100  m 200  m

8. Read out system RPN220× ４ ADC 2249W× ６ CCNET GATE BUSY Fanin Fanout Gate Gen. GATE 120 μs delay VETO Disc. RPN220 Belle-CDC Pre-amp. ×4 Belle-CDC Pre-amp. 30 m 0.5 m Strip Foil Pulse Trans. CAMAC System

9. One Event Display Channel ADC 0 63 ADC 0 63 Channel

10. ΔV GEM ＝ 370V Ed= 0.5 kV/cm Et=2.59kV/cm Ei=5.18 kV/cm ΔV GEM ＝ 370V Ed= 0.5 kV/cm Et=2.59kV/cm Ei=5.18 kV/cm  = 181.2± 0.3  m Ar-CO 2 (70/30) Charge distribution -1 0 1 Triple GEM g D, g T1, g T2, g I =1.5, 1, 1, 1mm dX （ each strip － COG) ｍｍ  = 359.7±0.4  m P10 ΔV GEM ＝ 330V Ed= 0.5 kV/cm Et=1.65 kV/cm Ei= 3.3 kV/cm ΔV GEM ＝ 330V Ed= 0.5 kV/cm Et=1.65 kV/cm Ei= 3.3 kV/cm ADC SUMADC -1 0 1

11. Measurement results  for a gauss fit in a charge distribution Unit : mm GEM structureTotal gapP10Ar-CO 2 Tripleg D,g T1,g T2,g I = 4, 2, 2, 170.465 g D,g T1,g T2,g I = 1.5, 2, 2, 15.750.4170.207 g D,g T1,g T2,g I = 1.5, 1, 1, 24.750.3900.203 g D,g T1,g T2,g I = 1.5, 1, 1, 13.750.3430.181 Doubleg D,g T1,g I = 1.5, 2, 13.750.3400.173 g D,g T1,g I = 1.5, 1, 12.750.157 Total gap : g D /2 + (g T1 + g T2 ) + g I

12. P10 Ar-CO 2 Data MagBoltz  2 (mm 2 )

13. MagBoltz vs. Measurement Data P10 Ar-CO 2 Data MagBoltz Electric field in transfer region (kV/cm)

14. Summary Japanese company can produce GEM foils with new methods ( Plasma or (and) Laser ). GEM chamber has been constructed and tested. Effective gas gain was measured for various parameters. Charge distribution was measured. It is consistent with naive estimation from diffusion without GEM structure.