1. GEM R&D Efforts at CNS Hideki Hamagaki Center for Nuclear Study University of Tokyo

2. 2007/03/23 GEM workshop with Sauli@RIKEN 2 Contents Recollection of Early Days –Motivation –Getting started –Making GEMs GEM application –GEM-TPC –HBD GEM characteristics and performances –Gain variation –Gain dependence on P/T –Ion feedback –Making it thicker Summary and outlook

3. 2007/03/23 GEM workshop with Sauli@RIKEN 3 What was the Motivation? PHENIX Upgrade of Inner Detectors –Discussions started in 2001 –HBD/TPC hybrid using CF4 gas & GEM

4. 2007/03/23 GEM workshop with Sauli@RIKEN 4 Requirements from Physics Low-mass e+e- pairs –better rejection power for e+e- pairs from Dalitz decay and photon external conversions –low-mass vector mesons -> chiral symmetry restoration –thermal pairs Better tracking capability

5. 2007/03/23 GEM workshop with Sauli@RIKEN 5 Effort Has Begun in 2002 M. Inuzuka joined my group –A main player of GEM development for 3 years until he got a permanent research position at Department of Conservation Science, National Research Institute for Cultural Properties, Tokyo ( 東京文化財研究所・保存科学部 ) Intimate collaboration with Toru Tamagawa Having started with CERN-GEM –learn what is GEM –purchase GEMs from CERN –building test setup

6. 2007/03/23 GEM workshop with Sauli@RIKEN 6 First Try with CERN-GEM July 2002: Gas chamber & readout pad designJuly 2002: Gas chamber & readout pad design Aug. 2002: fabricationAug. 2002: fabrication Sep. 2002: test with a RI sourceSep. 2002: test with a RI source Drift Plane GEM 2 GEM 1 2mm 3mm 1M Ω HV 1 (-1.5~-2.2kV) HV 2 (-1.4~-1.6kV)

7. 2007/03/23 GEM workshop with Sauli@RIKEN 7 Signal Amplification In the fall of 2002; the first signal from CERN-GEM ever seen in Japan V GEM =400V (HV2=-1600V), HV1=-2200V V GEM =390V (HV2=-1560V), HV1=-2160V

8. 2007/03/23 GEM workshop with Sauli@RIKEN 8 ADC Distributions Double-GEM Tripple-GEM P10 V GEM =395V Ed=2kV/cm ArCO 2 V GEM =445V Ed=2kV/cm P10 V GEM =335V Ed=2kV/cm ArCO 2 V GEM =380V Ed=2kV/cm CF 4 V GEM =535V Ed=0.3kV/cm

9. 2007/03/23 GEM workshop with Sauli@RIKEN 9 Gain vs. V GEM ● 3-GEM, P10 ▲ 2-GEM, P10 ● 3-GEM, ArCO 2 ▲ 2-GEM, ArCO 2 ● 3-GEM, CF 4 S.Bachmann et al. Nucl. Instr. and Meth. A438(1999)376 Weizmann Institute of Science; December, 2002

10. 2007/03/23 GEM workshop with Sauli@RIKEN 10 Making GEM with a Dry Etching Method Need to make GEM in Japan –convenience for further studies –variations & optimization Look for a capable company –Found a company in the fall of 2002 –Fuchigami Micro (now SciEnergy) has expertise on the dry etching technologies –ended up with a method different from CERN Some results by the spring of 2003 –(NIM A525, 529, 2004) CERN Fuchigami Micro 70μm

11. 2007/03/23 GEM workshop with Sauli@RIKEN 11 Characterstics of Early CNS-GEM Comparable gain to CERN-GEM Many have problems –Low resistance or sparks at low HV –Lower breakdown point than CERN-GEM

12. 2007/03/23 GEM workshop with Sauli@RIKEN 12 Improvement of CNS-GEM Efforts to improve resistance and to reduce sparks at initial HV-on –cleaning & desmear process –desmear; not needed in wet etching, but crucial in dry etching Breakdown voltage –Over-hung of Copper edges –Reduction of over-hung by the spring of 2004 CERN-GEM CNS-GEM

13. 2007/03/23 GEM workshop with Sauli@RIKEN 13 Test of Gain Variation Gain measurement with Fe55 source Gain of CNS-GEM seems to stabilize in shorter time Difference may be due to the difference in the hole shape? Many possibilities –hole shape –insulation material/surface CERN-GEM （ Gas : flow ） Blue : CERN-GEM （ Gas : flow ） CNS-GEM （ Gas : noflow ） Black: CNS-GEM （ Gas : noflow ） Red: CNS-GEM(Gas: flow)

14. 2007/03/23 GEM workshop with Sauli@RIKEN 14 Development of GEM-TPC Normal TPC uses MWPC for electron multiplication Use GEM (Gas Electron Multiplier) instead of MWPC

15. 2007/03/23 GEM workshop with Sauli@RIKEN 15 Advantage of GEM-TPC Ion Feedback to drift region can be smaller –Requirement to gating grid is less demanding Signals can be shorter because of no tail from ions E x B effect is less because of uniform E field parallel to B expect in a tiny region near GEM holes Flexible arrangement of readout pads is possible -> Better position resolution & two-particle separation R&D for ILC is under way (talk by A. Sugiyama)

16. 2007/03/23 GEM workshop with Sauli@RIKEN 16 Building GEM-TPC prototype Original TPC with MWPC was developed by T. Isobe & K. Ozawa in 2002 ~ 2003 (NIM A564, 190, 2006) Modified by S.X. Oda to use GEM in 2003 ~ 2004 (NIM A566, 312, 2006) Two types of readout pads –rectangular & chevron type –1.09 mm x 12 mm Charge-sensitive pre-amp –1  s time-constant Readout with 100 MHz FADC

17. 2007/03/23 GEM workshop with Sauli@RIKEN 17 FEE & DAQ development Charge sensitive Pre-amp –1pF feedback capacitance –100  difference drive FADC( 林栄精器 RPV-160) –100MHz sampling rate –8bit dynamic range Original DAQ System (By T. Isobe) –CES RIO3 module to control VME bus PowerPC on board CPU 100 MBytes/s bandwidth on VME –Linux base VMEDAQ TPC Pre-amp

18. 2007/03/23 GEM workshop with Sauli@RIKEN 18 Typical signals from GEM-TPC Time (6.4  s=640bin, 1bin=10ns) With 100 MHz FADC Gas = Ar-C 2 H 6 Drift length = 85mm Rectangular pad Beam = 1 GeV/c electron from KEK-PS in May 2004 Track

19. 2007/03/23 GEM workshop with Sauli@RIKEN 19 Performance of GEM-TPC (I) Position resolution –x direction –z direction –resolution gets worse with increase of drift length diffusion effect magnitude depends on gas species CF4 Ar+C2H6(30%) P10 R : P10 chevron B : P10 rect. Y : Ar+C 2 H 6 rect. G : CF 4 chevron Electric field (V/cm) Drift velocity (cm/  s) Diffusion (T)@1cm (  m) Diffusion (L)@1cm (  m) Ar(90%)+CH 4 (10%)1305.5570360 Ar(70%)+C 2 H 6 (30%)3905.0320190 CF 4 5708.911080

20. 2007/03/23 GEM workshop with Sauli@RIKEN 20 Performance of GEM-TPC (II) Energy loss measurement –P10:  (55Fe;5.9 keV) = 11 % Ne(primary) ~ 222 for 5.9keV X-ray in P10  ~1.7 times larger than statistical estimate –obtained energy loss is as expected for various particles with different momentum Beam rate effect –no change up to 5000 cps/cm2 –good enough for HI applications –further studies may be needed Z direction R : P10 chevron B : P10 rectangular 36 mm of P10 gas drift length = 85mm

21. 2007/03/23 GEM workshop with Sauli@RIKEN 21 UV Photon Detection Effort was started in the fall of 2003, by M. Inuzuka, and was succeeded by Y. Aramaki, backed up by Yokkaichi & Ozawa (2005 ~ 2006) CsI photo-cathode CF4 gas –Cherenkov radiator large index of refraction transparent down to low –Electron multiplication –no window in between; transmission, material Ne(Cherenkov) > Ne(ionization)

22. 2007/03/23 GEM workshop with Sauli@RIKEN 22 CsI Photo-cathode Nickel and Gold are plated on to Copper, before CsI evaporation –prevent CsI + Cu chemical reaction Development of Al-GEM –tried a few times –no success so far (spring of 2007)

23. 2007/03/23 GEM workshop with Sauli@RIKEN 23 Additional Complications Absorption of UV photons ( ~ 120 ~ 200 nm) by oxygen and water –oxygen < 10 ppm; water < 15ppm for transmission of more than 95 % for L = 36 cm Care for deliquescence of CsI –water contamination in radiator gas –handling procedure of GEM setup –reserve of CsI

24. 2007/03/23 GEM workshop with Sauli@RIKEN 24 QE Measurement of CsI Cut off CO2 ~ 7.2 eV CH4 ~ 8.5 eV CF4 ~ 11.5 eV Reasonable QE( ) obtained by Y. Aramaki

25. 2007/03/23 GEM workshop with Sauli@RIKEN 25 Understanding Characteristics and Performance of GEM Y. Yamagachi; 2004 ~ 2006 –long-term gain variation –p/T dependence –thick GEM –simulation S. Maki; 2005 –ion feedback S. Sano; 2005 ~ 2006 –simulation

26. 2007/03/23 GEM workshop with Sauli@RIKEN 26 p/T Dependence of Gain Electron multiplication in gas –a function of E/p, or more precisely E/n ~ ER(T/p) M ~ Aexp[aE/n] = Aexp[(aE/n 0 )(1 –  n)]; n = n 0 +  n

27. 2007/03/23 GEM workshop with Sauli@RIKEN 27 Measuring Ion Feedback Ion feedback factor: F =Ic/Ia HV1<HV2 50mm chamber drift region Pad(anode) GEM1 GEM2 GEM3 Mesh(cathode) Shield 3 mm 2 mm 3 mm R Xrays (~17keV) Typical values: HV1=-2200V, HV2=-2100V,V GEM =350V Mesh Current HV1 HV2 A A What to measure: –pad current: Ia –mesh current: Ic Parameters –V GEM ： voltage applied to each GEM (V) –E d ： electric field in the drift region (kV/cm) –E t ： electric field in the trasfer region (kV/cm) –number of GEMs ： 1,2 or 3 Ia Ic Ed ArCH 4 Pad Current

28. 2007/03/23 GEM workshop with Sauli@RIKEN 28 Experimental Configurations Voltage configuration 3 GEM configurations 3 mm 2 mm TripleDoubleSingle E t and E i changes together with V GEM. Measure F as functions ofV GEM, E d, and E t /E i HV1 HV2 E d = （ HV1-HV2 ） /0.3 [kV/cm] V GEM =HV2/6[V] R R R R R R EｔEｔ EiEi EｔEｔ

29. 2007/03/23 GEM workshop with Sauli@RIKEN 29 Dependence of Ia and Ic onV GEM E d =0.33(kV/cm) Both Ia and Ic increase exponentially with V GEM Gain is ~700 (Triple) at V GEM =320V

30. 2007/03/23 GEM workshop with Sauli@RIKEN 30 Dependence of F on V GEM E d =0.33(kV/cm) F decreases with increase of V GEM F for triple-GEM is large compared to single- and double-GEM At large V GEM, F value for triple-GEM approaches those of single- and double-GEM

31. 2007/03/23 GEM workshop with Sauli@RIKEN 31 Dependence of F on E d V GEM =320(V) F increases with increase of E d Ion feedback is less than 5% with small E d Evaluation is needed for performance at low E d Pad current Ia is constant, while mesh current Ic is changing with E d

32. 2007/03/23 GEM workshop with Sauli@RIKEN 32 Making it Thicker Motivation –Larger gain compared to using multiple thin-GEMs for the same voltage per GEM thickness –Smaller diffusion compared to the multiple-GEMs diffusion in the transfer region between the GEMs Electric field along the center of a GEM hole ● 150  m-GEM V GEM =750V ● 100  m-GEM V GEM =500V ● Standard-GEM (50  m) V GEM =250V

33. 2007/03/23 GEM workshop with Sauli@RIKEN 33 Making of 150  m-GEM Structure of 150  m-GEM –Cu(8  m) + LCP(150  m) + Cu(8  m) –hole pitch = 140  m,  = 70  m Large gain as expected Sparks at low voltage investigation is under way LCP? Overhung? limit for charge density? On thick-GEM, Toru Tamagawa’s talk in this afternoon

34. 2007/03/23 GEM workshop with Sauli@RIKEN 34 Summary and Outlook GEM development at CNS in the last 5 years was summed up –motivation –making GEM –R&D for applications; TPC and HBD –Basic characteristics long term gain variation, p/T dependence, ion feedback making it thicker Development in near future –Gain variation vs material choice and hole shape –Improvement of thick-GEM performance –Coarse-grained 2D readout (1~2mm pixel)