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GEM R&D Efforts at CNS

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

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GEM R&D Efforts at CNS

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

  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 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 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 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 GEM workshop with Sauli@RIKEN

  6. HV 1 (-1.5~-2.2kV) Drift Plane HV 2 (-1.4~-1.6kV) 3mm GEM 2 1MΩ 1MΩ 1MΩ 1MΩ 2mm GEM 1 2mm First Try with CERN-GEM • July 2002: Gas chamber & readout pad design • Aug. 2002: fabrication • Sep. 2002: test with a RI source GEM workshop with Sauli@RIKEN

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

  8. ArCO2 VGEM=445V Ed=2kV/cm P10 VGEM=395V Ed=2kV/cm ArCO2 VGEM=380V Ed=2kV/cm CF4 VGEM=535V Ed=0.3kV/cm P10 VGEM=335V Ed=2kV/cm ADC Distributions • Double-GEM • Tripple-GEM GEM workshop with Sauli@RIKEN

  9. Gain vs. VGEM ● 3-GEM, P10 ▲ 2-GEM, P10 ● 3-GEM, ArCO2 ▲ 2-GEM, ArCO2 ● 3-GEM, CF4 S.Bachmann et al. Nucl. Instr. and Meth. A438(1999)376 Weizmann Institute of Science; December, 2002 GEM workshop with Sauli@RIKEN

  10. Making GEM with a Dry Etching Method CERN • 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) 70μm Fuchigami Micro 70μm 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 GEM workshop with Sauli@RIKEN

  12. Improvement of CNS-GEM CERN-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 CNS-GEM 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 Blue : CERN-GEM（Gas : flow） Black:CNS-GEM（Gas : noflow） Red: CNS-GEM(Gas: flow) 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 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 • Ex 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) 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 ms time-constant • Readout with 100 MHz FADC GEM workshop with Sauli@RIKEN

  17. FEE & DAQ development • Charge sensitive Pre-amp • 1pF feedback capacitance • 100W 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 GEM workshop with Sauli@RIKEN

  18. Typical signals from GEM-TPC With 100 MHz FADC Gas = Ar-C2H6 Drift length = 85mm Rectangular pad Beam = 1 GeV/c electron from KEK-PS in May 2004 Time (6.4ms=640bin, 1bin=10ns) Track 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 P10 Ar+C2H6(30%) CF4 R : P10 chevron B : P10 rect. Y : Ar+C2H6 rect. G : CF4 chevron GEM workshop with Sauli@RIKEN

  20. Z direction R : P10 chevron B : P10 rectangular Performance of GEM-TPC (II) 36 mm of P10 gas drift length = 85mm • Energy loss measurement • P10: s(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 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 l • Electron multiplication • no window in between; transmission, material • Ne(Cherenkov) > Ne(ionization) 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) 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 GEM workshop with Sauli@RIKEN

  24. QE Measurement of CsI • Reasonable QE(l) obtained by Y. Aramaki Cut off CO2 ~ 7.2 eV CH4 ~ 8.5 eV CF4 ~ 11.5 eV 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 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/n0)(1 – dn)]; n = n0 + dn GEM workshop with Sauli@RIKEN

  27. A A Measuring Ion Feedback Xrays (~17keV) Ion feedback factor: F =Ic/Ia chamber ArCH4 50mm Mesh Current Shield • What to measure: • pad current: Ia • mesh current: Ic • Parameters • VGEM：voltage applied to each GEM (V) • Ed：electric field in the drift region (kV/cm) • Et：electric field in the trasfer region (kV/cm) • number of GEMs：1,2 or 3 Ic 3mm HV1 Mesh(cathode) drift region 3mm Ed HV2 GEM3 2mm GEM2 R 2mm GEM1 Pad(anode) 2mm Pad Current HV1<HV2 Ia Typical values: HV1=-2200V, HV2=-2100V,VGEM=350V GEM workshop with Sauli@RIKEN

  28. HV1 3mm 3mm 3mm HV2 Ed=（HV1-HV2）/0.3 [kV/cm] 2mm 2mm 2mm VGEM =HV2/6[V] 2mm 2mm R R Eｔ R Triple Double Single R Eｔ R R Ei Experimental Configurations • Voltage configuration • 3 GEM configurations • Et and Eichanges together with VGEM. • Measure F as functions ofVGEM,Ed, and Et/Ei GEM workshop with Sauli@RIKEN

  29. Dependence of Ia and Ic onVGEM Ed =0.33(kV/cm) Gain is ~700 (Triple) at VGEM=320V • Both Ia and Ic increase exponentially with VGEM GEM workshop with Sauli@RIKEN

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

  31. Dependence of F on Ed VGEM=320(V) • F increases with increase of Ed • Ion feedback is less than 5% with small Ed • Evaluation is needed for performance at low Ed • Pad current Ia is constant, while mesh current Ic is changing with Ed 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 • 150mm-GEM VGEM=750V • 100mm-GEM VGEM=500V • Standard-GEM (50mm) VGEM=250V GEM workshop with Sauli@RIKEN

  33. Making of 150mm-GEM • Structure of 150mm-GEM • Cu(8 mm) + LCP(150 mm) + Cu(8 mm) • hole pitch = 140 mm, f = 70 mm • 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 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) GEM workshop with Sauli@RIKEN

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