Development of GEM at CNS

1. Development of GEM at CNS Hideki Hamagaki Center for Nuclear Study University of Tokyo

2. Contents of This Presentation • What is GEM • How to make GEM • Plasma etching and its improvement • Test of gain variation • GEM application • GEM-TPC • HBD • X-ray detector with Xe gas • Summary and outlook • Improve GEM performance and stability • Applications MICRO PATTERN GAS DETECTOR 研究会　＠京大

3. What is GEM • Gas Electron Multiplier • Developed at CERN by Sauli et al. • Foil of Kapton with Copper coated at both sides • typical: Kapton 50mm, Copper 5mm with holes: • typical: pitch 140mm, and 70mmf • Electron multiplication in the strong field inside the holes • typical voltage between the two Copper foils = 300 ~ 550V MICRO PATTERN GAS DETECTOR 研究会　＠京大

4. Characteristics of GEM • simple structure with lost cost material • low mass • multiple stacking  high gain • less risk of severe sparks/breakdown S.Bachmann et al, NIM A438 (1999) 376 MICRO PATTERN GAS DETECTOR 研究会　＠京大

5. How GEM is or will be used • COMPASS experiment@CERN • tracking chambers near beam-pipe • high rate ~150 kHz • low mass & high resolution • Possible applications • Time Projection Chamber • PHENIX, STAR, TESLA, JLC, … • UV photon detector with CsI photocathode • Gas Cherenkov counter: e.g. PHENIX HBD • X-ray detection • Cosmology  T. Tamagawa’s talk • Biology/Medical applications MICRO PATTERN GAS DETECTOR 研究会　＠京大

6. How to make GEM • step1 • put proper masks to the copper foils • step2 • wet etching of masked copper foils • step3 • make holes to the Kapton foil • wet etching --- CERN GEM • laser etching --- persued by T. Tamagawa • plasma etching --- persued by us (CNS) • hybrid of the above --- persued by us (CNS) MICRO PATTERN GAS DETECTOR 研究会　＠京大

7. Plasma Etching Method • A method different from CERN • Fuchigami Micro has expertise on this • inherent gain variation in CERN GEM • our suspicion is on the hole shape CERN-GEM CNS-GEM MICRO PATTERN GAS DETECTOR 研究会　＠京大

8. Characterstics of CNS-GEM • Low resistance or sparks at low HV in the beginning  aging • surface roughness • small residues • Similar gain to CERN-GEM • Lower breakdown point than CERN-GEM MICRO PATTERN GAS DETECTOR 研究会　＠京大

9. Improvement of CNS-GEM CERN-GEM • Earlier breakdown • cleaning process • surface roughness • due to over-hung of Copper edges • Succeed to reduce over-hung • Still breakdown at lower HV • This is only crucial for high HV operation, needed for CF4 gas CNS-GEM MICRO PATTERN GAS DETECTOR 研究会　＠京大

10. Test of Gain Variation • gain measurement with Fe55 source • gain of CNS-GEM seems to stabilize in shorter time • After the first try, gain seems to stabilize much sooner, as long as GEM is kept inside the chamber • Need further work • condition; temperature, oxygen, moisture, … • simultaneous comparison Blue : CERN-GEM（Gas : flow） Black:CNS-GEM（Gas : noflow） Red: CNS-GEM(Gas: flow) MICRO PATTERN GAS DETECTOR 研究会　＠京大

11. GEM-TPC; motivation • Need of 3D-tracking device durable under high particle density and high rate at RHIC • position resolution, two-track separation, energy measurement • Expected advantage of GEM • small ion feedback; no need of gating grid • simple structure • flexible readout configuration MICRO PATTERN GAS DETECTOR 研究会　＠京大

12. GEM-TPC prototype Tested at KEK-PS • 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 MICRO PATTERN GAS DETECTOR 研究会　＠京大

13. Performance of GEM-TPC (I) • Position resolution • z direction • x 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 MICRO PATTERN GAS DETECTOR 研究会　＠京大

14. 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 MICRO PATTERN GAS DETECTOR 研究会　＠京大

15. Hadron Blind Detector • UV photon detector • with CsI cathode • CF4 gas radiator • Ne(Cherenkov) > Ne(ionization) • development at Weizmann Institute • Use to measure low mass electron pairs at RHIC • Rejection of Dalitz pairs and external conversion pairs MICRO PATTERN GAS DETECTOR 研究会　＠京大

16. Summary and Outlook • How to improve GEM performance and stability • improve etching procedure • cleaning procedure after etching • use wet etching (cleaning) to smoothen the surface • washing out small residues • choice of material • base: insulator  resistive plastics • prevent gain variation due to charge up • Copper  Aluminum • low mass, long radiation length MICRO PATTERN GAS DETECTOR 研究会　＠京大

17. Summary and Outlook (cont.) • X-ray detector with Xe gas • for medical/biological use; two versions • 2D radiation dose monitor • taking advantage of simple structure, and flexible configuration • precise 2D tomography • started development of a custom ADC chip with Tanaka’s group at NIAS MICRO PATTERN GAS DETECTOR 研究会　＠京大