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PHENIX 実験における GEM と CSI カソードを 用いた 光検出器の開発

PHENIX 実験における GEM と CSI カソードを 用いた 光検出器の開発. 東大 CNS 、 A 東京理科大学 小沢恭一郎、 浜垣秀樹、梶原福太郎、郡司卓、 磯部忠昭、織田勧、森野雄平、 荒巻陽紀、山口頼人、真木祥千子 A. Outline. CsI photo cathode R&D at PHENIX exp. R&D of GEM at CNS Outlook. 特徴. 紫外域に感度 を持つ光検出器 読み出しに Strip や Pad を用いることで 位置情報も得られる

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PHENIX 実験における GEM と CSI カソードを 用いた 光検出器の開発

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  1. PHENIX実験におけるGEMとCSIカソードを用いた光検出器の開発PHENIX実験におけるGEMとCSIカソードを用いた光検出器の開発 東大CNS、A東京理科大学 小沢恭一郎、 浜垣秀樹、梶原福太郎、郡司卓、 磯部忠昭、織田勧、森野雄平、 荒巻陽紀、山口頼人、真木祥千子A

  2. Outline • CsI photo cathode • R&D at PHENIX exp. • R&D of GEM at CNS • Outlook 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  3. 特徴 • 紫外域に感度を持つ光検出器 • 読み出しにStripやPadを用いることで位置情報も得られる • PHENIX実験では、Window lessのCherenkov検出器の光検出部分として用いられる。 • 具体的には、 • GEM３層を増幅部に使用 • １層あたりの増幅率は低く安定な動作 • GEM上面にCsIを蒸着 • Radiator ガスと増幅用のガスにCF4を用いた場合、５０ｃｍのRadiatorの長さで約40個のp.e. • References • 1. NIM A523, 345, 2004 • 2. NIM A546, 466, 2005 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  4. CSIを用いた光電面 • 3種類の光電子収集の方法 Transmissive By Weitzman • Transmissiveを選択 • 比較的高い量子効率 • 少ないphoton feedback 一番上のGEMにCSIを蒸着して実現 ５ １０ １５ [eV] CSIの量子効率 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  5. CsI Au Ni Cu Kapton Cu CsIの蒸着 • CSIのGEMへの蒸着 • GEMにニッケルと金をメッキし、CsIを蒸着 • 基本的な手順： • 真空度: a few x 10-7 Torr • GEMをマスクしCsIを事前に少し飛ばす • ボートやCsI表面の不純物の除去のため • （高純度のCsIを使用しているが） • GEMを少しあたためる • 不純物や水分の除去のため • Quartz で厚さをモニター • ５％程度 • ２０００A　ないし　５０００A程度の蒸着 • ベッセル内で、密封 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  6. Big Mac Provides • Large Volume (8’ diameter, 6’ tall) • High Vacuum (few 10-7 torr) • Lots of Feedthroughs • Lots of blank “do-it-yourself” ports • Mechanical Motions: • 2 tables covering 320o in f • One tower (up/down & rotate) • Several Large ports • 12” Inside Diameter 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  7. Mechanics Inside • All tables removable • One fixed table • Two rotating tables (320o) • Target holder does up/down as well as rotation 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  8. CｓI蒸着 • Arrange 6 GEMs in ARC facing down. • Rotates via Big Mac Tables. • Evaporate one-by-one5000 A (or 2000 A) • ~5 min elapsed before chicklet was vacuum sealed in the desiccatorin the vessel. • (Desiccator sat in Ar as the PC was placed within it.) • Used glass dessicator to transport PCUsed glove box (under N2 purge) to transport PC from dessicator to test flange: ~2 min. exposure to air total Top View 量子効率を測定 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  9. Photocathode Test Independent Lamp Monitor MgF2 Windows Photocathode or Triple GEM VUV beam Absorption Length ~ 30cm Vacuum Vessel (“cross”) Beam splitter/Collimator Testing Apparatus • Absolute QE of produced Photocathodes Vs Wavelength • Photoelectron signal in CF4 (CF4 transmittance) • GEM systematics (gain, stability, etc.) • Systematic Measurements of CsI Coated Triple GEM • (pe collection efficiency Vs ED, etc) 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  10. QE in CF4 at High and Low Collection Fields 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  11. Fe55 x-ray UV lamp 光検出器としてのテスト Gas gain Stainless steel box Pumped to 10-6 before gas filling • Gains in excess of 104 are easily attainable • Voltage for CF4 is ~140 V higher than for Ar/CO2 but slopes are similar for both gases • Gain increases by factor ~3 for ΔV = 20V • Pretty good agreement between gain measured with Fe55 and UV lamp Measurements: * Fe55 x-rays * Am241  source * UV lamp GEM foils of 3x3, 10x10 and 25x25 cm2 produced at CERN

  12. Small GEMs: 3x3 cm2 ΔVGEM HV segmented GEMs 10x10 cm2 ΔVGEM Discharge Probability • Stability of operation and absence of • discharges in the presence of heavily ionizing particles is crucial for the operation of the HBD • Use Am241 to simulate heavily ionizing particles • In Ar-CO2, discharges increase sharply when total charge is close to the Raether limit of 108 • In CF4 discharges do not depend on • the presence of  particles. It seems that • local defects are responsible for the • discharges • CF4 more robust against discharges • than Ar/CO2 • HBD expected to operate at gains < 104 • i.e. with comfortable margin below • the discharge threshold

  13. Hg lamp Independent of gas Absorber Mesh E=0 CsI GEM1 Independent of Et 1.5mm GEM2 1.5mm GEM3 2mm PCB Depends only on EI (at low EI some charge is collected at the bottom face of GEM3) pA Ion back-flow Fraction of ion back-flow defined here as: Iphc / IPCB Ions seem to follow the electric field lines. In all cases, ion back-flow is of order 1!!! 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  14. Aging CsI photocathode: * In spite of the large ion back-flow there is no dramatic deterioration of the CsI QE. * For a total irradiation of ~10mC/cm2 , the QE drops by only 20%. (The total charge in 10 years of PHENIX operation is conservatively estimated to 1mC/cm2.) Stability measurements performed during day 3 (4 mC/cm2 ), day 4 (3 mC/cm2 ), day 5 (2 mC/cm2 ). GEM foils: * During the whole R&D period we never observed aging effects (e.g. loss of gain) on the GEM foils. Total irradiation was well in excess of 10mC/cm2 .

  15. Cherenkov response to S1.S2.S4 Cosmic trigger S1.S2.S4 • pth 3.8 GeV • 1.30 m long • rate  1/min C: CO2 radiator • 50 cm long • directly coupled to detector S1.S2.S4.C  mip S1.S2.S4.C  “electron” CF4 Radiator • triple GEM + CsI • test with Fe55, UV lamp,  Detector Box Cosmic ray tests: Experimental Set-up C S4 S1,S2 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  16. ED = -0.5 KV/cm (“repulsion”) ED = 1 KV/cm (“collection”) Signal = Cherenkov photons Signal = mip + Cherenkov photons response to “electrons” All spectra calibrated into pe using the response to Fe55 x-rays. Npe = 25 - 45 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  17. Clearance +/- 3 mm Z= 656.4 mm HBD final design 2x21 HV connectors serving 2x3 detector modules Gas out Removable window FR4 frame all around the cover 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  18. HBD exploded view 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  19. Full Scale Prototype at Weizmann 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  20. カプトン (d=50μm) 銅電極 (d=5μm) 国産GEM 50μm カプトン 70μm CNSでのGEMの開発 • GEM • ポリイミド（カプトン）の両面の銅電極に電圧をかけ穴の中の電場で増幅 東大CNS+渕上ミクロ（株）で製作 　　　→ プラズマ・エッチング 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  21. Ar(90%)-CH4(10%) Gain 3-GEM 104 2-GEM ・CERN-GEM Ar(70%)-CO2(30%) Gain 104 2-GEM 3-GEM ３００ [V] ４００ 増幅率 GEMの増幅率 • 増幅率を測定 テストベンチ 詳細は、 M.Inuzuka et.al. NIM A525,529 ３層のGEMで十分な増幅 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  22. GEMの改良 • 放電 • 増幅率の変動 • 2時間で３０％増 • 部分的なCharge upか • エッチングプロセスの変更。 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  23. チェレンコフ検出器プロトタイプ Mesh: wireφ= 50μm Pitch=500μm CsI 1.5*1.5cm Readout Pad 3*3個使用 ガス：Ar(30%)C2H6(70%) Radiator: 75 cm 入射粒子 AD8058 3mm 2mm 2mm 2mm 1pF VME ADC CAEN V792 １MΩ HVmesh HVgain (～－2000V) 作成したプロトタイプをKEKでテスト 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  24. ビームテスト＠KEK • KEK-PSのπ２ラインで、負の1.0GeV/cの混合ビームを用い、 π中間子と電子に対する応答の違いを調べた。 • 電子とπ中間子は、ビームライン上のガスチェレンコフ検出器、TOF検出器、カロリメータを使って同定した。 実験エリアの様子 検出器プロトタイプ 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  25. π中間子と電子に対する応答 π中間子 Peak Value: 198.9 • ２次電子収集モードでの測定 • MeshとGEMの間でEnergy lossにより生成された２次電子を信号として検出 • 1GeV/cで、電子のEnergy lossは、πの１．３８倍 • 電子には、加えてチェレンコフ光による寄与がある １GeV/c　の粒子を用いた。 Charge [A.U.] 電子　　 Peak Value: 284.1 • π中間子の分布がEnergy lossによるものだとして、電子への寄与を計算すると、 • 198.9 * 1.38 = 274.5 • チェレンコフ光の寄与は10 ch程度 • (計算では、1.0 p.e　程度に相当) チェレンコフ光を捉えたという強い証拠は無い。 CSIのハンドリングか、ガスの問題 Charge [A.U.] 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  26. CSI動作確認 UVランプを使ったチェック 検出効率の測定 ガス透過率測定 水、酸素の影響 MgF2 PMT 回折格子 GEM検出器 真空紫外分光器 50 ～ 300 nm 分解能 0.2nm 重水素ランプ 115 ～ 400 nm 進行中 右の装置で測定予定 CSI GEMのHandlingのSchemeを確立させる 装置は購入済み、稼動準備中 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  27. CsI蒸着(Stony Brookの研究室の例） Objective:To develop and test the technique of CsI evaporation at Stony Brook for production of CsI coated GEM foils for HBD prototypes and possibly even the final detector. • Method • Use high purity CsI (Scintillator grade) • High Vacuum (1E-7 Torr) [diffusion pump w/ N2 trap] • Thoroughly clean vessel and all components • Bake the CsI • Mask substrates • Evaporate very small amount of CsI • This vaporizes any contaminants on molybdenum • boat and/or outer surface of CsI crystals • Vessel walls coated with CsI will also act as a “getter” • Warm up substrates before, during and after evaporation • Withholds water and contaminants from condensing onto • the substrates before deposition, and onto the CsI after • deposition • Thickness monitor • Quartz crystal oscillator, Al foil control substrate • Transportation/ Storage of Photocathodes (vacuum, gas flow) 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  28. Scaffolding: Photocathode substrate/Thickness monitors Bell Jar Diameter ~ 43cm Max. Height ~80cm mask Electrodes/CsI crystal/ Molybdenum Boat Dimensions of Evaporator Vessel 理研（放射線研）との協力で同様なものを進めていく予定。 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  29. Summary • PHENIX実験では、GEMとCSIカソードを用いた光検出器を読み出し部に用いるガスチェレンコフ検出器を開発している • R&Dは、Weizmannで行われ、Cosmic rayでのテストは、成功した。 • BNLでの検出器製作に向けた準備がBNLとStony Brookで行われている。 • 東大CNSにおいてもGEMの開発が行われ、安定したゲインが得られている。 • 東大CNSのCSIを用いた光検出器は、まだ、成功していない。CsIのハンドリングなどに問題があったと考えられ、今後、段階的に開発を行う予定である。 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  30. Back ups

  31. ガスチェレンコフ型電子検出器 • 荷電粒子がガス中を通過する事により発生するチェレンコフ光により、電子を同定する検出器 • 従来の検出器は、鏡とPMTを持つ • 大立体角を覆うのが難しい。 崩壊比の小ささからくる大きな立体角への要求 光電面の付いた電子増幅部を光検出部として一面に貼り付けることで、解決か？！ • 本講演では、 • あたらしい検出器のコンセプト • プロトタイプの製作、動作確認 • KEKでのテスト実験の結果、問題点 • 今後の取り組み PHENIXの次期検出器 PS-E325のガスチェレンコフ 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  32. チェレンコフ光 CSI GEM3層 パッド 検出器のアイデア • 鏡なしのチェレンコフ検出器 • 全体で一つのガスベッセル • Radiatorと光検出が同じガス • Ar-C2H6 (γｔｈ~　２５) 電子 Radiator ガス ハドロン • CSI光電面 • UV sensitive (6 eV, 200nm) • １４ p.e. for 75cm radiator 光電子増幅部でのハドロンのEnergy lossによりハドロンに対しても信号を出す可能性 光検出部 ガス 光電子 • 3層のGEMを使用 • 1層の増幅率は低くハドロンからの2次電子は、十分に増幅されない。 増幅 2次電子 開発要素：　GEM、CSIカソード、ガス 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  33. GEM チェレンコフ光 CSI GEM3層 パッド 主な開発要素の現状 電子 Radiator ガス 国内での製作に成功 長期的安定性を測定中 • CSIカソード 浜松PMTに依頼して蒸着 ビームで動作確認をトライした。 検出効率測定用の装置を準備 光検出部 ガス 光電子 • ガス 最適なガス、混合比を決定し、 水、酸素の影響を測定予定 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  34. Weitzman Institute CF4を使った同タイプの検出器の開発 KEKで共同でテスト 7 p.e. 程度のチェレンコフ光の信号を確認 BNL GEM TPCのR&D CERN, 渕上, ３Mの3種類のGEMを比較 ゲインの上昇を確認 関連のR&D electron p Gain stability by B. Azmoun Response of Weitzman detector 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  35. メモ Pion: 198.9 17.3electronに当る Electronは、1.38倍 198.9*1.38 = 274.5 (23.9) Electron(measured): 284.1 (24.7) 差は、チェレンコフ分で、1 p.e.くらい 光量　∝ N0 / γｔｈ^2 * L WeitzmanHBD40 p.e. L = 50 cm CNS 14 p.e. 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  36. Overall Set-up 50 cm long CF4 Radiator D2 UV Lamp Detector box Weizmannでのテスト Detector Box GEM foils of 3x3 and 10x10 cm2 produced at CERN 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  37. Fe55 x-ray UV lamp Gain Curve: Triple GEM with CsI in CF4:measured with Fe55 and with UV lamp • Pretty good agreement • between gain measured • with Fe55 and UV lamp. • Gains in excess of 104 are • easily attainable. • Voltage for CF4 is ~140 V • higher than for Ar/CO2 but • slopes are similar for both • gases. • Gain increases by factor ~3 • for ΔV = 20V 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  38. Total Charge in Avalanche in Ar-CO2 and CF4 measured with Am241 Charge saturation in CF4 !!! When the total charge in CF4 exceeds 4 x 106 a deviation from exponential growth is observed leading to gain saturation when the total charge is ~2 x 107. 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  39. Calibrated PMT Bandwidth: 6.2 – 10.3 eV PMT and CsI have same solid angle C1 optical transparency of mesh (81%) C2 opacity of GEM foil (83.3%) All currents are normalized to I(PMT-0) CsI on GEM QE(CsI) = QE(PMT) x I(CsI) / [ I(PMT) x C1 x C2 ] CsI absolute QE • Many measurements of CsI QE in 6-8 eV range • No data beyond 8.3 eV • Measurements extended to 10.3 eV confirm ~linear behavior of QE Extrapolation to 11.5 eV: N0 ≈ 820 cm-1

  40. In Ar-CO2, the discharge threshold is close to the Raether limit (at 108), whereas in CF4 the discharge threshold seems to depend on GEM quality and occurs at voltages VGEM 560-600V vs. ΔVGEM CF4 more robust against discharges than Ar/CO2 . HBD expected to operate at gains < 104 i.e. with very comfortable margin below the discharge threshold vs. Gain Discharge Probability • Stability of operation and absence of • discharges in the presence of heavily ionizing • particles is crucial for the operation of the HBD. • Use Am241 to simulate heavily ionizing particles. 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  41. At ED = 0: - signal drops dramatically as anticipated. - rate also drops dramatically large hadron suppression Charge Collection in Drift Gap : Mean Amplitude Rate 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  42. Hadron Blindness (I): UV photons vs.  particles At slightly negative ED, photoelectron detection efficiency is preserved whereas charge collection is largely suppressed. 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  43. Suppressed ionization ED = 0 Full charge collection GEM1 GEM2 GEM3 PCB Suppression limited by ionization between GEM1 and GEM2.  Asymmetric operation Hadron Blindness (II) :response to mip ED = 1 KV/cm (“collection”) ED = -0.5 KV/cm (“repulsion”) Average amplitude dropped by a factor of ~2.5 and rate dropped by a factor of 12 Strong Hadron Suppression

  44. Full Scale Prototype Gas Tightness Test • We started Nitrogen flow (200 l/h) with a single 50 um mylar window • With single mylar we reached 15-20 ppm water level • With double mylar window we reached 5-6 ppm • Bypassing the HBD showed 2 ppm in the gas system • On 19.04.05 we replaced 50 um window by 127 um mylar window coated with Al • With this single window we reached the same 5-6 ppm • On 06.05.05 we opened box and put into it several GEMs and resumed the Nitrogen flow I.Ravinovich 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  45. Radiation Length Budget CDR Preamps: 0.95 % Sockets: 0.60% Total = 0.92 + 0.54 + 0.95 +0.60 = 3.01 % 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  46. Water “peaks” Gas Quality Before and After Test • There were no means to test the gas quality during the test, however we did test the gas • quality before and after the test, under more or less the same conditions (i.e., similar purging • period and flow rates). B.Azmoun 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  47. CsI Photocathode B.Azmoun • Photocathode (produced at Stony Brook) was stored in a sealed vessel filled with N2 • (but possibly not the best environment) for two weeks prior to the test, and may have • suffered some additional deterioration during its installation into the detector • (we have no glove box !!). • The last time the GEM PC was measured, its integrated QE was ~ half that of the • nominal value. 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  48. Preliminary Measurements 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

  49. Photocathode Production Notes • 1st USB Chicklet Produced @ Big Mac • 1.  Big Mac Vac = 2.2 x 10-6 Torr2.  No heating of substrate before, during or after evap., No pre-evaporation of CsI3. Thickness target = 2000Angstroms • 4. The chicklet was transferred to a paint can while still within Big Mac, in an Ar environment (little contact with air)5.  Chicklet was transferred to BNL within an hour of evap. within Ar filled can6.  Chicklet was mounted to QE testing flange and put under Vac with ~10min exposure to air (had to solder on HV connector).7.  QE was measured in Vac (after 2 hours of pumping), Spectrometer Vac = 1.0 E-5 Torr. 2nd USB Chicklet Produced @ Big Mac 1. Big Mac Vac = 2.1 x 10-6 Torr. 2. Galvanized steel replaced with polished stainless steel. 3. No Chimney used 4. Pre-evap done ~ 10 min before deposition.  5. 5000 angstroms (instead of 2000) with about a 5% error 6. ~5 min elapsed before chicklet was vacuum sealed in the desiccator. (Desiccator sat in Ar as the PC was placed within it.) 7. Used glass dessicator to transport PC8. Used glove box (under N2 purge) to transport PC from dessicator to test flange: ~2 min. exposure to air total 9. QE was measured in Vac (after 2 hours of pumping), Spectrometer Vac = 1.0 E-5 Torr. Initial Chicklet Produced @ USB in Andrzej’s Lab 1. Bell Jar Vac ~ 7.5.0 x 10-8 Torr 2. Thickness Target = 5000Angstroms 3. Heated substrate before, during, and after evap 4. Pre-Evap of CsI 5. Placed PC in glass dissicator while in Ar atmosphere, pumped out dissicator, and transported to BNL 6. PC mounted onto test flange in air, total air exposure ~ 7min. 7. QE was measured in Vac (after 2 hours of pumping), Spectrometer Vac = 1.0 E-5 Torr. 光検出器研究会@KEK, 小沢恭一郎(東大CNS)

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