Hadron Blind Detector 東京大学　小沢恭一郎

PHENIX ws@RIKEN 小沢恭一郎(東大) Outline Hadron Blind Detector (HBD)　at PHENIX exp. R&D at RIKEN (advertisement) Outlook 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) Hadron Blind Detector 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) Realized example R.P. Pisani et. al, NIM A400(1997) 243 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) Realized example R.P. Pisani et. al, NIM A400(1997) 243 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) Realized example R.P. Pisani et. al, NIM A400(1997) 243 Total Charge [A.U.] 4 8 12 16 Number of Pad 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) PHENIX HBD 紫外域に感度を持つ光検出器 読み出しに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 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) 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 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) 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 CsI Au Ni Cu Kapton 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) 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) Beam splitter/Collimator MgF2 Windows VUV beam Photocathode or Triple GEM Absorption Length ~ 30cm Independent Lamp Monitor Photocathode Test Vacuum Vessel (“cross”) 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

QE in CF4 at High and Low Collection Fields @BNL QE in CF4 at High and Low Collection Fields 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) 光検出器としてのテスト @Weizmann Gas gain Stainless steel box Pumped to 10-6 before gas filling Fe55 x-ray 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 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 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

Cosmic ray tests: Experimental Set-up Cosmic trigger S1.S2.S4 C: CO2 radiator pth  3.8 GeV 1.30 m long rate  1/min C Cherenkov response to S1.S2.S4 S4 S1.S2.S4.C  mip S1.S2.S4.C  “electron” triple GEM + CsI test with Fe55, UV lamp,  50 cm long directly coupled to detector Detector Box CF4 Radiator S1,S2 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

response to “electrons” Signal = mip + Cherenkov photons ED = 1 KV/cm (“collection”) ED = -0.5 KV/cm (“repulsion”) Signal = Cherenkov photons Signal collected in pad 5 + any All spectra calibrated into pe using the response to Fe55 x-rays. 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大) @Weizmann

Discharge Probability ΔVGEM Small GEMs: 3x3 cm2 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 ΔVGEM HV segmented GEMs 10x10 cm2 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 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大) @Weizmann

Ion back-flow Independent of gas Independent of Et Depends only on EI (at low EI some charge is collected at the bottom face of GEM3) Mesh GEM1 GEM2 GEM3 PCB 1.5mm 2mm Absorber CsI pA Hg lamp E=0 Fraction of ion back-flow defined here as: Iphc / IPCB This is an upper limit. The exact definition should be: I_phc / ( I_PCB + I_GEM-bottom. Ions seem to follow the electric field lines. In all cases, ion back-flow is of order 1!!! 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大) @Weizmann

Aging CsI photocathode: GEM foils: * 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 . 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大) @Weizmann

PHENIX ws@RIKEN 小沢恭一郎(東大) Hadron Blind Suppress electrons from ionization Apply Reverse field 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

Hadron Blindness (I): UV photons vs.  particles @Weizmann At slightly negative ED, photoelectron detection efficiency is preserved whereas charge collection is largely suppressed. 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

Hadron Blindness (II) :response to mip @KEK ED = 1 KV/cm (“collection”) ED = -0.5 KV/cm (“repulsion”) 98-99% of events have single pad response. Suppression limited by ionization between GEM1 and GEM2.  Asymmetric operation GEM2 GEM3 PCB GEM1 Suppressed ionization Full charge collection ED = 0 Average amplitude dropped by a factor of ~2.5 and rate dropped by a factor of 12 Strong Hadron Suppression 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) 実機製作 筐体・GEM供給 Ｗｅｉｚｍａｎｎによる CsI蒸着 ＣｓＩには、潮解性　（取り扱い注意） 蒸着後、空気に触れずに組立、搬入が必要 BNL近く、Stony Brook校で、作業 組立 CsI潮解を考え、巨大グローブボックス内を数ppmレベルに 埃は、放電を呼ぶ。クリーン環境での作業 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) HBD final design 2x21 HV connectors serving 2x3 detector modules Gas out Z= 656.4 mm Clearance +/- 3 mm Removable window FR4 frame all around the cover 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) HBD exploded view 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

Full Scale Prototype at Weizmann 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

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 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) 蒸着・組立 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) signal electron Cherenkov blobs partner positron needed for rejection e+ e- qpair opening angle ~ 1 m 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) Performance in Run9 Rejection factor Hadron Projected Performance @ Run10 few pe Np.e. of single electron Single electron Signal significance 1.4 /nb recorded improves effective statistics by ≥ 35 ~20 pe Luminosity [unit of Run4 ] 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) R&D @ RIKEN 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) 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でのテストなどに成功した。その後、実機製作が行われ、実際に電子を捉えることに成功した。 理研・放射線研においても、CSIを用いた光検出器の開発を行っている。 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

Back ups

PHENIX ws@RIKEN 小沢恭一郎(東大) Scintillation of CF4 CF4 scintillates at 160nm. Two measurements in the literature: * NIM A371, 300 (1996):  110 ph/MeV * NIM A354, 262 (1995):  200 ph/MeV Planned to be measured at BNL 2/2003 Results of simple simulations: (using 200 ph/MeV, QE=0.3, Nch = 250) * signal/noise  10 * shades can reduce the noise by at least a factor of 3. 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) メモ Gas N0 E cutoff Γth index CF4 940 11.5 28 1.000620 CH4 185 8.5 34 1.000444 Ar 255 9 42 1.000283 C2H6 170 7.8 22 1.001038 Ar-C2H6 200? ? 25 1.000811 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 Weitzman　HBD　40 p.e. L = 50 cm CNS 14 p.e. 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) 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 PS-E325のガスチェレンコフ PHENIXの次期検出器 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) 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 チェレンコフ光 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 CSI 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。 GEM3層 増幅 2次電子 開発要素：　GEM、CSIカソード、ガス パッド 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) 主な開発要素の現状 GEM 電子 Radiator ガス 国内での製作に成功 チェレンコフ光 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。 CSI 検出効率測定用の装置を準備 光検出部 ガス 光電子 ガス GEM3層 最適なガス、混合比を決定し、 水、酸素の影響を測定予定 パッド 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) 関連のR&D 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 electron p Response of Weitzman detector Gain stability by B. Azmoun 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

GEM foils of 3x3 and 10x10 cm2 produced at CERN Weizmannでのテスト Detector Box 50 cm long CF4 Radiator Detector box D2 UV Lamp Overall Set-up Add note: many measurements done with Ar/Co2 for comparison GEM foils of 3x3 and 10x10 cm2 produced at CERN 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) 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 Fe55 x-ray UV lamp 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

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. 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

Extrapolation to 11.5 eV: N0 ≈ 820 cm-1 CsI absolute QE CsI on GEM Calibrated PMT 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 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) QE(CsI) = QE(PMT) x I(CsI) / [ I(PMT) x C1 x C2 ] Extrapolation to 11.5 eV: N0 ≈ 820 cm-1 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

Discharge Probability vs. ΔVGEM vs. Gain 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, 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 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 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

Charge Collection in Drift Gap : Mean Amplitude Rate At ED = 0: - signal drops dramatically as anticipated. - rate also drops dramatically large hadron suppression 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

Radiation Length Budget CDR Preamps: 0.95 % Sockets: 0.60% Total = 0.92 + 0.54 + 0.95 +0.60 = 3.01 % 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

Gas Quality Before and After Test Water “peaks” 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 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) 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. 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

Preliminary Measurements 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

Photocathode Production Notes 1st USB Chicklet Produced @ Big Mac 1.  Big Mac Vac = 2.2 x 10-6 Torr 2.  No heating of substrate before, during or after evap., No pre-evaporation of CsI 3. 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 can 6.  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 PC 8. 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. 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

Integrated Transmittance 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) 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 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) Mechanics Inside All tables removable One fixed table Two rotating tables (320o) Target holder does up/down as well as rotation 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) CｓI蒸着 Top View Arrange 6 GEMs in ARC facing down. Rotates via Big Mac Tables. Evaporate one-by-one　5000 A (or 2000 A) ~5 min elapsed before chicklet was vacuum sealed in the desiccator　in the vessel. (Desiccator sat in Ar as the PC was placed within it.) Used glass dessicator to transport PC Used glove box (under N2 purge) to transport PC from dessicator to test flange: ~2 min. exposure to air total 量子効率を測定 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

PHENIX ws@RIKEN 小沢恭一郎(東大) Thickness Uniformity Underside of Scaffolding CsI Thickness Target: 2000 Angstroms Al Foil Control Substrates for measuring CsI thickness r Quartz Crystal Thickness Monitor Quartz crystal thickness monitor Au-Ni-Cu clad G-10 Photocathode Substrates 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

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) 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)

Dimensions of Evaporator Vessel Max. Height ~80cm Scaffolding: Photocathode substrate/Thickness monitors Bell Jar Diameter ~ 43cm mask Electrodes/CsI crystal/ Molybdenum Boat 理研（放射線研）との協力で同様なものを進めていく予定。 2005/12/27 PHENIX ws@RIKEN 小沢恭一郎(東大)