Transcript GEMとCSIカソードを用いた ガスチェレンコフ型 電子検出器の開発

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
2005/12/27
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
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.
2005/12/27
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)
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
CSIの量子効率
2005/12/27
１５
[eV]
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
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
CsI
Au
Ni
Cu
Kapton
Cu
2005/12/27
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)
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
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
Mechanics Inside
• All tables
removable
• One fixed
table
• Two rotating
tables
(320o)
• Target
holder does
up/down as
well as
rotation
2005/12/27
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
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
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
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)
Photocathode Test
Independent Lamp Monitor
MgF2
Windows
Photocathode or
Triple GEM
VUV beam
Absorption Length
~ 30cm
Beam splitter/Collimator
2005/12/27
Vacuum Vessel
(“cross”)
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
QE in CF4 at High and Low Collection
Fields
Absolute QE in CF4 of CsI Photocathodes
(Corrected for Mesh Transparency)
Absolute QE [%]
100
90
WIS GEM PC [CF4]
80
1st Chicklet, [CF4], 0.78kV/cm
1st Chicklet, [CF4], 3.25kV/cm
70
2nd Chicklet, [CF4], 3.25kV/cm
60
50
40
30
20
10
0
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
Wavelength [Angstroms]
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光検出器研究会@KEK, 小沢恭一郎(東大CNS)
2100
光検出器としてのテスト
Stainless steel box
Pumped to 10-6 before gas filling
Gas gain
Fe55 x-ray
UV lamp
Measurements: * Fe55 x-rays
* Am241  source
* UV lamp
GEM foils of 3x3, 10x10 and
25x25 cm2 produced at CERN
• 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
12
measured with Fe55 and UV lamp
Discharge
Probability
Small GEMs: 3x3 cm2
• 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
ΔVGEM
13
Ion back-flow
Absorber
Hg lamp
Independent of gas
Mesh
GEM1
GEM2
GEM3
E=0
CsI
1.5mm
1.5mm
2mm
Independent of Et
PCB
pA
Fraction of ion back-flow
defined here as:
Iphc / IPCB
Depends only on EI
(at low EI some charge
is collected at the bottom
face of GEM3)
Ions seem to follow the electric field lines.
In all cases, ion back-flow is of order 1!!!
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光検出器研究会@KEK, 小沢恭一郎(東大CNS)
Aging
CsI photocathode:
* In spite of the large ion backflow
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
Cosmic ray tests:
Experimental Set-up
Cosmic trigger
S1.S2.S4
C
C: CO2 radiator
• pth  3.8 GeV
• 1.30 m long
• rate  1/min
Cherenkov response to S1.S2.S4
S4
S1,S2
S1.S2.S4.C•
50mip
cm long
CF4 Radiator
S1.S2.S4.C  “electron”
• directly coupled to detector
• triple GEM + CsI
Detector Box • test with Fe55, UV lamp, 
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光検出器研究会@KEK, 小沢恭一郎(東大CNS)
response to “electrons”
ED = 1 KV/cm (“collection”)
ED = -0.5 KV/cm
(“repulsion”)
Signal = mip + Cherenkov photons
Signal = Cherenkov photons
All spectra calibrated into pe using the response to Fe55 x-rays.
Npe = 25 - 45
2005/12/27
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
HBD final design
2x21 HV connectors serving 2x3 detector modules
Gas out
Clearance +/- 3 mm
Z= 656.4 mm
Removable window
2005/12/27
FR4 frame all around the cover
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
HBD exploded view
2005/12/27
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
at Weizmann
2005/12/27
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
CNSでのGEMの開発
カプトン
(d=50μm)
• 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
国産GEM
70μm
2005/12/27
50μm
カプトン
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
銅電極
(d=5μm)
GEMの増幅率
• 増幅率を測定
テストベンチ
Ar(90%)-CH4(10%)
Gain
104
3-GEM
2-GEM
・CERN-GEM
Ar(70%)-CO2(30%)
Gain
104
2-GEM
3-GEM
詳細は、
M.Inuzuka et.al. NIM A525,529
３層のGEMで十分な増幅
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３００
４００
増幅率
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
[V]
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。
2005/12/27
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
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
１MΩ
HVmesh
VME ADC
CAEN V792
HVgain (～－2000V)
作成したプロトタイプをKEKでテスト
2005/12/27
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
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。
検出器プロトタイプ
2005/12/27
実験エリアの様子
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
π中間子と電子に対する応答
π中間子
１GeV/c
の粒子を
用いた。
Peak Value:
198.9
Charge [A.U.]
電子
Peak Value:
284.1
• 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
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。
Charge [A.U.]
2005/12/27
CSIのハンドリングか、ガスの問題
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
進行中
• CSI動作確認
– UVランプを使っ
たチェック
– 検出効率の測定
MgF2
回折格子
PMT
GEM検出器
• ガス透過率測定
– 水、酸素の影響
右の装置で測定予定
CSI GEMのHandlingの
Schemeを確立させる
2005/12/27
真空紫外分光器
50 ～ 300 nm
分解能 0.2nm
重水素ランプ
115 ～ 400 nm
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)
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
2005/12/27
• Thickness monitor
• Quartz crystal oscillator, Al foil control substrate
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
• Transportation/ Storage of Photocathodes (vacuum, gas flow)
Dimensions of Evaporator Vessel
Scaffolding: Photocathode
substrate/Thickness monitors
Bell Jar
Diameter ~ 43cm
Max. Height
~80cm
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
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
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。
2005/12/27
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
Back ups
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
2005/12/27
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)
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)
• CSI光電面
Radiator
ガス
電子
ハドロン
チェレンコフ光
– UV sensitive (6 eV, 200nm)
– １４ p.e. for 75cm radiator
CSI
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
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。
開発要素： GEM、CSIカソード、ガス
2005/12/27
光検出部 光電子
ガス
GEM3層
増幅
パッド
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
2次電子
主な開発要素の現状
• GEM
国内での製作に成功
Radiator
ガス
長期的安定性を測定中
• CSI カソード
チェレンコフ光
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
• 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
光検出部 光電子
ガス
GEM3層
パッド
2005/12/27
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
電子
関連のR&D
• Weitzman Institute
• BNL
– 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
– 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
Gain Stability Comparison:
CERN, TECH ETCH and 3M Triple GEM
18000
TECH ETCH Set 1
(deltaV(Foil)=340V)
p
electron
Absolute Gain
16000
14000
TECH ETCH Set 2
(deltaV(Foil)=340V)
CERN
deltaV(Foil)=370V
12000
3M
(deltaV(Foil)=340V)
10000
8000
CERN
(deltaV(Foil)=340V)
6000
4000
CERN
(deltaV(Foil)=370V)
2000
0
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
Elapsed time after HV ON [hrs]
Response of Weitzman detector
2005/12/27
Gain stability by B. Azmoun
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
メモ
Gas
CF4
CH4
Ar
C2H6
Ar-C2H6
N0
940
185
255
170
200?
E cutoff
11.5
8.5
9
7.8
?
光量 ∝ N0 / γｔｈ^2 * L
Weitzman HBD 40 p.e. L = 50 cm
CNS 14 p.e.
2005/12/27
Γth
28
34
42
22
25
index
1.000620
1.000444
1.000283
1.001038
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
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
Weizmannでのテスト
Overall Set-up
Detector Box
50 cm long CF4 Radiator
D2 UV Lamp
Detector box
2005/12/27
2 produced at CERN
GEM
foils
of
3x3
and
10x10
cm
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
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.
Fe55 x-ray
UV lamp
2005/12/27
• Voltage for CF4 is ~140 V
higher than for Ar/CO2
but
slopes are similar for both
gases.
• Gain increases by factor
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
~3
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
2005/12/27
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
is observed leading to gain saturation when the total charge is ~2 x 107.
Calibrated
PMT
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
CsI on GEM
Bandwidth: 6.2 – 10.3 eV
PMT and CsI have same solid angle
QE(CsI) = QE(PMT) x I(CsI) / [ I(PMT) x C1 x C2 ]
C1 optical transparency of mesh (81%)
C2 opacity of GEM foil (83.3%)
All currents are normalized to I(PMT-0)
Extrapolation to 11.5 eV:
N0 ≈ 820 cm-1
40
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, 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
2005/12/27
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
vs. Gain
Charge Collection in Drift
Gap :
Mean Amplitude
2005/12/27
Rate
At ED = 0: - signal drops dramatically as anticipated.
- rate also drops dramatically
large hadron suppression
光検出器研究会@KEK,
小沢恭一郎(東大CNS)
Hadron Blindness (I): UV photons vs.
 particles
At slightly negative ED, photoelectron detection efficiency is preserved
2005/12/27
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
whereas charge collection is largely suppressed.
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
Suppression limited by ionization between GEM1 and GEM2.
 Asymmetric operation
ED = 0
GEM1
GE
M2
GEM3
PCB
Suppressed ionization
Full charge collection
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
2005/12/27
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
Length
Budget
Preamps: 0.95 %
Sockets: 0.60%
Total = 0.92 + 0.54 + 0.95 +0.60 = 3.01 %
2005/12/27
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
CDR
Gas Quality Before and After Test
Npe Vs PPM's of Gas Impurity
Trans. of Exhaust Gas (CF4) from WIS SS Proto-HBD Vessel Before
and After LEGS Test
(Using avg. measured Interaction X-sect)
1.2
1.1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1100
Before LEGS Test:
[H2O]=28.0ppm,
[O2]=3.6ppm,
Flow=450sccm
35
H2O
30
O2
25
Npe
Trans.
40
Water “peaks”
After LEGS Test:
[H2O]=19.0ppm,
[O2]=0.1,
Flow=835sccm
20
15
10
5
0
1200
1300
1400
1500
1600
1700
1800
1900
0
50
100
150
200
Wavelength [Angstroms]
250
300
350
400
450
500
550
PPM's of Impurity
• 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
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
Photocathode
Absolute QE of Large (10x10cm) CsI coated GEM PC
(Corrected for Mesh & GEM Transparency)
Absolute QE of Large (10x10cm) CsI coated GEM PC
(Corrected for Mesh & GEM Transparency)
Histroy of QE Scans of BNL PC
in CF4 and in Vac
70
90
Absolute QE [%]
CF4 [WIS, Ilia]
50
Vac [BNL]
Vac [BNL]: 3 days later
40
CF4 [BNL]
CF4 [BNL]: 3 days later
30
20
10
Absolute QE [%]
60
0
1100
Histroy of QE Scans of BNL PC
in CF4 and in Vac
100
80
70
60
CF4 [WIS, Ilia]
50
CF4 [BNL]
40
Linear (CF4 [BNL])
30
20
Linear (CF4 [WIS, Ilia])
10
1200
1300
1400
1500
1600
1700
Wavelength [Angstroms]
1800
1900
2000
0
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
Wavelength [Angstroms]
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
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
Preliminary Measurements
VUV Wavelength Scan (D2 lamp): Absolute
Photoelectron Current from CsI Sample Photocathode
300
200
Vacuum Scan
CF4 Scan
150
100
50
0
1100
1300
1500
1700
Wavelength [Angstroms]
Photoelectron Ratio: Gas/Vacuum
[%]
120
250
Photoelectron
Current [pA]
Ratio of thePhotoelectron Current in Gas and in Vacuum
100
80
CsI
60
PMT Monitor
40
20
0
1100
1900
1300
1500
1700
1900
Wavelength [Angstroms]
CsI Photocathode Output after exposure to CF4
Photoelectron Collection Efficiency Vs Collection Field
120
100
80
Gas: CF4 [Before Polish]
Vacuum [Before Polish]
60
Gas: CF4 [After Polish, P=30.98"Hg]
Gas: CF4 [After Polish, P=31.56"Hg]
40
Vacuum [After Polish]
20
0
0
0.5
1
Collection Field [kV/cm]
2005/12/27
1.5
~CsI Photocathode Current
[arb. Units]
Photoelectron Collection Efficincy
w.r.t. PE coll. in Vacuum [%]
(VUV Scans taken over a 10 day period during continuous CF4 flow)
(11/29/04)
100
(12/03/04)
80
1st Scan started 1 hour after
start of CF4 flow (11/24/04)
60
40
20
0
1100
-20
1200
1300
1400
1500
1600
Wavelength [Angstsoms]
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
1700
1800
1900
Photocathode Production Notes
• 1st USB Chicklet Produced @ Big Mac
2nd 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.
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.
光検出器研究会@KEK,
小沢恭一郎(東大CNS)
7.2005/12/27
QE was measured in Vac (after
2 hours of pumping), Spectrometer
Vac = 1.0 E-5 Torr.
Integrated Transmittance
Integrated Transmittance over VUV
spectrum
Integrated Transmittance: 1120 - 2000 Angstroms
110
H2O
100
O2
90
Calibrated Ar/O2 Mix
([O2]=10.3, 50.3ppm nominal)
80
70
60
50
40
30
20
10
0
0
50
100
150
200
250
300
350
400
PPM's [ppm]
2005/12/27
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
450
500
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
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
Thickness Uniformity
Underside of Scaffolding
CsI Thickness Target: 2000 Angstroms
Al Foil Control Substrates
for measuring CsI thickness
Thickness Uniformity of Evaporated CsI
CsI Thickness [Angstroms]
r
2500
2000
1500
Quartz Crystal Thickness Monitor
1000
* Height of substrates above CsI crystal = 31.75'',
* CsI molybdenum boat dimensions (i.e. size of evaporation
source)~1.0''x0.5''
500
0
0
5
10
15
Radius from Center of Circular Vessel of Evaporator [cm]
Quartz crystal
thickness monitor
2005/12/27
Au-Ni-Cu clad
G-10 Photocathode
Substrates
光検出器研究会@KEK, 小沢恭一郎(東大CNS)
20
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
光検出器研究会@KEK, 小沢恭一郎(東大CNS)