Alkali-antimonide Photocathodes for Gas-Avalanche Photomultipliers
description
Transcript of Alkali-antimonide Photocathodes for Gas-Avalanche Photomultipliers
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
Alkali-antimonide Photocathodes for Gas-Avalanche Photomultipliers
Recent review on GPMs: Chechik & Breskin NIM A595 (2008) 116Summary article visible-light GPM: Lyashenko et al. JINST 4 (2009) P07005
A. Lyashenko, R. Chechik and A. BreskinWeizmann Institute of Science, Rehovot, Israel
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
UV-exist:UV-exist:ALICE, HADES,COMPASS, J-LAB, PHENIX
Visible-in courseVisible-in courseMotivation: • large areas, flat geometry• operation in magnetic fields• sensitivity to single photons• visible spectral range• fast (ns range)• high localization accuracy (sub-mm range)
Gaseous Photo-Multipliers (GPM)Gaseous Photo-Multipliers (GPM)
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
Principles of GPM operation
Photoelectron emission fromphotocathode
Avalanche chargemultiplication in gas
Signal recording
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
• Alkali-antimonide pc production (QE 20-50% @ 350-400nm in vacuum for semi-transparent PC)• Hot Indium sealing to package @130-150ºC => critical for pc
Multi-chamber UHV setupMulti-chamber UHV setup
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
•PC substrate treatment in air •PC substrate treatment in vacuum (usually baking at 270-3000C )• Evaporation of alkali-metals
PC sensitivity Long term stability
PC fabrication process:
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
100 200 300 400 500 600 700 8000,1
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10
100
Na-K-Sb:Cs (S-20)
Spec
tral R
espo
nsivi
ty [m
A/W
]
Wavelength [nm]
Cs3Sb (S-11)
Na2KSbRb2CsSb
K2Cs-Sb
Photocathodes: Cs3Sb
Activation steps:
1. Evaporation of Sb at 180-2000C onto a substrate until it looses ~20% of its transparency
2. Exposure to Cs at 150-1800C until the maximum of photocurrent is reached.
3. Post-treatment if needed (removing of excess of Cs by baking at ~2000C)
Activation time: 30-60 minPC characteristics (typical):
• Wavelength of max response: λmax=370-400nm• Luminous sensitivity: 100-120μA/lm• Responsivity at λmax : 65-75mA/W• QE at λmax: 20-25%• Dark emission current at 250C: ≤0.1fA/cm2
• Surface resistance at 250C: 3*107Ohm/square
Designation: S-11
Large area: YES
Burle
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
Photocathodes: K2CsSb
PC characteristics (typical): • Wavelength of max response: λmax=380-420nm• Luminous sensitivity: 70-100 μA/lm• Responsivity at λmax : 100mA/W• QE at λmax: >30%• Dark emission current at 250C: ≤0.01fA/cm2
• Surface resistance at 250C: 6*109Ohm/square Features: Very high surface resistance
Activation steps:One possibility:1. Evaporation of Sb at 180-2000C onto a
substrate until 20% of transparency is lost
2. Exposure to K at 160-2000C until the maximum of photocurrent is reached (formation of K3Sb PC).
3. Repetitive (yo-yo) exposure to Cs & Sb at 180-2250C until the maximum of photocurrent is reached.
Another possibility: So called co evaporation
Large area: YES, needs a conductive layer100 200 300 400 500 600 700 800
0,1
1
10
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Na-K-Sb:Cs (S-20)
Spec
tral R
espo
nsivi
ty [m
A/W
]
Wavelength [nm]
Cs3Sb (S-11)
Na2KSbRb2CsSb
K2Cs-Sb
Burle
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
Photocathodes: Na2KSbActivation steps:1. Evaporation of Sb at 180-2000C on
substrate until it looses 20% of its transparency
2. Exposure to K at 160-2000C until maximum photocurrent reached (K3Sb).
3. Exposure to Na at ~2200C until the raise of PC current start slowing down*.
4. Alternating addition of Sb and K at ~160-1800C until maximum photocurrent reached.
* Simultaneous evaporation of K and Na is possiblePC characteristics (typical):
• Wavelength of max response: λmax=380-410nm• Luminous sensitivity: 65-80μA/lm• Responsivity at λmax : 64mA/W• QE at λmax: 19-21%• Dark emission current at 250C: ≤0.0001fA/cm2
• Surface resistance at 250C: 2*106Ohm/squareFeatures: Outstanding temperature stability (up to 2000C), lowest dark currentLarge area: YES, but production is rather complicated, QE< other Bi-alkali.
100 200 300 400 500 600 700 8000,1
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Na-K-Sb:Cs (S-20)
Spec
tral R
espo
nsivi
ty [m
A/W
]
Wavelength [nm]
Cs3Sb (S-11)
Na2KSbRb2CsSb
K2Cs-Sb
Burle
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
)()()()(
)()()()(
)()()(
PMTWdarkPDPD
darkPDtransPDtrans
darkPMTtransPMTtrans
darkPCPC QET
IIII
IIIIQE
PC characterization
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
0 10 20 30 40 50 600123456789
10
Num
ber o
f K2Cs
Sb P
Cs
QE at max
[%]
N=28Mean QE=28.3%
QE of alkali-antimonide photocathodes
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a)
QE
[%]
Wavelength [nm]
Cs3Sb
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10
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QE
[%]
Wavelength [nm]
Na2KSb c)
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30
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QE
[%]
Wavelength [nm]
K2CsSb PCs
QE~48%
RECENT PHOTOCATHODES
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
300 400 500 6000
10
20
30
40
50
700 Torr Ar/CH4 (95/5)
Edrift
~500 V/cm
Vacuum
QE
[%]
Wavelength [nm]
SbK2Cs
0.0
0.2
0.4
0.6
0.8
1.0
extr
0,0 0,5 1,0 1,5 2,0 2,50,0
0,2
0,4
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0,8
1,0
312 nm 365 nm 405 nm 436 nm 546 nm
K-Cs-Sb 700 Torr Ar/CH4 (95/5)
Tran
smis
sion
Electric field [kV/cm]
Photoelectron extraction from bi-alkali PC into gas
Optimal field for GPMHigher transmission in other gases, e.g. CH4
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
PC is stable in gas in the large vacuum chamber
Expected even better stability for sealed devices
Long-term photocathode stability in gasLong-term photocathode stability in gas
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file:
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-04_
PC
_sta
bilit
y_G
AS
312nm 365nm 405nm 436nm 546nm
QE
[%]
Time [days]
Cs3Sb PC, initial vacuum QE~25%@ 365 nm700 Torr Ar/CH
4 (95/5)
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file:
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PC
_sta
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AS
312nm 365nm 405nm 436nm 546nm
QE
[%]
Time [days]
K2CsSb PC initial vacuum QE~48%@365 nm700 Torr Ar/CH4 (95/5)
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
Secondary effects in visible-sensitive GPMs Secondary effects in visible-sensitive GPMs Gaseous Photo-Multiplier (GPM)
PChn
readout plane
+++ avalanche
photonsions
incident photon
+secondaryemission
secondaryemission
GAS
Main problem: Ions & photons secondary e emission ion/photon feedback pulses gain & performance limitations
Photon feedback is largely reduced
PC masked by electrode*GEM: Gas Electron Multiplier - Sauli, NIM A 386, (1997) 531.
GEM*
70μm50μm
GEM+
++
DV
1e in
>1000e out
Ehole
Edrift
Eind
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
IBF: Ion Back-Flow Fraction
Major efforts to limit ion backflow1 .GATING operation in “gated-mode” deadtime,
trigger2 .NEW e- - - - MULTIPLIERS operation in continuous mode
)cascaded-GEM, MICROMEGAS…&: OTHERS(
Challenge: BLOCK IONS WITHOUT AFFECTING ELECTRON COLLECTION
IBF: The average fraction of avalanche-generated ions back-flowing to the photocathode
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
Visible-sensitive GPM: Ion-feedback developmentVisible-sensitive GPM: Ion-feedback development
Visible-sensitive gas photomultiplier review: M. Balcerzyk et al., IEEE Trans. Nucl. Sci. Vol. 50 no. 4 (2003) 847
1 GIBFeff stable operation of visible sensitive GPMif
200 220 240 260 280 300 320 340100
101
102
103
104
700 Torr Ar/CH4 (95/5)
Edrift
=0.5kV/cm
Tota
l gai
n
VGEM
[V]
K-Cs-Sb QE=22%@375nm
CsI
K-Cs-Sb
K-Cs-Sb, Na-K-Sb, Cs-Sb : Current deviates from
exponential Max Gain ~ few 100, IBF~10%
G~105, γ+eff - ?, IBF - ?
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
Calculation of ion induced secondary emission probability from bi-alkali PCs γ+eff=γ+·εextr
Auger neutralization + Backscattering
PC K-Cs-Sb Na-K-Sbγ+
eff 0.027 0.029
PC
GAS
3 4 5 6 7 8 9 100,0
0,1
0,2
0,3
0,4
0,5
K-Cs-Sb
CH4+
N 0(Ek) [
elec
trons
per
ion
per e
V]
Ek [eV]
Na-K-Sb
4 6 8 10 12 14 16 18 200,0
0,1
0,2
0,3
0,4
0,5
0,6
+ [el
ectro
ns p
er io
n]E'
i [eV]
K-Cs-Sb PC
A.Lyashenko et al., J. Appl. Phys. (2009) accepted, arXiv:0904.4881
Most gases
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
Measurements of γ+eff=γ+·εextr
PC K-Cs-Sb Na-K-Sbγ+
eff (experiment) 0.03±0.01 0.02±0.006
200 220 240 260 280 300 320 340100
101
102
103
104
700 Torr Ar/CH4 (95/5)
Edrift
=0.5kV/cm
Tota
l gai
n
VGEM
[V]
K-Cs-Sb QE=22%@375nm
CsI
K-Cs-Sb
effmeas IBFGGG
1
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
Effective IISEE from K-Cs-Sb and Na-K-Sb PCs
PC K-Cs-Sb Na-K-SbIon CH4
+ CH4+
γ+eff (exp) 0.03±0.01 0.02±0.006
γ+eff(theory) ~0.03 ~0. 03
PC
extreff
Ar/CH4 (95/5), γeff+ ~0.03, Gain ~ 105 => IBF < 3.3*10-4
1 GIBFeff stable operation of visible sensitive GPMif
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
The Microhole & Strip plate (MHSP)Two multiplication stages on a single, double-sided, foil
R&D: Weizmann/Coimbra
30mm
100mm
100mm
70mm
140mm
210mm
Veloso et al. Rev. Sci. Inst. A 71 (2000) 237.
7 times lower IBF than with cascaded GEMs
Strips: multiply charges
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
Reverse-biased MHSP (R-MHSP) conceptReverse-biased MHSP (R-MHSP) concept
410V 70VAC
+++++ions
electrons Flipped-R-MHSPR-MHSP
Can trap its own ions
Ions are trapped by negatively biased cathode strips
Lyashenko et al., JINST (2006) 1 P10004 Lyashenko et al., JINST (2007) 2 P08004
Roth, NIM A535 (2004) 330Breskin et al. NIM A553 (2005) 46Veloso et al. NIM A548 (2005) 375
Can trap only ions from successive stages
Strips: collect ions
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
103 104 105 2x10510-4
10-3
10-2
F-R-MHSP/GEM/MHSP R-MHSP/GEM/MHSP
Edrift
=0.5kV/cm
Ar/CH4 (95/5), 760 Torr
IBF
Total gain
Lyashenko et al., JINST (2007) 2 P08004
IBF measured with 100% e-collection efficiency
IBF=3*10-4 @ Gain=105 is 100 times lower than with 3GEMs
1st R-MHSP or F-R-MHSP: ion defocusing (no gain!)Mid GEMs: gainLast MHSP: extra gain & ion blocking
BEST ION BLOCKING:BEST ION BLOCKING:““COMPOSITE” CASCADED MULTIPLIERSCOMPOSITE” CASCADED MULTIPLIERS::
IBF=3*10-
4
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
• 20% QE drop @ 2 μC/mm2 ion charge on photocathode: • only ~ 4 x faster drop compared to thin ST CsI (~8 μC/mm2)
K-Sb-Cs PC ageing in avalanche modeK-Sb-Cs PC ageing in avalanche mode
Real conditions: gain=105; IBF=3*10-4. •20% QE drop 46 years @ 5kHz/mm2 ph. same conditions with a MWPC (IBF~0.5) 3000 times shorter lifetime: ~5 days!
A. Breskin al. NIM A553 (2005) 46
0 2 4 6 8 10 12 14 160,0
0,2
0,4
0,6
0,8
1,0
1,2
CsI(300A) QE~7%(180nm) 50Torr, CH
4, G~103
K-Cs-Sb
PC1 QE~17% (375nm), 100Torr, G~103
PC2 QE~25% (375nm), 100Torr, G~20 PC3 QE~11% (375nm), 700Torr, G~103
Ar/CH4 (95:5)
0408
16_S
b-K-
Cs_P
Cage
ing
Rela
tive
PC c
urre
nt
PC accumulated charge [mC/mm2]
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
Sealed detectorTest detector setup
Visible-sensitive GPMVisible-sensitive GPMUHV compatible materials
Bi-alkaliphotocathode
cascadedmultiplier
GEM/MHSP
M. Balcerzyk et al., IEEE Trans. Nucl. Sci. Vol. 50 no. 4 (2003) 847
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
200 220 240 260 280 300100
101
102
103
104
105
106
107
K-Cs-Sb CsI (exp. fit)
Double-GEM
Edrift=0.5 kV/cm, QE~27%@375nm700 Torr Ar/CH4 (95/5)
K-Cs-Sb CsI (exp. fit)
F-R-MHSP/GEM/MHSP
Tota
l gai
nV
AC_MHSP, DV
GEM [V]
Continuous operation of F-R-MHSP/GEM/MHSPContinuous operation of F-R-MHSP/GEM/MHSP with K-Cs-Sb photocathodewith K-Cs-Sb photocathode
Gain ~105 at full photoelectron collection efficiencyFirst evidence of continuous high gain operation of visible-sensitive
GPM
K-Cs-Sb
CsI
Lyashenko et al., JINST (2009) 4 P07005
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
Short-term GPM stabilityShort-term GPM stability
Rate: 12kHz/mm2 photonsGain: 105
Total anode charge ~125μC
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fresh PC in vacuum in gas after 14 hours @ gain 105
file: 2
008-
05-2
5_FR
GM
_KCs
Sb_l
ong_
term
_sta
b
700 Torr Ar/CH4 (95/5)
QE
[%]
Wavelength [nm]
K2CsSb
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
Visible-sensitive GPM featuresVisible-sensitive GPM features
Single photon sensitivityNo ion-feedback
Fast ns pulses
19 ns0 100 200 300 400 500
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101
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103
104
105
Gain ~ 105
Gain ~ 2*105
Gain ~ 3*105
700 Torr Ar/CH4 (95/5)
K-Cs-Sb (QE~26%@375nm)F-R-MHSP/GEM/MHSP
Coun
ts
Channel
100 photoelectrons
A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09
SummarySummary
Alkali-antimonide PCs for GPMsHigh (>40%) QE values reached Stability in gas verifiedProbability of IISEE evaluated Required IBF estimated
MHSP/GEM-based CASCADED MULTIPLIERS• 100 times lower IBF than with cascaded GEMs with full efficiency for collecting primary electrons!• Gain ~105 reached with visible-sensitive K-Cs-Sb PC• Demonstrated stable GPM operation at a gain 105
• Atmospheric pressure operation Many potential applications in large-area photon detectors: Particle Physics, Medical Imaging, Astroparticle, Military, Bio
First evidence of high-gain continuous operation of visible-sensitive GPM