a. lyashenko instr08 – binp – feb. 2008 ion blocking & visible-sensitive gas-pms efficient...
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A. LyashenkoINSTR08 – BINP – Feb. 2008ION BLOCKING & visible-sensitive gas-PMs
Efficient ion blocking in gaseous Efficient ion blocking in gaseous detectors and its application to visible-detectors and its application to visible-
sensitive sensitive gas-avalanche photomultipliersgas-avalanche photomultipliers
A. Lyashenko, A. Breskin and R. ChechikWeizmann Institute of Science, Rehovot, Israel
AndJ.M.F. dos Santos, F.D. Amaro and J.F.C.A. VelosoJ.M.F. dos Santos, F.D. Amaro and J.F.C.A. Veloso
University of Coimbra, Portugal
A. LyashenkoINSTR08 – BINP – Feb. 2008ION BLOCKING & visible-sensitive gas-PMs
Secondary effects in gaseous detectors Secondary effects in gaseous detectors
Gaseous Photo-Multiplier (GPM) Time Projection Chamber (TPC)
readout plane
+++ avalanche
ions
+ dynamictrackdistortions
++
+
drift
GAS
PChn
readout plane
+++ avalanche
photonsions
incident photon
+secondaryemission
secondaryemission
GAS
Ions secondary e emission ion feedback pulses gain & performance limitations
Ions dynamic track distortions
A. LyashenkoINSTR08 – BINP – Feb. 2008ION BLOCKING & visible-sensitive gas-PMs
IBF: Ion Back-Flow Fraction
IBF: The fraction of avalanche-generated ions back-flowing to the drift region or to the photocathode
Major efforts to limit ion backflow1 .GATING operation in “gated-mode” deadtime,
trigger2 .NEW e- - - - MULTIPLIERS operation in DC mode
(cascaded-GEM*, MICROMEGAS…&: OTHERS)
Challenge: BLOCK IONS WITHOUT AFFECTING ELECTRON COLLECTION
*GEM: Gas Electron Multiplier - Sauli, NIM A 386, (1997) 531.
A. LyashenkoINSTR08 – BINP – Feb. 2008ION BLOCKING & visible-sensitive gas-PMs
Visible-sensitive GPMVisible-sensitive GPM: Ion-feedback development: Ion-feedback development
Visibile-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
Ar/CH4 (95/5), γeff+ ~0.03, Gain ~ 105 => IBF < 3.3*10-4
A. LyashenkoINSTR08 – BINP – Feb. 2008ION BLOCKING & visible-sensitive gas-PMs
IBF in cascaded GEM GPMs (high Edrift)High Edrift (>0.5 kV/cm) needed to efficiently extract photoelectrons
Bachman et al. NIMA438(1999)376 5% @ 0.5kV/cm, Gain ~105 Breskin et al. NIM A478(2002)225 2-5%@ 0.5kV/cm, Gain ~105
Bondar et al. NIM A496(2003)325 3% @ 0.5kV/cm, Gain ~ 105
Need another factor of 100!!!
A. LyashenkoINSTR08 – BINP – Feb. 2008ION BLOCKING & visible-sensitive gas-PMs
The Microhole & Strip plate (MHSP).
~80% of avalanche ions are trapped by cathode strips and plane
Two multiplication stages on a single, double-sided, foil
R&D: Weizmann/Coimbra
photocathode
cathode mesh
hv
VC-T
VA-C
E trans
E drift
CA
30mm
100mm
100mm
70mm
140mm
210mm
Veloso et al. Rev. Sci. Inst. A 71 (2000) 237.
A. LyashenkoINSTR08 – BINP – Feb. 2008ION BLOCKING & visible-sensitive gas-PMs
IBF: 3% @ Gain > 105
IBF: 20% @ Gain > 105
The benefit of MHSP in a cascade.
Maia et al. IEEE NS49 (2002)Maia et al. NIM A504(2003)364
Mörmann et al. NIM A516 (2004) 315
3GEMs+MHSP
4GEMs
7 times lower than with cascaded GEMs
A. LyashenkoINSTR08 – BINP – Feb. 2008ION BLOCKING & visible-sensitive gas-PMs
Reverse-biased MHSP (R-MHSP) concept
410V 70V
AC
+++++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
A. LyashenkoINSTR08 – BINP – Feb. 2008ION BLOCKING & visible-sensitive gas-PMs
1st R-MHSP or F-R-MHSP: ion defocusing (no gain!)Mid GEMs: gainLast MHSP: extra gain & ion blocking
BETTER ION BLOCKING:“COMPOSITE” CASCADED MULTIPLIERS:
R-MHSP/GEM/MHSP
F-R-MHSP/GEM/MHSP
A. LyashenkoINSTR08 – BINP – Feb. 2008ION BLOCKING & visible-sensitive gas-PMs
102 103 10410-5
10-4
10-3
10-2
10-1
F-R-MHSP/GEM/MHSP R-MHSP/GEM/MHSP
Edrift
=0.2kV/cm
Ar/CH4 (95/5), 760 Torr
IBF
Total gain 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
TPC conditions (low drift field)Gas PMT conditions (high drift field)
IBF=1.5*10-4 @ Gain=104
IBF=3*10-4 @ Gain=105
Lyashenko et al., JINST (2007) 2 P08004
IBF in “composite” micro-hole multipliersIBF measured with 100% e-collection efficiency
IBF is 100 times lower than with 3GEMs
A. LyashenkoINSTR08 – BINP – Feb. 2008ION BLOCKING & visible-sensitive gas-PMs
Example (R&D in course @ WEIZMANN/COIMBRA )
NEW! “COBRA”: GEM-LIKE PATTERNED ION-SUPPRESSING ELECTRODES (R. d’Oliveira, CERN)
New ideas for ion blocking
30mm
100mm
100mm
70mm
140mm
210mm
A. LyashenkoINSTR08 – BINP – Feb. 2008ION BLOCKING & visible-sensitive gas-PMs
IBF suppression with “Cobra”
103 104 105 10610-6
10-5
10-4
10-3
10-2
10-1
100
GPM
TPC
700 Torr Ar/CH4 (95/5)
Flipped-Cobra/2GEM
Edrift
=0.5kV/cm
IBF
Total Gain
IBF=2.7*10-5
Gain=104
IBF=3*10-6
Gain=105
IBF 1000 times lower than with GEMs, best results ever achieved
Though, presently at the expense of electron collection (~20%)
A. LyashenkoINSTR08 – BINP – Feb. 2008ION BLOCKING & visible-sensitive gas-PMs
IBF reduction summaryTPC (Edrift=0.1-0.2kV/cm, Gain=104)
GPM (Edrift=0.5kV/cm, Gain=105)
Detector type
IBF Collectionefficiency
IBF Collectionefficiency
3GEM 0.5% 100% 5% (20%)* 100%
4GEM 100% 2% (0.01%)**
100%
R-MHSP/GEM/MHSP
0.08% 100% 0.1% 100%
F-R-MHSP/GEM/MHSP
0.015% 100% 0.03% 100%
“Cobra”/2GEM
0.0027% 20% 0.0003% 20%
* Reflective PC **Gated mode
A. LyashenkoINSTR08 – BINP – Feb. 2008ION BLOCKING & visible-sensitive gas-PMs
Sealed detector
Test detector setup
Base plate made in Novosibirsk
Visible-sensitive GPM
UHV compatible materials
Bi-alkali PC
A. LyashenkoINSTR08 – BINP – Feb. 2008ION BLOCKING & visible-sensitive gas-PMs
Visible-sensitive GPM: Gain Divergence
200 220 240 260 280 300 320 340100
101
102
103
104
700 Torr Ar/CH4 (95/5)
Edrift
=0.5kV/cm
Tot
al g
ain
VGEM
[V]
K-Cs-Sb QE=22%@375nm
G
Gmeas
K-Cs-Sb, Na-K-Sb, Cs-Sb : Current deviates from exponential Max Gain ~ few 100, IBF~10%
D. Mörmann et al.,NIM A 504 (2003) 93
A. LyashenkoINSTR08 – BINP – Feb. 2008ION BLOCKING & visible-sensitive gas-PMs
A.Breskin et al. NIM A553 (2005) 46-52
Gated operation of visible-sensitive GPM
GATED MULTI-GEM
Gain~106
GAIN: ~100 in DC mode (ion feedback limit),IBF~10% ~106 in ion-gating mode; IBF~10-4
Ion gating electrode
A. LyashenkoINSTR08 – BINP – Feb. 2008ION BLOCKING & visible-sensitive gas-PMs
DC operation of visible-sensitive GPM
First evidence of DC high gain operation of visible-sensitive GPM
Gain >105 in DC mode single photon sensitivity
300 400 500 6000
10
20
30
40
50
QE
[%]
Wavelength [nm]
K-Cs-Sb PC
K-Cs-Sb 200 250 300 350101
102
103
104
105
106
K-Cs-Sb (QE~40%) CsI Exponential fit of Exponential fit of
Flipped-Cobra/2GEME
drift=0.5kV/cm
700 Torr Ar/CH4 (95/5)UV-LED 375nm
Tot
al G
ain
VGEM
[V]
Gain~105
K-Cs-Sb
CsI
DC Gain limit~100 in cascaded GEMs
Flipped Cobra + 2GEMs
A. LyashenkoINSTR08 – BINP – Feb. 2008ION BLOCKING & visible-sensitive gas-PMs
Gain ~104 at full collection efficiency for photoelectrons
IBF=7*10-3@Gain=104 was not optimized
260 280 300 320 340 360102
103
104
105
Edrift
=0.5kV/cm
2G/Cobra/G
CsI PC K-Cs-Sb PC QE~25%@375nm
Tot
al g
ain
VGEM3
[V]
700 Torr Ar/CH4 (95/5)
10-3
10-2
10-1
100
IBFGain~104
K-Cs-Sb
CsI
DC operation of visible-sensitive GPM
2GEMs + Cobra + GEM
A. LyashenkoINSTR08 – BINP – Feb. 2008ION BLOCKING & visible-sensitive gas-PMs
Summary Cascaded Patterned Hole Multipliers (PHM) significant improvement in ion blocking in gaseous
detectors
with MHSP/GEM-based CASCADED MULTIPLIERS• 100 times lower IBF than with cascaded GEMs with full efficiency for collecting primary electrons!• Not yet investigated with visible-sensitive photocathodes
with Cobra/GEM-based CASCADED MULTIPLIERS• 1000 times lower IBF than with cascaded GEMs• with so-far reduced efficiency for collecting primary electrons
– Gain >105 reached with visible-sensitive K-Cs-Sb PC• with full efficiency for collecting primary electrons
– Gain ~104 reached with visible-sensitive K-Cs-Sb PC
First evidence of high-gain DC operation of visible-sensitive GPM
Further work:• Operation of MHSP/GEM -based cascaded multiplier with visible PC
A. LyashenkoINSTR08 – BINP – Feb. 2008ION BLOCKING & visible-sensitive gas-PMs
Auger neutralization process
• Ei is the potential energy of the
ion
• Epe the photoemission threshold,
• E1 and E2 are the potential energy
of the photocathode electrons that
participate in the process, and
• Ekin the kinetic energy of the
emitted secondary electron.
Condition for the secondary electron emission: Ei>2Epe
Epe (K2SbCs)=2eV, while Ei=(CH4)=12.6 eV
A. LyashenkoINSTR08 – BINP – Feb. 2008ION BLOCKING & visible-sensitive gas-PMs
It takes 100 – 1000 collisions for Ar + + CH4 Ar + CH4
+
Mean free path ~10-5 cm at normal conditions
0.5cm
Charge exchange in 700 Torr Ar/CH4(95/5)
Only CH4+ remain after 10-3/p – 10-2/p cm (p=0.05 => 0.02 – 0.2 cm) of drift