A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs Efficient ion...

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


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


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.


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


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!!!


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.


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


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


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


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


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


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%)


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


Sealed detector

Test detector setup

Base plate made in Novosibirsk

Visible-sensitive GPM

UHV compatible materials

Bi-alkali PC


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.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


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


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


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


Additional slides


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


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


0 10 20 300

5

10

15

20

312nm 365nm 405nm 436nm 546nm

QE

[%]

Time [days]

K-Cs-Sb PC700 Torr Ar/CH

4 (95/5)

K-Cs-Sb stability in gas

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A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs Efficient ion...

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