a. breskin rd51 amsterdam 4/08 ion blocking & visible-sensitive gas-pms efficient ion blocking...

A. BreskinRD51 Amsterdam 4/08 ION BLOCKING & visible-sensitive gas-PMs

Efficient ion blocking in gaseous Efficient ion blocking in gaseous detectors and its application to detectors and its application to

visible-sensitive gaseous visible-sensitive gaseous photomultipliersphotomultipliers

A. Breskin, A. Lyashenko and R. ChechikWeizmann Institute of Science, Rehovot, Israel

&J.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 gaseous photomultipliers: Visible-sensitive gaseous photomultipliers: Ion-feedback developmentIon-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

eff : ion feedback coeff.


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 cascadeThe 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) conceptReverse-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:BETTER ION BLOCKING:““COMPOSITE” CASCADED MULTIPLIERSCOMPOSITE” 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


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”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 summaryIBF 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 GPMVisible-sensitive GPM

UHV compatible materials

Bi-alkali PC


Visible-sensitive GPM: Gain Divergence 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 GPMGated 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 GPMDC operation of visible-sensitive GPM

Gain >105 in DC mode single photon sensitivity

But: e- collection efficiency ~ 20%

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


DC operation of F-R-MHSP/GEM/MHSPDC 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 DC high gain operation of visible-sensitive

GPM

200 220 240 260 280103

104

105

106

K-Cs-Sb (QE~27%@375nm) CsI Exponential fit of Exponential fit of

F-R-MHSP/GEM/MHSPE

drift=0.5kV/cm

700 Torr Ar/CH4 (95/5)UV-LED 375nm

Gai

n

VAC2

[V]


SummarySummary Cascaded Patterned Hole Multipliers (PHM) significant improvement in ion blocking in gaseous

detectors of importance in: Tracking detectors (TPC) & Gaseous Photomultipliers

with 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

with Cobra/GEM-based CASCADED MULTIPLIERS• 1000 times lower IBF than with cascaded GEMs• with so-far low e- collection efficiency

– Gain >105 reached with visible-sensitive K-Cs-Sb PC

First evidence of high-gain DC operation of visible-sensitive GPM

Further work:• Optimization of COBRA• Double-sided patterned hole-multipliers


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 gasK-Cs-Sb stability in gas

a. breskin rd51 amsterdam 4/08 ion blocking & visible-sensitive gas-pms efficient ion blocking...

Documents