Lifetime of HPK Square-shape MCP-PMT

T. Mori (Nagoya University)On behalf of Belle II PID group

Dec. 1, 2010Fast Timing Workshop

Cracow, Poland

Belle detector3.5GeV

8GeV

Belle & Belle-II Experiments

• K/π-ID is important– Belle: 3σ

• K/π-ID power: 4σ– ex. S/N ×5 for B ππ

• High background rate

Dec. 1, 2010 Fast Timing WS, Cracow 2

Higher statistics ： Higher luminosity (×~40)B-factory

Higher accuracy ： Belle detector upgrade＆Super B-factory

2.6m

1.2

m

e- : 7GeV

e+: 4GeV

1.5T

ForwardBackward

Install here(10cm gap of barrel part)Belle II detector cross section

Belle II experiment

TOP counterFor barrel part

(Time Of Propagation)

TOF + ACC(ACC: Threshold type Aerogel Cherenkov Counter)

TOP Counter

Dec. 1, 2010 3Fast Timing WS, Cracow

～ O(1m)

πK

⊿t ~ O(100ps)

K, π with p = 4GeV/c⊿TOP = 40ps (L ~ 1m, θ⊿ C = 6mrad)⊿TOF = 30ps (L ~ 1m)

• Time Of Propagation counter– RICH + TOF technique– Cherenkov radiator + time sensitive screen– Position (x, y) (RICH) Position + time (x, t)⇒– Very compact & simple– Radiation hardness

Performance & Important Device• Performance definition

• σphotodetector : TTS of photodetector

• Ndet: number of detected photons

Dec. 1, 2010 Fast Timing WS, Cracow 4

dettop

NTOPTOF

S

Separation power :

Photo-detector is very important

Our selection: MCP-PMT

• Requirements– TTS : <50ps– Gain : 1.0×106

• Single photon detection• Enough statistics for TTS

– QE : >20%@λ=400nm– Available in B -field

2radiator

2torphotodetectop

> ~ 50ps (Chromatic)

Square-shaped MCP-PMT: SL10

Dec. 1, 2010 5Fast Timing WS, Cracow

φ11mm 27.5mm

27.5mm

Ordinary cylindrical MCP-PMT

SquareMCP-PMT

Co-development withHamamatsu Photonics K.K.

Typical signal shape

Single photon irradiation

Catalog spec

Photo-cathode Multi-alkali / Super bi-alkali

MCP Channel φ 10μm

MCP bias angle 13°

MCP thickness 400μm

MCP layers 2

Al protection layer On 2nd MCP

Anode channels 1×4 / 4×4

Sensitive region 64%

HV ~ 3000 – 3500 V

~400m

Channelφ ~ 10μm

~4mmMCP(Micro channel plate)

Performances of SL10

Dec. 1, 2010 6Fast Timing WS, CracowWavelength [nm]

QE

[%]

Multi-alkali PC

TDC [25ps]

Num

ber o

f eve

nts

σtts = 40 [ps]

• All requirements satisfied• Remaining factor: stability(Lifetime)

in high photon rate– ~7x1012 photons/cm2/year– ~0.17 C/cm2/year

• Estimated with TOF trigger hit rate

– Cylindrical type: enough lifetime

ADC [0.25pC]

Num

ber o

f eve

nts

Pedestal

G ~ 106

Single photon irradiation

Dec. 1, 2010 Fast Timing WS, Cracow 7

For single photon test

~40-photon/pulse1k – 40kHz

• Parameters– TTS

• σphotodetector

– Gain• Single photon detection• Enough statistics for TTS

– QE• Ndet

Lifetime measurement for SL10

Load of photons & single photon testdone in same setup

Measured PMT YJ0006 YJ0011

Anode channel 4×4 4×4

Al protection layer 1st MCP 2nd MCP

Initial gain (×106) 0.41 1.1

calibration PMT

Result: TTS, Gain

Dec. 1, 2010 Fast Timing WS, Cracow 8

• Decrease

• Good Stability

– TTS is stable– Single photon

detection is OK

0 0.01 0.02 0.03 0.04 0.05 0.0630405060708090

100 YJ0006 1chYJ0006 6chYJ0011 1chYJ0011 6ch

Output charge [C/cm2]

TTS[

ps]

0 0.01 0.02 0.03 0.04 0.05 0.060.600000000000002

0.700000000000002

0.800000000000002

0.900000000000002

1

1.1YJ0006 1chYJ0006 6chYJ0011 1chYJ0011 6ch

Output charge [C/cm2]

Rela

tive

gain

0 0.4 Time in Belle II experiment [years] No problem

• QE difference– SL10

– Cylindrical

Dec. 1, 2010 Fast Timing WS, Cracow 9

• Lifetime– QE degradation: predominant factor– Gain: linearly decrease; still OK for single photon detection & TTS– TTS: Stability confirmed

Why?

Result: QE

Cylindrical

Previous

SL10

Let’s see QE in detail

QE Variation: Wavelength

• Increase of work function dominatesDec. 1, 2010 Fast Timing WS, Cracow 10

Wave length [nm]

QE

[%]

Before aging

After aging

Work function

Fitting: ratio of QE

Three step model:

T : transmittanceA: mechanical factor (effective region)φ: work function

⊿φ: variation of work function

A(t)/A(t=0) 0.98±0.04 ⊿φ 0.27±0.07eV φ 1.56±0.13eV

YJ0011

QE Variation: Position

Dec. 1, 2010 11Fast Timing WS, Cracow

QE before aging

x [mm]

y [m

m]

QE after aging

y [m

m]

x [mm]

• Surrounding part: large QE drop– Ion feedback?– Structure?

x

y

1

16

Effect of Ion Feedback?• Ion feedback

• Mask: no effect

• Ion feedback

Dec. 1, 2010 Fast Timing WS, Cracow 12

Lifetime test with mask

QE variation without mask QE variation with mask

Positive Iondamages same positionas signal photon irradiation

Lifetime test with mask

Mask

MCP-PMTWindow

Inner Structure & Possible Cause

• Only NEUTRAL gas can pass through gap ( electric field)∵

Dec. 1, 2010 13Fast Timing WS, Cracow

Inner structure of Cylindrical type & square-shaped MCP-PMTs

WindowPC 1st MCP

2nd MCPAnode

WindowPC 1st MCP

2nd MCPAnodeE

Neutral gas

Cylindrical: separated Square: connected

Poisoning of multi-alkali PC with different gasses(INFN Milano – LASA, Via F.lli Cervi 201, 20090)

We also found report saying CO2 and H2O affect QE:(Japanese Journal of Applied Physics 29, No. 10, p. 2087 (1990))

Too much oxidation of Csvariation of band gapincrease of work function

Al-filmCeramic tube

Stainless tube

Al-film

Modification of Inner Structure

• Separate space to PC-side & anode-side– It is not high airtight

• MCPs are changed with that of low outgassing type– To reduce amount of out gas

Dec. 1, 2010 Fast Timing WS, Cracow 14

WindowPC

1st MCP

2nd MCPAnode

CeramicinsulatorCeramic

insulator

Al-film

Lifetime for New SL10

• 2.5 [C/cm2] for relative QE 80%– 1.2×1014[photons/cm2]

Dec. 1, 2010 15Fast Timing WS, Cracow

Aftermodification

Before modification

Rela

tive

QE

Output charge [C/cm2]

0 101 Time in Belle II experiment [year]

DOI:10.1016/j.nima.2010.10.145

SL10 is available

Summary• We are developing TOP counter for Belle-II experiment

– TOF + RICH technique TTS & Nphotons are important

• Square shape MCP-PMT (SL10) is developed for TOP– Satisfies required performances (TTS, gain) for TOP– Lifetime of QE in high photon rate

• We find possible cause of QE drop: Neutral gas (CO2 & H2O)

Improvement of inner structure against gas damage1. Separate space to PC-side & anode-side by ceramic insulator2. Low outgassing MCP

2.5C/cm2 for relative QE 80% achieved– > 10 years under ~7×1012 photons/year/cm2

Dec. 1, 2010 16Fast Timing WS, Cracow

BACKUP

Dec. 1, 2010 Fast Timing WS, Cracow 17

Photon Hit Rate Estimation

Dec. 1, 2010 Fast Timing WS, Cracow 18

Main source: spent electrons EM shower Cherenkov light

TOF hit rate in Belle experiment: 187kHz @ L=1034cm-2s-1

Belle spent electron simulator: 400 – 500 kHz @ L=1034cm-2s-1

Use 500 kHz electron Geant simulationTOP counter is implemented• Quartz radiator: 2650×454×20[mm3]• Without expansion volume• QE: 20% @ λ=400nm• CE: 60%

• To be conservative

Photon hit rate of MCP-PMT: 300kHz/(TOP module)Factor 20 is expected for Belle-II experiment with L~1036cm-2s-1

(20×300 / (45.4×2))×365/2×24×60×60 / (QE×CE)= 6.9×1012 [photons/cm2/year]• effective factor

(20×300 / (45.4×2))×365/2×24×60×60×G×e = 167 [mC/cm2/year]• Gain: 106

☆ Photon hit rate

☆ Typical output charge

Performance of TOP Counter

• Performance definition

• σtop

= √(σMCP-PMT2 + σchromatic

2 + σothers2)

• Ndet: number of detected photons

Dec. 1, 2010 19Fast Timing WS, Cracow

dettop

NTOPTOF

S

Separation power :

Photo-detector is very important

θ z

xy

Ndet 0.8Ndet S 0.9S

Suppression of Chromatic Dispersion

• Wavelength cut

Dec. 1, 2010 20Fast Timing WS, Cracow

Group velocityof light

Number ofCherenkov photons

Transmittance ofwavelength cut filter

350nmSuppression of chromatic dispersionwith 350nm wavelength cut filter

wavelength cut TTS improve⇒

⇒

Ndet decrease fine tune

σchromatic

50 25ps

Path length in quartz: 1m

Number of detected photons

Dec. 1, 2010 Fast Timing WS, Cracow 21

Photo-detector• Requirements

– Gain : 1.0×106

– TTS : <40ps– QE : >20%@λ=400nm– Available in B -field

Dec. 1, 2010 22Fast Timing WS, Cracow

(Micro Channel Plate)

Only photo-detectorsatisfies requirements MCP-PMT

Square type MCP-PMT

Co-developmentwith Hamamatsu Photonics

Channel

~400m

~10m

Channel φ~10μm, Bias angle of MCP : 13° Available in B-field

SL10

Dec. 1, 2010 Fast Timing WS, Cracow 23

Cylindrical & SL10

Dec. 1, 2010 Fast Timing WS, Cracow 24

• Lifetime difference– Cylindrical

– Square

Dec. 1, 2010 Fast Timing WS, Cracow 25

For single photon test

~40-photon/pulse1k – 40kHz

Cylindrical

Square

• Lifetime– QE degradation

• predominant factor– Gain & TTS

• stability confirmed

Why?

Lifetime measurement for SL10

Gain decrease

Dec. 1, 2010 Fast Timing WS, Cracow 26

Before photon load After photon loadOutput charge

• ADC plots

E - λ

Dec. 1, 2010 Fast Timing WS, Cracow 27

How the QE Degradation Occur?

• QE fall is not uniform– Ion feedback is not reasonable

Dec. 1, 2010 28Fast Timing WS, Cracow

x [mm]

QE

[%] (

y =

10[m

m])

QE fallBefore

After

Wave length [nm]

QE

[%]

Before

After

Increase of work function

Before measurement

x [mm]

y [m

m]

After measurement

y [m

m]

x [mm]

How the QE Degradation Occur?

• QE fall is not uniform– It is not reasonable if it caused by Ion feedback

Dec. 1, 2010 29Fast Timing WS, Cracow

x [mm]

y [m

m]

Initial QE

x [mm]y

[mm

]

Terminal QE

x [mm]

QE

[%] (

y =

10[m

m])

QE fallInitial

Terminal

Possibility of neutral gas

Inner structure of CT0790 & square-shaped MCP-PMTs

Neutral gas assumption

Dec. 1, 2010 Fast Timing WS, Cracow 30

Tube

Lifetime of SBA-PC

Dec. 1, 2010 Fast Timing WS, Cracow 31

0 101 Use in Belle II [years]

SBA1SBA2

MA

Set up for Beam Test

Dec. 1, 2010 32Fast Timing WS, Cracow

electron beam（ 2GeV/c）

MCP-PMT

TimingCounter

MWPC2

MWPC1

Veto counter

TriggerCounter

TOPCounter

x

y

x

y

Subtract EM-shower events

Beam trajectory

t0 determination

Quartz + MCP-PMTFuji test beam lineat KEK

Prototype test for TOP

• Consistency confirmed

Dec. 1, 2010 Fast Timing WS, Cracow 33

TTS（ 1st peak）Data 76.0±2.0 [ps]

Simulation 77.7±2.3 [ps]

ch29

1st

2nd3rd 1st

2nd

3rd

transit time[25ps]

N [p

hoto

ns]

transit time[25ps]

data simulation

Electron beam irradiation

875m

m915m

mquartz

3rd 2nd

1st