Performance of the MCP-PMT for the Belle II TOP counter Kodai - - PowerPoint PPT Presentation

Performance of the MCP-PMT for the Belle II TOP counter

Kodai Matsuoka (KMI, Nagoya Univ.)

• S. Hirose, T. Iijima, K. Inami, Y. Kato, Y. Maeda,
• R. Mizuno, Y. Sato, K. Suzuki (Nagoya Univ.)

TOP (Time Of Propagation) counter

 A novel “ring imaging” Cherenkov detector  A key device of PID in Belle II to extend the physics reach

toward New Physics.

  n

C

1 cos TOP  

Air (n=1) Quartz (n=1.47)

@ 400 nm

Air (n=1)

C K or p

e– e+

TOF (~1 m)

2 cm

TOP Mirror p K

Cherenkov photons generated in the quartz bar travel in the bar as they are totally reflected on the quartz/air boundaries.

Measure (TOF + TOP) with a resolution better than 50 ps for single photon detection.

(p efficiency > 95% and K fake rate < 5% for < 3 GeV/c)

2

MCP-PMT (Micro Channel Plate PMT)

 Square shape multi-anode MCP-PMT with a large photocoverage  Developed at Nagoya in collaboration with HAMAMATSU

Photonics K.K.

Micro channel e–

~1 kV / 400 mm

23 mm

10 mm 400 mm 13°

3

(Cross-section) Photocathode (NaKSbCs) MCP x 2 Photon

e–

5.275 mm 4 x 4 anodes

The best time resolution of photon sensors

10 mV 1 ns

Fast signal

KT0117 ch0 2480 V

1.9 x 106 gain

Mass production and testing

 Belle II TOP uses 512 MCP-PMTs in total.  Mass production started in March 2011 and finished in

March 2014.

 The first half of the PMTs uses a conventional MCP.  The latter uses an ALD (Atomic Layer Deposition) MCP to

extend the lifetime of the photocathode. Both of them are installed in Belle II.

 The following performances were measured for all

the 16 channels of every PMT:

 Quantum efficiency (QE)  Gain  Transit time spread (TTS)  Relative collection efficiency (CE)

All the measurements are fully automated and the performances can be systematically studied.

4

QE measurement setup

 Measure the photocathode current with

a picoammeter: 𝑅𝐹𝑁𝐷𝑄 =

𝐽𝑁𝐷𝑄 𝐽𝑄𝐸 ∙ 𝑅𝐹𝑄𝐸 5 Slit Light spot < 1 mm f MCP-PMT Photodiode Xe lamp

Monochro- mator Sharp cut filters Variable ND filter Moving stage Photocathode MCP1 MCP2 200 V A

QE measurement

 Scan the photocathode at 18 x 18 points x 20 l.

6

Photocathode QE at l = 360 nm

JT0629_20130320

QE peaks around 360 nm

QE

 On average, 28.1% of 283 conventional-MCP-PMTs

and 29.1% of 231 ALD-MCP-PMTs at 360 nm. (Requirement: 28%)

7 Conventional ALD 360 nm Peak QE at 420 nm

Laser measurement setup

 Single photon irradiation to each channel one by one.

8 Pico-second pulse laser (l = 400 nm) Slit

MCP-PMT

Slit

Light spot ≈ 1 mm f

ND filters Reference PMT

MCP-PMT Laser

Fiber ADC Dark box

Moving stage

Variable amp +19.5~35 dB –10 dB +33 dB

Amp ATT Discrim- inator

Threshold: –20 mV TDC

Gain measurement

 Define the gain as the mean of the output charge

distribution.

9

gain = exp(a ∙ HV + b)

KT0449_20140717 ch4

2750 V 2650 V 2550 V

ALD-MCP-PMT

Gain

 The ALD-MCP has

 a large gain at a lower HV or 

a sharper gain slope

than the conventional one  Higher secondary electron yield

10 Conventional ALD Conventional ALD

HV for 1 x 106 gain

HV (V) SE yield

~200 ~85 ~65 ~2

Rough drawing ALD Conventional

TTS measurement

 Fit double Gaussian to the TDC distribution after

time-walk correction.

 Define the TTS as s of the primary Gaussian.

11

TTS does not depend on HV.

JT0886_20150302 ch5

0.5 1.0 2.0 gain (x106) 3340 V

Photo electron recoil on the MCP1 surface

Photocathode MCP1 MCP2

TTS

 TTS less than 50 ps for every PMT

12 Requirement for the Belle II TOP counter

Relative CE measurement

13

 Count the number of TDC hits.

 Correct the laser intensity variation with the reference PMT.

Conventional ALD

Higher CE of the ALD-MCP by ~15% than the conventional one.

ALD Conventional

(same gain of 2 x 106) Normalized to the number of incident photons

JT0763_20140626 ch6 3460 V KT0162_20140612 ch6 2550 V

Increase of CE for the recoil photo electrons due to a higher secondary electron yield of the ALD-MCP

Aging of the photocathode

 Gas out of the MCPs damages the photocathode.

 QE drop

 The amount of outgassing depends on the output charge.

 Define the lifetime as the total output charge where QE decreases to 80%.

 Tried six methods of process to improve the lifetime. 14 Introduce some methods of process 0.01 0.1 1 10 Lifetime (C/cm2) Square shape with Al layer Added ceramic block 2011 2013 2015 ALD MCP Conventional MCP year Belle II beam bkgd MC (5 x 105 gain, 50 ab–1)

Mass production

Lifetime measurement setup

 Tested several samples of each method.

 Load the output charge of the MCP-PMTs by the LED.

 The output charge is measured by a CAMAC ADC.

 Monitor the hit rate (∝QE) by the laser single photons.

15

Reference PMT MCP-PMTs Pulse laser (400 nm) LED (100 kHz)

Extended lifetime

 Three methods of

process were found to be promising.

 20 C/cm2 or longer

lifetime can be expected with Method A+B+C.

16

YH0148 YH0149 YH0160 YH0163 YH0168 YH0170 YH0171 YH0173 YH0203 YH0205 YH0206

Method A Method B Method A+B+C

Summary

 We succeeded in development and mass production

• f the MCP-PMT for the Belle II TOP counter.

 We measured the performance of all the MCP-PMTs.

 QE: >28% (l = 360 nm) on average  Gain as a function of HV  TTS: ~30 ps above 5 x 105 gain  Higher CE of the ALD-MCP by ~15% than the conventional one

Those meet our requirements for the TOP counter

 The lifetime of the ALD-MCP-PMT can be extended by

applying the new methods of process.

 Expected lifetime: >20 C/cm2 (fully survive in Belle II environment)  The conventional-MCP-PMTs will be replaced with the life-

extended ALD-MCP-PMTs after a few years of Belle II operation.

17