The TORCH PMT: A close packing, multi-anode, long life MCP-PMT for Cherenkov applications

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The TORCH PMT:A close packing, multi-anode, long life MCP-PMT for Cherenkov applications

James Milnes

Workshop on picosecond photon sensors for physics and medical applications, Clermont Ferrand 12th March 2014

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Photek MCP-PMTs• Photek currently manufacture

the fastest PMTs in the world in “analogue mode”:– Whole pulse is captured by an

oscilloscope or digitiser– Applications often “single-shot,

high intensity”, e.g. Fusion Research

– We have several detectors on the diagnostics at the National Ignition Facility


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Photek MCP-PMTs• MCP-PMTs are also the leading detector for

time-resolved photon counting• Jitter in photon arrival measurements ~ 30

ps FWHM– Significantly better for multi-photon events

• Excellent fit for Cherenkov-based particle detection

• Drawbacks:– Detector Lifetime– Most models are round, single anode and

not close-packing


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The TORCH PMT


• In November 2012 Photek started the 3-year development of the TORCH (Timing Of internally Reflected CHerenkov photons) PMT

• A collaboration with CERN and the Universities of Oxford and Bristol for the LHCb upgrade– See talk by Maarten Van Dijk, Thursday 14.50

• Technical aims:– A lifetime of 5 C/cm2 of accumulated anode charge or better– A multi-anode readout of 8 x 128 pixels– Close packing on two apposing sides with a fill factor of 88% or better

• 53 mm working width within a 60 mm envelope

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The TORCH PMT

• Three main aims:1. Lifetime

2. High granularity multi-anode

3. Square


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1. MCP-PMT Lifetime• Standard MCP detectors suffer from sensitivity loss after prolonged

exposure:– An MCP has a very large surface area– Prolonged electron bombardment of this surface releases material that

is ionised– These ions are drawn back to the photocathode and reduce sensitivity

• Previous solutions have involved barrier films to prevent the ions reaching the photocathode– Limited success– Lowers MCP efficiency and overall sensitivity


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1. MCP-PMT Lifetime• Recent technology of ALD (Atomic Layer Deposition) coating on MCP has significantly

reduced out-gassing• Two PMT samples produced in 2011: Double-MCP 10 mm diameter working area

– One with coated MCPs, One control with standard MCPs

• Independently verified by Photek and others: Britting et al (PhotoDet 2012), Conneely et al (VCI 2013)


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1. MCP-PMT Lifetime

300.0n 400.0n 500.0n 600.0n 700.0n 800.0n 900.0n0.0

10.0m

20.0m

30.0m

40.0m

50.0m

60.0m ALD Coated MCP-PMT Accumulated Anode Charge: 0 C/cm2

0.38 C/cm2

0.71 C/cm2

1.13 C/cm2

1.95 C/cm2

2.49 C/cm2

3.18 C/cm2

3.71 C/cm2

5.11 C/cm2

Pho

tocu

rren

t (A

/W)

Wavelength (m)300.0n 400.0n 500.0n 600.0n 700.0n 800.0n 900.0n

0.0

10.0m

20.0m

30.0m

40.0m

50.0m

60.0m Uncoated MCP-PMT Accumulated Anode Charge: 0 C/cm2

0.13 C/cm2

0.17 C/cm2

0.20 C/cm2

0.25 C/cm2

0.28 C/cm2

0.30 C/cm2

0.32 C/cm2

0.36 C/cm2

Pho

tocu

rren

t (A

/W)

Wavelength (m)

• ALD coating results in no detectable sensitivity loss after > 5 C/cm2

• Some gain reduction• 6 test devices produced, 2 successfully

life tested at Photek, 1 currently being tested at CERN

-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

105

106

Gai

n

Integrated Anode Charge (C/cm2)

B5130419Volts per MCP:

600 V 550 V 500 V

G2130614Volts per MCP:

650 V 600 V 550 V


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1. MCP-PMT Lifetime• 1st year objective: produce 5

long-life MCP-PMTs– 1st build cycle produced 6

double-MCP devices plus 1 control

– ALD also gives major gain enhancement

– A 2nd build cycle will attempt to produce a photon counting device with 1 MCP

800 1000 1200 1400 1600 1800 2000102

103

104

105

106

107

Gai

n

Voltage across MCP pair (V)

G1130614 (modified scrub) G2130614 (modified scrub) G1130510 G2130510 B1130419 B4130419 (control) B5130419


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1. MCP-PMT Lifetime• In other respects, coated MCPs behave

as normal• Jitter measurement made with 40 ps

laser source

105 106 107 108

Voltages: 200 600 600 1000 200 650 650 1000 200 700 700 1000 200 750 750 1000

PMT225 G1130510PHD

Cou

nts

(nor

mal

ised

)

Gain0.0 2.0n 4.0n 6.0n 8.0n 10.0n

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

PMT225 G1130510200 750 750 1000LPG-1 @ 10 KHz6 dB AttenuatorAveraged 16 times

Vol

tage

(V)

Time (s)


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1. MCP-PMT Lifetime• At the RICH conference in Japan 2013 Albert Lehmann observed

substantial gain non-uniformity with ALD coated MCPs• We tried to repeat this observation but could not detect anything

significant

This region is due to an artefact in our scanning software

This region shows the gain suppression after the life test


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2. High granularity multi-anode• Traditional multi-anode manufacturing uses multiple

pins brazed through a solid ceramic• Prone to leaking, also unrealistic for a 128 x 8 array!

• Our aim is to use multilayer ceramic with filled vias

• Much smaller pad size allows for finer pitch

• The pads on this design are 0.75 mm wide on a 0.88 mm pitch

Vacuum side Air side


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2. High granularity multi-anode

• Contact made to anodes by Anisotropic Conductive Film (ACF)– ACF are filled with conductive

particles which provides electrical interconnection between pads through the film thickness (z-direction)

– The conductive particles are distributed far apart thus not electrically conductive in the plane direction (x & y) of the film

– PCB could contain front-end electronics and/or connectors

Detector

ACF

PCB

x

yz

ACF is insulating in x and y but conducting in z


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2. High granularity multi-anode - readout• NINO ASIC• 32 channel differential amplifier

/discriminator developed at CERN • 10 ps RMS jitter on the leading

edge• >>10 MHz maximum rate• The time-over-threshold technique

uses the discriminator output pulse width to determine the event charge

• High Performance Time-to-Digital Convertor (HPTDC)

• A programmable TDC developed for ALICE time-of-flight RPCs at the LHC

• Two modes of 100 ps LSB resolution with 32 channels, or 24.4 ps LSB resolution with 8 channels

• Default maximum rate is 2.5 MHz per channel, can be increased beyond 10 MHz using higher logic clock


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2. High granularity multi-anode• Using a method of charge

sharing between pads, we can reduce the channel count and the required granularity of the multi-anode structure

• The plot shows the simulated position resolution of a parallel readout, charge sharing detector (using the NINO and HPTDC as readout electronics) in the fine direction of the required 8 × 64 pad layout but aiming for 8 × 128 resolution

• The position resolution strongly depends on the NINO threshold and detector gain, with this plot showing a gain of 1 × 106 or greater being required to achieve the desired resolution


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3. Square Tube Development• Square tube manufacturing is new to Photek• Currently developing methods of

– Square body brazing– Square MCP locating– Square photocathode sealing– Square anode sealing

• Current status:– Producing leak-tight square test cells


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3. Square Tube Development – Anode Seal• Traditional method of sealing

anode – welding – is unusable due to close packing requirements

• We are experimenting with – Indium seal– Brazing– Fritting

2 inch square body with solid ceramic anode indium sealed

Indium seal


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Summary• TORCH PMT in development at Photek• 3 year development aims to finish in November 2015• 1st year task complete: To produce long-life demonstrators• 2nd year task on-going: To produce high-granularity multi-anode

demonstrator• Final year task: Fully functioning detector


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Thank you for listening


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The TORCH PMT: A close packing, multi-anode, long life MCP-PMT for Cherenkov applications

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