Experimental set-up

Abstract Modeling of processes in the MCP PMT

Timing and Cross-Talk Properties of BURLE Multi-Channel MCP PMTsS.Korpara,b, R.Dolenecb, P.Križanc,a, R.Pestotnikb, A.Stanovnikc,a

aUniversity of Maribor, Slovenia, bJožef Stefan Institute, Ljubljana, Slovenia, cUniversity of Ljubljana, Slovenia,

#ch(rad)

Uniformity of response

For the Belle particle identification system upgrade, a proximity focusing RICH detector with aerogel as radiator is being considered. One of candidates for the detector of Cherenkov photons is a microchannel plate PMT. With its excellent timing properties, such a counter could serve in addition as a time-of-flight counter. A prototype of this novel device using BURLE 85011 64-anode, microchannel plate PMT, was tested in the test beam at KEK. Excellent performance of this counter could be demonstrated (left). In particular, a good separation of pions and protons was observed in the test beam data with a time-of-flight resolution of 35ps (right).

Motivation

We report on on-the-bench studies of the two types of BURLE multi anode micro-channel plate (MCP) PMTs, one with 64 channels and 25um pores and the other with 4 channels and 10um pores. A possible applications of this tubes are RICH and time-of-flight counters. We have investigated the timing properties of the tubes and studied various cross-talks and their influence on the timing and spatial resolution.

Present study:-measure detailed timing properties and cross-talk,-determine their influence on the position resolution and time resolution.

BURLE 85011 MCP-PMT:

- multi-anode PMT with two MCP steps

- 2x2(8x8) anode pads

- 10(25) mm pores

- bialkali photocathode

- gain ~ 0.6 x 106

- collection efficiency ~ 60%

- box dimensions ~ 71mm square

Outside dark box:

- PiLas diode laser system EIG1000D (ALS)

- 404 nm and 635 nm laser heads (ALS)

- neutral density filters (0.3%, 12.5%, 25%)

- optical fiber coupler (focusing)

- optical fiber (single mode,~4mm core)

Signal processing:

- laser rate 2kHz (~DAQ rate)

- amplifier: 350MHz (<1ns rise time)

- discriminator: leading edge, 300MHz

- TDC: 25ps LSB(s~11ps)

- QDC: dual range 800pC, 200pC

- HV 2400V

Inside dark box mounted on 3D stage:

- optical fiber coupler (expanding)

- semitransparent plate

- reference PMT (Hamamatsu H5783P)

- focusing lens (spot size s ~ 10mm)

TDC vs. ADC correlation is fitted with

and used for TDC correction

3

21

PADC

PPTDC

ADC

raw TDCTime walk correction

Comparison of the charge sharing effects for red (635 nm) and blue (405 nm) laser.

red

blue

bluered

1 2

21

= range of back-scattered photo-electrons2 x 12mm

Surface response of PMTs is fairly uniform. Multiple counting is observed at pad boundaries due to charge sharing.

Photo-electron: d

0,max~0.8 mm

t0 ~ 1.4 ns

Δt0 ~ 100 ps

e−

d0

l

Parameters used:- cathode to MCP potential difference U = 200 V- photocathode to MCP distance L = 6 mm- photoelectron initial energy E0 = 1 eV

Uniformity of timing

Charge sharing

Distributions assuming that back-scattering by angle is uniform over the solid angle.

~ 2.8ns~ 12mm

2sin21 ld sin2 01 tt

= 40ps = 37ps

= 38ps = 39ps

70%

20%

10%

Time resolution of the main peak is dominated by the photo-electron time spread (26ps rms, estimated from the model); other contributions are laser timing (15ps rms) and electronics (12ps rms).

TDC distribution has three contributions:- prompt signal ~ 70%- short delay ~ 20%- uniform distribution ~ 10%

back-scattering Timing

Backscattering: d

1,max=2L=12 mm

t1,max

~ 2.8 ns

Charge sharing

e−

d1

l

Slice of 2D distribution shows uniform response within the pads, short range cross-talk due to charge sharing and long range photoelectron backscattering cross-talk.

Distributions of hits with equal signals on both pads for the red and blue lasers. The distribution is broadened for the blue light due to larger initial photoelectron energy.

2x2 channel tube 8x8 channel tube

Time-walk corrected TDC distributions of all four channels of 2x2 MCP PMT.

amplifierORTEC

FTA820A

signal splitterpassive 3-way

discriminatorPhilips

model 806

QDCCAENV965

VME

TDCKaizu worksKC3781A

CAMAC

NIM

PCLabWindows

CVI

ALSPiLas

controller

Fraction of the signal measured on the left pad vs. light spot position while scanning over pad boundary using red and blue lasers.

Photo-electron range, projected

Photo-electron travel time