OPTICAL MODULE OF THE BAIKAL

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OPTICAL MODULE OF THE BAIKAL EXPERIMENT
V.Aynutdinov INR RAS 2-nd VLV?T 10 November 2005
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Outline

• Phototube Quasar-370
• Design of optical module
• Basic OM parameters
• Long term operation underwater
• Outlook

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Phototube
Large-area PMT for neutrino telescopes
Cluster of small PMT ?
Classical PMT
Hybrid PMT
PHILIPS for DUMAND project XP2600 XP2600 was a
prototype for Baikal PMT Quasar-370 Quasar-370
was specially designed for Baikal
experiment (L.B.Besrukov, B.K.Lubsandorzhiev) and
produced at Novosibirsk factory
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Quasar-370 design

• Hybrid scheme
• Large hemispherical
• preamplifier photocathode
• K2CsSb 25 kV
• ? 370 mm
• Scintillator
• Y2SiO5
• Conventional PMT
• K2CsSb 13-stage
• ? 25 mm

scintillator
Conventional PMT UGON
1 photoelectron at large photocathode
2030 photoelectrons at small PMT
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Phototube timing parameters

• Transit time difference
• Scintillator decay time
• Little PMT time resolution

nonspherical (mushroom) form of photocathode
Transit time difference lt 2 ns
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Phototube time parameters
Luminescent screen pulverized phosphor Y2SiO5
Block diagram of a double threshold
discriminator (first PE from small PMT
detection) D1 timing discriminator (0.25
q1) D2 - strobe discriminator (0.3 Q1)
Scintillator time distribution
? 40 ns
?/G lt 2 ns
2030
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Phototube time parameters
1. Preamplifier photocathode transit time
differences ?t 1.5 ns 2.
Scintillator decay time ? /G 1.5 2 ns 3.
Small PMT SPE time resolution ?t 2 ns
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Phototube amplitude parameters
Single PE resolution SPR 70 FWHM
Peak-to-valley ratio P/V 2.5
G25
Small PMT M 107 for 2 kV P/V
1.21.5 Linearity up to 150 mA
Quasar-370 charge distribution for multi PE
events
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Optical module
Transparent jelley
LED
2 kV supply
25 kV supply
DA Amplifier
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Optical contact
Glyzerine refraction index 1.47 Semicosil
refraction index 1.40
Transmission curves of the EKRAN spheres
(S49-1), the VITROVEX spheres (Rasotherm) SEMICOSI
L jelley and glycerine
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Optical module
LED
Relative amplitude
Test facility for studies of OM response to a
plane wave S(?)
Cos(?)
Angular sensitivity of the Baikal OM
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Front-end electronics
Two OM are switched in coincidence and define a
channel
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Determination of the registration probability of
vertical muons as a function of their passing
distance to the OM
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OM effective volume and area for cascade and muon
detection
(Baikal water)
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Sedimentation
Trigger rates for 4 upward channels hit (up) and
4 downward channels hit (down) 1993
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Stability photomultipliers, FE electronics, etc
Channel multiplicity distributions across the
year April 1998 February 1999
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Photocathode sensitivity
Photocathode sensitivity estimation was made on
the basis of confrontation of experimental and
simulation data amplitude spectrum and muon
detection efficiency systematic errors 20.
2-nd string permanently operated since
1998 Channels 13, 14, 15, 16, 17, 18, 23
Time dependences of PMT photocathode
sensitivity. Each point corresponds to 2 OM
switched in coincidence.
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Reliability

• - 36 OM
• - 72 OM
• - 96 OM
• - 144 OM
• - 144 OM
• - 192 OM
• - 192 OM
• - 192 OM
• - 192 OM
• - 192 OM
• - 192 OM
• - 192 OM
• - 228 OM

29 OM went out of operation
29/1300 2.2 year-1
(?70 - average value of PMT operation time per
year cable communications, underwater
connectors, FE electronics, etc)
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Outlook

• Optical modules designed for Baikal experiment
  are successfully
• operating since 1993
• The key component of OM hybrid PMT Quasar-370
• - large photocathode area
• - large viewing angle
• - good SPE and time resolution
• - prepulses suppression
• - insensitivity to the Earth magnetic field
• BUT long pulse duration ( scintillator time
  constant)
• Tasks
• - search the possibility to decrease hybrid
  PMT pulse duration
• - studies of another types of photomultipliers
• - studies the advantages of pulse form analysis
  for
• large volume neutrino telescopes

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• Thank You

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Quasar noise spectrum
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