Transcript Characterization of 18mm round and 50mm square MCP-PMTs

Large Area, Low Cost PMTs
Neutrinos and Arms Control Workshop
Paul Hink
6 February 2004
BURLE INDUSTRIES
BURLE INDUSTRIES Overview
BURLE INDUSTRIES, INC.
Conversion Tubes
Power Tubes
Real Estate
BURLE ELECTRO-OPTICS, INC.
BURLE INDUSTRIES GmbH
BURLE INDUSTRIES UK LIMITED
BURLE deMexico
6 Feb 2004
Neutrinos and Arms Control Workshop
Core Competencies
 Conversion Tubes,
Lancaster PA
 Conventional PMT design
and fabrication
 Photocathode processing
 Image tube design and
fabrication
 PMT packaging
 Electronics: VDN,
Miniature HVPS, Frontend electronics
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 Power Tubes, Lancaster PA
 Design and fabrication of
vacuum tubes for power
generation and switching
 Plating and environmental
testing
 Ceramic-to-Metal joining
techniques
 BEO, Sturbridge MA
 Microchannel plates
 Channel multipliers
 Fiber optics
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PMT Construction/Processing
 Electron multiplier is
supported by bulb spacers
and leads to the stem
 Envelope is evacuated
through an exhaust tubulation
 Cathode processed in-situ
with Sb and alkali dispensers
 Tip-off of tubulation using
flame or electric oven
Photocathode
Bulb
Sb bead
Dynode
Structure
Alkali
Channels
Stem
Exhaust tubulation
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Manufacturing
 Discrete multiplier fabrication is labor intensive
 Materials and processes are critical
 Sealing of bulb to stem assembly is semiautomated
 Multiple PMTs can be processed simultaneously
on an exhaust system
 Post-exhaust processing can be done in large
batches
 Testing is semi-automated
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Neutrinos and Arms Control Workshop
Planacon™ MCP-PMTs
 Two inch square flat PMT
with dual MCP multiplier.
 Anodes, 2x2 and 8x8
configurations. Additional
configurations available.
 Bi-alkali cathode on
quartz faceplate or
cryogenic bi-alkali.
 Intrinsically low
radioactivity
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Neutrinos and Arms Control Workshop
MCP-PMT Operation
photon
Faceplate
Photocathode
Photoelectron
Dual MCP
DV ~ 2000V
Gain ~ 106
Anode
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DV ~ 200V
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DV ~ 200V
MCP-PMT Construction
Indium Seal
Faceplate
MCP Retainer
Dual MCP
Ceramic Insulators
Anode & Pins
Cathode is processed separate from multiplier and sealed to
body under vacuum
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Neutrinos and Arms Control Workshop
Transfer Cathode Manufacturing
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Large UHV chambers required
Parts and materials preparation critical
Movement of parts inside vacuum chamber(s) difficult
Only a few PMTs can be processed simultaneously
Indium sealing is reliable but expensive material costs.
 Alternative sealing techniques available.
 Can become highly automated, but large capital
investments required
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Neutrinos and Arms Control Workshop
Hybrid Photodetectors
 Photo-electron bombarded
electron detector
 Can use Silicon detector,
APD, scintillator + light
Photoelectron
detector, …
 Excellent single pe
resolution
 Typically requires very
high accelerating voltage
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photon
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Faceplate
Photocathode
DV ~ 10,000V
Electron
Detector
Gas Electron Multipliers
 Vacuum not required
 Low cost envelope
 Excellent single pe
resolution
 Degradation of
photocathode/gas in sealed
devices needs to be
addressed
 Solid cathode must be
made under vacuum
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photon
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Faceplate
Photocathode
Photoelectron
Large Area PMT Program
 Selected for a DOE SBIR to develop a large area
PMT
 Phase I began in July 2003 and has proceeded well
 Focus is to design a low-cost bulb that can be
manufactured using automated techniques and
allows the use of simple electron-optics
 Also investigating low-cost processing techniques
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Requirements
Parameter
Value
Units
Comments
Spectral Response
300 - 650
nm
Response < 300nm not very useful due to
attenuation length in water
Cathode QE at 390nm
20
%
Desire as high as possible
Collection Efficiency
75
%
Desire as high as possible
Gain
1 x 107
Dark Counts
3-4
kcps
Transit Time Spread (FWHM)
5.5
ns
Desire 3 ns
Photocathode area, head-on
1700
cm2
Sized to give lowest cost per unit area
High Voltage
+2000
V
Could be higher
Pressure
8
atm
Total outside – inside pressure difference. Could
use acrylic pressure vessel if needed.
Packaging
VDN + HV and signal cables, hermetically sealed
Chemical resistance
Pure H2O
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Neutrinos and Arms Control Workshop
Arms Control PMT Assumptions
 4km of water (~400 atmospheres)
 40% coverage on a 10Megaton detector, or ~8 x
104 m2 of photocathode area
 Requires ~ 400,000 PMTs having 2000 cm2 of
projected area (~20” diameter)
 Production of 40M PMTs for 1 array, $6B at $200 per
PMT ($0.10 / cm2)
 Maintain performance of existing PMTs, including
QE, Dark Counts, and Timing
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Neutrinos and Arms Control Workshop
Traditional PMT Approach
 Vacuum Envelope is critical to the performance of the
PMT
 Envelope must withstand 400 atmospheres unless a
separate pressure vessel is used, which will add cost.
 Window must be made out of low cost glass, resistant
to ultra-pure H2O, low strain (low expansion
Borosilicate)
 Remainder of the vacuum envelope can be made of
glass or appropriate metal or composite.
 Vacuum envelope requires electrical feed-throughs for
bias, signal, and processing of photocathode.
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Traditional PMT Sealing
 Vacuum Envelope can be sealed using a flame. However, annealing
temperatures are too high to be done with the multiplier and
cathode processing materials in the PMT.
 Vacuum envelope can be welded together if appropriate flanges
have been attached to the glass sections. Residual strain a problem.
 Low temperature glass process yields high strength bonds, but tight
flatness tolerance on seal surfaces.
 Vacuum feed-throughs must be inserted and annealed. Minimum
number of feed-throughs is desired
 Exhaust tubulation typically has some residual strain and will be a
weak point. Could use a metal tubulation
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Neutrinos and Arms Control Workshop
Multiplier Selection
 Standard discrete dynode structure is hard to automate
and labor intensive.
 Spherical bulb, while strongest, is not ideal for good
timing performance. Electron Optics design work
required
 Silicon detector or APD has the fewest feed-throughs
required
 Micro-channel plate multiplier is simple and also has
fewer feed-throughs. In high volume may approach the
cost of silicon detectors.
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Neutrinos and Arms Control Workshop
Example of Spherical PMT
 Schott produces
hemispheres of size
needed
 Sealed with low
temperature process
 18mm wall good to
>4km depth
 Silicon electron
detector preferred
Glass Hemisphere
Photoelectron
APD
Leads
Focus
Element
Tubulation
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Example Fabrication Flow
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Glass hemispheres are formed out of a melt
Sealing surfaces are machined to high tolerance
Feed-throughs are installed in one hemisphere
Both hemispheres are annealed
Multiplier/Detector, electron optics, and process
materials are installed on rear hemisphere
Low temperature glass-to-glass seal of two halves
Tube is exhausted and processed
Tubulation is tipped-off
PMT is aged and tested
6 Feb 2004
Neutrinos and Arms Control Workshop
Design Challenges
 High precision machining of the hemisphere
seal surfaces (few microns)
 Installation of electrical feed-throughs and
tubulation
 Annealing the rear hemisphere to remove all
strain
 Exhaust and processing of tube needs to be
automated with no handling of PMTs between
processes.
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Neutrinos and Arms Control Workshop
Feasibility of this Design
 Requires significant glass manufacturing capabilities.
At 28kg per bulb, three 1Gton arrays, and 15 years to
manufacture, ~8 large glass lines (100,000 kg/day/line)
would be required.
 Raw glass cost could be ~$15 per bulb.
 Hemispheres could be pressed/molded out of the melt
or vacuum formed out of float glass.
 Precision machining and grinding of seal surfaces
would need to be highly automated
 All basic technologies are developed, but requires
development of automated processing
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Neutrinos and Arms Control Workshop
Alternative Design
 Alternative designs could provide lower
manufacturing costs, but have some technology
developments associated with them.
 Transfer design could be lowest cost per unit,
but may have higher capital requirements.
 The pressure requirement drives all designs.
6 Feb 2004
Neutrinos and Arms Control Workshop
Conclusions
 PMTs for < $0.10/cm2 photocathode area are not
limited by existing technology
 Manufacturing and processing techniques require
significant R&D
 Can learn from picture tube and semiconductor industries
 Questions about business strategies in responding to
this opportunity.
 Partnering opportunities
 Government involvement
 Concerns about limited lifetime of project
6 Feb 2004
Neutrinos and Arms Control Workshop