Large Area, Low Cost PMTs Neutrinos and Arms Control Workshop Paul Hink 6 February 2004 BURLE...
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Transcript of Large Area, Low Cost PMTs Neutrinos and Arms Control Workshop Paul Hink 6 February 2004 BURLE...
Large Area, Low Cost PMTs
Neutrinos and Arms Control Workshop
Paul Hink
6 February 2004BURLE INDUSTRIESBURLE INDUSTRIES
6 Feb 2004 Neutrinos and Arms Control Workshop
BURLE INDUSTRIES Overview
BURLE INDUSTRIES, INC.Conversion TubesPower TubesReal Estate
BURLE ELECTRO-OPTICS, INC.BURLE INDUSTRIES GmbHBURLE INDUSTRIES UK LIMITEDBURLE 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, Front-end electronics
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
6 Feb 2004 Neutrinos and Arms Control Workshop
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
Sb bead
Alkali Channels
Stem
Exhaust tubulation
Bulb
Dynode Structure
Photocathode
6 Feb 2004 Neutrinos and Arms Control Workshop
Manufacturing
Discrete multiplier fabrication is labor intensive Materials and processes are critical Sealing of bulb to stem assembly is semi-
automated Multiple PMTs can be processed simultaneously
on an exhaust system Post-exhaust processing can be done in large
batches Testing is semi-automated
6 Feb 2004 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
6 Feb 2004 Neutrinos and Arms Control Workshop
MCP-PMT Operation
Faceplate
Photocathode
Dual MCP
Anode
Gain ~ 106
Photoelectron V ~ 200V
V ~ 200V
V ~ 2000V
photon
6 Feb 2004 Neutrinos and Arms Control Workshop
MCP-PMT Construction
Faceplate
Anode & Pins
Indium Seal
Dual MCP
MCP Retainer Ceramic Insulators
Cathode is processed separate from multiplier and sealed to body under vacuum
6 Feb 2004 Neutrinos and Arms Control Workshop
Transfer Cathode Manufacturing
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
6 Feb 2004 Neutrinos and Arms Control Workshop
Photo-electron bombarded electron detector
Can use Silicon detector, APD, scintillator + light detector, …
Excellent single pe resolution
Typically requires very high accelerating voltage
Hybrid Photodetectors
Faceplate
Photocathode
Electron
Detector
Photoelectron V ~ 10,000V
photon
6 Feb 2004 Neutrinos and Arms Control Workshop
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
Gas Electron Multipliers
Faceplate
Photocathode
Photoelectron
photon
6 Feb 2004 Neutrinos and Arms Control Workshop
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
6 Feb 2004 Neutrinos and Arms Control Workshop
RequirementsParameter 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
6 Feb 2004 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
6 Feb 2004 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.
6 Feb 2004 Neutrinos and Arms Control Workshop
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
6 Feb 2004 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.
6 Feb 2004 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
APDAPDFocusFocusElementElement
PhotoelectronPhotoelectron
Glass HemisphereGlass Hemisphere
TubulationTubulation
LeadsLeads
6 Feb 2004 Neutrinos and Arms Control Workshop
Example Fabrication Flow
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.
6 Feb 2004 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
6 Feb 2004 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