Large Area, Low Cost PMTs Neutrinos and Arms Control Workshop Paul Hink 6 February 2004 BURLE INDUSTRIES

6 Feb 2004Neutrinos and Arms Control Workshop 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 2004Neutrinos 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 2004Neutrinos 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 2004Neutrinos 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 2004Neutrinos 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 2004Neutrinos and Arms Control Workshop MCP-PMT Operation Faceplate Photocathode Dual MCP Anode Gain ~ 10 6 Photoelectron  V ~ 200V  V ~ 2000V photon

6 Feb 2004Neutrinos 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 2004Neutrinos 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 2004Neutrinos 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 2004Neutrinos 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 2004Neutrinos 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 2004Neutrinos and Arms Control Workshop Requirements ParameterValueUnitsComments Spectral Response nmResponse < 300nm not very useful due to attenuation length in water Cathode QE at 390nm20%Desire as high as possible Collection Efficiency75%Desire as high as possible Gain1 x 10 7 Dark Counts3 - 4kcps Transit Time Spread (FWHM)5.5nsDesire 3 ns Photocathode area, head-on1700cm 2 Sized to give lowest cost per unit area High Voltage+2000VCould be higher Pressure8atmTotal outside – inside pressure difference. Could use acrylic pressure vessel if needed. PackagingVDN + HV and signal cables, hermetically sealed Chemical resistancePure H 2 O

6 Feb 2004Neutrinos and Arms Control Workshop Arms Control PMT Assumptions  4km of water (~400 atmospheres)  40% coverage on a 10Megaton detector, or ~8 x 10 4 m 2 of photocathode area  Requires ~ 400,000 PMTs having 2000 cm 2 of projected area (~20” diameter)  Production of 40M PMTs for 1 array, $6B at $200 per PMT ($0.10 / cm 2 )  Maintain performance of existing PMTs, including QE, Dark Counts, and Timing

6 Feb 2004Neutrinos 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 H 2 O, 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 2004Neutrinos 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 2004Neutrinos 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 2004Neutrinos 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 APD FocusElement Photoelectron Glass Hemisphere Tubulation Leads

6 Feb 2004Neutrinos 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 2004Neutrinos 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 2004Neutrinos 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 2004Neutrinos 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 2004Neutrinos and Arms Control Workshop Conclusions  PMTs for < $0.10/cm 2 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