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Using Large Area Microchannel Plate Photodetectors in the Next Generation Water Cherenkov Neutrino Detectors
Available online at www.sciencedirect.com
Nuclear Physics B (Proc. Suppl.) 229–232 (2012) 525 www.elsevier.com/locate/npbps
Using Large Area Microchannel Plate Photodetectors in the Next Generation Water Cherenkov Neutrino Detectors M.C. Sancheza,b , M. Wetsteinb,c , for the LAPPD Collaboration a Department
of Physics and Astronomy, Iowa State University, Ames, Iowa 50011 USA National Laboratory, Argonne, Illinois 60439, USA c Enrico Fermi Institute, University of Chicago, Chicago, IL 60637, USA b Argonne
Abstract The next generation of neutrino experiments will require massive water Cherenkov detectors to reach the sensitivity needed to measure CP violation in the lepton sector and the neutrino mass hierarchy. The Large Area Picosecond Photodetector Development (LAPPD) Collaboration is developing new methods to fabricate a 20 cm2 thin planar microchannel plate photo-multiplier tube (MCP) at a cost comparable to those of traditional photomultiplier tubes (PMT). The application of these novel devices to large water Cherenkov detectors could significantly enhance background rejection and vertex resolution in these detectors by improving spatial and timing information. We present details of the MCP fabrication method, and preliminary results from testing and characterization facilities at Argonne National Laboratory. The application of these devices to neutrino detectors is also discussed. Keywords: Neutrino Interactions, Design of Experiments, Water Cherenkov
In the past the neutrino experiments have relied on traditional PMTs as photosensors in large Water Cherenkov detectors. The next generation of experiments will require yet larger detectors where the cost of PMTs has a high impact in the feasibility of these projects. One possible candidate to replace PMTs are microchannel plate photomultiplier tubes. These devices are arrays of small pores acting as electron multipliers and oriented in parallel to each other. Typical channel diameters are 10-100 μm and length to diameter ratios between 40 and 100. The simpler planar construction lends itself to large-area flat detectors. Conventional fabrication of microchannel plates is expensive and requires a long conditioning process to achieve the right combination of resistance and secondary electron emission characteristics. The LAPPD collaboration is working on applying advances in material science and nanotechnology to enable new fabrication methods that would result in large area and fast photosensors using MCPs. Starting with a porous, insulating substrate with the appropriate channel structure, 0920-5632/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2012.09.162
the use of batch processes such as Atomic Layer Deposition (ALD) allow resistive and emissive coatings to be applied uniformly to large surface areas in bulk and with potential for significant cost reduction. Thermal evaporation or sputtering techniques are then used to deposit a conductive coating on each side of the plate. The issue of large-area photocathodes is also being explored. In an electron neutrino search, the main source of background is the neutral current interactions of neutrinos where a π0 is produced. Large-area coverage and faster timing by MCPs could improve tracking and vertex resolution with the goal of better suppressing the π0 background. The uncertainty in rise time increases with the size of the detector. However for a given detector size the rise time stays constant and the spread becomes smaller if larger photodetector coverage is considered. A combined improvement of photodetector coverage (for reduced uncertainty in the rise time) and faster timing (to better sample the rise time) opens the door to a more extensive use of timing information in Water Cherenkov detectors.
Nuclear Physics B (Proc. Suppl.) 229–232 (2012) 525 www.elsevier.com/locate/npbps
Using Large Area Microchannel Plate Photodetectors in the Next Generation Water Cherenkov Neutrino Detectors M.C. Sancheza,b , M. Wetsteinb,c , for the LAPPD Collaboration a Department
of Physics and Astronomy, Iowa State University, Ames, Iowa 50011 USA National Laboratory, Argonne, Illinois 60439, USA c Enrico Fermi Institute, University of Chicago, Chicago, IL 60637, USA b Argonne
Abstract The next generation of neutrino experiments will require massive water Cherenkov detectors to reach the sensitivity needed to measure CP violation in the lepton sector and the neutrino mass hierarchy. The Large Area Picosecond Photodetector Development (LAPPD) Collaboration is developing new methods to fabricate a 20 cm2 thin planar microchannel plate photo-multiplier tube (MCP) at a cost comparable to those of traditional photomultiplier tubes (PMT). The application of these novel devices to large water Cherenkov detectors could significantly enhance background rejection and vertex resolution in these detectors by improving spatial and timing information. We present details of the MCP fabrication method, and preliminary results from testing and characterization facilities at Argonne National Laboratory. The application of these devices to neutrino detectors is also discussed. Keywords: Neutrino Interactions, Design of Experiments, Water Cherenkov
In the past the neutrino experiments have relied on traditional PMTs as photosensors in large Water Cherenkov detectors. The next generation of experiments will require yet larger detectors where the cost of PMTs has a high impact in the feasibility of these projects. One possible candidate to replace PMTs are microchannel plate photomultiplier tubes. These devices are arrays of small pores acting as electron multipliers and oriented in parallel to each other. Typical channel diameters are 10-100 μm and length to diameter ratios between 40 and 100. The simpler planar construction lends itself to large-area flat detectors. Conventional fabrication of microchannel plates is expensive and requires a long conditioning process to achieve the right combination of resistance and secondary electron emission characteristics. The LAPPD collaboration is working on applying advances in material science and nanotechnology to enable new fabrication methods that would result in large area and fast photosensors using MCPs. Starting with a porous, insulating substrate with the appropriate channel structure, 0920-5632/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2012.09.162
the use of batch processes such as Atomic Layer Deposition (ALD) allow resistive and emissive coatings to be applied uniformly to large surface areas in bulk and with potential for significant cost reduction. Thermal evaporation or sputtering techniques are then used to deposit a conductive coating on each side of the plate. The issue of large-area photocathodes is also being explored. In an electron neutrino search, the main source of background is the neutral current interactions of neutrinos where a π0 is produced. Large-area coverage and faster timing by MCPs could improve tracking and vertex resolution with the goal of better suppressing the π0 background. The uncertainty in rise time increases with the size of the detector. However for a given detector size the rise time stays constant and the spread becomes smaller if larger photodetector coverage is considered. A combined improvement of photodetector coverage (for reduced uncertainty in the rise time) and faster timing (to better sample the rise time) opens the door to a more extensive use of timing information in Water Cherenkov detectors.