The LAPPD is a 400 cm^2 microchannel plate photomultiplier with a timing resolution better than 100 pS. It has sensitivity to single photoelectrons with a gain of ~7E6. It incorporates a bi-alkali Na2KSb photocathode, with a peak sensitivity near 360 nm. Photocathodes with quantum efficiencies as high as 30% have been fabricated. The anode has a parallel stripline configuration, with a position resolution of ~4mm or better.
The large area makes the LAPPD suitable for viewing large area scintillator radiation detectors. The high speed response makes it useful for applications such as neutron detectors (i.e. Weinfurther et al., 2018), or Cerenkov light detectors for high energy physics applications. Two LAPPDs were recently used as a telescope in a 150 MeV cancer therapy proton beam, in a project designed to verify beam targeting.
LAPPDs are manufactured with a borosilicate glass envelope, and a fused silica window. The microchannel plates are fabricated using a glass substrate, with 20 micron pores. Thin films are applied to the substrate with the Atomic Layer Deposition technique. These films impart the resistive and emissive qualities needed for charge multiplication within the microchannels. Recently, improvements in the deposition method for an MgO secondary electron emission film have provided a breakthrough in gain, as the MgO retains a high gain throughout the manufacturing process of the LAPPD.
Recent measurements of gain, timing, position and quantum efficiency will be shown, and applications discussed.
Microchannel plates have been made by combining glass capillary substrates with thin films. The films impart the resistance and secondary electron emission (SEE) properties of the MCP. This approach permits separate choices for the type of glass, the MCP resistance and the SEE material. For example, the glass may be chosen to provide mechanical strength, a high open area ratio, or a low potassium-40 concentration to minimize dark rates. The resistive film composition may be tuned to provide the desired resistance, depending on the power budget and anticipated count rate. Finally, the SEE material may be chosen by balancing requirements for gain, long term stability of gain with extracted charge, and tolerance to air exposure.
Microchannel plates have been fabricated by Incom Inc., in collaboration with Argonne National Laboratory and UC Berkeley. Glass substrates with microchannel diameters of 10 and 20 microns have been used, typically with a length to diameter ratio of 60:1. Thin films for resistance and SEE are applied using Atomic Layer Deposition (ALD). The ALD technique provides a film with uniform thickness throughout the high aspect ratio microchannels. MCPs have been made in sizes up to 8”x8”. This three-component method for manufacturing MCPs also makes non-planar, curved MCPs possible.
Life testing results will be presented for 10 and 20 micron, 60:1 l/d ratio MCPs, with an aluminum oxide SEE film and two types of glass substrates. Results will include measurements of resistance, dark count rates, gain, and pulse height distributions as a function of extracted charge.
Atomic layer deposition (ALD) has enabled the development of a new technology for fabricating microchannel plates (MCPs) with improved performance that offer transformative benefits to a wide variety of applications. Incom uses a “hollow-core” process for fabricating glass capillary array (GCA) plates consisting of millions of micrometer-sized glass microchannels fused together in a regular pattern. The resistive and secondary electron emissive (SEE) functions necessary for electron amplification are applied to the GCA microchannels by ALD, which – in contrast to conventional MCP manufacturing– enables independent tuning of both resistance and SEE to maximize and customize MCP performance.
Incom is currently developing MCPs that operate at cryogenic temperatures and across wide temperature ranges. The resistive layers in both, conventional and ALD-MCPs, exhibit semiconductor-like behavior and therefore a negative thermal coefficient of resistance (TCR): when the MCP is cooled, the resistance increases, and when heated, the resistance drops. Consequently, the resistance of each MCP must be tailored for the intended operating temperature. This sensitivity to temperature changes presents a challenge for many terrestrial and space based applications.
The resistivity of the ALD-nanocomposite material can be tuned over a wide range. The material’s (thermo-) electrical properties depend on film thickness, composition, nanostructure, and the chemical nature of the dielectric and metal components. We show how the structure-property relationships developed in this work can be used to design MCPs that operate reliably at cryogenic temperatures. We also present data on how the resistive material’s TCR characteristics can be improved to enable MCPs operating across wider temperature ranges than currently possible.
The increasing availability of small satellites such as CubeSats have improved low cost access to space. New scientific measurements may be made, and new concepts may be tested for larger scale missions in the future. Particle detection instruments in conventional size spacecraft have to meet significant constraints on mass, power and volume. These constraints are more substantial in the CubeSat platform. Microchannel plate (MCP) electron multipliers are frequently used in particle detection instruments because of their high gain, low mass, and thin planar configuration. However, non-planar MCPs can be used to improve instrument performance and make better use of available volume by adopting a shape that is compatible with the natural instrument geometry. Non-planar MCPs have been made in this work using a novel method, in which a glass microchannel substrate is coated with thin films that provide the necessary resistive and secondary electron emissive properties. The glass substrates were first slumped at a high temperature to a mandrel of the desired shape, after which the thin films were applied. The MCPs were cylindrically curved, with radii of curvature of 75 mm and 20 mm, and with angular spans of 90 degrees and 180 degrees respectively. The azimuthal gain and resistance uniformity was measured and will be presented.
Bundles of hollow glass capillaries can be tapered to produce quasi-focusing x-ray optics. These optics are known
as Kumakhov lenses. These optics are interesting for lab-based sources because they can be used to collimate
and concentrate x-rays originating from a point, such as a laser focus or an electron-beam focus in a microtube.
We report pilot production and advanced development performance results achieved for Large Area Picosecond
Photodetectors (LAPPD). The LAPPD is a microchannel plate (MCP) based photodetector, capable of imaging with
single-photon sensitivity at high spatial and temporal resolutions in a hermetic package with an active area of 400 square
centimeters. In December 2015, Incom Inc. completed installation of equipment and facilities for demonstration of
early stage pilot production of LAPPD. Initial fabrication trials commenced in January 2016. The “baseline” LAPPD
employs an all-glass hermetic package with top and bottom plates and sidewalls made of borosilicate float glass. Signals
are generated by a bi-alkali Na2KSb photocathode and amplified with a stacked chevron pair of “next generation” MCPs
produced by applying resistive and emissive atomic layer deposition coatings to borosilicate glass capillary array (GCA)
substrates. Signals are collected on RF strip-line anodes applied to the bottom plates which exit the detector via pinfree
hermetic seals under the side walls. Prior tests show that LAPPDs have electron gains greater than 107, submillimeter
space resolution for large pulses and several mm for single photons, time resolutions of 50 picoseconds for
single photons, predicted resolution of less than 5 picoseconds for large pulses, high stability versus charge extraction,
and good uniformity. LAPPD performance results for product produced during the first half of 2016 will be reviewed.
Recent advances in the development of LAPPD will also be reviewed, as the baseline design is adapted to meet the
requirements for a wide range of emerging application. These include a novel ceramic package design, ALD coated
MCPs optimized to have a low temperature coefficient of resistance (TCR) and further advances to adapt the LAPPD
for cryogenic applications using Liquid Argon (LAr). These developments will meet the needs for DOE-supported RD
for the Deep Underground Neutrino Experiment (DUNE), nuclear physics applications such as EIC, medical, homeland
security and astronomical applications for direct and indirect photon detection.
Very large (20 cm × 20 cm) flat panel phototubes are being developed which employ novel microchannel plates (MCPs). The MCPs are manufactured using borosilicate microcapillary arrays which are functionalized by the application of resistive and secondary emissive layers using atomic layer deposition (ALD). This allows the operational parameters to be set by tailoring sequential ALD deposition processes. The borosilicate substrates are robust, including the ability to be produced in large formats (20 cm square). ALD MCPs have performance characteristics (gain, pulse amplitude distributions, and imaging) that are equivalent or better than conventional MCPs. They have low intrinsic background (0.045 events cm-2 sec-1)., high open area ratios (74% for the latest generation of borosilicate substrates), and stable gain during >7 C cm-2 charge extraction after preconditioning (vacuum bake and burn-in). The tube assemblies use a pair of 20 cm × 20 cm ALD MCPs comprised of a borosilicate entrance window, a proximity focused bialkali photocathode, and a strip-line readout anode. The second generation design employs an all glass body with a hot indium seal and a transfer photocathode. We have achieved >20% quantum efficiency and good gain uniformity over the 400 cm2 field of view, spatial resolution of <1 cm and obtained event timing accuracy of close to 100 ps FWHM.
A new spectrometer design that will result in a highly efficient, easy to handle, low-cost, high-resolution spectroscopy system with excellent background suppression is being developed for the NSLS-II Inner-Shell Spectroscopy beamline. This system utilizes non-diffractive optics comprised of fused and directed glass capillary tubes that will be used to collect and pre-collimate fluorescence photons. There are several advantages enabled by this design; a large energy range is accessible without modifying the s-stem, a large collection angle is achieved per detection unit: 4-5% of the full solid angle, easy integration in complex and harsh environments is enabled due to the use of a pre-collimation system as a secondary source for the spectrometer, and background from a complex sample environment can be easily and efficiently suppressed.
The polycapillary X-ray focusing optics segment of this application has been under development. This includes improvement in manufacturing methods of polycapillary structure for x-ray optics, forming the polycapillary structure to produce X-ray optics to achieve the required solid angle collection and transmission efficiency, and measurement of X-ray focusing properties of the optics using an X-ray source. Two promising advances are large open area ratios of 80% or more, and the possibility of adding coatings in the capillaries using Atomic Layer Deposition techniques to improve reflection efficiency.
Borosilicate microcapillary arrays have been functionalized by Atomic Layer Deposition (ALD) of resistive and secondary emissive layers to produce robust microchannel plates (MCPs) with improved performance characteristics over traditional MCPs. These techniques produce MCP’s with enhanced stability and lifetime, low background rates, and low levels of adsorbed gas. Using ALD to functionalize the substrate decouples the two and provides the opportunity to explore many new materials. The borosilicate substrates have many advantages over traditional lead glass MCPs, including the ability to be fabricated in large areas (currently at 400 cm2).