High Energy Physics Detectors and Instrumentation; A High Bandwidth LAPPD Anode
The development of large-area (m2) photodetectors with time resolutions of picoseconds (10-12 seconds) and submillimeter space resolutions would open new opportunities in many areas, including collider detectors, rare kaon experiments, and neutrino experiments in particle and nuclear physics, X-ray detection at light sources, and Time-Of -Flight Positron Emission Tomography (TOF-PET). This proposal is focused on bringing advanced RF-engineering tools and techniques to the design of very fast large-area photodetectors with picosecond-level resolution for providing better resolution in time-of-flight (TOF) systems at colliders. RF-strip-line anodes for large-area microchannel plate (MCP)-based photodetectors provide for the foundation of the proposed fast photodetectors. MCPs-based TOF detectors offer the small intrinsic spatial scale (typically pores are 10-20 microns in diameter) necessary for small fluctuations in timing due to path length variations, but, at the same time, are scalable to large areas. To cover large-areas inexpensively while preserving the time resolution method of digitizing the signal, RF transmission line anodes with bandwidths matched to the fast signals inherent in a small-pore microchannel plate were developed the Large Area Picosecond Photodetector (LAPPD) Collaboration. The LAPPD group has achieved or exceeded three out of the four parameters needed to achieve a predicted time resolution of a picosecond (ps); these three are the sampling rate, noise, and signal size. The only parameter that falls short is the analog bandwidth. Measurements of the LAPPD `frugal glass- based RF strip-line anodes show the analog bandwidth decreases from 1.6 GHz to 0.4 GHz as the anode length increases from 289 mm to 916 mm when the strip-line anodes are daisy-chained in series to cover more area with the same electronics channel count. This proposal brings to bear professional RF engineering expertise and unique custom simulation tools on the development of RF strip-line anodes for use in large-area microchannel plate photodetectors with time resolutions of picosecond or less. Specifically, a unique electromagnetic simulation code will be utilized to develop a design that is capable of an analog bandwidth of close to 6 GHz while maintaining the large area of the photodetector. Our design will suppress the inter-strip coupling and cross-talk that currently limits the analog bandwidth of the circuit and, as a result, time resolution of the photodetector. The tool we will use to accomplish the design is a finite difference time domain (FDTD) or, as some would call it, a 4-dimensional simulation code (3D plus time) which InnoSys and its Principals have spent close to 20 years to develop. The unique capabilities of our FDTD simulation code pertinent to this proposed study include that active devices, including optical or electrical sources, and multiple layer structures can also be easily included in the simulation code. Furthermore, our FDTD simulation code is equipped with features to handle arbitrary shape metals and also arrays of devices or circuits. Since the FDTD simulation can perform field, frequency, impedance, spectrum, and power analysis, we believe it is uniquely equipped to handle this proposed study and perform full analysis of the picosecond large area MCP-based photodetectors in terms of being able to theoretically optimize the design and achieve the best performance to provide guidance to the experimental work Dr. Hwu of InnoSys received a Presidential Faculty Fellow Award from the White House based on this line of work she lead before she founded InnoSys to continue her further development of this code in simulating vacuum electronic devices. and has extensive experience in providing vacuum tube designs and optoelectronic designs including, for example, high power microwave amplifiers and picosecond optical pulse generators.
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