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|FEBRUARY 2018 FEATURE ARTICLES - THESE ARE OPEN ACCESS FOR A LIMITED TIME|
We present a field-programmable gate array (FPGA) implementation of a time-to-digital converter (TDC) based on a low-cost, low-area Spartan 6 device. The converter is based on a tapped delay line model. Several implementation details are discussed with a particular focus on critical blocks such as the input stage and thermometer-to-binary decoding techniques. We implemented a tap filtering technique to improve the differential nonlinearity (DNL) of the single delay line while keeping a good LSB value of 25.57 ps with a single-shot precision (SSP) between 0.69 - 1.46 LSB. Measured DNL and integral nonlinearity (INL) lie in the range between -0.90 + 1.23 and -0.43 ÷ 2.96 LSB, respectively. Measured DNL and INL lie in the range between -0.90 ÷ 1.23 and -0.43 ÷ 2.96 LSB, respectively. We then implemented an interpolating TDC to overcome the limitations of a single delay line in terms of linearity and measurement range. The interpolating TDC uses the sliding scale technique, where the time interval to be measured is asynchronous with respect to the FPGA clock, achieving DNL and INL in the range -0.072 ÷ 0.070 and -0.755 ÷ 0.872 LSB. SSP is in the 1.096 ÷ 2.815 range. Moreover, we present a novel comparison between the DNLs obtained with two different methods: statistical code density test and using a finely controlled delay source. Finally, we present the results of a Monte Carlo simulation used to investigate the effects of nonlinear propagation of the signal through the delay line. more...
A new probabilistic model aiming to cover all aspects of the solar energetic particle (SEP) environment required for mission specifications is presented; the solar accumulated and peak proton and heavy ion radiation environment model. This model includes an updated reference data set upon which the analysis is based, a thorough evaluation of fitting procedures for SEP fluxes, a probabilistic helium model not based on proton fluxes, an extension to heavier ions based on new analysis of the Advanced Composition Explorer/solar isotope spectrometer data set, and a careful extrapolation of all output spectra to cover energies from 0.1 MeV/nuc to 1 GeV/nuc. Also included in this paper are derivations of spectra for rare solar particle events, which would occur at a given mean frequency and a new description for implementing the model to make it accessible to the public through systems, such as SPace ENVironment Information System or OMERE. more...
Simulation Model of Transmitted X-Rays in Polycapillary Optics for TES Microcalorimeter EDS System on Scanning Transmission Electron Microscopeby Akira Takano, Keisuke Maehata, Naoko Iyomoto, Toru Hara, Kazuhisa Mitsuda, Noriko Yamasaki, and Keiichi Tanaka
We created a simple simulation model of transmitted X-rays in polycapillary optics for improved understanding of the transmission characteristics and to aid in the design of the geometrical parameters of the polycapillary optics. New polycapillary optics for a 64-pixel array transition-edge sensor (TES) microcalorimeter energy-dispersive spectrometer system that was installed in a scanning transmission electron microscope (STEM) were developed using the simulation model. The characteristic X-rays that are emitted from the STEM specimen were transmitted and focused on the pixel array TES microcalorimeter by the polycapillary optics. The experimental X-ray transmission characteristics of the manufactured polycapillary optics agreed with the simulated results. more...
A PUBLICATION OF THE IEEE NUCLEAR AND PLASMA SCIENCES SOCIETY
|FEBRUARY 2018 | VOLUME 65 | NUMBER 2 | IETNAE | (SSN 0018-9499)|
NUCLEAR POWER INSTRUMENTATION AND CONTROL
Data-Driven Subspace Predictive Control of a Nuclear Reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . V. Vajpayee, S. Mukhopadhyay, and A. P. Tiwari
Design and Characterization of a Low-Cost FPGA-Based TDC . . . . . . . . . . . . . . . . . . . . . . . A. Tontini, L. Gasparini, L. Pancheri, and R. Passerone
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