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  • 1
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    Accurate Cold-Test Model of Helical TWT Slow-Wave Circuits (1998)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: Recently, a method has been established to accurately calculate cold-test data for helical slow-wave structures using the three-dimensional (3-D) electromagnetic computer code, MAxwell's equations by the Finite Integration Algorithm (MAFIA). Cold-test parameters have been calculated for several helical traveLing-wave tube (TWT) slow-wave circuits possessing various support rod configurations, and results are presented here showing excellent agreement with experiment. The helical models include tape thickness, dielectric support shapes and material properties consistent with the actual circuits. The cold-test data from this helical model can be used as input into large-signal helical TWT interaction codes making It possible, for the first time, to design complete TWT via computer simulation.
    Keywords: Electronics and Electrical Engineering
    Type: IEEE Transactions on Electron Devices (ISSN 0018-9383); Volume 45; No. 4; 966-971
    Format: text
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  • 2
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    Effect of Helical Slow-Wave Circuit Variations on TWT Cold-Test Characteristics (1998)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: Recent advances in the state of the art of computer modeling offer the possibility for the first time to evaluate the effect that slow-wave structure parameter variations, such'as manufacturing tolerances, have on the cold-test characteristics of helical traveling-wave tubes (TWT's). This will enable manufacturers to determine the cost effectiveness of controlling the dimensions of the component parts of the TWT, which is almost impossible to do experimentally without building a large number of tubes and controlling several parameters simultaneously. The computer code MAxwell's equations by the Finite Integration Algorithm (MAFIA) is used in this analysis to determine the effect on dispersion and on-axis interaction impedance of several helical slow-wave circuit parameter variations, including thickness and relative dielectric constant of the support rods, tape width, and height of the metallized films deposited on the dielectric rods. Previous computer analyzes required so many approximations that accurate determinations of the effect of many relevant dimensions on tube performance were practically impossible.
    Keywords: Electronics and Electrical Engineering
    Type: IEEE Transactions on Electron Devices (ISSN 0018-9383); Volume 45; No. 4; 972-976
    Format: text
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  • 3
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    Multiplexed Readout of Thermal Bolometers with Superconducting Transition Edge Thermometers (2001)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: History shows that in astronomy, more is better. In the near future, direct detector arrays for the far-infrared and submillimeter will contain hundreds to thousands of elements. A multiplexed readout is necessary for practical implementation of such arrays, and has been developed using SQUIDs. The technology permits a 32 x 32 array of bolometers to be read out using approximately 100 wires rather than the 〉2000 needed with direct wiring. These bolometer arrays are made by micromachining techniques, using superconducting transition edge sensors as the thermistors. We describe the development of this multiplexed superconducting bolometer array architecture as a step toward bringing about the first astronomically useful arrays of this design. This technology will be used in the Submillimeter and Far Infrared Experiment (SAFIRE) instrument on Stratospheric Observatory for Infrared Astronomy (SOFIA), and is a candidate for a wide variety of other spectroscopic and photometric instruments.
    Keywords: Electronics and Electrical Engineering
    Type: Proceedings of the Twenlfth International Symposium on Space Terahertz Technology; 122-130; JPL-Publ-01-18
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  • 4
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    Performance of an X-ray Microcalorimeter with a 240 m Absorber and a 50 m TES Bilayer (2018)
    In:  Other Sources
    Details
    Publication Date: 2019-07-20
    Description: Superconducting transition-edge sensor (TES) microcalorimeters are being developed for a variety of potential astrophysics missions, including Athena. The X-ray integral field unit instrument on this mission requires close-packed pixels on a 0.25 mm pitch, and high quantum efficiency between 0.2 and 12 keV. In this work, we describe a new approach with 50 m square TESs consisting of a Mo/Au bilayer, deposited on silicon nitride membranes to provide a weak thermal conductance to a ~50 mK heat bath. Larger TESs usually have additional normal metal stripes on top of the bilayer to reduce the noise. However, we have found that excellent spectral performance can be achieved without the need for any normal metal stripes on top of the TES. A spectral performance of 1.58+/-0.12 eV at 5.9 keV has been achieved, the best resolution seen in any of our devices with this pixel size.
    Keywords: Electronics and Electrical Engineering
    Type: GSFC-E-DAA-TN68358 , GSFC-E-DAA-TN61299 , Journal of Low Temperature Physics (ISSN 0022-2291) (e-ISSN 1573-7357); 193; 3-4; 337–343
    Format: text
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  • 5
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    Traveling-Wave Tube Efficiency Enhancement (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Traveling-wave tubes (TWT's) are used to amplify microwave communication signals on virtually all NASA and commercial spacecraft. Because TWT's are a primary power user, increasing their power efficiency is important for reducing spacecraft weight and cost. NASA Glenn Research Center has played a major role in increasing TWT efficiency over the last thirty years. In particular, two types of efficiency optimization algorithms have been developed for coupled-cavity TWT's. The first is the phase-adjusted taper which was used to increase the RF power from 420 to 1000 watts and the RF efficiency from 9.6% to 22.6% for a Ka-band (29.5 GHz) TWT. This was a record efficiency at this frequency level. The second is an optimization algorithm based on simulated annealing. This improved algorithm is more general and can be used to optimize efficiency over a frequency bandwidth and to provide a robust design for very high frequency TWT's in which dimensional tolerance variations are significant.
    Keywords: Electronics and Electrical Engineering
    Type: E-17665 , 12th IEEE International Vacuum Electronics Conference; Feb 21, 2011 - Feb 24, 2011; Bangalore; India
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  • 6
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    Phonon Mechanisms for Excess Heat Capacity in Membrane Isolated Superconducting Transition Edge Sensors (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The mechanics of phonon transport in membrane-isolated superconducting transition edge sensors is discussed. Surveys of the literature on this type of sensor reveal a number of designs with excess heat capacity and a smaller subset that exhibit decoupling of the superconducting film from the underlying dielectric. A simple model is addressed in which the membrane, despite its thermal isolation, fails to fully thermalize to the temperature of the metal film heating it. A population of phonons exists which is emitted by the metal film, partially thermalizes the dielectric and is then reabsorbed in the metal film without escaping from the device structure to the thermal bath. The size of this population and its contribution to the heat capacity are estimated for several device scenarios.
    Keywords: Electronics and Electrical Engineering
    Type: GSFC.OVPR.7472.2012 , GSFC.ABS.01102.2012 , Applied Superconductivity Conference; Oct 08, 2012 - Oct 12, 2012; Portland, OR; United States
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  • 7
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    Sub-micron surface plasmon resonance sensor systems (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: A sensor for detecting the presence of a target analyte, ligand or molecule in a test fluid, comprising a light transmissive substrate on which an array of surface plasmon resonant (SPR) elements is mounted is described. A multi-channel sensor for detecting the presence of several targets with a single microchip sensor is described. A multi-channel sensor including collections of SPR elements which are commonly functionalized to one of several targets is also described. The detectors sense changes in the resonant response of the SPR elements indicative of binding with the targets.
    Keywords: Electronics and Electrical Engineering
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  • 8
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    Fabrication and Performance of Large Format Transition Edge Sensor Microcalorimeter Arrays (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-19
    Description: We have produced a variety of superconducting transition edge sensor array designs for microcalorimetric detection of x-rays. Designs include kilopixel scale arrays of relatively small sensors (~75 micron pitch) atop a thick metal heatsinking layer as well as arrays of membrane-isolated devices on 250 micron pitch and smaller arrays of devices up to 600 micron pitch. We discuss the fabrication techniques used for each type of array focusing on unique aspects where processes vary to achieve the particular designs and required device parameters. For example, we evaluate various material combinations in the production of the thick metal heatsinking, including superconducting and normal metal adhesion layers. We also evaluate the impact of added heatsinking on the membrane isolated devices as it relates to basic device parameters. Arrays can be characterized with a time division SQUID multiplexer such that greater than 10 devices from an array can be measured in the same cooldown. Device parameters can be measured simultaneously so that environmental events such as thermal drifts or changes in magnetic fields can be controlled. For some designs, we will evaluate the uniformity of parameters impacting the intrinsic performance of the microcalorimeters under bias in these arrays and assess the level of thermal crosstalk.
    Keywords: Electronics and Electrical Engineering
    Type: GSFC.ABS.01103.2012 , Applied Superconductivity Conference; Oct 08, 2012 - Oct 12, 2012; Portland, OR; United States
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  • 9
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    Compact Micromachined Bandpass Filters for Infrared Planetary Spectroscopy (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-19
    Description: The thermal instrument strawman payload of the Jupiter Europa Orbiter on the Europa Jupiter Science Mission will map out thermal anomalies, the structure, and atmospheric conditions of Europa and Jupiter within the 7-100 micron spectral range. One key requirement for the payload is that the mass cannot exceed 3.7 kg. Consequently, a new generation of light-weight miniaturized spectrometers needs to be developed. On the path toward developing these spectrometers is development of ancillary miniaturized spectroscopic components. In this paper, we present a strategy for making radiation hard and low mass FIR band pass metal mesh filters. Our strategy involves using MEMS-based fabrication techniques, which will permit the quasi-optical filter structures to be made with micron-scale precision. This will enable us to achieve tight control over both the pass band of the filter and the micromachined silicon support structure architecture, which will facilitate integration of the filters for a variety of applications.
    Keywords: Electronics and Electrical Engineering
    Type: 22nd International Symposium on Space Terahertz Technology; Apr 26, 2011 - Apr 28, 2011; Tucson, AZ; United States
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  • 10
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    Longitudinal Proximity Effects in Superconducting Transition-Edge Sensors (2009)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: We have found experimentally that the critical current of a square superconducting transition-edge sensor (TES) depends exponentially upon the side length L and the square root of the temperature T. As a consequence, the effective transition temperature T(sub c) of the TES is current-dependent and at fixed current scales as 1/L(sup 2). We also have found that the critical current can show clear Fraunhofer-like oscillations in an applied magnetic field, similar to those found in Josephson junctions. The observed behavior has a natural theoretical explanation in terms of longitudinal proximity effects if the TES is regarded as a weak link between superconducting leads. We have observed the proximity effect in these devices over extraordinarily long lengths exceeding 100 microns.
    Keywords: Electronics and Electrical Engineering
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