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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2015

Comparison of Instantaneous Frequency Scaling from Rain Attenuation and Optical Disdrometer Measurements at K/Q bands

Rain attenuation is strongly dependent on the rain rate, but also on the rain drop size distribution (DSD). Typically, models utilize an average drop size distribution, such as those developed by Laws and Parsons, or Marshall and Palmer. However, individual rain events may possess drop size distributions which could be significantly different from the average and will impact, for example, fade mitigation techniques which utilize channel performance estimates from a signal at a different frequency. Therefore, a good understanding of the characteristics and variability of the raindrop size distribution is extremely important in predicting rain attenuation and instantaneous frequency scaling parameters on an event-toevent basis. Since June 2014, NASA Glenn Research Center (GRC) and the Politecnico di Milano (POLIMI) have measured the attenuation due to rain in Milan, Italy, on the 20/40 GHz beacon signal broadcast from the Alphasat TDP#5 Aldo Paraboni Q/V-band Payload. Concomitant with these measurements are the measurements of drop size distribution and rain rate utilizing a Thies Clima laser precipitation monitor (disdrometer). In this paper, we discuss the comparison of the predicted rain attenuation at 20 and 40 GHz derived from the drop size distribution data with the measured rain attenuation. The results are compared on statistical and real-time bases. We will investigate the performance of the rain attenuation model, instantaneous frequency scaling, and the distribution of the scaling factor. Further, seasonal rain characteristics will be analysed.

millimeter wave↗
NASA NTRS1988

Fine structure in RF spectra of lightning return stroke wave forms

The power spectra of the wide-band (10 Hz to 100 kHz) magnetic-field signals for a number of lightning return strokes measured during a thunderstorm which occurred in Lindau in August, 1984 have been calculated. The RF magnetic field data are obtained with the engineering unit of the Galileo Jupiter Probe lightning experiment. Each return stroke data stream is passed through an adaptive filter designed to whiten its spectrum. The spectra of the magnetic field data definitely show fine structure, with two or three distinct peaks in the spectra of many of the waveforms. A peak at f of about 60-70 kHz is often seen in the power spectra of the waveform time segments preceding and following the rise-to-peak amplitude of the return stroke.

Lanzerotti, L. J.↗
NASA NTRS1984

A review of ionospheric effects on Earth-space propagation

A short description is given of each ionospheric total electron content (TEC) effect upon radio waves, along with a representative value of the magnitude of each of these effects under normal ionospheric conditions. A discussion is given of the important characteristics of average ionospheric TEC behavior and the temporal and spatial variability of TEC. Radio waves undergo several effects when they pass through the Earth's ionosphere. One of the most important of these effects is a retardation, or group delay, on the modulation or information carried on the radio wave that is due to its encounter with the free, thermal electrons in the Earth's ionosphere. Other effects the ionosphere has on radio waves include: radio frequency (RF) carrier phase advance; Doppler shift of the RF carrier of the radio wave; Faraday rotation of the plane of polarization of linearly polarized waves; angular refraction or bending of the radio wave path as it travels through the ionosphere; and amplitude and phase scintillations.

Klobuchar, J. A.↗
NASA NTRS1973

Performance of an ion-cyclotron-wave plasma apparatus operated in the radiofrequency sustained mode

An experimental study has been made of an ion-cyclotron-wave apparatus operated in the RF-sustained mode, that is, a mode in which the Stix RF coil both propagates the waves and maintains the plasma. Problems associated with this method of operation are presented. Some factors that are important to the coupling of RF power are noted. In general, the wave propagation and wave damping data agree with theory. Some irregularities in wave fields are observed. Maximum ion temperature is 870 eV at a density of five times 10 to the 12th power cu cm and RF power of 90 kW. Coupling efficiency is 70 percent.

Swett, C. C.↗
DOE OSTI2025

First characterisation of the MAGO cavity, a superconducting RF detector for kHz–MHz gravitational waves

Heterodyne detection using microwave cavities is a promising method for detecting high-frequency gravitational waves (GWs) or ultralight axion dark matter. In this work, we report on studies conducted on a spherical 2-cell cavity developed by the MAGO collaboration for high-frequency GWs detection. Although fabricated around 20 years ago, the cavity had not been used since. Due to deviations from the nominal geometry, we conducted a mechanical survey and performed room-temperature plastic tuning. Measurements and simulations of the mechanical resonances and electromagnetic properties were carried out, as these are critical for estimating the cavity’s GW coupling potential. Based on these results, we plan further studies in a cryogenic environment. The cavity characterisation does not only provide valuable experience for a planned physics run but also informs the future development of improved cavity designs.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS2017

Pilot Wave Model for Impulsive Thrust from RF Test Device Measured in Vacuum

A physics model is developed in detail and its place in the taxonomy of ideas about the nature of the quantum vacuum is discussed. The experimental results from the recently completed vacuum test campaign evaluating the impulsive thrust performance of a tapered RF test article excited in the TM212 mode at 1,937 megahertz (MHz) are summarized. The empirical data from this campaign is compared to the predictions from the physics model tools. A discussion is provided to further elaborate on the possible implications of the proposed model if it is physically valid. Based on the correlation of analysis prediction with experimental data collected, it is proposed that the observed anomalous thrust forces are real, not due to experimental error, and are due to a new type of interaction with quantum vacuum fluctuations.

White, Harold↗
NASA NTRS2001

A High Efficiency, Miniaturized Ka Band Traveling Wave Tube Based on a Novel Finned Ladder RF Circuit Design

Space communications architectures are being planned to meet the high rate data distribution requirements of future NASA Enterprise missions. These will require the use of traveling wave tube amplifiers (TWTAs) to provide the high frequency, RF (radio frequency) power and efficiency needed for many of the communications links. A program addressing these requirements is currently underway at NASA Glenn Research Center (GRC) for the development of a high efficiency, 20 watt, 32 GHz TWT of reduced size and weight that is based on a novel high gain n circuit design, termed the 'finned ladder'.

Wintucky, E. G.↗
DOE OSTI2020

Hybrid semiconductor-piezoacoustic radiofrequency device

An amplifying radiofrequency device includes a piezoelectric film and a semiconductor amplifier layer. The piezoelectric film is conformed as an acoustic waveguide. The piezoelectric film has a principal acoustic propagation direction parallel to the principal conduction direction of the amplifier layer. Interdigitated transducers are positioned on the piezoelectric film to respectively launch an acoustic wave in response to an input RF signal, and transduce the acoustic wave back to an output RF signal. There is a distance of less than the acoustic wavelength between the semiconductor amplifier layer and the piezoelectric film. The piezoelectric film has a thickness of less than the acoustic wavelength. According to a method for making such a device, a stack of III-V layers is epitaxially grown on a III-V substrate, wherein the stack comprises a first etch stop layer, a second etch stop layer, an amplifier layer, and a contact layer. The stack is bonded to a lithium niobate film. The III-V substrate is removed by etching down to the first etch stop layer. Deposition windows are opened by etching from the first etch stop layer down to the contact layer. Metal contact electrodes are deposited in the deposition windows.

36 MATERIALS SCIENCE↗
NASA NTRS2024

Secondary Electron Suppression with Carbonized Aerogels

The goal addressed by this project is reduced DC power for high data rate RF communications by increasing the efficiency of traveling Wave Tubes (TWT) for RF communication, which are used by most space missions for communication and radio science at microwave frequencies. The capability needed is a robust electron collector surface with a secondary electron emission lower than ordinary graphite, which is the state of the art. While it is known that replacing a smooth surface with a textured one will reduce secondary electron emission, no robust textured surface is known. Carbonized polyimide aerogels promise the necessary robustness along with reduced secondary electron emission, allowing further improvement of TWT efficiency, achieving a very good return on the low investment made. Aerogels are known to be robust materials, and carbon aerogels are expected to have low secondary electron emission because of their open surface structure. The objective of this proposal is to demonstrate the low secondary electron emission of carbon aerogels and their robustness.

Secondary electron sippression↗
DOE OSTI2020

A 1D coupled transport/cold plasma wave model for parallel ponderomotive density modification near RF actuators

The plasma density profile close to RF actuators plays a vital role in the efficiency of power coupling from the antenna to the core plasma of fusion devices. Nonlinear interactions can be significant when considering the interaction of applied RF power and the tenuous SOL plasma, and the inclusion of this region in computational analysis is essential to providing robust predictive simulations of plasma response to RF application. Of particular interest is the observed density modification during RF operation. Here we present a self consistent description of the nonlinear ponderomotive force in the antenna near field region, via coupling a 1D field aligned transport model with a 1D cold plasma wave model. Results are presented, which show a parallel electric field of 300 Vm -1 drove a density reduction of ~ 20% over 25 RF periods.

Barnett, Rhea↗
NASA NTRS1972

The influence of polarization on millimeter wave propagation through rain

A program for the measurement and analysis of the depolarization and differential attenuation that occur when millimeter wave signals propagate through rain is described. Initial data are taken along a 1.43 km path at 17.65 GHz and a supporting theoretical model is developed to relate the propagation effects to rainfall rate and wind velocity. A block diagram of the overall experiment is included. It consists of: (1) an RF system (millimeter wave transmitter and receiver), (2) transmitting and receiving antennas, (3) a weather system with rain gauges, wind sensors, and drop counters, and (4) a digital control, processing, and data storage system.

Bostian, C. W.↗
NASA NTRS1986

RF characterization of monolithic microwave and mm-wave ICs

A number of fixturing techniques compatible with automatic network analysis are presented. The fixtures are capable of characterizing GaAs Monolithic Microwave Integrated Circuits (MMICs) at K and Ka band. Several different transitions are used to couple the RF test port to microstrip. Fixtures which provide chip level de-embedding are included. In addition, two advanced characterization techniques are assessed.

Romanofsky, R. R.↗
DOE OSTI2022

LCLS-II Cryomodules Production Experience and Lessons Learned Towards LCLS-II-HE Project

LCLS-II is an upgrade project for the linear coherent light source (LCLS) at SLAC. The LCLS-II linac consists of thirty-five 1.3 GHz and two 3.9 GHz superconducting RF (SRF) continuous wave (CW) cryomodules with high quality factor cavities. Cryomodules were produced at Fermilab and at Jefferson Lab in collaboration with SLAC. Fermilab successfully completed the assembly, testing and delivery of seventeen 1.3 GHz and three 3.9 GHz cryomodules. LCLS-II-HE is a planned upgrade project to LCLS-II. The LCLS-II-HE linac will consist of twenty-three 1.3 GHz cryomodules with high gradient and high quality factor cavities. This paper presents LCLS-II-HE cryomodule production plans, emphasizing the improvements done based on the challenges, mitigations, and lessons learned from LCLS-II.

43 PARTICLE ACCELERATORS↗