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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Investigating Holey Metamaterial Effects in Terahertz Traveling-Wave Tube Amplifier

Applying subwavelength holes to a novel traveling-wave tube amplifier is investigated. Plans to increase the on-axis impedance are discussed as well as optimization schemes to achieve this goal. Results suggest that an array of holes alone cannot significantly change the on-axis electric field in the vicinity of the electron beam. However, models of a beam tunnel with corrugated walls show promise in maximizing the amplifier s on-axis impedance. Additional work is required on the subject, and suggestions are made to determine research directions.

Starinshak, David P.↗
NASA NTRS2008

Investigating Dielectric and Metamaterial Effects in a Terahertz Traveling-Wave Tube Amplifier

Adding material enhancements to a terahertz traveling-wave tube amplifier is investigated. Isotropic dielectrics, negative-index metamaterials, and anisotropic crystals are simulated, and plans to increase the efficiency of the device are discussed. Early results indicate that adding dielectric to the curved sections of the serpentine-shaped slow-wave circuit produce optimal changes in the cold-test characteristics of the device and a minimal drop in operating frequency. Additional results suggest that materials with simultaneously small relative permittivities and electrical conductivities are best suited for increasing the efficiency of the device. More research is required on the subject, and recommendations are given to determine the direction.

Starinshak, David P.↗
NASA NTRS1991

Pulsed response of a traveling-wave tube

The consequence of frequency-domain multiple access (FDMA) channelization in a satellite communications system is that the ground- and space-based components are often required to operate at reduced output power to prevent the generation of distortions. However, the components of a time-division multiple access (TDMA) satellite system, such as a traveling-wave tube (TWT), can operate at the highest output power because the channelization technique is relatively insensitive to the distortions resulting from saturated operation. A Hughes 30-GHz TWT was tested to determine the suitability of such a device in a TDMA system. Testing was focused on the ability of the TWT to rise up to full power at the leading edge of TDMA bursts, which were simulated by a pulse train. A Wavetek model 8502A peak power meter was used to display and measure the pulsed signal waveform. Measurements of the TWT output signal rise time indicate that the TWT lengthened the rise time by 10 to 20 nsec. Imposing a modulator turn-on time that precedes the data burst by the TWT rise time is a logical approach to coordinating the traveling-wave tube amplifier and modulator specifications.

May, Brian D.↗
NASA NTRS1980

Coupled-cavity traveling-wave tubes

Computer program is developed for analysis of coupled cavity traveling waves tubes (TWT's) which are used in variety of radar and communications applications. Programmers can simulate tubes of arbitrary complexity such as input and output couplers and other features peculiar to one or few cavities which may be modeled by correct choices of input data.

Connolly, D. J.↗
NASA NTRS1980

X-band, low-noise, traveling-wave maser

The development and performance of X-band traveling-wave maser (TWM) systems with effective input noise temperature of 3.5 K and bandwidths varying from 65 to 108 MHz is discussed. These TWMs are used on the 64-meter antennas at Deep Space Stations 14, 43 and 63 at 8420 MHz to meet the requirements of the Voyager-Saturn encounter. The TWMs use shortened and cooled signal input waveguide to reduce noise and are equipped with superconducting magnets and solid-state pump sources to provide the required stability performance.

Trowbridge, D. L.↗
NASA NTRS1984

A Study of DSN Traveling Wave Maser System Reliability

Reliability and availability characteristics of the DSN traveling wave maser (TWM) Assemblies are reported for the years 1981 through 1983, the charcteristics determined are: mean time between failures (MTBF) - 1200 hours; mean time to restore service (MTTRS) - 2.5 hours; and availability - 99.83%. The TWM MTBF is very good as compared to other DSN subsystems and assemblies. The TWM MTTRS is currently about three times as long as the average of other DSN subsystems. The dominant cause of TWM failures is contamination of the helium gas in the closed cycle refrigerators. Station configurations that do not provide TWM redundancy are subject to reception outages for long periods of time. Recommendations are made to improve the TWM Assembly availability characteristics for future mission support operations.

Stevens, R.↗
NASA NTRS1988

The determination of the propagation constant for the traveling wave in an infinite ground plane

The propagation constant for the traveling wave in a trough in an infinite ground plane is examined. The null-field integral is used to determine the EM field in the trough structure, and pulse basis functions give the distribution of the aperture fields. From this, the propagation constant is solved for, using the Newton-Raphson iterative scheme. Various sizes of geometries are examined. The far-field patterns are calculated and compared with other solutions, thereby validating the integral formulation which subsequently provided the propagation constant. Measurements of two trough geometries are performed to validate the theoretical results.

Shamansky, Harry T.↗
NASA NTRS1991

A three-dimensional finite-element thermal/mechanical analytical technique for high-performance traveling wave tubes

Current research in high-efficiency, high-performance traveling wave tubes (TWT's) has led to the development of novel thermal/ mechanical computer models for use with helical slow-wave structures. A three-dimensional, finite element computer model and analytical technique used to study the structural integrity and thermal operation of a high-efficiency, diamond-rod, K-band TWT designed for use in advanced space communications systems. This analysis focused on the slow-wave circuit in the radiofrequency section of the TWT, where an inherent localized heating problem existed and where failures were observed during earlier cold compression, or 'coining' fabrication technique that shows great potential for future TWT development efforts. For this analysis, a three-dimensional, finite element model was used along with MARC, a commercially available finite element code, to simulate the fabrication of a diamond-rod TWT. This analysis was conducted by using component and material specifications consistent with actual TWT fabrication and was verified against empirical data. The analysis is nonlinear owing to material plasticity introduced by the forming process and also to geometric nonlinearities presented by the component assembly configuration. The computer model was developed by using the high efficiency, K-band TWT design but is general enough to permit similar analyses to be performed on a wide variety of TWT designs and styles. The results of the TWT operating condition and structural failure mode analysis, as well as a comparison of analytical results to test data are presented.

Bartos, Karen F.↗
NASA NTRS1992

A three-dimensional finite-element thermal/mechanical analytical technique for high-performance traveling wave tubes

Current research in high-efficiency, high-performance traveling wave tubes (TWT's) has led to the development of novel thermal/mechanical computer models for use with helical slow-wave structures. A three-dimensional, finite element computer model and analytical technique used to study the structural integrity and thermal operation of a high-efficiency, diamond-rod, K-band TWT designed for use in advanced space communications systems. This analysis focused on the slow-wave circuit in the radiofrequency section of the TWT, where an inherent localized heating problem existed and where failures were observed during earlier cold compression, or 'coining' fabrication technique that shows great potential for future TWT development efforts. For this analysis, a three-dimensional, finite element model was used along with MARC, a commercially available finite element code, to simulate the fabrication of a diamond-rod TWT. This analysis was conducted by using component and material specifications consistent with actual TWT fabrication and was verified against empirical data. The analysis is nonlinear owing to material plasticity introduced by the forming process and also to geometric nonlinearities presented by the component assembly configuration. The computer model was developed by using the high efficiency, K-band TWT design but is general enough to permit similar analyses to be performed on a wide variety of TWT designs and styles. The results of the TWT operating condition and structural failure mode analysis, as well as a comparison of analytical results to test data are presented.

Shalkhauser, Kurt A.↗
NASA NTRS1993

The barotropic normal modes in certain shear flows and the traveling waves in the atmosphere

It is shown analytically and numerically that in certain shear flows the linearized nondivergent barotropic vorticity equation has a limited number of neutral normal modes. The latitudinal structures of these shear flows can be expressed as polynomials of the sine of latitude. The first few such shear flows resemble the gross features of the zonal winds in the atmosphere of the earth at different times and altitudes. The spatial structures of the neutral normal modes in these shear flows are spherical harmonics, and, as a consequence, these modes are also the exact solutions of the fully nonlinear equation because the nonlinear interaction term vanishes identically. The spatial structures of the observed 5-, 4-, 2-, and 16-day free traveling waves in the atmosphere are often identified with the spherical harmonics with indices of (m, n) = ( 1, 2), (2, 3), (3, 3), and ( 1, 4), which are known previously as the neutral normal modes of the nondivergent barotropic vorticity equation in a motionless background state. Our results could explain why these free traveling waves can survive the shearing effects of zonal flows that are far different from rest because these spherical harmonics are also normal modes in certain shear flows that resemble the observations of the atmosphere.

Chen, Ping↗
DOE OSTI2024

Kinetic Inductance Traveling Wave Amplifier Designs for Practical Microwave Readout Applications

Abstract A Kinetic Inductance Traveling Wave Amplifier (KIT) utilizes the nonlinear kinetic inductance of superconducting films, particularly niobium titanium nitride (NbTiN), for parametric amplification. These amplifiers achieve remarkable performance in terms of gain, bandwidth, and compression power and frequently approach the quantum limit for noise. However, most KIT demonstrations have been isolated from practical device readout systems. Using a KIT as the first amplifier in the readout chain of an unoptimized microwave SQUID multiplexer coupled to a transition-edge sensor microcalorimeter, we see an initial improvement in the flux noise [1]. One challenge in KIT integration is the considerable microwave pump power required to drive the non-linearity. To address this, we have initiated efforts to reduce the pump power by using thinner NbTiN films and an inverted microstrip transmission line design. In this article, we present the new transmission line design, fabrication procedure, and initial device characterization—including gain and added noise. These devices exhibit over 10 dB of gain with a 3 dB bandwidth of approximately 5.5–7.25 GHz, a maximum practical gain of 12 dB, and typical gain ripple under 4 dB peak to peak. We observe an appreciable impedance mismatch in the NbTiN transmission line, which is likely the source of the majority of the gain ripple. Finally, we perform an initial noise characterization and demonstrate system-added noise of three quanta or less over nearly the entire 3 dB bandwidth.

Physics↗
NASA NTRS1974

High-efficiency, 200 watt, 12-gigahertz traveling wave tube

Design and performance of a highly efficient experimental 200-watt traveling wave tube for space communications are described. The tube uses a coupled cavity slow wave structure with periodic permanent magnet focusing. A two-step velocity taper is incorporated in the slow wave structure for velocity resynchronization with the modulated beam. The spent beam is reconditioned in a refocusing section before it is collected in a novel multistage depressed collector. The collector is radiation cooled and heat insulated from the tube body. At saturation the tube provides peak output power of 240 watts with a 35-db gain and an overall maximum efficiency of 56 percent.

Kosmahl, H. G.↗
NASA NTRS1980

Improved traveling wave tubes

Techniques, pioneered by NASA, which will allow substantial improvements in traveling wave tube (TWT) amplifier efficiency, are described. It is shown that using design techniques developed at the Lewis Research Center, it is possible to approximately double the efficiency of the critical amplifier TWT. Attention is given to a quick method of computing the expected improvement to an ECM TWT. The benefits of such improvements such as less input power, a smaller and lighter power supply, and easier cooling are surveyed, and it noted that it is now possible to build efficient TWT's which rather than operating at saturation, can be very linear amplifiers. Finally, a new approach to power supplies is also covered.

Buck, E.↗
NASA NTRS1981

Traveling-wave maser, closed cycle refrigerator automation

At the present time all traveling-wave maser and closed-cycle refrigerator system (TWM-CCR) and their power supply and helium compressor assemblies are operated manually. Many man-hours are required of highly trained and experienced operators, resulting in high operator cost. Of greater importance are the problems of unpredictable failure and long downtimes. Since field performance is not monitored, system degradation is detected only when it has progressed to the point of catastrophic failure. Without the aid of performance histories, failure diagnosis is arduous and slow. Rational and functional requirements for the TWM-CCR Automation project are the following: (1) to improve reliability and reduce downtime by providing unattended monitor and control, alarm and fault location, failure prediction and self-corrective action; (2) to reduce operator cost by providing automatic tuning and cooldown procedures; and (3) to improve system operations and development by providing the needed engineering data.

Mcneil, J. A.↗