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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Saturation of cyclotron maser instability driven by an electron loss-cone distribution

The resonance diffusion of electrons in velocity space caused by the excited EM wave fields is considered to be the dominant saturation process of cyclotron maser instability that is driven by an electron loss-cone distribution. An upper bound of the saturation level is derived analytically. Since the resulting saturation level is low, the resonance diffusion is indeed responsible for the saturation of the cyclotron maser instability.

Kuo, S. P.↗
NASA NTRS1986

Resonant electron diffusion as a saturation process of the synchrotron maser instability

The theory of resonant electron diffusion as an effective saturation process of the auroral kilometric radiation has been formulated. The auroral kilometric radiation is assumed to be amplified by the synchrotron maser instability that is driven by an electron distribution of the loss-cone type. The calculated intensity of the saturated radiation is found to have a significantly lower value in comparison with that caused by the quasi-linear diffusion process as an alternative saturation process. This indicates that resonant electron diffusion dominates over quasi-linear diffusion in saturating the synchrotron maser instability.

Lee, M. C.↗
NASA NTRS1986

Electron-cyclotron maser emission from the sun and stars Variations with plasma temperature and density

Very bright and highly circularly polarized radio bursts from the sun, the planets, flare stars, and close binary stars are attributed to the electron-cyclotron maser instability. The mode and frequency of the dominant radiation from the maser instability is shown to be dependent on the plasma temperature and the ratio omega(p)/Omega(e) of the plasma frequency to the electron-frequency. For the emission from the sun omega(p)/Omega(e) is probably greater than 0.3 and for omega(p)/Omega(e) greater than 0.3 and less than the square root of 2, the emission can be either in the x-mode at the second harmonic or in the 0- and/or z-modes at the fundamental. For higher omega(p)/Omega(e), the emission moves to higher harmonics of Omega(e) with the emission being predominately in the z-mode when omega(p)/Omega(e) is greater than about the square root of 3.

Winglee, R. M.↗
NASA NTRS1987

In-Vacuum Dissociator for Atomic-Hydrogen Masers

Thermal control and vacuum sealing achieved while contamination avoided. Simple, relatively inexpensive molecular-hydrogen dissociator for atomic-hydrogen masers used on Earth or in vacuum of space. No air cooling required, and absence of elastomeric O-ring seals prevents contamination. In-vacuum dissociator for atomic hydrogen masers, hydrogen gas in glass dissociator dissociated by radio-frequency signal transmitted from surrounding 3-turn coil. Heat in glass conducted away by contacting metal surfaces.

Vessot, R. F.↗
NASA NTRS1987

Coating a Hydrogen-Maser Chamber With CF4

Coating of carbon tetrafluoride formed on interior surface of atomic-hydrogen maser by allowing gas to freeze on surface. New coating enables maser to oscillate down to 26 K; most effective previous coating, fluorinated ethylene/polypropylene (FEP) copolymer allowed oscillation down to about 50 K.

Vessot, Robert F. C.↗
NASA NTRS1986

Relativistic dispersion modifications to the cyclotron maser theory of planetary radio emissions

The effects of relativistic dispersion on the electron-cyclotron maser instability are investigated by linear theory, electromagnetic particle simulation, and quasilinear theory. When vsq/csq greater than or = omega pesq/Omega sq for the energetic electrons, the instability is localized just below k c/Omega e = 1, and the growth rate is strongly peaked for emission at 90 deg to the magnetic field. Saturation of the instability is due to perpendicular diffusion in momentum space, and the saturation level increases as omega pe/Omega e is decreased. Applications of the maser instability to the generation of the Earth's auroral kilometric radiation are discussed.

Pritchett, P. L.↗
NASA NTRS1986

Electron-cyclotron maser emission during flares: Emission in various modes and temporal variations

Absorption of radiation at the electron-cyclotron frequency, OMEGA sub e, generated by the electron-cyclotron maser instability was proposed as a possible mechanism for transporting energy and heating of the corona during flares. Radiation from the same instability but at harmonics of OMEGA sub e is believed to be the source of solar microwave spike bursts. The actual mode and frequency of the dominant emission from the maser instability is shown to be dependent on: (1) the plasma temperature, (2) the form of the energetic electron distribution, and (3) on the ratio of the plasma frequency omega sub p to OMEGA sub e. As a result, the emission along a flux tube can vary, with emission at harmonics being favored in regions where omega sub p/OMEGA sub e approx. equal to or greater than 1. Changes in the plasma density and temperature in the source region associated with the flare can also cause the characteristics of the emission to change in time.

Winglee, R. M.↗
NASA NTRS1987

Use of a 2.3-GHz traveling-wave maser on the Usuda 64-meter antenna

A 2.3 GHz traveling-wave maser/closed-cycle refrigeration system was installed on the 64 m antenna at Usuda, Japan. This was done to evaluate the beam-waveguide antenna noise performance, and to support the International Cometary Explorer's (ICE's) comet flyby mission. System noise temperature at 2270 MHz was measured to be 15 K, including the maser noise contribution of 2.5 K. Maser installation and noise performance are described. The Usuda 64 m antenna is of high quality with a system operating noise temperature better than the DSN 64 m antennas.

Neff, D.↗
NASA NTRS1986

A search for cyclotron maser radiation from substellar and planet-like companions of nearby stars

Several stars within 5 pc have variations in their rectilinear or Keplerian motion that suggest that they have substellar or planetlike companions. However, direct, unambiguous evidence of such companions is difficult to obtain. It is argued that such objects should commonly emit cyclotron maser radiation and that this radiation should be observable with modern radio telescopes. Its detection would confirm the presence of the companions and permit many of the properties of the stars and companions to be derived. A search was made for the cyclotron maser emission from six nearby stars with suspected companions using the VLA at frequencies of 0.33 and 1.4 GHz. None was detected. Typical observing times were 3.5 hr, and typical upper limits were 30 mJy at 0.33 GHz and 0.3 mJy at 1.4 GHz.

Winglee, Robert M.↗
NASA NTRS1986

Relativistic dispersion modifications to the cyclotron maser theory of planetary radio emissions

The effects of relativistic dispersion on the electron-cyclotron maser instability are investigated by means of linear theory, electromagnetic particle simulation, and quasilinear theory. Saturation of the instability is due to perpendicular diffusion in momentum space, and the saturation level increases as the plasma frequency/electron cyclotron ratio is decreased. Applications of the maser instability to the generation of the the earth's auroral kilometric radiation are discussed.

Pritchett, P. L.↗
NASA NTRS1987

Pumping the stellar hydroxyl maser

IRAS far-IR flux data for 163 OH maser stars were analyzed to quantify the contributions 35 and 53 microns inversions make to pumping of the hydroxyl maser. The 35 microns transition is from the 3,3 ground state to the 1,5 rotationally excited level and subsequent decay; the 53 microns transition is a change from the ground state to the 1,3 excited level and relaxation. The stars examined included Mira, short period semi-regular and long-period semi-regular variables. Both transition lines had rough parity in contributing to the approximately 8 percent pumping efficiency at 1612 MHz. However, the individual contributions of the lines could not be determined for the stellar population studied.

Dickinson, Dale F.↗
NASA NTRS1987

Narrow polarized components in the OH 1612-MHz maser emission from supergiant OH-IR sources

High-resolution (300 Hz) OH 1612-MHz spectra of the supergiant OH-IR sources VY CMa, VX Sgr, IRC 10420, and NML Cyg are presented. Linewidths as small as 550 Hz (0.1 km/s) are found for narrow components in the spectra. The present results are consistent with current models for maser line-narrowing and for the physical properties in the OH maser regions. A significant degree of circular polarization is noted in many of the narrow components. The circular polarization suggests the presence of magnetic fields of about 1 mG in the circumstellar envelopes which would be strong enough to influence the outflow from the stars, and which may explain asymmetries found in the circumstellar envelopes.

Cohen, R. J.↗
NASA NTRS1988

Improved State Selection For Hydrogen Masers

Improved selection system for hydrogen maser helps exclude hydrogen atoms from storage bulb in undesired quantum states not contributing to amplification/oscillation process. Atoms in undesired states limit stability of maser by reducing storage lifetime of atoms in desired state, reducing output power, and colliding with atoms in desired state under circumstances that causing systematic shifts in frequency.

Vessot, Robert F. C.↗
NASA NTRS1988

An 8.4-GHz dual maser front end for Parkes reimplementation

An 8.4 GHz front-end system consisting of a feedhorn, a waveguide feed assembly, dual masers, and downconverters is being reimplemented at Parkes as part of the Parkes-Canberra Telemetry Array for the Voyager Neptune encounter. The front-end system was originally assembled by the European Space Agency on the Parkes antenna for the Giotto project. It was also used on a time-sharing basis by the DSN as part of the Parkes-Canberra Telemetry Array to enhance the data return from Voyager 2 at Uranus. At the conclusion of these projects in 1986, the front-end system was dismantled, packed, and shipped to Europe. Part of the system was then shipped to JPL on loan for reimplementation at Parkes for the Voyager Neptune encounter. The system is being redesigned and refurbished for operation at Parkes. Tasks include new microwave front-end control cabinets, a closed-cycle refrigeration data acquisition system, a new noise-adding radiometer system, a front-end controller assembly, and refurbishment of the dual 8.4 GHz traveling-wave masers (TWMs) and waveguide feed system.

Trowbridge, D. L.↗
NASA NTRS1987

Single-state selection system for hydrogen masers

The design and operation of a single-state selection system based on the adiabatic fast-passage technique for atomic state inversion is described. The system uses a variable-pitch dc solenoid and orthogonal four-wire RF coil to create the state-changing magnetic fields, and a half-wavelength state selection magnet to remove the inverted state atoms from the hydrogen beam. The system's performance was determined by measuring maser power as a function of line Q. The system removes more than 85 percent of undesired atoms from the beam. The potential effects of improvements in the maser on its frequency stability have been calculated. The use of single-state selection combined with increased RF coupling to the cavity and increased storage bulb collimation offers the possibility of frequency stability in the 10 to the -17th regime over intervals on the order of 60,000 s.

Mattison, Edward M.↗
NASA NTRS1988

A 32-GHz reflected-wave maser amplifier with wide instantaneous bandwidth

An eight stage, 32 GHz reflected wave ruby maser was built. The maser operates in a 3 watt closed cycle refrigerator at 4.5 K and is capable of 21 dB of net gain with an instantaneous bandwidth of 400 MHz. The input noise temperature referred to the room temperature flange is approximately 21 K.

Shell, J.↗
NASA NTRS1989

Operational parameters for the superconducting cavity maser

Tests of the superconducting cavity maser (SCM) ultra-stable frequency source have been made for the first time using a hydrogen maser for a frequency reference. In addition to characterizing the frequency stability, the sensitivity of the output frequency to several crucial parameters was determined for various operating conditions. Based on this determination, the refrigeration and thermal control systems of the SCM were modified. Subsequent tests showed substantially improved performance, especially at the longest averaging times.

Wang, R. T.↗
NASA NTRS1988

Advances in the development of piezoelectric quartz-crystal oscillators, hydrogen masers, and superconducting frequency standards

This paper describes recent research advances made in the development of radiation-hardened piezoelectric quartz oscillators, hydrogen masers, and superconducting oscillators, with emphasis placed on the principles involved in the operation of these oscillators and the factors affecting the operation. Particular attention is given to the radiation-susceptibility studies of quartz-crystal resonators, the hydrogen-maser relaxation process and noise sources, and low-phase-noise superconducting oscillators. Diagrams of these devices and performance graphs are included.

Suter, Joseph J.↗