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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Apparent sizes and spectral line profiles for spherical ('three-dimensional') astrophysical masers

Calculations are performed for the frequency-dependent transport of radiation in a uniform spherical maser. Coupling between the intensities at different frequencies is treated. Spherical masers are commonly utilized as idealized geometries in which to assess possible deviations (sometimes, 'three-dimensional effects') from the approximation of a linear geometry. We find that the spectral line profile rebroadens in approximately the same manner as that for a linear maser so that the relationship between the line breadth and the luminosity, beaming angle, and degree of saturation is essentially unchanged. The variation of the apparent size of a spherical maser with frequency is not found to be significant at frequencies within the line profile at which the intensity is appreciable. The 'standard approximation' is adequate for obtaining most of the basic properties of spherical masers that have been examined including the relationship between the pumping (or molecular populations) and the intensity of maser radiation. The improved methods employed here are, however, necessary to obtain variation of the apparent size with frequency in the saturated regime. These conclusions differ from those of previous investigators. The calculations here are more reliable than those of previous investigators because these are self-consistent and avoid certain inaccurate simplifications.

Emmering, Robert T.↗
NASA NTRS2003

[Probing Planck-scale Physics with a Ne-21/He-3 Zeeman Maser]

The Ne-21/He-3 Zeeman maser is a recently developed device which employs co-located ensembles of Ne-21 and He-3 atoms to provide sensitive differential measurements of the noble gas nuclear Zeeman splittings as a function of time, thereby greatly attenuating common-mode systematic effects such as uniform magnetic field variations. The Ne-21 maser will serve as a precision magnetometer to stabilize the system's static magnetic field, while the He-3 maser is used as a sensitive probe for violations of CPT and Lorentz symmetry by searching for small variations in the 3He maser frequency as the spatial orientation of the apparatus changes due to the rotation of the Earth (or placement on a rotating table). In the context of a general extension of the Standard Model of particle physics, the Ne-21/He-3 maser will provide the most sensitive search to date for CPT and Lorentz violation of the neutron: better than 10(exp -32) GeV, an improvement of more than an order of magnitude over past experiments. This exceptional precision will offer a rare opportunity to probe physics at the Planck scale. A future space-based Ne-21/He-3 maser or related device could provide even greater sensitivity to violations of CPT and Lorentz symmetry, and hence to Planck-scale physics, because of isolation from dominant systematic effects associated with ground-based operation, and because of access to different positions in space-time.

Source record↗
NASA NTRS1963

Masers for the telstar satellite communications experiment

This paper discusses the design and characteristics of ruby traveling-wave masers operating at 4 gc. These masers, characterized by an average gain of ≈35 db over a bandwidth of 25 mc, are equipped with waveguide input transmission lines, rather than the previously employed coaxial cables. This change results in an over-all noise temperature of 3.5°K for these devices, rather than the 10°K exhibited by earlier masers. The maser noise temperature now closely approximates sky temperatures, which set the ultimate limit on earthbound receiver sensitivity. The improvements to be had by further reduction in amplifier noise are therefore almost negligible. A less well known maser property, i.e., its freedom from distortion, even when driven well into gain saturation, is discussed.

TELSTAR SATELLITE↗
NASA NTRS1973

NASA hydrogen maser accuracy and stability in relation to world standards

Frequency comparisons were made among five NASA hydrogen masers in 1969 and again in 1972 to a precision of one part in 10 to the 13th power. Frequency comparisons were also made between these masers and the cesium-beam ensembles of several international standards laboratories. The hydrogen maser frequency stabilities as related to IAT were comparable to the frequency stabilities of individual time scales with respect to IAT. The relative frequency variations among the NASA masers, measured after the three-year interval, were 2 + or - 2 parts in 10 to the 13th power. Thus time scales based on hydrogen masers would have excellent long-term stability and uniformity.

Peters, H. E.↗
NASA NTRS1973

Flexible bulb large storage box hydrogen maser

The principal limitation on the accuracy of the hydrogen maser as a primary frequency standard has been the irreproducibility of the frequency shift caused by collisions of the radiating atoms with the walls of the vessel containing them. The flexible bulb-large storage box hydrogen maser allows correction for this wall shift within a single device, sidestepping the reproducibility problem, and reducing the frequency error from the wall shift to the level imposed by the device's stability. The principles of the device are discussed including the flexible bulb technique and the complications caused by a multiple region storage bulb. The stability of the device is discussed including a comparison with an ordinary hydrogen maser. Data is presented from a working flexible bulb-large storage box hydrogen maser demonstrating the feasibility of the device and showing some of its operating characteristics. The flexibility of the device is demonstrated by showing how the device's added degrees of freedom allow measurement of parameters unmeasurable in an ordinary hydrogen maser.

Reinhardt, V.↗
NASA NTRS1977

Low-noise receivers: Microwave maser development

An S-Band traveling-wave maser with a 2260- to 2400-MHz tuning capability has been built and installed on the 26-m antenna. The traveling-wave maser closed cycle refrigerator package was assembled within a limited time schedule and at low cost to meet the requirements of the very long baseline interferometry validation task. The maser uses a superconducting magnet with a field staggering coil for gain/bandwidth adjustment. The maser pump source is a Gunn effect oscillator with the capability of continuous tuning throughout the entire maser tuning range. The package was assembled from surplus components that have been used previously in the Deep Space Network in a variety of applications.

Quinn, R.↗
NASA NTRS1977

Hydrogen maser frequency standards for the Deep Space Network

A field operable maser has been developed for use in the Deep Space Network. Maser design was based on two experimental hydrogen maser frequency standards in operation since 1970 at DSN stations. Many design changes have been incorporated into the maser design, both in physics and electronics systems. Short and long term frequency, RF isolation of maser output lines and the lifetime of active physics components have been improved. Automatic fault detection and location, and performance and reliability of the receiver-synthesizer system have also been altered.

Dachel, P. R.↗
NASA NTRS1978

Very long baseline interferometric observations of the hydroxyl masers in VY Canis Majoris

Results are presented for spectral-line VLBI observations of the OH emission from VY CMa. The main-line (1665 and 1667 MHz) emission was mapped with an angular resolution of 0.02 arcsec by analyzing interferometer phase data. The main-line emission comes from many maser components of apparent size less than 0.03 arcsec which are separated by up to 0.5 arcsec. New maser features near the center of the OH spectra were detected and found to lie within the region encompassed by the low-velocity OH emission. The 1612-MHz emission was mapped by Fourier inversion of the VLBI data from two baselines. All spatially isolated maser components appeared smaller than 0.15 arcsec; however, the maser emission is very complex at most velocities. Maser components within a velocity range of 1.3 km/s are often separated by more than 1 arcsec, while components more than 10 km/s apart in each emission complex are often coincident to 0.2 arcsec.

Reid, M. J.↗
NASA NTRS1982

Cryogenic masers

Various factors affecting the frequency stability of hydrogen masers are described and related to maser design parameters. The long-term frequency stability of a hydrogen maser is limited by the mechanical stability of the cavity, and the magnitudes of the wall relaxation, spin exchange, and recombination rates which affect the Q of the line. Magnetic resonance studies of hydrogen atoms at temperatures below 1 K and in containers coated with liquid helium films demonstrated that cryogenic masers may allow substantial improvements in all of these parameters. In particular the thermal expansion coefficients of most materials are negligible at 1 K. Spin exchange broadening is three orders of magnitude smaller at 1 K than at room temperature, and the recombination and wall relaxation rates are negligible at 0.52 K where the frequency shift due to the 4 He-coated walls of the container has a broad minimum as a function of temperature. Other advantages of the helium-cooled maser result from the high purity, homogeneity, and resilence of helium-film-coated walls and the natural compatibility of the apparatus with helium-cooled amplifiers.

Berlinsky, A. J.↗
NASA NTRS1984

Electron-cyclotron maser emission - Relative growth and damping rates for different modes and harmonics

The temporal growth rate and the number of e-folding growths are calculated and compared for the following wave modes due to a loss-cone-driven cyclotron maser: fundamental x, o, and z modes and second harmonic x and o modes. The dominant mode of the maser should be the fastest growing mode for a saturated maser and should be the mode with the greatest number of e-folding growths for an unsaturated maser; this mode is the fundamental x mode) for a plasma frequency to cyclotron frequency ratio of less than about 0.3; it is the z mode (or perhaps the fundamental o mode) for ratios between 0.3 and 1.0, and the z mode (or perhaps the second harmonic x mode) for ratios between 1.0 and 1.3. Two main points are made: the dominance of the z mode over the range of ratios considered and the very weak effect of cyclotron damping. Electron-cyclotron maser emission is seen as responsible for auroral kilometric radiation, decametric radio emission from Jupiter and Saturn, solar microwave spike bursts, and microwave emission from some flare stars.

Melrose, D. B.↗
NASA NTRS1987

Dual-polarization 8.45 GHz traveling-wave maser

An 8.5 GHz dual-channel, dual-polarization traveling-wave maser (TWM) amplifier was installed in the XKR solar system radar cone at DSS 14. The TWM is based on the Blk IIA 8.45 GHz maser structure, with two of the four maser stages being used for each channel, and each maser half then followed by a high-performance GaAs FET amplifier to achieve the desired net gain. A shortened low-noise input waveguide and an orthogonal-mode junction which is cooled to 4.5 K feeds each amplifier chain. The rotation of an external polarizer permits the polarization of each channel to be defined as either linear or circular. A circular waveguide switch was also developed to provide for noise calibration and to protect the maser from incident transmitter power.

Quinn, R. B.↗
NASA NTRS1986

The electron-cyclotron maser instability as a source of plasma radiation

The generation of continuum bursts from the sun at dm and m wavelengths (in particular, type IV bursts) via the electron-cyclotron-maser instability is examined. The maser instability can be driven by an electron distribution with either a loss-cone anisotropy or a peak at large pitch angles. For omega(p)/Omega(e) much greater than 1, the maser emission is produced by electrons interacting through a harmonic (cyclotron) resonance and is electrostatic, being in the upper hybrid mode at frequencies approximately equal to omega(p). Coalescence processes are required to convert the electrostatic waves into transverse radiation which can escape from the source region. Whether the resultant spectrum is nearly a smooth continuum or has a zebra-stripe pattern (both of which occur in type IV bursts) depends on the form of the electron distribution, inhomogeneities in the density and magnetic field, and whether the maser reaches saturation. For at least the case of some type IV dm bursts with fine structure, comparison with observations seems to indicate that the electrons producing the emission are more likely to have a loss-cone distribution, and that the maser instability is not at saturation.

Winglee, R. M.↗
NASA NTRS1988

Multiple, narrow lines in the spectrum of an astrophysical maser in a velocity gradient

The emergent radiation spectrum is obtained for an astrophysical maser in the presence of a velocity gradient without making the 'large velocity gradient' (or 'Sobolev') approximation on which previous calculations have been based. Even in the presence of a velocity gradient, the spectral lines of saturated masers are found to remain narrow. More surprisingly, however, the spectrum breaks up into multiple narrow lines. Hence, individual features in the observed spectra of astrophysical masers need not always be interpreted as separate clumps of gas. Specifically, this result may be related to the occurrence of multiple lines from the same location in the H2O masers in star-forming regions and to be the occurrence of numerous, narrow features recently detected in the spectra of circumstellar OH masers.

Nedoluha, Gerald E.↗
NASA NTRS1990

Ultralow noise performance of an 8.4-GHz maser-feedhorn system

A total system noise temperature of 6.6 K was demonstrated with an 8.4-GHz traveling wave maser and feedhorn operating in a cryogenic environment. Both the maser and feedhorn were inserted in the helium cryostat, with the maser operating in the 1.6-K liquid bath and the feedhorn cooled in the helium gas, with a temperature gradient along the horn ranging from the liquid bath temperature at its lower end to room temperature at its top. The ruby maser exhibited 43 dB of gain with a bandwidth of 76 MHz(-3 dB) centered at 8400 MHz. Discussions of the maser, cooled feedhorn, and cryostat designs are presented along with a discussion of the noise temperature measurements.

Johnson, D. L.↗
NASA NTRS1991

Spectral line profiles and luminosities of astrophysical water masers

The spectral line narrowing and rebroadening that occurs for astrophysical masers as a function of the emergent radiative flux is calculated for the prominent, 22 GHz masing transition of water. The increased line breadths due to hyperfine structure lead to reliable, essentially model-independent upper limits to the emergent flux that tend to be lower than other estimates for these masers. For many 22 GHz masers, including the outbursts in W49 and Orion, the observed line breadths are less than 0.9 km/s. For these, the upper limit to the emergent maser flux is 10 to the 10th K-sr when expressed in terms of the brightness temperature and the solid angle for beaming. It is concluded that the extreme brightness of the interstellar water masers is due to a high degree of beaming and not to more effective pumping.

Nedoluha, Gerald E.↗
NASA NTRS1991

Excitation of millimeter and submillimeter water masers

The excitation of maser emission in millimeter and submillimeter transitions of interstellar and circumstellar water is considered. An escape probability method is used to determine the equilibrium populations in 349 rotational states of both ortho- and para-water under varying conditions of gas temperature, density, water abundance, and radiation field. It is shown that, under those conditions believed to prevail around late-type stars and within star-forming regions, strong millimeter and submillimeter water maser emission can be generated by collisional excitations by H2. Several maser transitions can have strengths close to that of the 22 GHz line. The water maser line which can be observed from mountaintop facilities and those which will require air- or space-borne platforms are indicated. The exact portion of parameter space in which each maser transition exhibits peak emission is shown.

Neufeld, David A.↗
NASA NTRS1991

Solar and stellar radio spikes - Limits on the saturation of the electron-cyclotron maser

The solar millisecond radio 'spikes' have been explained in terms of X-mode radiation generated by a maser near the electron gyrofrequency, acting on fast coronal electrons with a loss cone. This maser is a phenomenon described by quasi-linear theory. It is sensitive to the small first-relativistic correction to the gyrofrequency. Thus, it might be disrupted rather easily by nonlinear effects. The maximum radiation density that can be reached before the radiation entrains (phase-locks) the electrons and saturates the maser is discussed. If the observed durations of solar radio spikes are a measure of the rate of scattering into the loss-cone, then the inferred energy density is at least two orders of magnitude less than the energy density at which entrainment sets in. Also, maser emission from auroral kilometric radiation does not reach wave energies critical for electron entrainment. Maser emissions from flare stars, however, show 3-4 orders of magnitude higher radio fluxes and brightness temperatures than for the solar case and are likely to be saturated by entrainment.

Wentzel, Donat G.↗
NASA NTRS1992

Probing the circumstellar environments of very young low-mass stars using water masers

The VLA is used to search nearby very young low-mass stars for water maser emission. The sample consists of 26 low-luminosity IRAS sources embedded in dense molecular cores, a class of sources suspected to be newly forming low-mass stars on the order of a few hundred thousand years old. Three sources were detected. High spatial resolution maps show the region of maser emission is generally confined to an area smaller than about 0.5 arcsec near the star, and the velocities of individual components span intervals ranging from 20 to 40 km/s. It is inferred from the fact that the maser velocities are too large to be due to gravitational motions in at least two of the sources that the masers are associated with the winds from the young low-mass stars. A comparison of the high spatial resolution maser data to lower-resolution CO data shows no evidence for higher collimation close to the star; the stellar wind cavity appears to have similar collimation at 10 exp 15 cm as at 10 exp 7 to 10 exp 18 cm.

Terebey, S.↗