SEARCH · Engineering Papers
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
The frequency stability of hydrogen masers in variable volume storage bulbs is discussed in terms of wall shift. Variable volume devices discussed include: Brenner flexible bulb, Debely device, and the concertina hydrogen maser. A flexible cone variable volume element outside the cavity is described.
The design and performance of a simple two-stage reflection maser for use between 9 and 10 GHz are described. The maser is used to improve the sensitivity of a transmission electron spin resonance spectrometer. A ruby-filled waveguide structure permits broad tunability and straightforward construction. All microwave components except the ruby section are at room temperature.
An X-band traveling wave maser of the folded-comb type is presented, with two figure-eight coils for gain and bandwidth control. One figure-eight coil covers the full lengths of the comb structure for bandwidth adjustment of an external magnetic field. The other coil covers a central half of the comb structure for independent gain adjustment of the external magnetic field. The half of each figure-eight coil at the turn around end of the comb structure is oriented to aid the external magnetic field, and the half of each coil at the input-output end of the comb structure is oriented to buck the external magnetic field. The maser is pumped in the push-push mode with two different frequencies.
The paper considers the energy input to H2O masers in a dense molecular cloud and analyzes the response time scales for both collisional and radiative pump models. Specific mechanisms for magnetic energy input are given. The evolution of dense H2O maser clouds is studied in the environment of a young pre-main-sequence star that has developed an appreciable supersonic wind. It is shown that compact clouds can be ejected at high velocity to distances of order 1 pc. It is suggested that these clouds (referred to as interstellar bullets) might explain the phenomena of Herbig-Haro objects and high-velocity gas motions observed near compact infrared objects.
Field operable hydrogen masers based on prior maser designs are presented. These units incorporate improvements in magnetic shielding, lower noise electronics, better thermal control, and have a microprocessor for operation, monitoring, and diagnostic functions. They are ruggedly built for transportability and ease of service anywhere in the world.
Spacecraft navigation to the outer planets (Jupiter and beyond) places very stringent demands upon the performance of frequency and time (F&T) reference standards. The Deep Space Network (DSN) makes use of hydrogen masers as an aid in meeting the routine F&T operational requirements within the 64 m antenna network. Results as of October 1980 indicate the hydrogen masers are performing within the required specifications. Two problem areas are discussed: insufficient control over the environment in which the reference standards reside; and frequency drift.
The application of passive hydrogen masers to satellites was investigated. The NRL maser is of compact design suitable for the space environment. It is based on a dielectrically loaded sapphire cavity and uses a computer optimized set of four shields. The servo design is a phase sensitive method which directly measures the phase dispersion of the interrogating signal as it passes through the cavity.
Hydrogen masers used as aids in meeting the routine frequency and time operational requirements within the 64 m antenna Deep Space Network. Both the operational syntonation (frequency synchronization) and the the clock (epoch) synchronization requirements were established through the use of specifically calibrated H-P E215061A flying clock. The sync/synt to UTC was maintained using LORAN and TV in simultaneous reception mode. The sync/synt within the 64 m net was maintained through the use of very long base interferometry. Results indicate that the hydrogen masers perform well within the required specifications.
Published data on a select group of SiO maser sources have been analyzed for velocity variations as a function of phase. No apparent correlation was found to a level of about 2 km/s. This places constraints on the location of the maser molecules. Such a correlation should be present at some level. The implications for future high resolution infrared measurements are discussed.
The development of a multifrequency upconverter-maser system for the DSN has created the need to develop a closed-cycle refrigerator (CCR) capable of providing more than 3 watts of refrigeration capability at 4.5 K. In addition, operating concerns such as the high cost of electrical power consumption and the loss of maser operation due to CCR failures require that improvements be made to increase the efficiency and reliability of the CCR. One refrigeration method considered is the replacement of the Joule-Thomson expansion circuit with a magnetic refrigeration. Magnetic refrigerators can provide potentially reliable and highly efficient refrigeration at a variety of temperature ranges and cooling power. The concept of magnetic refrigeration is summarized and a literature review of existing magnetic refrigerator designs which have been built and tested and that may also be considered as possibilities as a 4 K to 15 K magnetic refrigeration stage for the DSN closed-cycle refrigerator is provided.
Vibration tests on high permeability magnetic shields used in the SAO-NRL Advanced Development Model (ADM) hydrogen maser were made. Magnetic shielding factors were measured before and after vibration. Preliminary results indicate considerable (25%) degradation. Test results on the NRL designed vacuum pumping station for the ADM hydrogen maser are also discussed. This system employs sintered zirconium carbon getter pumps to pump hydrogen plus small ion pumps to pump the inert gases. In situ activation tests and pumping characteristics indicate that the system can meet design specifications.
Very low temperature atomic hydrogen masers were developed. The advantages over room temperature hydrogen masers include higher radiated power due to the higher beam intensities possible using low temperature techniques and the much smaller electron spin flip cross section at low temperatures, lower cavity and amplifier noise temperatures, increased stability against mechanical creep at low temperatures, and opportunities to extend H atom collision studies to low temperatures, where quantum effects and details of the interatomic potentials are much more important.
Electron cyclotron maser instability has been suggested as the cause of the observed short (10-20 msec), intense (an approximate brightness temperature of 10 to the 15th K) and up to 100% polarized microwave solar emission. It is shown that plasma effects and thermal cyclotron damping, ignored in previous theories, play an important role in controlling the frequency range of the emission. The radio emission is suppressed for ratios of the plasma frequency to the cyclotron frequency smaller than 0.4. An examination of the cyclotron damping, reveals that the maser action is suppressed unless a large fraction (i.e., over 10%) of the accelerated electrons participates in the emission process.
The masers were tested for environmental sensitivities (magnetic field, temperature, barometric pressure) and long-term aging. Allan variance runs of 72 days were made in order to attain averaging times from several seconds to 1 million seconds. Auto- and cross-correlation techniques were used to determine the effects of uncontrolled parameters such as humidity. Three-cornered-hat and other data reduction techniques were used to determine the characteristics of the individual masers.
The design of the new small passive hydrogen maser prototype and some anticipated design changes between the version reported and the commercial versions are discussed. Specifications of the commercial hydrogen maser and performance data of the prototype are given.
Results are presented suggesting that loss cone driven cyclotron maser emission by upgoing electrons, closely analogous to auroral kilometric radiation (AKR), may be the mechanism behind the observed Z mode radiation. With this hypothesis, the lack of a strong correlation between the Z mode radiation and AKR is not surprising; the ray paths for the X mode and the Z mode are markedly different, with the former directed upward and the latter downward. In addition, it is expected that the generation of the Z mode will be favored only in regions where the ratio of the plasma frequency to the electron cyclotron frequency is greater than or approximately equal to 0.3, that is, where the X mode radiation is suppressed. If the fraction of the radiation generated that crosses the cyclotron layer is large, then the argument in favor of the loss cone driven cyclotron maser as the source of the observed Z mode radiation is a strong one. The spatial growth rates are fairly large in comparison with those for the X mode, and there seems to be little doubt that Z mode radiation should be generated under conditions that differ only slightly from those for the generation of X mode radiation in AKR.
In response to a NASA Goddard Space Flight Center Work Assignment, Bendix Field Engineering Corporation evaluated the performance of the Oscilloquartz EPOS-2 hydrogen maser along with that of NASA NX-3 and NP-2 hydrogen masers in early 1983. This paper presents the results of that evaluation.
A low temperature atomic hydrogen maser was developed using frozen atomic neon as the storage surface. The maser has been operated in the pulsed mode at temperatures from 6 K to 11 K and as a self-excited oscillator from 9 K to 10.5 K.