Power processor for a 30cm ion thruster

A thermal vacuum power processor for the NASA Lewis 30cm Mercury Ion Engine was designed, fabricated and tested to determine compliance with electrical specifications. The power processor breadboard used the silicon controlled rectifier (SCR) series resonant inverter as the basic power stage to process all the power to an ion engine. The power processor includes a digital interface unit to process all input commands and internal telemetry signals so that operation is compatible with a central computer system. The breadboard was tested in a thermal vacuum environment. Integration tests were performed with the ion engine and demonstrate operational compatibility and reliable operation without any component failures. Electromagnetic interference data were also recorded on the design to provide information on the interaction with total spacecraft

Electric prototype power processor for a 30cm ion thruster

An electrical prototype power processor unit was designed, fabricated and tested with a 30 cm mercury ion engine for primary space propulsion. The power processor unit used the thyristor series resonant inverter as the basic power stage for the high power beam and discharge supplies. A transistorized series resonant inverter processed the remaining power for the low power outputs. The power processor included a digital interface unit to process all input commands and internal telemetry signals so that electric propulsion systems could be operated with a central computer system. The electrical prototype unit included design improvement in the power components such as thyristors, transistors, filters and resonant capacitors, and power transformers and inductors in order to reduce component weight, to minimize losses, and to control the component temperature rise. A design analysis for the electrical prototype is also presented on the component weight, losses, part count and reliability estimate. The electrical prototype was tested in a thermal vacuum environment. Integration tests were performed with a 30 cm ion engine and demonstrated operational compatibility. Electromagnetic interference data was also recorded on the design to provide information for spacecraft integration

Operation of high power converters in parallel

High power converters that are used in space power subsystems are limited in power handling capability due to component and thermal limitations. For applications, such as Space Station Freedom, where multi-kilowatts of power must be delivered to user loads, parallel operation of converters becomes an attractive option when considering overall power subsystem topologies. TRW developed three different unequal power sharing approaches for parallel operation of converters. These approaches, known as droop, master-slave, and proportional adjustment, are discussed and test results are presented

Does matter wave amplification work for fermions?

We discuss the relationship between bosonic stimulation, density fluctuations, and matter wave gratings. It is shown that enhanced stimulated scattering, matter wave amplification and atomic four-wave mixing are in principle possible for fermionic or non-degenerate samples if they are prepared in a cooperative state. In practice, there are limitations by short coherence times.Comment: 5 pages, 1 figure

Extended performance electric propulsion power processor design study. Volume 1: Executive summary

Several power processor design concepts were evaluated and compared. Emphasis was placed on a 30cm ion thruster power processor with a beam supply rating of 2.2kW to 10kW. Extensions in power processor performance were defined and were designed in sufficient detail to determine efficiency, component weight, part count, reliability and thermal control. Preliminary electrical design, mechanical design, and thermal analysis were performed on a 6kW power transformer for the beam supply. Bi-Mod mechanical, structural, and thermal control configurations were evaluated for the power processor, and preliminary estimates of mechanical weight were determined. A program development plan was formulated that outlines the work breakdown structure for the development, qualification and fabrication of the power processor flight hardware

Extended performance electric propulsion power processor design study. Volume 2: Technical summary

Electric propulsion power processor technology has processed during the past decade to the point that it is considered ready for application. Several power processor design concepts were evaluated and compared. Emphasis was placed on a 30 cm ion thruster power processor with a beam power rating supply of 2.2KW to 10KW for the main propulsion power stage. Extension in power processor performance were defined and were designed in sufficient detail to determine efficiency, component weight, part count, reliability and thermal control. A detail design was performed on a microprocessor as the thyristor power processor controller. A reliability analysis was performed to evaluate the effect of the control electronics redesign. Preliminary electrical design, mechanical design and thermal analysis were performed on a 6KW power transformer for the beam supply. Bi-Mod mechanical, structural and thermal control configurations were evaluated for the power processor and preliminary estimates of mechanical weight were determined

Ground State Energy of the One-Component Charged Bose Gas

The model considered here is the `jellium' model in which there is a uniform, fixed background with charge density $-e\rho$ in a large volume $V$ and in which $N=\rho V$ particles of electric charge $+e$ and mass $m$ move --- the whole system being neutral. In 1961 Foldy used Bogolubov's 1947 method to investigate the ground state energy of this system for bosonic particles in the large $\rho$ limit. He found that the energy per particle is $-0.402 r_s^{-3/4} {me^4}/{\hbar^2}$ in this limit, where $r_s=(3/4\pi \rho)^{1/3}e^2m/\hbar^2$. Here we prove that this formula is correct, thereby validating, for the first time, at least one aspect of Bogolubov's pairing theory of the Bose gasComment: 38 pages latex. Typos corrected.Lemma 6.2 change

Suppression and enhancement of impurity scattering in a Bose-Einstein condensate

Impurity atoms propagating at variable velocities through a trapped Bose-Einstein condensate were produced using a stimulated Raman transition. The redistribution of momentum by collisions between the impurity atoms and the stationary condensate was observed in a time-of-flight analysis. The collisional cross section was dramatically reduced when the velocity of the impurities was reduced below the speed of sound of the condensate, in agreement with the Landau criterion for superfluidity. For large numbers of impurity atoms, we observed an enhancement of atomic collisions due to bosonic stimulation. This enhancement is analogous to optical superradiance.Comment: 4 pages, 4 figure

Dynamics of Fermionic Four-Wave Mixing

We study the dynamics of a beam of fermions diffracted off a density grating formed by fermionic atoms in the limit of a large grating. An exact description of the system in terms of particle-hole operators is developed. We use a combination of analytical and numerical methods to quantitatively explore the Raman-Nath and the Bragg regimes of diffraction. We discuss the limits in diffraction efficiency resulting from the dephasing of the grating due the distribution of energy states occupied by the fermions. We propose several methods to overcome these limits, including the novel technique of ``atom echoes''.Comment: 8 pages, 7 figure

"Supersolid" self-bound Bose condensates via laser-induced interatomic forces

We show that the dipole-dipole interatomic forces induced by a single off-resonant running laser beam can lead to a self-bound pencil-shaped Bose condensate, even if the laser beam is a plane-wave. For an appropriate laser intensity the ground state has a quasi-one dimensional density modulation --- a Bose "supersolid".Comment: 4 pages, 3 eps figure