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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 235 records · Page 13

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NASA NTRS1980

Ion beams from laser-generated plasmas

The paper describes the space-charge-limited beams produced by the plasma blowoffs generated by 20-MW bursts of 1.06-micron radiation from an active Q-switched Nd:YAG laser. Laser power densities near 10 to the 11th/sq cm on solid targets generate thermalized plasma plumes which drift to a 15-kV gridded extraction gap where the ions are extracted, accelerated, and electrostatically focused; the spatially defined ion beams are then magnetically analyzed to determine the charge state content in the beams formed from carbon, aluminum, copper, and lead targets. This technique preserves time-of-flight (TOF) information in the plasma drift region, which permits plasma ion temperatures and mass flow velocities to be determined from the Maxwellian ion curve TOF shapes for the individual charge species.

Hughes, R. H.↗

NASA NTRS1987

Switching Circuit for Shop Vacuum System

No internal connections to machine tools required. Switching circuit controls vacuum system draws debris from grinders and sanders in machine shop. Circuit automatically turns on vacuum system whenever at least one sander or grinder operating. Debris safely removed, even when operator neglects to turn on vacuum system manually. Pickup coils sense alternating magnetic fields just outside operating machines. Signal from any coil or combination of coils causes vacuum system to be turned on.

Burley, R. K.↗

NASA NTRS2004

Filtering and Control of High Speed Motor Current in a Flywheel Energy Storage System

The NASA Glenn Research Center has been developing technology to enable the use of high speed flywheel energy storage units in future spacecraft for the last several years. An integral part of the flywheel unit is the three phase motor/generator that is used to accelerate and decelerate the flywheel. The motor/generator voltage is supplied from a pulse width modulated (PWM) inverter operating from a fixed DC voltage supply. The motor current is regulated through a closed loop current control that commands the necessary voltage from the inverter to achieve the desired current. The current regulation loop is the innermost control loop of the overall flywheel system and, as a result, must be fast and accurate over the entire operating speed range (20,000 to 60,000 rpm) of the flywheel. The voltage applied to the motor is a high frequency PWM version of the DC bus voltage that results in the commanded fundamental value plus higher order harmonics. Most of the harmonic content is at the switching frequency and above. The higher order harmonics cause a rapid change in voltage to be applied to the motor that can result in large voltage stresses across the motor windings. In addition, the high frequency content in the motor causes sensor noise in the magnetic bearings that leads to disturbances for the bearing control. To alleviate these problems, a filter is used to present a more sinusoidal voltage to the motor/generator. However, the filter adds additional dynamics and phase lag to the motor system that can interfere with the performance of the current regulator. This paper will discuss the tuning methodology and results for the motor/generator current regulator and the impact of the filter on the control. Results at speeds up to 50,000 rpm are presented.

Kenny, Barbara H.↗

NASA NTRS1966

DC to DC converter controlled by a magnetically-coupled multivibrator with asymmetrical output.

Nondissipatively regulated variable frequency DC TO DC converter with variable on time and variable off time

VOLTAGE REGULATOR↗

NASA NTRS2014

Development of Cryogenic Filter Wheels for the HERSCHEL Photodetector Array Camera & Spectrometer (PACS)

This paper describes the two PACS Filter Wheels that are direct-drive rotational mechanisms operated at a temperature below 5K inside the PACS focal plane unit of the Herschel Satellite. The purpose of the mechanisms is to switch between filters. The rotation axis is pivoted to the support structure via a slightly preloaded pair of ball bearings and driven by a Cryotorquer. Position sensing is realized by a pair of Hall effect sensors. Powerless positioning at the filter positions is achieved by a magnetic ratchet system. The key technologies are the Cryotorquer design and the magnetic ratchet design in the low temperature range. Furthermore, we will report on lessons learned during the development and qualification of the mechanism and the paint.

Koerner, Christian↗

NASA NTRS1977

Potential damage to DC superconducting magnets due to the high frequency electromagnetic waves

Experimental data are presented in support of the hypothesis that a dc superconducting magnet coil does not behave strictly as an inductor, but as a complicated electrodynamic device capable of supporting electromagnetic waves. Travel times of nanosecond pulses and evidence of sinusoidal standing waves were observed on a prototype four-layer solenoidal coil at room temperature. Ringing observed during switching transients appears as a sequence of multiple reflected square pulses whose durations are related to the layer lengths. With sinusoidal excitation of the coil, the voltage amplitude between a pair of points on the coil exhibits maxima at those frequencies such that the distance between these points is an odd multiple of half wavelength in free space. Evidence indicates that any disturbance, such as that resulting from switching or sudden fault, initiates multiple reflections between layers, thus raising the possibility for sufficiently high voltages to cause breakdown.

Gabriel, G. J.↗

NASA NTRS1996

A Hybrid Nonlinear Control Scheme for Active Magnetic Bearings

A nonlinear control scheme for active magnetic bearings is presented in this work. Magnet winding currents are chosen as control inputs for the electromechanical dynamics, which are linearized using feedback linearization. Then, the desired magnet currents are enforced by sliding mode control design of the electromagnetic dynamics. The overall control scheme is described by a multiple loop block diagram; the approach also falls in the class of nonlinear controls that are collectively known as the 'integrator backstepping' method. Control system hardware and new switching power electronics for implementing the controller are described. Various experiments and simulation results are presented to demonstrate the concepts' potentials.

Xia, F.↗

NASA NTRS1984

Metal vapor vacuum arc switching - Applications and results

The design of metal-vapor vacuum-arc switches (MVSs) for electromagnetic launchers is discussed, and preliminary results are presented for an experimental MVS. The general principles of triggered-vacuum-gap and vacuum-interrupter MVSs are reviewed, and the requirements of electromagnetic launchers are analyzed. High-current design problems such as electrode erosion, current sharing, magnetic effects, and thermal effects are examined. The experimental MVS employs stainless-steel flanges, a glass vacuum vessel, an adjustable electrode gap, autonomous internal magnetic-field coils, and a tungsten-pin trigger assembly. Some results from tests without magnetic augmentation are presented graphically.

Cope, D.↗

NASA NTRS2019

Design of Low Inductance Busbar for 500 kVA Three-Level ANPC Converter

The adoption of SiC devices in high power applications enables higher switching speed, which requires lower circuit parasitic inductance to reduce the voltage overshoot. This paper presents the design of a busbar for a 500 kVA three-level active natural clamped converter. The layout of the busbar is discussed in detail based on the analysis of the multiple commutation loops, magnetic cancelling effect, and DC-link capacitor placement. The loop inductance of the designed busbar is verified with simulation, impedance measurements and converter experiment. The results can match with each other and the inductances of small and large loop are 6.5 nH and 17.5 nH respectively, which is significantly lower than the busbars of NPC type converters in other references.

SiC MOSFET↗

NASA NTRS1975

The Rome-GSFC magnetic field experiment for Helios A and B /E 3/

The Rome-GSFC magnetic field experiment utilizes a triaxial fluxgate (saturable inductor) magnetometer. The sensor unit is mounted on the end of a boom approximately four meters from the spacecraft spin axis. The three analog outputs of the magnetometer are converted into three 9 bit digital words. The experiment utilizes an automatic inflight range switch to select the optimum dynamic range out of 4 ranges. A nonmagnetic thermally oscillating actuator is used to reorient the sensor unit by 90 deg to determine all three axes zero levels. The accuracy should be approximately plus or minus 0.1 gamma. The vector measurements are made at equal intervals in time ranging from 16 per second down to 1 per second depending on the telemetry bit rate.

Scearce, C.↗

NASA NTRS1983

Advanced electrical power system technology for the all electric aircraft

The application of advanced electric power system technology to an all electric airplane results in an estimated reduction of the total takeoff gross weight of over 23,000 pounds for a large airplane. This will result in a 5 to 10 percent reduction in direct operating costs (DOC). Critical to this savings is the basic electrical power system component technology. These advanced electrical power components will provide a solid foundation for the materials, devices, circuits, and subsystems needed to satisfy the unique requirements of advanced all electric aircraft power systems. The program for the development of advanced electrical power component technology is described. The program is divided into five generic areas: semiconductor devices (transistors, thyristors, and diodes); conductors (materials and transmission lines); dielectrics; magnetic devices; and load management devices. Examples of progress in each of the five areas are discussed. Bipolar power transistors up to 1000 V at 100 A with a gain of 10 and a 0.5 microsec rise and fall time are presented. A class of semiconductor devices with a possibility of switching up to 100 kV is described. Solid state power controllers for load management at 120 to 1000 V and power levels to 25 kW were developed along with a 25 kW, 20 kHz transformer weighing only 3.2 kg.

Finke, R. C.↗

NASA NTRS1983

Advanced electrical power system technology for the all electric aircraft

Finke, R. C.↗

NASA NTRS1984

Global excitation of wave phenomena in a dissipative multiconstituent medium. I - Transfer function of the earth's thermosphere. II - Impulsive perturbations in the earth's thermosphere

A transfer function approach is taken in constructing a spectral model of the acoustic-gravity wave response in a multiconstituent thermosphere. The model is then applied to describing the thermospheric response to various sources around the globe. Zonal spherical harmonics serve to model the horizontal variations in propagating waves which, when integrated with respect to height, generate a transfer function for a vertical source distribution in the thermosphere. Four wave components are characterized as resonance phenomena and are associated with magnetic activity and ionospheric disturbances. The waves are either trapped or propagate, the latter becoming significant when possessing frequencies above 3 cycles/day. The energy input is distributed by thermospheric winds. The disturbances decay slowly, mainly due to heat conduction and diffusion. Gravity waves appear abruptly and are connected to a sudden switching on or off of a source. Turn off of a source coincides with a reversal of the local atmospheric circulation.

Mayr, H. G.↗

NASA NTRS1988

Adiabatic demagnetization refrigerator for use in zero gravity

In this effort, a new design concept for an adiabatic demagnetization refrigerator (ADR) that is capable of operation in zero gravity has been developed. The design uses a vortex precooler to lower the initial temperature of magnetic salt from the initial space superfluid helium dewar of 1.8 K to 1.1 K. This reduces the required maximum magnetic field from 4 Tesla to 2 Tesla. The laboratory prototype vortex precooler reached a minimum temperature of 0.78 K, and had a cooling power of 1 mW at 1.1 K. A study was conducted to determine the dependence of vortex cooler performance on system element configuration. A superfluid filled capillary heat switch was used in the design. The laboratory prototype ADR reached a minimum temperature of 0.107 K, and maintained temperatures below 0.125 K for 90 minutes. Demagnetization was carried out from a maximum field of 2 T. A soft iron shield was developed that reduced the radial central field to 1 gauss at 0.25 meters.

Dingus, Michael L.↗

NASA NTRS1982

Component technology for space power systems

The Lewis/OAST program for the development of Component Technology for Space Power Systems is described. The program is divided into five generic areas: semiconductor devices (transistors, thyristors, and diodes); conductors (materials and transmission lines); dielectrics; magnetic devices; and thermal control devices. Examples of progress in each of the five areas is discussed. Bipolar power transistors up to 1000 V at 100 A with a gain of 10 and a 0.5 mu sec rise and fall time are presented. A new class of semiconductor devices with a possibility of switching 1000 000 V is described. Several 100 kW rotary power transformer designs and a 25 kW, 20 kHz transformer weighting 3.2 kg have been developed. Progress on the creation of diamond-like films for thermal devices and intercalated carbon fibers with the strength of steel and the conductivity of copper at one third the mass of copper is presented.

Finke, R.↗

NASA NTRS2001

The Electromagnetic Compatibility (EMC) Design Challenge for Scientific Spacecraft Powered by a Stirling Power Converter

A 55 We free-piston Stirling Technology Demonstration Convertor (TDC) has been tested as part of an evaluation to determine its feasibility as a means for significantly reducing the amount of radioactive material required compared to Radioisotope Thermoelectric Generators (RTGs) to support long-term space science missions. Measurements were made to quantify the low frequency magnetic and electric fields radiated from the Stirling's 80 Hertz (Hz) linear alternator and control electronics in order to determine the magnitude of reduction that will be required to protect sensitive field sensors aboard some science missions. One identified "Solar Probe" mission requires a 100 dB reduction in the low frequency magnetic field over typical military standard design limits, to protect its plasma wave sensor. This paper discusses the electromagnetic interference (EMI) control options relative to the physical design impacts for this power system, composed of 3 basic electrical elements. They are (1) the Stirling Power Convertor with its linear alternator, (2) the power switching and control electronics to convert the 90 V, 80 Hz alternator output to DC for the use of the spacecraft, and (3) the interconnecting wiring including any instrumentation to monitor and control items 1 and 2.

Sargent, Noel B.↗

NASA NTRS1975

Self-scanned Digicon - A digital image tube for astronomical spectroscopy

We have successfully fabricated, tested, and operated a digital image tube consisting of a magnetically focused image intensifier tube in which a self-scanned linear array of 1024 silicon photodiodes operating in the EBS mode serves as the photoelectron image detector, amplifier, and intermediate image storage device. Integral on-chip MOS shift registers driven by an external clock sequentially interrogate the photodiodes through MOS FET multiplex switch arrays. Each output frame is a sequence of 256 analog pulses on each of four video lines. Laboratory and observing tests show that the output signal is photoelectron shot noise limited over at least a range of 1-100,000 detected photoelectrons per picture element, indicating that single photon detection is achieved. High-resolution astronomical spectroscopy has been carried out in the coude spectrograph of the 2.7-m telescope at McDonald Observatory. Examples are shown.

Tull, R. G.↗

NASA NTRS1999

Diffusion, Fluxes, Friction Forces, and Joule Heating in Two-Temperature Multicomponent Magnetohydrodynamics

The relationship between Joule heating, diffusion fluxes, and friction forces has been studied for both total and electron thermal energy equations, using general expressions for multicomponent diffusion in two-temperature plasmas with the velocity dependent Lorentz force acting on charged species in a magnetic field. It is shown that the derivation of Joule heating terms requires both diffusion fluxes and friction between species which represents the resistance experienced by the species moving at different relative velocities. It is also shown that the familiar Joule heating term in the electron thermal energy equation includes artificial effects produced by switching the convective velocity from the species velocity to the mass-weighted velocity, and thus should not be ignored even when there is no net energy dissipation.

Chang, C. H.↗