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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Prototype Coil Evaluation for NSTX-U Replacement Inner Poloidal Field Coils

The National Spherical Torus eXperiment Upgrade (NSTX-U) is an innovative magnetic fusion device constructed at the Princeton Plasma Physics Laboratory (PPPL). In 2016, because of the failure of the PF-1a upper divertor coil, which experienced a coolant blockage, the NSTX-U operation was suspended. A postmortem investigation indicated that an undetected gradual deterioration of coil inductance preceded the coolant blockage leading up to the operational suspension. The project team decided that all inner poiloidal field (PF) upper and lower coil pairs, denoted PF-1a, PF-1b, and PF-1c, shall be replaced with new coils of improved design and manufacture. Here, the new prototype inner PF coils from four suppliers across the globe were evaluated at PPPL following a prototype technical evaluation procedure. Mechanical inspection and electrical testing were performed to qualify each supplier.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

3D vacuum magnetic field modelling of the ITER ELM control coil during standard operating scenarios

In-vessel, non-axisymmetric, control coils have proven to be an important option for mitigating and suppressing edge-localized modes (ELMs) in high performance operating regimes on a growing number of tokamaks. Additionally, an in-vessel non-axisymmetric ELM control coil is being considered in the ITER baseline design. For this paper, in preparing for the initial operation of this coil set, a comprehensive study was carried out to characterize the linear superposition of the 3D vacuum magnetic field, produced by the ELM coil, on a series of equilibria representing nine standard ITER operating scenarios. Here, the spatial phase angle of toroidally distributed currents, specified with a cosine waveform, in the upper and lower rows of the ITER ELM coil (IEC) set is varied in 2° steps while holding the current in the equatorial row of coils constant. The peak current in each of the three toroidal rows of window-frame coils making up the IEC is scanned between 5 kAt and 90 kAt in 5 kAt steps and the width of the edge region covered by overlapping vacuum field magnetic islands is calculated. This width is compared to a vacuum field ELM suppression correlation criterion found in DIII-D. A minimum coil current satisfying the DIII-D criterion, along with an associated set of phase angles, is identified for each ITER operating scenario. These currents range from 20 kAt to 75 kAt depending on the operating scenario being used and the toroidal mode number (n) of the cosine waveform. Comparisons between the scaling of the divertor footprint area in cases with n = 3 perturbation fields versus those with n = 4 show significant advantages when using n = 3. In addition, it is found that the DIII-D correlation criterion can be satisfied in the event that various combinations of individual IEC window-frame coils need to be turned off due to malfunctioning components located inside the vacuum vessel. Finally, details of these results for both the full set of 27 window-frame coils and various reduced sets, using either n = 3 and n = 4 perturbation fields, are discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

The hybrid reactor project based on the straight field line mirror concept

The straight field line mirror (SFLM) concept is aiming towards a steady-state compact fusion neutron source. Besides the possibility for steady state operation for a year or more, the geometry is chosen to avoid high loads on materials and plasma facing components. A comparatively small fusion hybrid device with 'semi-poor' plasma confinement (with a low fusion Q factor) may be developed for industrial transmutation and energy production from spent nuclear fuel. This opportunity arises from a large fission to fusion energy multiplication ratio, Q{sub r} = P{sub fis}/P{sub fus}>>1. The upper bound on Q{sub r} is primarily determined by geometry and reactor safety. For the SFLM, the upper bound is Q{sub r} Almost-Equal-To 150, corresponding to a neutron multiplicity of k{sub eff}=0.97. Power production in a mirror hybrid is predicted for a substantially lower electron temperature than the requirement T{sub e} Almost-Equal-To 10 keV for a fusion reactor. Power production in the SFLM seems possible with Q Almost-Equal-To 0.15, which is 10 times lower than typically anticipated for hybrids (and 100 times smaller than required for a fusion reactor). This relaxes plasma confinement demands, and broadens the range for use of plasmas with supra-thermal ions in hybrid reactors. The SFLM concept is based on a mirror machine stabilized by qudrupolar magnetic fields and large expander tanks beyond the confinement region. The purpose of the expander tanks is to distribute axial plasma loss flow over a sufficiently large area so that the receiving plates can withstand the heat. Plasma stability is not relying on a plasma flow into the expander regions. With a suppressed plasma flow into the expander tanks, a possibility arise for higher electron temperature. A brief presentation will be given on basic theory for the SFLM with plasma stability and electron temperature issues, RF heating computations with sloshing ion formation, neutron transport computations with reactor safety margins and material load estimates, magnetic coil designs as well as a discussion on the implications of the geometry for possible diagnostics. Reactor safety issues are addressed and a vertical orientation of the device could assist passive coolant circulation. Specific attention is put to a device with a 25 m long confinement region and 40 cm plasma radius in the mid-plane. In an optimal case (k{sub eff}= 0.97) with a fusion power of only 10 MW, such a device may be capable of producing a power of 1.5 GW{sub th}.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2015

Spin coherence of the two-dimensional electron gas in a GaAs quantum well

The coherent spin dynamics of the quasi-two-dimensional electron gas in a GaAs quantum well is experimentally investigated using the time-resolved spin Kerr effect in an optical cryostat with a split coil inducing magnetic fields of up to 6 T at a temperature of about 2 K. The electron spin dephasing times and degree of anisotropy of the spin relaxation of electrons are measured in zero magnetic field at different electron densities. The dependence of the spin-orbit splitting on the electron-gas density is established. In the integral quantum-Hall-effect mode, the unsteady behavior of the spin dephasing time of 2D electrons of the lower Landau spin sublevel near the odd occupation factor ν = 3 is found. The experimentally observed unsteady behavior of the spin dephasing time can be explained in terms of new-type cyclotron modes that occur in a liquid spin texture.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Evidences of Hydrogen Trapping in Tungsten and Implications for Plasma-Facing Components

Trapping effects that include significant delays in permeation saturation, abrupt changes in permeation rate associated with temperature changes, and larger than expected inventories of hydrogen isotopes in the material, were seen in implantation-driven permeation experiments using 25-μm and 50-μm thick tungsten foils at temperatures of 638-825 K. Computer models that simulate permeation transients reproduce the steady-state permeation and reemission behavior of these experiments with expected values of material parameters. However, the transient time characteristics were not successfully simulated without the assumption of traps of substantial trap energy and concentration. An analytical model based on the assumptions of thermodynamic equilibrium between trapped hydrogen atoms and a comparatively low mobile atom concentration successfully accounts for the observed behavior. Using steady-state and transient permeation data from experiments at different temperatures, the effective trap binding energy may be inferred. We analyze a tungsten coated divertor plate design representative of those proposed for ITER and ARIES and consider the implications for tritium permeation and retention if the same trapping we observed was present in that tungsten. Inventory increases of several orders of magnitude may result.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1965

Proceedings of the Magnetics Workshop

Conference on measurement and reduction of spacecraft magnetic fields - materials and design criteria - magnetic decontamination of components - testing facilities and human tests

CONFERENCE↗
NASA NTRS1982

The NASA Space Environment Simulation Laboratory

The NASA Space Environment Simulation Laboratory (SESL) features a chamber for studying specific space plasma physics phenomena. The test chamber, an upright domed cylinder having a 17 m diam and a 27 m height for an inner working volume, is lined with magnetic field generator coils. The chamber pressure is nominally 1/1,000,000th torr. Equipment positioning is carried out by remote control from outside guided by a closed circuit television system. Plasma is generated in the chamber by means of a 30 cm Kaufman thruster which produces ion densities of 100,000-1,000,000/cu cm. The ion bulk flow energy is in the range of 20-50 eV and a charge exchange with the ambient gas produces a cold isotropic ion component. Langmuir probes provide measurements of the electron temperature and density, and the composition and pressure are monitored by mass spectrometry and ion gages. Experiments have been performed on electron beam-plasma interactions, VLF antenna impedance measurements, and high voltage plasma sheaths which may be encountered by spacecraft.

Jost, R. J.↗
NASA NTRS1992

The Galileo plasma wave investigation

The purpose of the Galileo plasma wave investigation is to study plasma waves and radio emissions in the magnetosphere of Jupiter. The plasma wave instrument uses an electric dipole antenna to detect electric fields, and two search coil magnetic antennas to detect magnetic fields. The frequency range covered is 5 Hz to 5.6 MHz for electric fields and 5 Hz to 160 kHz for magnetic fields. Low time-resolution survey spectrums are provided by three on-board spectrum analyzers. In the normal mode of operation the frequency resolution is about 10 percent, and the time resolution for a complete set of electric and magnetic field measurements is 37.33 s. High time-resolution spectrums are provided by a wideband receiver. The wideband receiver provides waveform measurements over bandwidths of 1, 10, and 80 kHz. Compared to previous measurements at Jupiter this instrument has several new capabilities. These new capabilities include (1) both electric and magnetic field measurements to distinguish electrostatic and electromagnetic waves, (2) direction finding measurements to determine source locations, and (3) increased bandwidth for the wideband measurements.

Gurnett, D. A.↗
NASA NTRS2017

Mercury Trapped Ion Frequency Standard for Ultra-Stable Reference Applications

An atomic clock including an ion trap assembly, a C-field coil positioned for generating a first magnetic field in the interrogation region of the ion trap assembly, a compensation coil positioned for generating a second magnetic field in the interrogation region, wherein the combination of the first and second magnetic fields produces an ion number-dependent second order Zeeman shift (Zeeman shift) in the resonance frequency that is opposite in sign to an ion number-dependent second order Doppler shift (Doppler shift) in the resonance frequency, the C-field coil has a radius selected using data indicating how changes in the radius affect an ion-number-dependent shift in the resonance frequency, such that a difference in magnitude between the Doppler shift and the Zeeman shift is controlled or reduced, and the resonance frequency, including the adjustment by the Zeeman shift, is used to obtain the frequency standard.

Burt, Eric A.↗
NASA NTRS2007

Loss-of-Control-Inhibitor Systems for Aircraft

Systems to provide improved tactile feedback to aircraft pilots are being developed to help the pilots maintain harmony between their control actions and the positions of aircraft control surfaces, thereby helping to prevent loss of control. A system of this type, denoted a loss-of-control-inhibitor system (LOCIS) can be implemented as a relatively simple addition to almost any pre-existing flight-control system. The LOCIS concept offers at least a partial solution to the problem of (1) keeping a pilot aware of the state of the control system and the aircraft and (2) maintaining sufficient control under conditions that, as described below, have been known to lead to loss of control. Current commercial aircraft exhibit uneven responses of primary flight-control surfaces to aggressive pilot control commands, leading to deterioration of pilots ability to control their aircraft. In severe cases, this phenomenon can result in loss of control and consequent loss of aircraft. For an older aircraft equipped with a purely mechanical control system, the loss of harmony between a pilot s command action and the control- surface response can be attributed to compliance in the control system (caused, for example, by stretching of control cables, flexing of push rods, or servo-valve distortion). In a newer aircraft equipped with a fly-by-wire control system, the major contributions to loss of harmony between the pilot and the control surfaces are delays attributable to computer cycle time, control shaping, filtering, aliasing, servo-valve distortion, and actuator rate limiting. In addition, a fly-by-wire control system provides no tactile feedback that would enable the pilot to sense such features of the control state as surface flutter, surface jam, position limiting, actuator rate limiting, and control limiting imposed by the aircraft operational envelope. Hence, for example, when a pilot is involved in aggressive closed-loop maneuvering, as when encountering a wake-vortex upset on final landing approach, the control-surface delay can lead to loss of control. Aggressive piloting can be triggered and exacerbated by control-system anomalies, which the pilot cannot diagnose because of the lack of symptoms caused by the absence of feedback through the controls. The purpose served by a LOCIS is to counteract these adverse effects by providing real-time feedback that notifies the pilot that the aircraft is tending to lag the pilot s commands. A LOCIS (see figure) includes cockpit control input-position sensors, control-surface output-position sensors, variable dampers (for example, shock absorbers containing magneto-rheological fluids such that the damping forces can be varied within times of the order of milliseconds by varying applied magnetic fields) attached to the cockpit control levers, electromagnet coils to apply the magnetic fields, and feedback control circuits to drive the electromagnet coils. The feedback control gains are chosen so that the current applied to each electromagnet coil results in a damping force that increases in a suitable nonlinear manner (e.g., exponentially) with the difference between the actual and commanded positions of the affected control surface. The increasing damping force both alerts the pilot to the onset of a potentially dangerous situation and resists the pilot s effort to command a control surface to change position at an excessive rate

AHarrah, Ralph C.↗
NASA NTRS2000

The NASA Inductrack Model Rocket Launcher at the Lawrence Livermore National Laboratory

The Inductrack magnetic levitation system, developed at the Lawrence Livermore National Laboratory, is being studied for its possible use for launching rockets. Under NASA sponsorship, a small model system is being constructed at the Laboratory to pursue key technical aspects of this proposed application. The Inductrack is a passive magnetic levitation system employing special arrays of high-field permanent magnets (Halbach arrays) on the levitating carrier, moving above a "track" consisting of a close-packed array of shorted coils with which are interleaved with special drive coils. Halbach arrays produce a strong spatially periodic magnetic field on the front surface of the arrays, while canceling the field on their back surface. Relative motion between the Halbach arrays and the track coils induces currents in those coils. These currents levitate the carrier cart by interacting with the horizontal component of the magnetic field. Pulsed currents in the drive coils, synchronized with the motion of the carrier, interact with the vertical component of the magnetic field to provide acceleration forces. Motional stability, including resistance to both vertical and lateral aerodynamic forces, is provided by having Halbach arrays that interact with both the upper and the lower sides of the track coils. In its completed form the model system that is under construction will have a track approximately 100 meters in length along which the carrier cart will be propelled up to peak speeds of Mach 0.4 to 0.5 before being decelerated. Preliminary studies of the parameters of a full-scale system have also been made. These studies address the problems of scale-up, including means to simplify the track construction and to reduce the cost of the pulsed-power systems needed for propulsion.

Tung, L. S.↗
NASA NTRS1972

Design and testing of a magnetic suspension and damping system for a space telescope

The basic equations of motion are derived for a two dimensional, three degree of freedom simulation of a space telescope coupled to a spacecraft by means of a magnetic suspension and isolation system. The system consists of paramagnetic or ferromagnetic discs confined to the magnetic field between two Helmholtz coils. Damping is introduced by varying the magnetic field in proportion to a velocity signal derived from the telescope. The equations of motion are nonlinear, similar in behavior to the one-dimensional Van der Pol equation. The computer simulation was verified by testing a 264-kilogram air bearing platform which simulates the telescope in a frictionless environment. The simulation demonstrated effective isolation capabilities for disturbance frequencies above resonance. Damping in the system improved the response near resonance and prevented the build-up of large oscillatory amplitudes.

Ockman, N. J.↗
NASA NTRS1989

Ultra-Stable Superconducting-Maser Oscillator

Unprecedented stability of frequency in superconducting, triple-cavity ruby maser oscillator achieved by incorporation of amplitude-control subsystem. New design enhances ultra-stable measurements of time by reducing fluctuations to 2 X 10 to negative 19th power routinely, and to as little as 10 to negative 20th power in exceptional cases. Currents induced in superconducting pickup coil by changes in magnetic field in ruby. Currents from coil fed to superconducting quantum-interference device (SQUID) magnetometer, output used to generate control signal for electronically variable attenuator. Attenuator varies pump-signal amplitude in response to magnetic-field fluctuations in ruby. Very high feedback-loop gain used for sensitivity of control and adequate compensation of fluctuations.

Strayer, Donald M.↗
DOE OSTI2012

Control of ion density distribution by magnetic traps for plasma electrons

The effect of a magnetic field of two magnetic coils on the ion current density distribution in the setup for low-temperature plasma deposition is investigated. The substrate of 400 mm diameter is placed at a distance of 325 mm from the plasma duct exit, with the two magnetic coils mounted symmetrically under the substrate at a distance of 140 mm relative to the substrate centre. A planar probe is used to measure the ion current density distribution along the plasma flux cross-sections at distances of 150, 230, and 325 mm from the plasma duct exit. It is shown that the magnetic field strongly affects the ion current density distribution. Transparent plastic films are used to investigate qualitatively the ion density distribution profiles and the effect of the magnetic field. A theoretical model is developed to describe the interaction of the ion fluxes with the negative space charge regions associated with the magnetic trapping of the plasma electrons. Theoretical results are compared with the experimental measurements, and a reasonable agreement is demonstrated.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗