Return Flux Research Articles

Modeling of Atmosphere Explorer‐D Return Flux Experiment

Codes for the prediction of spacecraft environments are currently in widespread use; however, few if any comparisons of code results with experimental measurements have been performed. In this paper we report the results of calculations performed for the Atmosphere Explorer‐D satellite at an altitude of approximately 250 km. Measurements of the atmospheric composition at the ram surface of the spacecraft were obtained by a closed source mass spectrometer before and during the operation of a return flux experiment in which a neon plume was directed into the spacecraft velocity vector. Calculations using the Integrated Spacecraft Environment Model (ISEM) reproduced the measured fluxes of the ambient species immediately before and during the venting operation. The presence of the neon plume reduced the flux of ambient species reaching the detector. The model reproduced these trends and gave a range of calculated neon return flux with a mean approximately equal to the value derived from the measurements. The model predicted a surface density of ambient species approximately 33 times the ambient level with and without the plume and nonnegligible scattering of neon into the wake of the spacecraft during plume operation.

The relationship of sunspot magnetic fields to umbral sizes in return flux theory

view Abstract Citations (20) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Relationship of Sunspot Magnetic Fields to Umbral Sizes in Return Flux Theory Osherovich, Vladimir A. ; Garcia, Howard A. Abstract The relationship between the relative size of a sunspot umbra and the relative magnitude of the magnetic field at the outer edge of the penumbra is studied. It is found that the sunspot magnetic topology is composed of two magnetic regimes, one consisting of open field lines emerging from the core and extending to infinity, and the second consisting of lines returning to the photosphere. The relative quantity of the return magnetic flux is closely associated with the size of the umbra relative to the penumbra. Publication: The Astrophysical Journal Pub Date: January 1989 DOI: 10.1086/167025 Bibcode: 1989ApJ...336..468O Keywords: Penumbras; Solar Magnetic Field; Sunspots; Umbras; Magnetic Field Configurations; Magnetic Flux; Magnetohydrodynamics; Solar Physics; Solar Physics; HYDROMAGNETICS; SUN: MAGNETIC FIELDS; SUN: SUNSPOTS full text sources ADS |

Helmholtz coils revisited

Two circular coaxial current rings of radius a, separated by a distance b, are usually called Helmholtz coils if b=a. That is the well-known prescription for greatest uniformity of field in the neighborhood of the center of symmetry. Examined here is the magnetic field of a pair of current rings at a distance r from the center large compared to the ring radius a. Expanding the distant field in powers of a/r, each term may be associated with a magnetic 2k-pole source and a field falling off as (a/r)k+2. The dipole field k=1, falling as (a/r)3, has as its source the total dipole moment of the two rings. It eventually swamps the contribution of higher multipoles. The term (a/r)5 with k=3 has for its source the octupole (23-pole) moment of the pair of rings. Its coefficient vanishes if b=a. Thus the Helmholtz pair, thanks to its seemingly irrelevant specialization for uniform central field, is also endowed with zero octupole moment. The term-by-term connection between the expansion of the distant field and the expansion of the central field holds for currents entirely confined to the surface of a sphere, which is the case for the Helmholtz pair of thin current rings. The dipole field can be nullified by nesting the Helmholtz pair within a larger Helmholtz pair designed to have equal area × ampere–turns but carrying reversed current. At the cost of a minor reduction in central field and without compromising the central field’s uniformity, the total dipole moment of the four rings can thus be made zero. The current system now has zero dipole moment and zero octupole moment. As 2k -poles with k even are ruled out by symmetry, the lowest surviving multipole is the 25-pole, the ‘‘32-pole.’’ The residual distant field, of which it is now the dominant source, falls as (a/r)7. An exact calculation of the ratio of field magnitude B to central field B0 shows that B/B0 is closely proportional to (a/r)7 everywhere in the field beyond r≊5a. Already at r≊6a, B/B0 has fallen to 10−4. It is shown how equivalent results can be achieved with coils of finite cross section. This scheme can drastically reduce the ‘‘stray field’’ around a superconducting magnet. In effect, it closely confines most of the return flux. Another application involves the induction of alternating currents by precessing magnetic moments. The four coils connected in series constitute a receiving coil tightly coupled to any oscillating dipole at its center, but virtually immune to disturbance by external sources.

Tactile stimulation device for hearing‐impaired individuals

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Scattering from a magnetic flux line due to the Lorentz force of the return flux.

The differential cross section for the scattering of an electron by an impenetrable, infinitely long magnetic flux line with return magnetic flux uniformly distributed on the surface of a cylinder of radius a is calculated. The scattering is due to the Lorentz force from the magnetic field of the return flux. In the limit as the radius of the return flux goes to infinity (a\ensuremath{\rightarrow}\ensuremath{\infty}), the differential scattering cross section is the same as that obtained by Aharonov and Bohm (AB) for the scattering of an electron by an impenetrable, infinitely long magnetic flux line without return flux. The AB scattering cross section is, however, attributed to the effect of the vector potential in a field-free region so no force acts on the electron.

Spacelab-1 observations of suprathermal electrons induced by artificial electron beams

Suprathermal electrons precipitated in response to SEPAC electron accelerator activity on board Spacelab 1 have been observed by a channeltron electron spectrometer covering the energy range from 0.1 to 12.5 keV. Three series of beams of 1 to 5 seconds duration with current strengths up to 300 mA and energies up to 5 keV induced electron fluxes up to 10 11 electrons eV −1cm −2s −1sr −1. The FO-2 series showed a very high electron enhancement below and at the beam energy and a distinct fall off above it, while the FO-7-1 and FO-7-2 series showed a somewhat lower electron enhancement without indication of the beam energy in the flux density curves. A characteristic feature of all SEPAC series was an enhanced electron flux above the beam energy of more than 100 times the background level. The return flux distribution did not respect the forbidden single particle trajectory regime resulting from spacecraft obstruction but seemed to depend mainly on the coelevation angle according to the beam direction and on the line of sight from the spectrometer to the accelerator.

Return flux measurements in response to short-time electron beams aboard Spacelab-1

Measurements of the returning electron flux distribution in response to 8 keV, 10 to 100 mA, 20 to 40 ms electron beams of the PICPAB particle accelerator on board Spacelab-1 were performed by an electron spectrometer in the energy range from 0.1 to 12.5 keV (experiment 1ES019A). The electron flux followed almost immediately the beam within the sampling interval of 1 ms. A major flux increase was found at low energies, but also up to the beam energy. The effects of different beam currents and of payload charging are discussed.

Space Shuttle Orbiter molecular environment induced by the supplemental flash evaporator system

The water vapor environment of the Space Shuttle Orbiter induced by the supplemental flash evaporator during the on-orbit flight phase has been analyzed based on Space II model predictions and orbital flight measurements. Model data of local density, column density, and return flux are presented. Results of return flux measurements with a mass spectrometer during STS-2 and of direct flux measurements during STS-4 are discussed and compared with model predictions.

Does the return flux result in the Aharonov-Bohm scattering amplitude?

Introducing a new Aharonov-Bohm-type scattering model, the ambiguity of the incoming wave function is avoided and the single-valued wave function is uniquely determined by proper boundary conditions. In our model, however, the return flux plays an important role in deriving the Aharonov-Bohm scattering amplitude.

The loop-gap resonator. II. Controlled return flux three-loop, two-gap microwave resonators for ENDOR and ESR spectroscopy

In a previous paper ( I, W. Froncisz and J. S. Hyde, J. Magn. Reson. 47, 515 (1982) ), one-loop, multigap microwave resonators were described with emphasis on applications to ESR spectroscopy. In the present paper, n-loop, m-gap resonators are introduced, where there are n parallel loops with a shared gap connecting adjacent loops, there being ( n − 1) = m gaps in all, and an analysis of three-loop, two-gap resonators is presented. Calculations of resonant frequencies are compared with experiment. The structure exhibits two resonant modes, a fundamental mode where magnetic flux is excluded from the central loop, and a higher frequency mode in which flux links all three loops. This latter mode is used for ESR and ENDOR spectroscopy. The sample fills the central loop with a filling factor of about 0.4, and one side loop is used for inductive coupling. A 25% tuning range can be achieved by introduction of a metallic conductor into the intense magnetic field of the other side loop. Lines of magnetic flux are well controlled in the three-loop, two-gap resonator, permitting juxtaposition of radiofrequency coils suitable for ENDOR without interference between the coils and the microwave fields.

A note on the values of the vertical gradient of the magnetic field in the return flux sunspot model

The Return Flux (RF) sunspot model (Osherovich, 1982) imposes a restriction on the value of the vertical gradient of the magnetic field, dB/dz, analogous to a restriction implied by the self-similar sunspot model of Schluter and Temesvary (ST). The maximum value of the gradient, (dB/dz)max, is shown to be 10% smaller in the RF model than in the ST model. The dependence of (dB/dz)max on the sunspot radius is predicted.

Elaboration of the new magnetohydrostatic sunspot theory (double return flux model)

An extension of the recently formulated Return Flux Sunspot Model is presented. The basic equation for a Double Return Flux Sunspot Model is derived, and a pressure distribution and magnetic field are calculated. The possible topology of the magnetic structure and its thermodynamic consequences are discussed. The paper includes a magnetogram of a single round sunspot (9 August, 1981). The authors attempt to interpret the observational data for the vertical component of magnetic field of this sunspot on the basis of the Double Return Flux Model.

Kinetics of zinc absorption by the rat jejunum: effects of adrenalectomy and dexamethasone.

Effects of dexamethasone and adrenalectomy on the kinetics of jejunal 65Zn uptake and absorption were studied in the anesthetized adult rat. The jejunal lumen was perfused in situ with 5 mM glucose in 150 mM saline containing 65Zn and [14C]polyethylene glycol as volume marker. Over the 30-min perfusion period, the rate of net 65Zn removal from the perfusate was biexponential due to the establishment of a return flux to the lumen. An open two-compartment model satisfactorily describes these observations: (formula; see text) Dexamethasone (2 mg/kg ip 7 h before perfusion) increased k12 by 75% (P less than 0.0002) and decreased k20 by 45% (P less than 0.04). Both effects were independent of adrenalectomy. Mathematical simulations using the compartmental model and experimentally determined kinetic constants predicted that transfer of 65Zn into the body should be enhanced by adrenalectomy and retarded by dexamethasone administered to adrenalectomized rats. Dexamethasone and adrenalectomy thus differentially affect Zn uptake and absorption in this system, suggesting a possible adrenocortical hormone involvement in the regulation of Zn absorption. These changes are apparently not mediated via metallothionein.

Angular momentum paradoxes with solenoids and monopoles

The Poynting vector produced by crossing the Coulomb field from a charged particle with a distant external magnetic field gives rise to a physical angular momentum which must be included in applications of angular momentum conservation and quantization. Simple examples show how the neglect of the return flux in an infinite solenoid or in two-dimensional models can lead to unphysical effects, how the Dirac charge quantization is obtained and can be modified by the presence of additional long range forces, and why the origin must be excluded in describing the motion of a point charge in the field of a fixed point monopole.

Vibratory ribbon speaker

A vibratory ribbon speaker according to this invention as disclosed comprises a series of permanent magnets secured on opposite faces of a pair of soft iron bars mounted in edge-opposed, spaced-apart relation providing an air return flux path and a working air gap in which is suspended an elongated wavy or corrugated non-magnetic ribbon, several feet in length, flexibly and resiliently supported in said air gap at numerous spaced-apart stations along the ribbon length.

Future Prospects of the TPC Idea

General aspects affecting TPC size, readout plane characteristics and operation in the LEP environment are presented, with the general conclusion that modest improvements relative to PEP-4 can be realized in several areas. The problem of positive ion reduction is discussed according to two qualitatively new operating modes, asynchronous and synchronous gating. Either gating mode appears to offer a means to eliminate almost completely the ion return flux. Some speculative ideas involving 3-component gas mixtures, low-mass components and parallel plane geometry are presented as future possibilities.

Spacecraft outgas ambient flow interaction

An investigation has been made of the extent to which outgassed or emitted molecules return to a spacecraft as a result of intermolecular collisions with ambient freestream molecules. The governing parameters are discussed and heuristic arguments are used to predict the combination of parameters that is most likely to describe the return flux ratio. This is then tested by an extensive set of numerical calculations using the direct simulation Monte Carlo method. Computations have been made for the flow past spheres and past circular cylinders with their axes normal in the stream. The numerical results lead to empirical expressions that can be used for engineering estimates in spacecraft contamination studies.

A Rapid Cycling Synchrotron Magnet with Separate AC and DC Circuits

In present rapid cycling synchrotron magnets ac and dc currents flow in the same coil to give the desired field. The circuit reactance is made zero at dc and the operating frequency by running the magnet in series with an external parallel resonant LC current. We propose to return the ac flux in a gap next to the synchrotron. The dc coil encloses the ac magnetic circuit and thus links no ac flux. A shorted turn between the dc coil and ac flux enhances the separation of the two circuits. Several interesting developments are possible. The dc coil could be a stable superconductor to save power. The ac flux return gap could be identical with the synchrotron gap and contain a second synchrotron. This would double the output of the system. If the return flux gap were used for a booster, the ac coil power could be greatly reduced or radiation hardening of the ac coil could be simplified.

One-dimensional outgassing problem

A predominantly numerical study, using the direct simulation Monte Carlo method, of the flow from outgassing surfaces with plane, cylindrical, or spherical geometry is presented. The numerical results for the plane flow case are compared with existing theoretical and experimental results, and also with a new formulation of the jump conditions across the Knudsen layer between the surface and the continuum outflow. This outflow is sonic for the free expansion case, but subsonic in the presence of back-pressure effects. The self-scattered return flux is 19% of the outgassed flux in the sonic outflow case and increases at lower Mach numbers. Thermal accomodation and reflection of this return flux produces an outgassing cooling effect. The cylindrical and spherical geometries introduce an additional Knudsen number defined by the ratio of the mean free path in the effusing gas to the radius. The plane flow results apply when this Knudsen number is less than 0.001 and, when it is of order unity or above, the return flux is inversely proportional to it.

Comparison of satellite self‐contamination experiments and scattering return flux calculations

Gaseous emissions from a spacecraft modify the orbital environment and degrade the observations of distant radiation sources. These emissions also provide contamination fluxes induced by self‐scattering and scattering with ambient particles. Experiments were carried out on the orbiting Atmosphere Explorer D satellite (AE‐D) to verify the calculated return fluxes of a neon source. Known rates of neon were emitted in the direction of the velocity vector on command from the MRMU (molecular return measurement unit). At 250 km the neutral mass spectrometer indicated a total neon return flux of 2.46 × 10−2 times the emitted flux. The calculated fraction was 1.23 × 10−2, including 9.14 × 10−3 for the ambient scatter and 3.54 × 10−3 for the altitude‐independent self‐scatter. The pressure gages indicated pressures less than 7 × 10−6 torr at altitudes from 161 to 210 km. The maximum pressure for 161‐km orbit was calculated as 7.4 × 10−7 torr.