Reconstruction Of Density Profiles Research Articles

Reconstruction of Edge-Plasma Density Profiles by Neutral Beam Probe Spectroscopy

Thermal neutral beam probing combined with a spectroscopic technique is numerically developed to reconstruct electron-density profiles of edge plasmas. Although the reconstruction has been performed by assuming all beam atoms to have a thermal velocity, the influence of a beam-velocity distribution has not received as much attention. It is shown that the method which neglects the beam-velocity distribution reconstructs electron densities lower than the true values by a factor of ∼2 in the density range up to ∼1×1013 cm-3, while the procedure which takes into account the velocity distribution yields true density profiles in the same density range. Some results of the beam probe mounted in the Heliotron-E device are also described, and good agreement with Langmuir probe measurements is found.

Resolution analysis of tomographic reconstruction of electron density profiles in the Ionosphere

AbstractTraditionally, knowledge of the ionospheric electron density is obtained using Faraday rotation or differential Doppler techniques which measure total electron content in columns of the ionosphere. Conventional data processing can only image the electron density in the direction perpendicular to these columns, thereby forming one‐dimensional images. Because this data is proportional to line integrals through the region of interest, tomographic techniques may be used to reconstruct two‐dimensional electron density images. In this paper, the resolution limit of the image reconstruction process is analyzed in terms of limited‐angle tomography.

Abel reconstruction of piecewise constant radial density profiles from x-ray radiographs

We present a method for reconstructing the radial density profile of a cylindrically symmetric object from a single x-ray projection, when the profile consists of a number of different constant sections. A forward Abel transform based algorithm is employed whereby the profile is recovered recursively, onion peelinglike, starting from the outside diameter of the object and moving in. Distortions originating in the Gibbs phenomenon, unavoidable in most available Abel inversion methods, are completely eliminated. The method is simple enough to be carried out on a handheld calculator or a spreadsheet program on a personal computer, and no elaborate computer fits or application programming are required. The method is demonstrated by inverting a simulated three-section noisy set of data and is shown to yield results of a quality equal to that of a recent powerful Abel inversion method, based on full nonlinear least-squares computer fits.

Reconstruction of discontinuous density profiles of cylindrically symmetric objects from single x-ray projections

Reconstruction of discontinuous density profiles of cylindrically symmetric objects from single x-ray projections

Pseudotomographic fitting algorithm for density profile reconstruction from a sparse 1-D interferometer array

An algorithm has been developed for fast analysis of a sparse multichord interferometer array, yielding peak density, Gaussian width, radial offset, ellipticity, and instability amplitude and frequency from line-integrated density measurements. A nonlinear least-squares fit is performed over many short time intervals, with independent variables reduced to one dimension. Assumptions of plasma rigidity and slowly evolving rotation rate are necessary to trade temporal resolution (on instability timescales) for spatial resolution across the moving plasma column. Results from the Tara tandem mirror experiment are shown.

The effect of noisy reflection data on an inverse method for determining the structure of a layered ocean bottom

A basic inverse problem in underwater acoustics is the determination of the structure of the seabed from a limited knowledge of the reflection coefficient. For many applications, an adequate model for studying the acoustic interaction is provided by the scattering of plane waves by a layered liquid medium. In contrast to formally exact solutions to this inverse scattering problem, Candel et al. [J. Sound Vib. 68, 571–595 (1980)] develop and approximate scheme which is readily implemented numerically. Under the assumption of nonabsorptive media, the reconstruction of both density and sound-speed profiles is effected by the numerical integration Of a system of four first-order differential equations requiring impulse response data for two distinct grazing angles. In this paper, the effect of additive noise on the inversion algorithm is examined for synthetic reflection data generated for a geoacoustic model of deep-sea sediments representative of the Hatteras Abyssal Plain.

Direct reconstruction of velocity and density profiles from scattered field data

A direct Born inversion algorithm is presented which separates the effects of stratified medium velocity and density gradients, thus facilitating the simultaneous reconstruction of the velocity and density profiles from scattered field data. A significant but not unexpected conclusion is that velocity and density variations cannot be separated and resolved from data acquired by a single source‐receiver configuration. Measurements at a minimum of two offset angles are required.

Morphology of the magnetospheric barium release

The magnetospheric barium release experiment of September 21, 1971, was observed by a high-performance image intensifier television camera system from Kitt Peak National Observatory, Tucson, Arizona. The system produced high-resolution video recordings of the dynamic morphology of the barium ion cloud. The system was calibrated for absolute sensitivity, thus enabling the reconstruction of the barium density profiles in the cloud. The ionized plasma expands along the field line with the velocity somewhat greater than the neutral expansion velocity. Perpendicular to the magnetic field line, the expansion of the cloud is limited by the forces exerted by the earth's magnetic field. Thus, the cloud takes up a field-aligned filamentary structure. As early as 30 sec after release, two major filaments could be distinguished. Two minutes after release, the cloud already consisted of at least 8 or 10 filamentary striationlike structures. These are formed in the low-density expanded part of the cloud. These striations and the diffuse parts of the cloud move in a direction perpendicular to the magnetic field with a velocity different from that of the main dense core of the cloud. This differential velocity moves the lower-density parts away from the main core. These lower-density parts appear to be highly structured in the form of fieldaligned striations. During the first 8 min after release, the high-density main core part erodes to a very narrow strip, which is about 12 km wide. This width of the central core is less than the diameter of the gyro-orbit of the initial velocity barium ions in the ambient magnetic field. The rapid fragmentation of the cloud to such narrow forms has interesting implications for the stability of dense magnetospheric plasma clouds.