Engineering topics

Summers, D.

Publications and source records attributed to Summers, D..

7 records

NASA NTRS1986

A model of the Io plasma ribbon

The plasma ribbon noted by Trauger's (1984) in earth-based measurements of the Io plasma torus is presently identified as the source of density fluctuations driving the plasma diffusion outward, in a linearized convection model. This model, which is found to be consistent with the Trauger data, yields simple expressions which encompass the thickness of the source ring, a linear convection cell dimension, and the exponent of the zenocentric radius power law satisfied by the plasma density in the source ring.

Summers, D.↗

NASA NTRS1985

Calculation of charge-state ratios for satellite Tor I

The diffusion of ions in a satellite plasma torus is presently modeled in terms of a one-dimensional random walk in which the particle source is at 0, the particle sink is at an N value that is an integer greater than 2, and the scale size of the diffusion cell is unity. The probability distribution function of the number of steps to exit for an ion is obtained and used in a model which incorporates ionization by electron impact to derive steady state expressions for the ratio of doubly to singly ionized ions, as well as the total number of ions in the torus. The results thus obtained are applied to the torus of the Jovian satellite Io, in order to predict mean residence times for sulfur and oxygen ions.

Summers, D.↗

NASA NTRS1985

Wave modes of the Io plasma torus

The corotating magnetospheric convection model is analyzed with the objective of deriving the fundamental wave modes present in the Io torus. The time-dependent equations of motion are linearized for the case of the absence of plasma mass and momentum sources. By separating the magnetosphere-ionosphere coupling equation into two equations and by adopting a specific analytic form for the equilibrium plasma density, a cubic equation is derived for the dispersion relation defining the angular frequencies of the fundamental wave modes. A detailed analysis of the dispersion relation yields three fundamental wave modes. One of the modes is identified as the previously studied inertial interchange (unstable) mode, while the other two are newly derived decaying modes. The results obtained are discussed in the context of plasma transport in the Io torus.

Summers, D.↗

NASA NTRS1985

Coupled low-energy - ring current plasma diffusion in the Jovian magnetosphere

The outwardly diffusing Iogenic plasma and the simultaneously inwardly diffusing ring current plasma in the Jovian magnetosphere are described using a coupled diffusion model which incorporates the effects of the pressure gradient of the ring current into the cross-L diffusion coefficient. The coupled diffusion coefficient is derived by calculating the total energy available to drive the diffusion process. The condition is imposed that the diffusion coefficient takes on a local minimum value at some point in the region L = 7-8, at which point the gradient of the Io plasma density is specified as ramp value given by Siscoe et al. (1981). The hypothesis that the pressure gradient of the ring current causes the diminution of radial plasma transport is tested, and solution profiles for the Iogenic and ring current plasma densities are obtained which imply that the Io plasma ramp is caused by a high-density, low-energy component of the ring current hitherto unobserved directly.

Summers, D.↗

NASA NTRS1982

Solutions to the equations for corotating magnetospheric convection

The equations of centrifugally driven convection appropriate to a treatment of the transport of Io plasma in Jupiter's magnetosphere are solved for two special cases of the source distribution. The results show that, in the corotating frame of Jupiter, the mass flows outward from the source, forming spirallike streamlines. It is found that the pitch of a spiral depends on the amount of resident mass and the ionospheric conductivity and that the outflow speed depends on the size of the source region, the resident mass, and the source strength of new ions. An example of a wide source and slow outflow is presented. It is noted that, in the limit of a narrow source, the outflow is rapid and the streamlines are nearly radial.

Summers, D.↗

NASA NTRS1981

Centrifugally driven diffusion of Iogenic plasma

The plasma distribution around Io as measured by Voyager 1 displays an asymmetric discontinuity at Io's orbit that has been suggested to be the signature of centrifugally driven interchange diffusion fed by plasma derived from Io. This hypothesis is explored further and found to be valid. The particular form for the diffusion coefficient appropriate to centrifugally driven turbulence is derived. The nonlinear character of this kind of diffusion is thereby made explicit. Solutions to the nonlinear, time-independent and linearized, time-dependent diffusion equations are given. These display a markedly conservative behavior. The nonlinear, steady state solutions are identical in form to the solutions of the previously studied equation of linear, atmospherically driven diffusion. The linearized, time-dependent solutions exhibit a negative feed-back quality that buffers the response of the density to changes in the source strength. Estimates of the source strength, the diffusion coefficient, and the signal propagation speed are also given.

Siscoe, G. L.↗

NASA NTRS1980

Measuring coal thickness

Laboratory tested concept, for measuring thickness of overhead coal using noncontacting sensor system coupled to controller and high pressure water jet, allows mining machines to remove virtually all coal from mine roofs without danger of cutting into overlying rock.

Barker, C.↗