Strong Diffusion Limit Research Articles

Endloss from a slender high beta plasma column contained in a linear solenoid

A model is presented to simulate endloss from a high beta plasma contained laterally in a straight solenoid. For slender plasma columns, the plasma lifetime depends on both the acoustic transit time (time for a sound wave to traverse one-half of the plasma length), and the characteristic radial diffusion time (diffusion of plasma across the magnetic field). In the limit of strong diffusion (which occurs for narrow high beta plasma columns), the plasma lifetime equals the hybrid lifetime which is proportional to the geometric mean of the acoustic and diffusion times. This predicted behavior stands in marked contrast with conventional endloss theories which have confinement time proportional to acoustic time alone. It is also shown that the endloss process may be accelerated considerably if the ratio of plasma radius to magnet radius is not small, due to inverse mirroring effects in the streaming plasma.

Effects of coking on the transport properties of H-mordenite

An experimental study of the relationships between coke content, catalyst activity, and intraparticle diffusivity is reported for cumene cracking on a commercial H-mordenite. Coking conditions were varied from 230 to 350 °C at space velocities from 0.20 to 0.65 wt/hr/wt and time on stream up to 6 hr. Effective diffusivities of the catalysts were found to decrease by over a factor of 2 during the coking process and are nonlinearly related to the coke level, independent of the temperature of coking. Under conditions of strong diffusion limitation, this change in diffusivity alters the catalytic effectiveness in proportion to the square root of the diffusivity ratio, ( D eff D 0 eff ) 1 2 .

Wave‐particle interactions in the magnetosphere and ionosphere

Two distinct aspects of the interaction between waves and particles in the earth's magnetosphere and ionosphere were discussed at the Yosemite Conference on Magnetosphere‐Ionosphere Coupling; these will be briefly reviewed. Intense field‐aligned currents flow between the ionosphere and magnetosphere at auroral latitudes. Under certain conditions these currents can become unstable, permitting potential drops to be established along the field lines. The present status of experimental evidence favoring such parallel electric fields is somewhat controversial. Theoretical models for their origin invoke regions of anomalous resistivity or electrostatic double layers. To date it is impossible to distinguish between these alternatives on the basis of experimental data. The nonadiabatic behavior of magnetospheric ring current particles during geomagnetic storms is largely controlled by wave‐particle processes. During the storm main phase, intense fluctuating convection electric fields are responsible for injecting trapped particles into the outer radiation zone. The outer radiation zone also moves in closer to the earth following the storm time compression of the plasmapause. Simultaneous pitch angle scattering by higher‐frequency plasma turbulence causes precipitation loss near the strong diffusion limit throughout the outer magnetosphere. During the storm recovery phase the plasmapause slowly moves out toward its prestorm location; energetic particle loss at such times appears to be dominated by cyclotron resonant scattering from electromagnetic turbulence.

A possible cause of dayside relativistic electron precipitation events

Energetic radiation belt electrons can resonate with plasma waves resulting in pitchangle scattering and a concomitant precipitation loss to the upper atmosphere. Enhanced levels of electromagnetic ULF and ELF turbulence have recently been reported in association with detached regions of high density plasma in the outer magnetosphere. This is consistent with unstable cyclotron resonant generation which occurs most favourably at plasma densities higher than normally existant outside the plasmapause. The observed amplitude of ULF turbulence is sufficient to induce parasitic pitch-angle scattering of relativistic electrons at the strong diffusion limit. Such electrons should thus precipitate with an isotropic pitch-angle distribution and for 5 ≲ L ≲ 7 could produce sufficient D-region ionization below 70 km to account for the anomalous dayside attenuation of forward scatter signals reported by Bailey. In association with such REP events one should also observe intense precipitation of less energetic electrons and protons. Similar precipitation events should occur at night preceding the dayside REP by up to 1 hr.