The adiabatic motion of charged dust grains in rotating magnetospheres

Abstract

Dust grains in the ring systems and rapidly rotating magnetospheres of the outer planets such as Jupiter and Saturn may be sufficiently charged that the magnetic and electric forces on them are comparable with the gravitational force. The adiabatic theory of charged particle motion has previously been applied to electrons and atomic size particles. But it is also applicable to these charged dust grains in the micrometer and smaller size range. We derive here the guiding center equation of motion, drift velocity, and parallel equation of motion for these grains in a rotating magnetosphere. The effects of periodic grain charge-discharge have not been treated previously and have been included in this analysis. Grain charge is affected by the surrounding plasma properties and by the grain plasma velocity (among other factors), both of which may vary over the gyrocircle. The resulting chargedischarge process at the gyrofrequency destroys the invariance of the magnetic moment and causes a grain to move radially. The magnetic moment may increase or decrease, depending on the gyrophase of the charge variation. If it decreases, the motion is always toward synchronous radius for an equatorial grain. But the orbit becomes circular before the grain reaches synchronous radius, a conclusion that follows from an exact constant of the motion. This circularization can be viewed as a consequence of the gradual reduction in the magnetic moment. This circularization also suggests that dust grains leaving Io could not reach the region of the Jovian ring, but several effects could change that conclusion. Excellent qualitative and quantitative agreement is obtained between adiabatic theory and detailed numerical orbit integrations.1.

Analysis of Midlatitude Auroral Emissions Observed during the Impact of Comet Shoemaker–Levy 9 with Jupiter

“…Assuming adiabatic particle motions (Northrop and Hill 1983) we calculated trajectories of electrons and ions launched from the impact site (height 50 km) to get rough estimates of transfer times (see Appendix for equations). We picked 100 eV as the initial energy characteristic of secondary electrons, because of the similarity of spectra observed with the IUE and auroral emissions ).…”

“…We use the gyrotropic approximation (Northrop and Hill 1983) to calculate times for the hemispheric transfer of energetic charged particles. Particles are started with certain energies (see main text) and small (<5 • ) pitch angles and are followed to the other hemisphere.…”

Statistical charge distribution over dust particles in a non-Maxwellian Lorentzian plasma

“…1-10 Depending on physical system and plasma environment, the charged flux over the dust surface can be attributed to the accretion of electrons and ions from the ambient plasma and electron generation by means of photoelectric/thermionic/ secondary/electric field emission from the grain surface. 10 These charging mechanisms are random in nature which gives rise to fluctuations [11][12][13] in charge (ze) on the dust particle, even in steady state; such fluctuations causes the charge distribution over dust particles, around an average value. An intuitive expression to estimate the charge fluctuation was derived by Morfill et al 14 which suggest that the root mean square fluctuation is given by Dz ¼ z 1=2 , here z is the average charge on the dust particles; on the basis of numerical simulation this relation was further modified Cui and Goree 15 as Dz ¼ ð1=2Þ z 1=2 .…”

Dust-lower-hybrid instability with fluctuating charge in quantum plasmas

“…For example, fluctuations can alter the dust motion even in a plasma with constant electromagnetic fields, because both the electrostatic and the Lorentz forces will fluctuate as the charges fluctuate. [12][13][14] If the grain's charge fluctuates then it will affect the magnetic diffusion and the ionization fraction in dense molecular clouds and the grain motion in the planetary magnetospheres. In order to eliminate the dust particulates from the plasma discharge, the information about the dust charge becomes essential.…”