Dusty plasmas
1. Crystallization
When dust grains are immersed in a plasma they become charged negatively because impinging electrons move faster than impinging ions.
The negatively charged dust grains can be considered a third plasma species so the plasma consists of electrons (negative), ions (positive), and dust grains (negative).
The dust grains can capture a substantial fraction of the electrons and so become highly charged.
The mutual repulsive force between highly charged dust grains can result in crystallization of the dust grains
A new model has been developed to explain the crystallization threshold.
This model is described in:
P. M. Bellan, A model for the condensation of a dusty plasma, Phys. Plasmas 11, 3368 (2004).
2. Astrophysical dynamos
Dust grains exposed to ultraviolet radiation can emit electrons and become positively charged. If the charge to mass ratio of these grains has a critical value they develop peculiar trajectories in combined magnetic and gravitational fields. Particles with these special trajectories can act as a dynamo suitable for driving an astrophysical jet. This process is outlined in:
P. M. Bellan, Consideration of the relationship between Kepler and cyclotron dynamics leading to prediction of a nonmagnetohydrodynamic gravity-driven Hamiltonian dynamo, Phys. Plasmas 14, Art. No. 122901 (2007)
The dynamo mechanism requires substantially more dust grains than one might expect would be available if one used the dust to gas mass ratio of the Interstellar Medium. By taking into account differences in slowing down proportions when dust and gas impinge on a molecular cloud it is shown that the dust to gas mass ratio in a molecular cloud can be substantially enriched compared to its ISM value. This enrichment process is shown in:
P. M. Bellan, Enrichment of the dust-to-gas mass ratio in Bondi/Jeans accretion/cloud systems due to unequal changes in dust and gas incoming velocities, Astrophysical Journal 678, 1099 (2008), preprint at http://arxiv.org/abs/0801.4106
3. Noctilucent clouds
Noctilucent clouds are formed from sub-micron size ice dust grains located at about 85 km altitude in polar regions (mesospheric altitude) of Earth. The dust grains can become electrically charged so as to form a dusty plasma. These clouds have unexpectedly high radar reflectivity, a phenomenon known as polar mesospheric summer echoes. It has traditionally assumed that the radar reflects from free electrons in the dusty plasma, but this idea is not consistent with observations of radar echo in situations where the dust grains have scavenged all available electrons so there are no free electrons. An alternative radar reflection mechanism has been developed whereby the radar reflects from conduction electrons in a thin layer of metallic iron or sodium coating a dust grain. This model takes into account observations showing that the presence of ice dust grains results in substantial depletion of iron and sodium atomic vapor that normally exists in distinct layers at mesospheric altitudes. The model is presented in:
P. M. Bellan, Ice iron/sodium film as cause for high noctilucent cloud radar reflectivity, JGR-Atmospheres 2008 (in press), preprint