Dusty plasmas

1.  Water ice dusty plasmas

We have built a dusty plasma experiment where the dusty is composed of spontaneously formed water ice. The ice forms quickly and at low background pressures is not spherical but instead has a long linear shape.  These experiments are described in:

K. B. Chai and P. M. Bellan, Vortex motion of dust particles due to non-conservative ion drag force in a plasma, Phys. Plasmas 23, 023701 (2016)

K. B. Chai and P. M. Bellan, Formation and alignment of elongated, fractal-like water-ice grains in extremely cold, weakly ionized plasma, Astrophysical Journal 802, 112 (2015)

K. B. Chai and P. M. Bellan, Study on morphology and growth of water-ice grains spontaneously generated in a laboratory plasma, J. Atmos. and Solar-Terrestrial Phys. 127, 83 (2015) 

K. B. Chai and P. M. Bellan, Spontaneous formation of nonspehrical water ice grains in a plasma environment, Geophys. Res. Letters 40, 1, 2013

 

2. Dust orbits

 P. M. Bellan, Orbits of magnetized charged particles in parabolic and inverse electrostatic potentials, J. Plasma Physics 82, 615820101 (2016)

 

. 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).

 

4. 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

Three-dimensional particle orbits in combined toroidal magnetic fields, poloidal magnetic fields, and gravitational fields are shown to produce dynamos suitable for powering astrophysical jets. This is shown in:

P. M. Bellan, Dust-driven Dynamos in Accretion Disks, Astrophysical Journal 687, 311 (2008), preprint at http://arxiv.org/abs/0807.1373

 

5. 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 VOL. 113, D16215, doi:10.1029/2008JD009927, 2008

 

A later paper (see item below) notes that a metallic layer is insufficient to produce sufficient reflection and proposes that needle-shaped grains might provide sufficient reflection.

P. M. Bellan, Comment on comment by Markus Rapp and Franz-Josef Lubken on "Ice iron/sodium film as cause for high noctilucent cloud radar reflectivity" , JGR-Atmospheres 115, D13206, 2010

An analytic expression for 3-species ambipolar diffusion relevant to Polar Mesopheric Summer Echoes has been developed. This is reported in

P. M. Bellan, Meta-equilibrium state of multi-species ambipolar diffusion and its relevance to Polar Mesospheric Summer Echoes, preprint,  Journal of Atmospheric and Terrestrial Physics (JASTP) 73, 2166 (2011)

 

 

 

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