Dusty plasma
Encyclopedia
A dusty plasma is a plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...

 containing nanometer or micrometer-sized particles suspended in it. Dust particles may be charged and the plasma and particles behave as a plasma, following electromagnetic laws for particles up to about 10 nm (or 100 nm if large charges are present). Dust particles may form larger particles resulting in "grain plasmas".

Dusty plasmas are encountered in:
  • Industrial processing plasmas
  • Space plasmas
    Astrophysical plasma
    An astrophysical plasma is a plasma the physical properties of which are studied as part of astrophysics. Much of the baryonic matter of the universe is thought to consist of plasma, a state of matter in which atoms and molecules are so hot, that they have ionized by breaking up into their...



Dusty plasmas are interesting because the presence of particles significantly alters the charged particle equilibrium
Charged particle equilibrium
In nuclear physics the charged-particle equilibrium occurs when the number charged particles, of each type, leaving a volume are equal to the number entering. This equilibrium exists for a volume in a medium when, for a given volume of medium, every charged particle leaving is countered by another...

 leading to different phenomena. It is a field of current research. Electrostatic coupling between the grains can vary over a wide range so that the states of the dusty plasma can change from weakly coupled (gaseous) to crystalline. Such plasmas are of interest as a non-Hamiltonian system
Hamiltonian system
In physics and classical mechanics, a Hamiltonian system is a physical system in which forces are momentum invariant. Hamiltonian systems are studied in Hamiltonian mechanics....

 of interacting particles and as a means to study generic fundamental physics of self-organization
Self-organization
Self-organization is the process where a structure or pattern appears in a system without a central authority or external element imposing it through planning...

, pattern formation, phase transition
Phase transition
A phase transition is the transformation of a thermodynamic system from one phase or state of matter to another.A phase of a thermodynamic system and the states of matter have uniform physical properties....

s, and scaling
Scaling
Scaling may refer to:* Scaling , a linear transformation that enlarges or diminishes objects* Reduced scales of semiconductor device fabrication processes...

.

Characteristics

The temperature of dust in a plasma may be quite different from its environment. For example:







Dust plasma componentTemperature
Dust temperature10 K
Molecular temperature100 K
Ion temperature1,000 K
Electron temperature10,000 K


The electric potential
Electric potential
In classical electromagnetism, the electric potential at a point within a defined space is equal to the electric potential energy at that location divided by the charge there...

of dust particles is typically 1–10 V (positive or negative). The potential is usually negative because the electrons are more mobile
Electron mobility
In solid-state physics, the electron mobility characterizes how quickly an electron can move through a metal or semiconductor, when pulled by an electric field. In semiconductors, there is an analogous quantity for holes, called hole mobility...

 than the ions. The physics is essentially that of a Langmuir probe
Langmuir probe
A Langmuir probe is a device named after Nobel Prize winning physicist Irving Langmuir, used to determine the electron temperature, electron density, and electric potential of a plasma. It works by inserting one or more electrodes into a plasma, with a constant or time-varying electric potential...

 that draws no net current, including formation of a Debye sheath
Debye sheath
The Debye sheath is a layer in a plasma which has a greater density of positive ions, and hence an overall excess positive charge, that balances an opposite negative charge on the surface of a material with which it is in contact...

 with a thickness of a few times the Debye length
Debye length
In plasma physics, the Debye length , named after the Dutch physicist and physical chemist Peter Debye, is the scale over which mobile charge carriers screen out electric fields in plasmas and other conductors. In other words, the Debye length is the distance over which significant charge...

. If the electrons charging the dust grains are relativistic, then the dust may charge to several kilovolts http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1979Ap%26SS..65....5M&db_key=AST&data_type=HTML&format=&high=42ca922c9c04735. Field electron emission, which tends to reduce the negative potential, can be important due to the small size of the particles. The photoelectric effect
Photoelectric effect
In the photoelectric effect, electrons are emitted from matter as a consequence of their absorption of energy from electromagnetic radiation of very short wavelength, such as visible or ultraviolet light. Electrons emitted in this manner may be referred to as photoelectrons...

 and the impact of positive ions may actually result in a positive potential of the dust particles.

Dynamics

The motion of solid particles in a plasma follows the momentum equation for ions and electrons:


where m, q are the mass and charge of the particle, g is the gravitation acceleration, mvcv is due to viscosity, and f represents all other forces including radiation pressure. q (E + v x B) is the Lorentz force
Lorentz force
In physics, the Lorentz force is the force on a point charge due to electromagnetic fields. It is given by the following equation in terms of the electric and magnetic fields:...

, where E is the electric field, v is the velocity and B is the magnetic field.

Then depending in the size of the particle, there are four categories:
  1. Very small particles, where q (E + v × B) dominates over mg.
  2. Small grains, where q/m ≈ √G, and plasma still plays a major role in the dynamics.
  3. Large grains, where the electromagnetic term is negligible, and the particles are referred to as grains. Their motion is determined by gravity and viscosity, and the equation of motion becomes mvcv = mg.
  4. Large solid bodies. In centimeter and meter-sized bodies, viscosity may cause significant perturbations that can change an orbit. In kilometer-sized (or more) bodies, gravity and inertia dominate the motion.
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