Dusty plasma

A plasma containing millimeter to nanometer sized particles

A dusty plasma is a plasma containing micrometer (10−6) to nanometer (10−9) sized particles suspended in it. Dust particles are charged and the plasma and particles behave as a plasma.[1][2] Dust particles may form larger particles resulting in "grain plasmas". Due to the additional complexity of studying plasmas with charged dust particles, dusty plasmas are also known as complex plasmas.[3]: 2

Dusty plasmas are encountered in:

* Space plasmas
* The mesosphere of the Earth[4]
* Specifically designed laboratory experiments[5]

Dusty plasmas are interesting because the presence of particles significantly alters the charged particle equilibrium 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, forming so-called plasma crystals. Such plasmas are of interest as a non-Hamiltonian system of interacting particles and as a means to study generic fundamental physics of self-organization, pattern formation, phase transitions, and scaling.

## Characteristics

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

Dust plasma component  | Temperature

|

Dust temperature  | 10 K
Molecular temperature  | 100 K
Ion temperature  | 1,000 K
Electron temperature  | 10,000 K

The electric potential of dust particles is typically 1–10 V (positive or negative). The potential is usually negative because the electrons are more mobile than the ions. The physics is essentially that of a Langmuir probe that draws no net current, including formation of a Debye sheath with a thickness of a few times the Debye length. If the electrons charging the dust grains are relativistic, then the dust may charge to several kilovolts.[6] Field electron emission, which tends to reduce the negative potential, can be important due to the small size of the particles. The photoelectric effect and the impact of positive ions may actually result in a positive potential of the dust particles.

## Dynamics

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Interest in the dynamics of charged dust in plasmas was amplified by the detection of spokes in the rings of Saturn.[3] : 85  The motion of solid particles in a plasma follows the following equation:

m d v d t = F L + F G + F P + F D + F T {\displaystyle m{\frac {dv}{dt}}=\mathbf {F_{L}} +\mathbf {F_{G}} +\mathbf {F_{P}} +\mathbf {F_{D}} +\mathbf {F_{T}} }

where terms are for the Lorentz force, the gravitational forces, forces due to radiation pressure, the drag forces and the thermophoretic force respectively.[3]: 70

The Lorentz force, the contributions from the electric and magnetic force, is given by:

F L = q ( E + v c × B ) {\displaystyle F_{L}=q\left(\mathbf {E} +{\frac {\mathbf {v} }{c}}\times \mathbf {B} \right)}

where E is the electric field, v is the velocity and B is the magnetic field.[3] : 71

F g {\displaystyle \mathbf {F_{g}} } is the sum of all gravitational forces acting on the dust particle, whether it be from planets, satellites or other particles[3]: 75, 76  and  F P {\displaystyle \mathbf {F_{P}} } is the force contribution from radiation pressure. This is given as:

F P = π r d 2 c I e i ^ {\displaystyle F_{P}={\frac {\pi r_{d}^{2}}{c}}I\mathbf {\hat {e_{i}}} }

The direction of the force vector,  e i ^ {\displaystyle \mathbf {\hat {e_{i}}} } is that of the incident radiation of photon flux  I {\displaystyle I} . The radius of the dust particle is  r d {\displaystyle r_{d}} .[3]: 83

For the drag force there are two major components of interest, those from positive ions-dust particle interactions, and neutral-dust particle interactions.[3]: 76  Ion-dust interactions are further divided into three different interactions, through regular collisions, through Debye sheath modifications, and through coulomb collisions.[3]: 77

The thermophoretic force is the force that arises from the net temperature gradient that may be present in a plasma, and the subsequent pressure imbalance; causing more net momentum to be imparted from collisions from a specific direction.[3]: 80

Then depending in the size of the particle, there are four categories:

1. Very small particles, where  F L {\displaystyle \mathbf {F_{L}} } dominates over  F G {\displaystyle \mathbf {F_{G}} } .
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.
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.

## Laboratory dusty plasmas

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Dusty plasmas are often studied in laboratory setups. The dust particles can be grown inside the plasma, or microparticles can be inserted. Usually, a low temperature plasma with a low degree of ionization is used. The microparticles then become the dominant component regarding the energy and momentum transport, and they can essentially be regarded as single-species system. This system can exist in all three classical phases, solid, liquid and gaseous, and can be used to study effects such as crystallization, wave and shock propagation, defect propagation, etc.

When particles of micrometer-size are used, it is possible to observe the individual particles. Their movement is slow enough to be able to be observed with ordinary cameras, and the kinetics of the system can be studied. However, for micrometer-sized particles, gravity is a dominant force that disturbs the system. Thus, experiments are sometimes performed under microgravity conditions during parabolic flights or on board a space station.

Dust plays also an important role in fusion plasma research. Magnetic confinement fusion energy generation requires burning D-T plasma discharges for extended periods, as anticipated for ITER and any Fusion Pilot Plant. However, this presents challenges related to dust formation inside the vacuum chamber, causing impurities and affecting performance.[7][8] Dust particles, ranging from nano- to millimeter size, can be produced due to damage to plasma-facing components (PFCs) caused by high particle and heat fluxes. In fusion devices like ITER, disruptions caused by dust could significantly damage PFCs, and in-vessel dust inventory limits must be met. In some cases, dust (powders) can play a positive role, such as in-situ wall conditioning, suppression of edge-localized modes, and reduction of heat fluxes to the divertor.[9][10]

## See also

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* Padma Kant Shukla—coauthor of Introduction to Dusty Plasma Physics
* Heremba Bailung

## Notes

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1. ^ Mendis, D. A. (September 1979). "Dust in cosmic plasma environments". Astrophysics and Space Science. 65 (1): 5–12\. Bibcode:1979Ap&SS..65....5M. doi:10.1007/BF00643484. S2CID 121972351.
2. ^ Hill, J. R.; Mendis, D. A. (August 1979). "Charged dust in the outer planetary magnetospheres. I - Physical and dynamical processes". Moon and the Planets. 21 (1): 3–16\. Bibcode:1979M&P....21....3H. doi:10.1007/BF00897050. S2CID 125321897.
3. ^ a b c d e f g h i Shukla, P. K.; Mamun, A. A. (2002). Introduction to Dusty Plasma Physics. CRC Press. pp. 70–83\. ISBN 978-0-7503-0653-9.
4. ^ "Max-Planck-Institut für Sonnensystemforschung". Archived from the original on 2011-05-12. Retrieved 2012-09-30.
5. ^ Morfill, G. E.; Ivlev, Alexei (2009). "Complex plasmas: An interdisciplinary research field". Reviews of Modern Physics. 81 (4): 1353–1404\. Bibcode:2009RvMP...81.1353M. doi:10.1103/RevModPhys.81.1353.
6. ^ Mendis, D. A. (1979). "Dust in cosmic plasma environments". Astrophysics and Space Science. 65 (1): 5–12\. Bibcode:1979Ap&SS..65....5M. doi:10.1007/bf00643484. S2CID 121972351.
7. ^ Winter, J; Gebauer, G (1999). "Dust in magnetic confinement fusion devices and its impact on plasma operation". Journal of Nuclear Materials. 266–269: 228–233\. Bibcode:1999JNuM..266..228W. doi:10.1016/S0022-3115(98)00526-1.
8. ^ Krasheninnikov, S I; Smirnov, R D; Rudakov, D L (2011). "Dust in magnetic fusion devices". Plasma Physics and Controlled Fusion. 53 (8): 083001. Bibcode:2011PPCF...53h3001K. doi:10.1088/0741-3335/53/8/083001. S2CID 122645233.
9. ^ Bortolon, A; Rohde, V; Maingi, R; Wolfrum, E; et al. (2019). "Real-time wall conditioning by controlled injection of boron and boron nitride powder in full tungsten wall ASDEX Upgrade". Nuclear Materials and Energy. 19: 384–389\. Bibcode:2019NMEne..19..384B. doi:10.1016/j.nme.2019.03.022. S2CID 139572365.
10. ^ Effenberg, F; Bortolon, A; Casali, L; et al. (2022). "Mitigation of plasma–wall interactions with low-Z powders in DIII-D high confinement plasmas". Nucl. Fusion. 62 (10): 106015. arXiv:2203.15204. Bibcode:2022NucFu..62j6015E. doi:10.1088/1741-4326/ac899d. S2CID 247778852.

## External links

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* Forschungsgruppe komplexe Plasmen - DLR Oberpfaffenhofen

## References

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* Dusty Plasmas: Physics, Chemistry and Technological Impacts in Plasma Processing, John Wiley & Sons Ltd.
* Merlino, Robert L., "Experimental Investigations of Dusty Plasmas" (2005) (PDF preprint); highlights some of the history of laboratory experiments in dusty plasmas,
* Morfill, Gregor E. and Ivlev, Alexei V., "Complex plasmas: An interdisciplinary research field", Rev. Mod. Phys. 81, 1353 (2009)