Recovered: Dusty Plasmas

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Re: Recovered: Dusty Plasmas

Unread postby StefanR » Tue Jul 14, 2009 4:51 am

Under certain conditions novel phenomena appear at the lower boundary of this void under gravity conditions: Bubbles form, which ''explode'' upwards into the void, like shown on the picture to the right (Enlarge. Courtesy of M. Kretschmer). Droplets or blobs such as the one shown on the cover appear, ejecting particles into the void. Another phenomenon is the formation of cusps in the particle cloud, which are pointing upwards. These cones remind of so-called ''Taylor cones'', which form in liquids under the influence of electric fields and surface tension.
Image

Image
The picture on the cover demonstrates that the blobs were completely independent from the rest of the particle cloud. The illustration results from a tomographic procedure in which the droplet is recorded in vertical cuts that are later combined to a three-dimensional image.

Even though the droplets and bubbles contain only a few hundreds of particles, they demonstrate many effects typical for fluids. The particles inside the blobs move in vortices like in the case of water drops in an air stream, and there is evidence of surface tension. In contrast to water molecules, in complex plasmas the individual particles can be directly observed and examined. This makes complex plasmas the ideal model system for the dynamical analysis of such phenomena.
http://www.mpe.mpg.de/PKE/News_e.html

Evidence of dust dynamics near surfaces in the solar system ranges from particles observed levitating above the lunar horizon by the Surveyor spacecraft to the more recently discovered dust ‘ponds’ on asteroid Eros. Such dust dynamics are most likely the result of interactions between charged dust particles and plasma sheaths above planetary surfaces.
Image
Particles of JSC-1 (lunar regolith simulant) levitating in a plasma sheath above a plate in the laboratory.

My thesis work involved experimental investigations of dust charging and dynamics near surfaces with sheaths and related the results to environments on the Moon, Eros, and Mercury. Thus I have a continuing interest in dust dynamics near the surfaces of bodies in the Solar System. For additional details, please see my publications on dust dynamics (listed below) and/or the Univ. of Colorado's dusty plasma group.
http://amandagulbis.saao.ac.za/gulbis-dust-dynamics/
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Re: Recovered: Dusty Plasmas

Unread postby Harry Costas » Tue Jul 14, 2009 6:26 am

G'day from the land of ozzzzzz

Thank you for that information.

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Re: Recovered: Dusty Plasmas

Unread postby StefanR » Tue Mar 23, 2010 9:46 am

Image
One of the experiments in the PK-3 Plus laboratory will deal with "binary" complex plasmas: if two kinds of particles with different sizes are suspended in a homogeneous plasma, one could expect them to mix due to mutual repulsion. Previous experiments on board the ISS, however, have shown a clear phase separation of the two particles clouds (see figure 2).

"This phenomenon is well known from many different systems, such as molecular liquids or colloidal suspensions, and has been studied for a long time," says Hubertus Thomas, MPE-scientist and coordinator of the PK-3 Plus experiments. "In complex plasmas, for the first time we can now study these processes looking at the movement of individual particles and we hope that our latest experiments will lead to new insights into the physics of phase separation."

http://www.mpe.mpg.de/Highlights/PR20100127/text.html
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Re: Recovered: Dusty Plasmas

Unread postby solrey » Tue Mar 23, 2010 11:45 am

Thanks stefanr. Good stuff. Found this in the course of my digging into it a bit.

Magnetic fields and electrodynamics of dense interstellar plasma clouds

The aim of the project is to study and better understand the physics of dense interstellar plasma clouds. Such clouds, which are often filamentary, consist of cold and dusty plasma and are the sites where stars and planetary systems are formed. In recent years it has become increasingly clear that magnetic fields are of vital importance for the behaviour of the clouds. The clouds are mainly studied in several molecular lines, in integrated light, and by means of polarimetric methods. The studies are performed in close co-operation with astronomers at the Stockholm and Helsinki observatories. Clear evidence of helical magnetic fields in some of the clouds has been found implying the presence of electric currents. As a complement to the observational investigations, theoretical and numerical modelling of the clouds and their electrodynamic and polarimetric properties are performed. New insights have also been gained concerning the capability of the clouds to polarise light of background stars.


Research leader is Per Carlqvist.
A fine example of current plasma cosmology research for those skeptics who think it ends with Peratt's work in the early 90's. It's happening, but one has to look in Eurasia (primarily) to find it.
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Re: Recovered: Dusty Plasmas

Unread postby StefanR » Thu Mar 25, 2010 8:49 am

solrey wrote:A fine example of current plasma cosmology research for those skeptics who think it ends with Peratt's work in the early 90's. It's happening, but one has to look in Eurasia (primarily) to find it.

Yep, these are nice places to wander around a bit.
These annual reports on that site you give also are very interesting:
http://www.spp.ee.kth.se/KTH-EE-SPP-Annual-Report-2008.pdf

Also Per Carlqvist is now researching Electric Mammoth's ;) :

Abstract
NGC 1316 is a giant, elliptical galaxy containing a complex network of dark, dust features. The morphology of these features has been examined in some detail using a Hubble Space Telescope, Advanced Camera for Surveys image. It is found that most of the features are constituted of long filaments. There also exist a great number of dark structures protruding inwards from the filaments. Many of these structures are strikingly similar to elephant trunks in H ii regions in the Milky Way Galaxy, although much larger. The structures, termed mammoth trunks, generally are filamentary and often have shapes resembling the letters V or Y. In some of the mammoth trunks the stem of the Y can be resolved into two or more filaments, many of which showing signs of being intertwined. A model of the mammoth trunks, related to a recent theory of elephant trunks, is proposed. Based on magnetized filaments, the model is capable of giving an account of the various shapes of the mammoth trunks observed, including the twined structures.

http://www.springerlink.com/content/k13840m964x10103/

And in another article there was this:

Growth procedure
On Earth, the injected dust particles fall down on the electrode after an experiment.
This layer of deposited matter is sputtered to generate a new dust particles population. In the
PKE-Nefedov chamber, this growth has been obtained in GREMI laboratory at high pressure
(~1 mbar) and low power (~1 W) with a typical appearance time (on screen) around 2 to 3
min. After this growing step with monodisperse particles, a constant process of sputtering and
growth leads to particles of various sizes (between 0.2 and 0.8 μm in diameter as shown by
scanning electron microscopy). This size dispersion can be also achieved by working for few
minutes at higher power. New dust particles are grown from the previous grown dust cloud.
Image
Image
Image
Image
This situation leads to successive generations of dust particles as shown in figure 1a. The Xray
fluorescence analysis reveals that these particles are principally constituted of carbon (no
more nitrogen as in melamine formaldehyde). Due to their submicron size, gravity is not the
predominant force and they can be trapped in the whole volume of the plasma even on Earth.
The "void" and large crystalline regions have been observed (figure 1). We can also notice
vortex-like regions near the electrode edge.
http://epsppd.epfl.ch/Montreux/pdf/O4_34.pdf ;) ;)
Last edited by davesmith_au on Sat Mar 27, 2010 4:52 pm, edited 1 time in total.
Reason: Added image which was inadvertently left out :)
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Self-charging of the Eyjafjallajökull volcanic ash plume

Unread postby StefanR » Thu May 27, 2010 7:03 pm

Self-charging of the Eyjafjallajökull volcanic ash plume

Abstract. Volcanic plumes generate lightning from the electrification of plume particles. Volcanic plume charging at over 1200 km from its source was observed from in situ balloon sampling of the April 2010 Eyjafjallajökull plume over Scotland. Whilst upper and lower edge charging of a horizontal plume is expected from fair weather atmospheric electricity, the plume over Scotland showed sustained positive charge well beneath the upper plume edge. At these distances from the source, the charging cannot be a remnant of the eruption itself because of charge relaxation in the finite conductivity of atmospheric air.
Image
1. Introduction

Electrification of volcanic plumes provides a spectacular source of lightning [1, 2]. Volcanic lightning can facilitate remote sensing [3] of an active eruption, from which aircraft can be warned of hazards from volcanic ash clouds [1]. Volcanic plume electrification has previously been investigated using surface measurements of charged sedimenting particles [4] and below-plume surface determinations of atmospheric electric fields [5]. Observations [1] of volcanic particle charging have previously been made up to 200 km from the vent [6].

The eruption of the Icelandic volcano Eyjafjallajökull (63.63°N, 19.62°W, 1666 m a.s.l), which began on 20 March 2010 provided an opportunity to study plume electrical properties over Europe, far from its source. The eruption initially produced lava fountains on 21 March, ejected from a 500 m long fissure. The activity was dominated by fissure-fed lava fountains and basaltic lava flows until late 13/14 April, when new vents opened on the southern rim of the central caldera, capped by the glacier. This resulted in an ash ( ~ 58% SiO2)Note4 plume rising to more than 8 km altitude being blown eastwards, with tephra-fall being reported in SE Iceland. The eruption plume reached mainland Europe on 15 April, causing substantial airspace closureNote5. During this long range plume transit, any remnant particle charge generated during the eruption itself would have dissipated, due to typical atmospheric charge relaxation times [1] of order 100–1000 s. In situ charge measurements of the Eyjafjallajökull eruption plume over western Scotland on 19 April are reported here, using a balloon-carried package combining charge and aerosol particle sensors [7].

.....

Several mechanisms [1, 2] have been proposed to explain the substantial electrification necessary to generate volcanic lightning, which may be relevant considerations in explaining the charging observed. These include electrification associated with plume formation (fractoemission or boiling), thundercloud-like charging, and radioactive decay. Of these, the energetic processes associated with plume formation can be rejected at such large distances from the vent, and the thundercloud-like charging also seems unlikely because of the low relative humidity measured in the plume. The unipolar nature of particle charge observed is known to be characteristic of radioactive charging [19], but there is no further evidence to support this possibility.
Image
5. Discussion

These findings demonstrate that charge exists well within a volcanic plume, the origin of which is not readily attributable either to the eruption directly or subsequent fair weather charging. In general, particle charging will modify vertical deposition speeds in the fair weather atmospheric electric field [20] and modify particle–particle agglomeration rates and particle wet removal by droplets [16, 21]. Charged particles can cause aircraft radio interference [22] and, if introduced into aircraft cabins, charged ash may present an electrostatic hazard to occupants or aircraft systems.

http://iopscience.iop.org/1748-9326/5/2/024004/fulltext
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Re: Recovered: Dusty Plasmas

Unread postby starbiter » Thu May 27, 2010 7:15 pm

The opposite of this is a pyroclastic flow. The particles in the flow are small, and smaller. The temperature is up to 1800 degrees F. The heated particles go DOWN against all thermodynanic laws. I assume the particles are charged oppositely to the plume.

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Re: Recovered: Dusty Plasmas

Unread postby StefanR » Fri May 28, 2010 11:37 am

starbiter wrote:The opposite of this is a pyroclastic flow. The particles in the flow are small, and smaller. The temperature is up to 1800 degrees F. The heated particles go DOWN against all thermodynanic laws. I assume the particles are charged oppositely to the plume.

Perhaps there might be some chargedness in play, though the article-link you gave didn't mention any of it. Personally I do think more "mechanical" forces dominate in the pyroclastic flow. The downflow from an ashplume contributing to the pyroclastic flow seems to consist of particles to heavy to be born aloft for too long. Being heated is not a certainty of going UP, in my view, but the heat in the pyroclastic flow does contribute to the voluminosity of that flow.
But perhaps there are other articles concerning this subject that do mention charge?
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Re: Recovered: Dusty Plasmas

Unread postby StefanR » Fri May 28, 2010 11:44 am

The Lunar Dusty Exosphere: The Extreme Case of an Inner Planetary Atmosphere

Introduction
The lunar surface, as many other objects in the solar system, is directly exposed to the harsh space environment including a continual bombardment by interplanetary impactors large and small, high energy radiation, UV/xrays, and solar wind plasma. In addition, the Moon spends about 1/4 of its orbit within the terrestrial magnetosphere, exposed to similar warm/hot plasma conditions to moons orbiting within other planetary magnetospheres. As indicated in Figure 1, in direct response to these intense and variable environmental drivers, the Moon releases a low density neutral gas forming a collisionless atmosphere.
Image
This ~100 tons of gas about the Moon is commonly called the lunar surface-bounded exosphere (or SBE, see Stern [1999] and references therein). Ions are also created directly either by surface sputtering or subsequent neutral photoionization, forming a tenuous exo-ionosphere about the Moon. Due to the incident solar radiation and solar wind plasma, the lunar surface becomes charged much like the wall of a plasma chamber [Manka, 1973], and electrostatic forces appear to be capable of lifting dust from the surface [Stubbs et al., 2006]. The efficiency of this process, as well as the height these small charged particles might reach, remains an intensely debated issue since the Apollo era. By analogy, the Moon is essentially a nearby laboratory to study the evolution of exposed surfaces to the harsh space environment with direct applications to other near-airless bodies (e.g., Mercury, asteroids, KBO) throughout the solar system. The neutral, plasma and dust environment of the Moon is largely shaped by the Sun. This solar-lunar connection will be explored by NASA’s Lunar Atmosphere and Dust Detection Explorer (LADEE) to be launched early 2012, when solar activity is the greatest and storms are expected to force the dusty exosphere to expand and contract in cadence with the extreme events [LADEE SDT report, 2008]. Some of the most critical questions of the Moon’s dusty exosphere are listed in Table1.
Comparative Planetology and Basic Processes
The response of the dust, plasma and atmospheric environment to the variable solar conditions at the Moon is of great interest and can serve as the ‘Rosetta stone’ of understanding the vast differences in the evolutionary path of the near surface environments of other solar system objects.
First, the outgassing and sputtering of lunar neutrals represents the most primitive atmosphere in the inner solar system. While Venus represents one ‘high density’ extreme, the Moon is our ‘low density’ extreme in the spectrum of atmospheric systems. The lunar surface gas concentration consisting primarily of Ar-40 and He is less than 106 cm-3 - compared to 1019 cm-3 at Earth and 1017 cm-3 at Mars. In many ways the lunar exosphere looks more like the atmosphere of an asteroid or KBO, and thus its understanding represents a gateway to understanding other low density SBE’s at icy/rocky bodies and especially that at Mercury. In fact, some of the newly discovered hot neutral gases at Mercury ejected at temperatures in excess of 30000K are reminiscent of the hot sodium ejected from the lunar surface. How these escaping gases leave the surface at such high temperatures is simply not understood at this time.
Second, the polar regions of near-airless bodies represent special regions where volatiles can collect within cold traps. Of interest is the collection of water and other volatiles that is either delivered to the surface via cometary impacts or created via regolith/micro-meteoroid interactions [Vondrak and Crider, 2003]. From a comparative planetology perspective, there is a tendency for cool inner solar system rocky bodies to collect water/volatiles at the poles. The exact processes for the collection may differ depending upon whether the atmosphere is collisional (convection driven circulation) or collisionless (surface-atom migration), but there appears to be a certain universality to polar water and volatile collection. The processes at the Moon would clearly represent the collisionless collection extreme. An engaging white paper featuring an extended discussion of lunar volatiles by Hurley et al. has been submitted to the Inner Planets Decadal Survey team - providing further information on the current state of knowledge of volatile processes and path forward.
Third, another common set of processes acting on rocky bodies are the mobilization, lofting, and transport of particulate matter (aerosol, dust) from their surfaces –creating dust-laden atmospheres. In the case of Earth, dust is lifted via gas dynamic forces created in a collisional atmosphere. However, particles are also lofted from the surfaces of objects having collisionless atmospheres like the Moon and asteroids like Eros. For collisionless exospheres exposed to the space environment, electrostatic forces are suspected to be a primary driver to create dust transport. In essence, the near-surface intense E-fields in these dusty plasma systems now play the role of the gas-dynamic forces in collisional atmospheres in creating the surface stress. In the case of Mars, it has been suggested that electrostatic forces work in tandem with gas-dynamic forces to enhance dust lifting – making Mars a hybrid case where electrical forces at times become comparable to gas-dynamic forces [Kok and Renno, 2008]. As such, surface-originating aeolian particles (aerosols, dust) are a component of any atmosphere/exosphere system - the Moon and other airless bodies are no exception. A comprehensive white paper has also been submitted on the basic issues of lunar dust by O’Brien, Dyer, et al. that addresses more detailed science, engineering, and operational aspects of lunar dust – which has direct applications to any future exploration to dusty environments like near-Earth asteroids and Mars.
Image
Fourth, the inner planets are all connected to the Sun –via radiation and conductive coupling. However, the nature of the solar connection for inner solar system bodies differs depending upon both the thickness of the body’s atmosphere and strength of its magnetic field. Inner solar system bodies provide a unique range of magnetic shielding from fully unprotected enabling the direct deposition of solar wind plasma, to a 'magnetosphere-like' setup where sufficiently intense magnetic anomalies can divert the solar wind flow. The near-airless, weak-field Moon again represents one extreme case where variable solar energy and matter has direct contact and influence on the surface – responsible for driving surface activity. The Earth and Venus represent the other extremes. It is for this reason that the LADEE mission will occur in 2012, during the peak in the solar cycle when the probability of a solar storm is high. LADEE will be joined by the ARTEMIS 2-spacecraft fleet (see Khurana et al. White Paper) that will make simultaneous space plasma observations. LADEE and ARTEMIS enable an unprecedented opportunity to explore the solar-lunar connection, and the study of this strongly driven exosphere that is expected to expand and contract in cadence with variable solar conditions. It is one of the highest priorities of the lunar community to simultaneously operate LADEE and the ARTEMIS fleet in 2012 during solar maximum conditions.
Finally, due to sputtered gases and lofted dust, there is a space weathering/surface erosion effect continually ongoing on the lunar surface (Figure 3). This environmental weathering is not as great as within the terrestrial atmosphere, but has an estimated erosion rate on rocks of about 1-m loss for every billion years [Horz et al., 1991; Stern et al., 1999]. It is often suggested that the Moon contains pristine, unaltered samples from the cataclysmic bombardment period ~3.8 Gyr ago. In fact, any samples from that period have been exposed to long-term space weathering: Today’s few kilogram rock sample has most likely lost a substantial fraction of its original mass since the late heavy bombardment period. As such, the study of the lunar dusty atmosphere (as a by-product of surface erosion) has a direct connection to the nature of surface samples used as the chronological record of the cataclysmic bombardment from lunar basins. Understanding the erosion rates (as ejected flux of material into the atmosphere) is vital to placing any return sample in proper historical context.

http://www.lpi.usra.edu/decadal/leag/WilliamMFarrellDAWhitepaper091409.pdf
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Re: Recovered: Dusty Plasmas

Unread postby StefanR » Fri May 28, 2010 11:47 am

Threshold Phenomena in a Throbbing Dusty Plasma

A dust cloud trapped in a plasma often contains a dust-free region ("void") near the plasma
center. This void has important effects [1, 2]: it induces a spatial inhomogeneity of the dust
particle distribution and is at the origin of many intricate unstable phenomena. One of this
behavior is the heartbeat instability consisting of successive contractions and expansions of
the void [3].

http://ocs.ciemat.es/EPS2010ABS/pdf/O3.312.pdf
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Re: Recovered: Dusty Plasmas

Unread postby StefanR » Fri May 28, 2010 11:49 am

II. WHERE ARE DUSTY PLASMAS
Dusty plasmas are ubiquitous in the universe; examples are proto-planetary and solar
nebulae, molecular clouds, supernova explosions, interplanetary medium, circumsolar rings,
and asteroids. Within the solar system there are the planetary rings, cometary tails and
comae, and dust clouds on the moon. Closer to earth, are the noctilucent clouds composed
of small ice particles that form in the summer polar mesosphere at an altitude of about 85
km where the temperature can dip as low as 100 K. Dust also turns out to be common in
laboratory plasmas, such as tokamaks, plasmas used in the processing of semiconductors,
and even in electron storage rings. In plasmas used to manufacture semiconductor chips,
dust particles are actually formed in the discharge from the reactive gases used to form the
plasmas. These particles can then grow by agglomeration and accretion and eventually fall
onto the semiconductor chips contaminating them, resulting in an overall significant
reduction in yield. The increased interest in dusty plasmas was due to two major
discoveries in very different areas: (1) the discovery by the Voyager 2 spacecraft in 1980 of
the radial spokes in Saturn’s B ring, and (2) the discovery in the early 80’s of the dust
contamination problem in semiconductor plasma processing devices. More recently, the
realization of the presence of dust particles in magnetic fusion plasmas, has led to expanded
efforts to understand how these particles interact with plasmas. This is of particular concern
for the design of the ITER device.
III. CHARGING OF THE DUST
Dust is important in plasmas because it becomes charged. This can occur due to the
collection of electrons and ions from the plasma, secondary emission, or photoelectron
emission from UV radiation, which is often the predominant mechanism for charging of
dust in space and astrophysical plasmas. The dust in typical laboratory dusty plasmas is
negatively charged, due to the fact that the electrons move about more swiftly than the ions.
A 1 micron radius dust particle in a plasma with an electron temperature of a few eV, will
have a charge corresponding to a few thousand electrons, with a resulting charge to mass
ratio, Q/m <1.
What makes dusty plasmas interesting other than Q/m <1? There are several reasons.
First, in the naturally occurring dusty plasmas there is typically have a range of sizes. The
mass of the dust scales as the size cubed and the charge scales directly with the size. Thus,
unlike ordinary plasmas, there will be a distribution of Q/m values. Secondly, the charge on
a dust particle is not fixed, but fluctuates. For example, in the presence of plasma
potentialfluctuations, Q will vary. Also since Q depends on the electron temperature, it will vary if
the dust moves through regions of varying Te. The fact that Q is variable leads to
phenomena, such as new collisionless wave damping mechanisms that are unique to dusty
plasmas.
http://www.physics.uiowa.edu/~rmerlino/Dusty_Plasma_Primer.pdf
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Re: Recovered: Dusty Plasmas

Unread postby StefanR » Fri May 28, 2010 11:54 am

Topic 7: Dust in astrophysical plasmas

7.1 Introduction and current status

In the astrophysical environment, the fraction of the ionized particles varies widely from
nearly no ionization in cold regions to fully ionized in regions of high temperature. This leads to
a wide range of parameters where astrophysical plasmas can exist. While the astrophysical
plasma environment is often dominated by the presence of the plasma, this plasma is often
strongly influenced by and coupled to the presence of embedded particulates (i.e., dust). These
dust grains – which range in size from a few nanometers to micron-sized objects – can become
either positively or negatively charged due to interactions with the background plasma
environment and/or ionizing radiation sources in the astrophysical environment. Understanding
the processes that govern these plasma – particle interactions is critical to the study of
astrophysics because it is the agglomeration and growth of larger particles from single atoms and
dust grains that leads to the eventual formation of objects that are large enough for gravity to
become the dominant force that controls their subsequent evolution.
In any plasma environment, the charged species can be dominated by or at least perturbed by
electromagnetic forces. For most systems, it is the ion and electron dynamics that is dominated
by these forces, while charged dust grains are perturbed by these forces. The uncharged species
(i.e., neutral particles), will not be directly affected by these electromagnetic forces. However,
the charged and uncharged particles interact through collisions, which transfer energy and
momentum from one species to another.
Furthermore, larger particles (i.e., dust grains), can become both an important source and
sink of charged particles. For example, in regions of space with ionizing radiation,
photoionization processes at the surface of the grains can lead to the generation of electrons from
the surface of the grains at the same time generating charged dust. Similarly, in regions where
the grains are can become significantly heated through collisions with the background plasma
particles or neutrals, the grains can become heated to the point of thermionic emission – again
leading to the grains becoming a source of electrons for the plasma. At the other extreme, in
very cold regions of space, atoms and molecules can become trapped on the surfaces of these
dust grains leading to growth of the particles as well as becoming a sink for the background gas
and plasma environment. The presence of dust can alter the density, energy distribution, and the
composition of its plasma environment.
From this wide range of phenomena that can occur in astrophysical plasmas, it is important to
consider those processes where it is possible to perform laboratory studies that will enable new
insights and new understanding to be gained of the astrophysical plasma environment. Three
topics have emerged as “grand challenges” for laboratory astrophysics in the area of plasmaparticle
interactions.
1) How do the dust grains become charged in astrophysical plasmas?
2) How does the plasma influence the growth and breakup of macroscopic particles in
astrophysical environments?
3) What is the role of magnetic fields in influencing charged macroscopic particles?
4) How does the presence of neutrals atoms and/or charged or neutral macroscopic particles
affect the evolution of the plasma environment?

7.2 Key Scientific Challenges

In the context of astrophysical plasmas, these three questions are part of a singular,
overarching theme – how are larger objects - comets, planets, stars - formed from clouds of gas
and dust? At the same time, these three questions also have a strong connection to very tangible
issues in modern laboratory plasma science research in areas such as plasma manufacturing and
fusion. Each of these challenges is discussed in the following section.

Topic 1: How do dust grains become charged in astrophysical plasmas?
Perhaps the dominating question for much of dusty plasma research – for laboratory, fusion,
and astrophysical plasma environments – is defining the mechanisms that lead to the charging of
the grains. In laboratory plasmas, the charging process is primarily due to the collection of ions
and electrons from the background plasma. However, in astrophysical plasmas, the charging
process will not only be driven by the collection of ions and electrons, but also will be influenced
– and possibly dominated by – sources of ionizing radiation. Understanding the charging
process, particularly in highly collisional environments or regions with large magnetic fields are
areas of research in which much theoretical and experimental work remains to be done.
As a scientific problem, the determination of the charge of dust grains in an astrophysical
plasma is quite challenging. First, the material composition of the dust grain is important
because this determines the work function of the grain. Also, the charge distribution oon an
individual grain is determined by whether the grain is insulating or conducting. Second, the
shape of the grain can determine how much surface area is available for charge to be collected.
And third, the size of the grain, with respect to the local Debye length, can have a significant
influence on how free charges (ions and electrons) are captured by the grain. These are all issues
for which significant theoretical and computational efforts are needed.
In terms of the astrophysical plasma environment, the dust grains can become charged either
positively or negatively – depending upon the conditions of the local plasma and radiation
environment. Once charged, the particles can be influenced by electromagnetic as well as
gravitational forces. The formation of the radial spoke structures in Saturn’s rings are often cited
as an example of this competition between electromagnetic and gravitational forces on the
transport of charged grains in the space environment. Ultimately, the dust grains can play an
important role in the distribution of charge in astrophysical plasmas because they can transport
substantial quantities of charge from one region to another. As such, these grains can be
important sources and sinks of plasma.

Topic 2: How does the plasma influence the growth and breakup of macroscopic particles in
astrophysical environments?
The growth and agglomeration of particles from clusters to atoms to the size of dust grains or
larger is a long-standing problem in astrophysics. The matter that eventually forms the stars,
planets, comets, and the other objects in solar systems begins its life as small grains of dust
particles. These particles interact with and are influenced by the neutral and plasma particles in
the space environment. However, because of the strength of the electromagnetic force is so
much larger than the gravitational force – when considering small, nanometer and micron-sized
grains – precisely how these small particles become charged, the sign of the charge, the number
of charges on the particles, and the spatial distribution of charges on these particles all can have a
significant influence on the processes that eventually lead to the building of stars and planets.
Initially, in the gas phase – as atoms are first combined to form molecules and then atomic
clusters – the growth of particles is believed to be driven by a Brownian motion growth process
for particles up to ~100 nm.1,2,3 As particles grow to larger sizes, a number of environmental
features begin to have a stronger influence on the growth process. These include the density and
temperature of source materials (neutral atoms, plasma ions, and smaller agglomerates) as well
as the thermal properties of the grains themselves. If these particles can be become charged, this
can have a significant impact on the rate at which further particle growth can occur.
Of course, it is well known that the electrostatic force is many orders of magnitude stronger
than the gravitational force. Therefore in the simplest approximation, two small dust grains that
carry even a single, but opposite charge will experience an attractive force that is far greater than
the gravitational attraction. Consequently, if those two same particles have the same sign of
charge, the electrostatic repulsion will far exceed the gravitational attraction. Therefore it is
immediately obvious that the presence of charged dust can have a significant influence on the
evolution of a planetary nebula in an astrophysical environment by simply taking into account
the charge state of the grains and how those charged grains are distributed in space.
However, it is not simply the fact that individual grains are charged, because these grains are
generally not conductors nor are they uniformly shaped. Thus, the underlying physical
phenomenon that influences all of the aforementioned issues is how the grains become charged.
In the astrophysical environment, the charging of the grains is a complex process. Not only do
the grains collect ions and electrons from the background plasma as occurs in laboratory
experiments, but these grains are often in environments with ionizing radiation or strong heating
processes. Furthermore, grains in space are subjected to high-energy particles that can lead to
the production of secondary electrons. As a result of these different charging processes, dust
grains in space can be found to carry either a net positive or net negative charges depending upon
the details of the plasma environment.
Therefore, current experimental, theoretical, and numerical studies all point to the need to
have a better understanding of the initial formation of large scale dust grains in astrophysical
environments. And, because charged grains can have a profound impact on the coagulation of
material into these larger grains, having detailed knowledge of the plasma environment and it
coupling to the dust is vital.

Topic 3: What is the role of magnetic fields in influencing charged macroscopic particles?
Just as plasmas are ubiquitous in the universe, magnetic fields are just as pervasive. For
much of the development of astrophysics, the role of the magnetic field has not been considered
to play a significant role. However, as the importance of charged particle effects is becoming
more evident, it has become increasingly necessary to determine if the presence of magnetic
fields can also have an influence on plasma – particle interactions. In this context, it is not only
vital to determine how the magnetic field may shape the properties of the background plasma,
but also to determine how the magnetic field may have a direct influence on the charge
macroscopic particles themselves.
Although the consideration of the influence of the magnetic fields on macroscopic particles
in astrophysical plasmas has not always been a prominent topic, early works in the 1950’s by
Alfven4 and Mestel and Spitzer5 show that the idea of the coupling between the plasma, dust, and
magnetic fields has been a topic of discussion for some time. More recent work by Goertz shows
that – in the context of phenomena within a solar system, notably in planetary rings or particles
in planetary magnetospheres – it is quite important to include magnetic field fields in order to
properly reconstruct the dynamical behavior of these systems.6 Magnetic field effects on the
dust particles in astrophysical plasmas can be considered from two aspects. First, how does the
presence of a magnetized plasma affect the coupling with the dust? And second, how does the
presence of a magnetic field affect the dynamics of the charged grains?
As noted in Topics 1 and 2, the underlying phenomenon that connects the dust grains to the
plasma is the charging process. Over the years, there have been many theoretical works that
have modeled the charging processes in laboratory and astrophysical plasmas in the presence of
magnetic fields. The magnetic field alters the ion and electron fluxes to the grains and can result
in differences in the both the final charge of the grains and the distribution of charge on the
grains. At the microscopic level, this could alter the agglomeration processes that lead to the
growth in particle size.
In terms of direct magnetic field effects on the charged dust, at the present time it remains
unclear under which regimes of the astrophysical environment that such observations could be
made. While there are some theoretical works, there are few direct observations or experimental
studies to validate these models. Thus, this is an area of research that is ripe for new scientific
discoveries to be made.

7.3 Major opportunities

The three topical areas described in this section represent areas of scientific study that can
each stand on their own merit. However, as a major thrust of this work is to make connections
between laboratory studies and astrophysical processes, these three areas are particularly wellsuited
to be bridge the gap between the lab and space. The underlying issues of dust grain
charging, dust grain growth and breakup, and the effect of the magnetic fields are all areas that
have strong overlap with current and future research directions of the laboratory plasma
community.

Particle charging: At the present time, there are a number of dusty plasma laboratory
experiments in which the charging of the dust grains is a component of the research program.
However, these studies are primarily focused on ion/electron collection from the background
plasma. In order to extend this work to areas of relevance to astrophysical system, it would be
necessary to have dedicated studies that are also focused on charging in intense radiation
environments.

Particle growth and breakup: In the area of particle growth and breakup, there are important
issues that relevant to the plasma astrophysics community that have a great deal in common with
the industrial plasma processing and fusion research communities. In both of these applied
areas, the formation of nanometer and micrometer sized particles from the gas phase in reactive
plasma is often considered to be a major source of contamination. Nonetheless, the particles
formed in these environments share a number of common features with their astrophysical
counterparts – namely, the particles were charged while they were in the plasma and large
particles are clearly shown to be formed from the coagulation of many smaller particles.7,8 To
date, there have only been few dedicated experiments on the formation of grain aggregation /
coagulation processes. 9,10 To make progress in this area, experimental studies that can simulate
specific aspects of the space plasma environment (e.g., choosing the ratio of ion, electron, dust
and neutral gas densities to mirror a particular planetary nebula region) may provide a more
complete representation of the processes that occur in nature. Additionally, studies performed in
chemically active plasmas that can mimic processes that occur in space environments (e.g., star
forming regions), may give insight into the material properties of the dust grains.

Magnetic field effects: If there is any aspect of dust-plasma interaction studies that remains
essentially unexplored in the laboratory it is the role of magnetic field effects. Almost all studies
to date have been performed without a magnetic field or at magnetic field strengths where only
the electrons are magnetized. This is because there are significant technical challenges to
building an experiment that can operate in a regime where the electrons, ions, and charged dust
can be magnetized (e.g., typically requiring steady-state, multi-Tesla magnetic field strengths
and the ability to detect nanometer-sized particles). There is currently one operating, 4-Tesla
dusty plasma experiment and various groups in the community are planning up to 3 additional
experiments to come online within the next 5 years.
These new experiments offer a unique opportunity to verify and validate which of the various
numerical models have properly captured the role of the magnetic field. Moreover, studies with
magnetic fields open up entirely new regimes of dust – plasma interactions that have not
previously been considered. Experiments on dust transport parallel to the magnetic field,
perpendicular to the magnetic field (e.g., Hall effects, E × B), and parallel to electric fields and
perpendicular to magnetic fields (e.g., Pedersen effects) can be investigated. Moreover, the
study of fully magnetized plasmas with magnetized dust may allow the study of new wave
modes such as dust cyclotron, dust magnetosonic, and dust Alfvén modes.

7.4 Impacts and Major Outcomes
Because the laboratory study of dusty plasmas is still in its infancy, there are many possible
directions for the field to go and, subsequently, many areas of plasma physics research that could
be impacted. Perhaps the most important impact of this work is gaining an understanding of a
plasma in the most “general” state. Because plasmas, dust, and magnetic fields are found
throughout the universe – often in combination with each other – the study of astrophysical
plasmas should focus on understanding the various complex interactions among these three
components. While it recognized that this is a difficult problem, a new generation of dusty
plasma laboratory experiments are becoming available that may make it possible to explore
aspects of this complex system.

7.5 Connections to Other Topics
The topic of dusty plasmas in astrophysical plasmas has connections to many other areas of
plasma astrophysics research. In particular, studies of radiation from charged dust (Radiative
Hydrodynamics group) is particularly important in interpreting data from star forming regions.
Additionally, the presence of shocks (Collisionless Shock and Particle Acceleration group) can
“process” dust grains leading to changes in their morphology, material characteristics, and
charge state. Finally, there is already experimental evidence that the presence of charged dust
grains can modify many existing plasma waves and give rise to new waves and instabilities
(Waves and Turbulence group). Mapping these results to the astrophysical plasma environment
represents a new area of research for the community.

http://www.pppl.gov/conferences/2010/WOPA/report/Dust-final.pdf
The illusion from which we are seeking to extricate ourselves is not that constituted by the realm of space and time, but that which comes from failing to know that realm from the standpoint of a higher vision. -L.H.
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Re: Recovered: Dusty Plasmas

Unread postby StefanR » Wed Dec 15, 2010 2:27 pm

Nice article on UniverseToday, I'll just lift out a small quote:
Lunar Dust Transport Still a Mystery

Horanyi and other scientists have done lab experiments to try and replicate the lunar environment to see if a dust transport takes place.

“For the first set of experiments, imagine just a piece of surface with dust particles on it, and we shine light on this surface,” he said, “so that half is illuminated, half is not, pretending that there is a terminator region, that the sun is set on one side and is still shining light on the other. When you shine light on the surface with properties that are appropriate, you can emit photo electrons, but you only emit electrons from the lit side, and some of those electrons land on the dark side, — you have a positive charge surplus on the lit and a negative charge pile-up on the night side. Across a couple of millimeters you can easily generate a potential difference of maybe a watt, or a handful of watts, which translates actually as a small-scale, but incredibly strong electric fields. This could be like a kilowatt over a meter. But of course, it only exists over a sharp boundary, and that sharp boundary may be the key to understanding how you get dust moving to begin with.”

Horanyi said in the transient region where boundaries match up – lit and dark boundaries, or boundaries between where the surface is exposed to a plasma and where it is not – those sharp transitions could actually overcome adhesion between dust and the rest of the surface and start moving.

“And that’s where the story gets really interesting,” he said.

http://www.universetoday.com/81727/lunar-dust-transport-still-a-mystery/#more-81727


A previous post about lunar dust a little earlier in this thread:
http://www.thunderbolts.info/forum/phpBB3/viewtopic.php?p=8012#p8012

and for completeness, a nice thread by MrAmsterdam:
SHEATH PHENOMENA IN DUSTY PLASMAS
http://www.thunderbolts.info/forum/phpBB3/viewtopic.php?f=3&t=3930#p43147
The illusion from which we are seeking to extricate ourselves is not that constituted by the realm of space and time, but that which comes from failing to know that realm from the standpoint of a higher vision. -L.H.
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Re: Recovered: Dusty Plasmas

Unread postby StefanR » Sat Feb 26, 2011 9:12 am

Electrical Phenomena on the Moon and Mars
Gregory T. Delory
Space Sciences Laboratory

Abstract—The Moon and Mars represent intriguing and divergent case studies where natural
electrical processes may occur in environments beyond our more familiar terrestrial
experience. The windy, Aeolian environment of Mars likely produces substantial electrical
activity via the tribo-electrification of individual dust grains that occurs during atmospheric
disturbances. While there may be some analogies between atmospheric electrical processes on
the Earth and Mars, the highly rarefied, dry Martian atmosphere imposes unique conditions
that govern the charging and discharge dynamics of particulates. In contrast to the windswept
surface of Mars, the Moon is a small airless body whose surface is directly exposed to
variable space plasmas and solar irradiation. Measurements during the Apollo missions, together
with more recent data from orbital spacecraft, indicate that there are active and dynamic
charging processes occurring on and near the lunar surface. One possible consequence
of dynamic lunar electrical activity may be the levitation and perhaps large scale transport of
lunar dust. For both the Moon and Mars we only have indirect evidence at best for the existence
of electrical activity of any real global consequence. This paper is a brief, semi-tutorial
review that discusses the background and history behind these investigations, highlights key
ongoing research, and describes future efforts that will help resolve the fundamental, outstanding
questions that remain.


D. Open Questions and Future Directions
While plasmas and dust have been studied together and separately in both the lab and
space, the presence of the lunar surface introduces many uncertainties that have yet to be
resolved. While the photoelectric effect is well understood, the energy distribution of
photoelectrons stimulated from the complex, unconsolidated lunar regolith is poorly constrained,
with only a few laboratory measurements indicating that they are distinctly non-
Maxwellian [76]. Plasma sheaths have been generally thought to be well understood,
with a simple exponential spatial dependence of the electric field as one approaches the
plasma-surface interface. However the photo-emissive properties of the lunar regolith
may in fact produce a unique spatial variation in the electric field that is non-monotonic
in nature, in which a region of negative potential is encountered prior to the larger positive
potential expected at the surface due to the photoemission current. This sheath configuration
has been shown to be possible both analytically [77] and more recently simulated
using a 1-D particle-in-cell code [78]. If true, this configuration of the sheath fields
could explain measurements made by the MAG-ER instrument on LP indicating negative
potentials in sunlight under some circumstances. This field structure would also have
implications for dust dynamics, in that oscillatory motion of dust within the sheath potential
well would in effect appear as levitation. Progress in this area will be enabled by a
better knowledge of the detailed photoelectron energy distribution at the Moon.
Electric fields generated in the lunar plasma sheath serve to illustrate a simple example
of how electric fields vary over the lunar surface. However the electric fields in the area
of most interest – near the lunar terminator – are in reality likely to be much more complex.
Farrell et al [79] have examined the importance of electric fields generated by the
formation of the lunar wake, where enhanced electron fluxes may create large negative
potentials at the surface near the terminator regions. These fields could explain the fast
moving dust detected by LEAM. Additionally, smaller scale variations in lunar topography
at higher latitudes can form “mini-wakes,” and lead to enhanced surface charging in
small, localized plasma voids [55]. The impact of these new electric field structures on
the electrical environment at the lunar surface are now just beginning to be explored.
Other uncertainties include the importance of secondary electron emission – the ejection
of an electron from the surface in response to incident ions and electrons in the
plasma currents. For sufficiently high incident particle energies of a few hundred eV or
more, the efficiency of this process can be greater than one and thus lead to a significant
contribution to the overall current balance of the system. While this effect is probably not
important in the solar wind due to the low densities and energies of the incident plasma,
it could represent a significant current source in darkness and in more energetic plasmas
encountered in the geomagnetic environment or during solar storms.
The prospect for large scale dust transport remains an open question. An increased understanding
of the lunar surface potential will certainly help address this problem. Details
regarding dust charging mechanisms also need to be explored. Charging by plasma and
photocurrents were touched upon earlier; additionally, lunar dust may be subject to triboelectric
charging mechanisms. The regimes in which frictional, plasma, or photocharging
processes are important remains to be settled. Dust adhesion and cohesion on
the lunar surface is also relatively unconstrained, and is important to understand in order
for dust lifting processes to be realistically modeled. Ongoing laboratory experiments
will help address some of these open questions [80-86].
Two upcoming lunar missions will reveal more details about the lunar plasma and dust
environment – in essence, the “lunar weather” outlined in Fig 3. These include the Acceleration
Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with
the Sun (ARTEMIS) multi-spacecraft mission that will measure the plasma conditions in
the lunar wake, and extend measurements of the lunar surface potential to both positive
and negative regimes [87]. The upcoming Lunar Atmosphere and Dust Environment Explorer
(LADEE) will determine if there is any appreciable dynamic dust transport occurring
on km or larger scales [88]. The newly formed NASA Lunar Science Institute is also
worth mentioning, which has funded several teams of researchers to study the dynamics
of the variable dusty plasma environment of the Moon. Ultimately, as is the case for
Mars, measurements on the lunar surface are the best hope for definitive resolution to
many of the outstanding issues. A minimum surface package would include instruments
to measure ion and electron energy distributions, electric fields, and dust properties, including
size, charge, and density.

http://www.electrostatics.org/images/ESA2010_A1_Delory.pdf
The illusion from which we are seeking to extricate ourselves is not that constituted by the realm of space and time, but that which comes from failing to know that realm from the standpoint of a higher vision. -L.H.
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Re: Recovered: Dusty Plasmas

Unread postby StefanR » Sat Dec 06, 2014 2:44 am

Interesting videos talking about dusty plasmas associated with Moon, Mercury, Mars, interplanetary and interstellar dust. The first vid is nice in overview of the several aspects of dusty plasma research done at Colorado and the second vid goes into some subjects a little deeper. Not immediately giving new information not in this thread yet, but still there will be some remarks that are very interesting, for instance about interstellar dust or dynamics on the Moon. Mr. Horanyi is fair in many places in stating that a lot is still unknown and untested.
Enjoy!



Dr. Mihály Horányi, PI of the Colorado Center for Lunar Dust and Atmospheric Studies (CCLDAS), discusses dusty plasma processes on the surfaces on airless planetary objects with a group of science communicators on July 21, 2012.
The 2012 Laboratory for Atmospheric and Space Physics (LASP) New Media Practitioners Professional Development Workshop brought seventeen bloggers, podcasters, and other science communicators to Boulder, Colorado, for a two-day intensive workshop with space scientists. The workshop was a collaborative professional development opportunity for attendees to learn about current issues surrounding future exploration of the Moon and other small bodies in our Solar System. CCLDAS sponsored the event.

https://www.youtube.com/watch?v=CCc3-HnaoYc

and

CosmoQuest Science Hour with special guest Mihály Horányi.
Dr. Horányi discusses plasma physics and his work with lunar dust, space dust, and instrumentation on the New Horizons mission. Jason Davis hosting.

https://www.youtube.com/watch?v=2isxr6uSYSM
The illusion from which we are seeking to extricate ourselves is not that constituted by the realm of space and time, but that which comes from failing to know that realm from the standpoint of a higher vision. -L.H.
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