Researcher uses 100,000 degree heat to study plasma

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Using one of the greatest sources of radiation energy created by man, University of Nevada, Reno researcher and faculty member Roberto Mancini is studying ultra-high temperature and non-equilibrium plasmas to mimic what happens to matter in accretion disks around black holes.

Physics department professor and chair Mancini has received a $690,000 grant from the U.S. Department of Energy to continue his research in high energy density plasma; plasmas are considered to be the fourth state of matter. He will serve as principal investigator for a project titled"Experiments and Modeling of Photo-ionized Plasmas at Z."

"Receiving awards such as this exemplifies the academic caliber and national importance of the work in our Physics Department,"Jeff Thompson, dean of the College of Science said."We're proud of the team of researchers here working on cutting-edge science."

Mancini has been studying the atomic and radiation properties of high-energy density plasmas for more than 15 years, and this new grant will allow him to further explore what happens to matter when it is subjected to extreme conditions of temperature and radiation - similar to what happens to many astrophysical objects in the universe.

The research will enable astrophysicists to better understand what happens aroundblack holesand in active galactic nuclei. Scientists will also better understand the application of high-energy density plasmas to energy production, such as controllednuclear fusion(produced in the laboratory), and production of X-ray sources for a variety of applications.

"Using theories and tools created here at the University to design and analyze experiments, we then go to the only national facility that has the capacity to deliver the high-intensity flux of X-rays required to perform and measure these experiments,"Mancini said."We custom build instrumentation in our machine shop that meets the high standard set by the national facility so that it will fit onto the target chamber of the pulsed-power Z-machine, enabling us to conduct this unique experiment."

The pulsed-power machine at the Sandia National Laboratories in New Mexico (similar in concept but larger than the University's Nevada Terawatt Facility Zebra accelerator) is the most powerful source of X-rays on earth, Mancini said.

"We subject a very small cell - a 1-inch by½-inch cube - filled with a gas, such as neon, to this tremendous, short burst of X-ray energy,"he said."It's about 10 nanoseconds of the most intense power on earth - creating conditions of hundreds of thousands of degrees and millions of atmospheres in pressure - in the form of X-rays."

The researchers can then compare their extensive computer modeling and calculations with the measurements so they can study and explain the extreme state of matter (plasma) created during those 10 nanoseconds, which mimics the majority of matter found throughout the universe.

"We are using a unique imaging X-ray spectrometer to measure the intensity distribution of radiation as a function of wavelength, which tells us what happens with the plasma,"Mancini said. From detailed analysis of the data, Mancini can extract the plasma's density, ionization and temperature.

He said the plasma reaches extreme conditions, very unlike the low-energy plasma found in a neon light or a plasma television screen, with light 1,000 times more energetic than visible light, temperature as high as 100,000 degrees Fahrenheit, and ionization mainly driven by the action of the X-ray flux going through theplasma.

The University of Nevada, Reno Physics Department has a team of about 20 scientists, faculty and research associates working on a variety of projects in the field of High Energy DensityPlasmaPhysics Research. Mancini emphasized that having strong research programs is critical for the quality of education and training that the University can provide to students.

Source: University of Nevada, Reno

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Signs of ideal surfing conditions spotted in ocean of solar wind

(PhysOrg.com) -- Researchers at the University of Warwick have found what could be the signal of ideal wave"surfing"conditions for individual particles within the massive turbulent ocean of the solar wind. The discovery could give a new insight into just how energy is dissipated in solar system sized plasmas such as the solar wind and could provide significant clues to scientists developing fusion power which relies on plasmas.

The research, led by Khurom Kiyanai and Professor Sandra Chapman in the University of Warwick's Centre for Fusion, Space and Astrophysics, looked at data from the Cluster spacecraft quartet to obtain a comparatively"quiet"slice of the solar wind as it progressed over an hour travelling covering roughly 2,340,000 Kilometres.

In space, on these large scales, and quiet conditions, nature provides an almost perfect experiment to study turbulence which could not be done on Earth in a laboratory. This plasma energy does eventually dissipate. One obvious way of understanding how such energetic plasma could dissipate this energy would be if the particles within the plasma collided with each other. However the solar wind is an example of a"Collisionless Plasma". The individual particles within that flow are still separated by massive distances so cannot directly interact with each other. They typically collide only once or twice with anything on their journey from the Sun to the Earth.

The University of Warwick Centre for Fusion, Space and Astrophysics led team drilled down into the data on this 2,340,000 Kilometres zooming down to see how the turbulence works on these different length scales which might provide some clue as to how the plasma was able to dissipate energy.

When the researchers were able to make observations all the way down to about I kilometre they could resolve the behaviour of individual particles within the total 2,340,000 kilometres slice ofsolar wind. These regions, which held just one particle of the plasma, were themselves almost a kilometre in size. The researchers were surprised to see a new kind of turbulence on these small scales.

At this particular scale they saw that the levels of turbulence switched from being mutlifractal to single fractal pattern. This single fractal pattern turbulence appears just right to create and sustain waves that can interact with the individual particles in thesolar wind. University of Warwick astrophysicist Khurom Kiyani said:"The particles in this"collisionless plasma"may too spread out to collide with each other but this could indicate that they can, and do, interact with waves and surfing these ideal waves is what allows them to dissipate their energy."

University of Warwick astrophysicist Professor Sandra Chapman said"We have been able to drill down through a vast ocean of data covering well over two million kilometres to get an insight in to what is happening in an area about the size of a beach, and on all length scales in between. We believe we are seeing waves on that beach that are providing the ideal surfing conditions to allow plasma particles to exchange energy without collisions."

Professor Sandra Chapman also said"These results are not just an interesting piece of astrophysics as the work has been led by a 'Centre for Fusion, Space and Astrophysics' the results have also immediately come to the attention of our colleagues working to increase the stability of plasmas involved in the generation of fusion energy. Turbulence is a big problem in keeping the hot plasma confined long enough for burning to take place to generate fusion power."

More information:The research entitled Global Scale-Invariant Dissipation in CollisionlessPlasmaTurbulencehas just been published inPhysical Review Letters.

Source: University of Warwick (news:web)

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Cool plasma packs heat against biofilms

Though it looks like a tiny purple blowtorch, a pencil-sized plume of plasma on the tip of a small probe remains at room temperature as it swiftly dismantles tough bacterial colonies deep inside a human tooth. But it's not another futuristic product of George Lucas' imagination. It's the exciting work of USC School of Dentistry and Viterbi School of Engineering researchers looking for new ways to safely fight tenacious biofilm infections in patients - and it could revolutionize many facets of medicine.

Two of the study's authors are Chunqi Jiang, a research assistant professor in the Ming Hsieh Department of Electrical Engineering-Electrophysics, and Parish Sedghizadeh, assistant professor of clinical dentistry and Director of the USC Center for Biofilms."Nanosecond Pulsed Plasma Dental Probe"appears in the June 2009 issue ofPlasma Processes and Polymers.

Sedghizadeh explained that biofilms are complex colonies of bacteria suspended in a slimy matrix that grants them added protection from conventional antibiotics. Biofilms are responsible for many hard-to-fight infections in the mouth and elsewhere. But in the study, biofilms cultivated in the root canal of extracted human teeth were easily destroyed with the plasma dental probe, as evidenced by scanning electron microscope images of near-pristine tooth surfaces after plasma treatment.

Plasma, the fourth state of matter, consists of electrons, ions, and neutral species and is the most common form found in space, stars, and lightning, Jiang said. But while many natural plasmas are hot, or thermal, the probe developed for the study is a non-thermal, room temperature plasma that's safe to touch. The researchers placed temperature sensors on the extracted teeth before treatment and found that the temperature of the tooth increased for just five degrees after 10 minutes of exposure to the plasma, Jiang said.

The cooler nature of the experimental plasma comes from its pulsed power supply. Instead of employing a steady stream of energy to the probe, the pulsed power supply sends 100-nanosecond pulses of several kilovolts to the probe once every millisecond, with an average power less than 2 Watts, Jiang said.

"Atomic oxygen {a single atom of oxygen, instead of the more common O2 molecule} appears to be the antibacterial agent,"according to plasma emission spectroscopy obtained during the experiments, she said.

Sedghizadeh said the oxygen free radicals might be disrupting the cellular membranes of the biofilms in order to cause their demise and that the plasma plume's adjustable, fluid reach allowed the disinfection to occur even in the hardest-to-reach areas of the root canal.

Given that preliminary research indicates that non-thermal plasma is safe for surrounding tissues, Sedghizadeh said he was optimistic about its future dental and medical uses. Much like the spread of laser technology from research and surgical applications to routine clinical and consumer uses, plasma could change everything; especially since nonthermal plasmas don't harbor the risks of tissue burns and eye damage that lasers do, he said.

"Plasma is the future,"Sedghizadeh said."It's been used before for other sterilization purposes but not for clinical medical applications, and we hope to be the first to apply it in a clinical setting."

"We believe we're the first team to applyplasmafor biofilm disinfection in root canals,"Jiang added."This collaboration is very unique. We're attacking frontier problems, and we're happy to be broadening our fields."

Source: University of Southern California (news:web)

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Scientists Control Plasma Bullets

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(PhysOrg.com) -- On the nanoscale, things aren’t always what they seem. What first looked like a continuous plasma jet has turned out to be a train of tiny, high-velocity plasma bullets. Using a camera with an exposure time of a few nanoseconds, researchers have further investigated the plasma bullets, and have even found a way to control them.

Using a high-speed intensified charge coupled device (ICCD), Professor Mounir Laroussi and his students from the Laser&Plasma Engineering Institute at Old Dominion University in Norfolk, Virginia, has taken an up-close look at the little-known plasma bullets. Their study is published in a recent issue of theJournal of Physics D: Applied Physics.

The plasma bullets are created by a“plasma pencil,” which is a pulsed plasma source that the researchers previously developed. The plasma pencil is a hollow tube about 2.5 cm in diameter that contains two copper electrodes. To ignite the plasma, the researchers sent a gas mixture of helium and oxygen through holes in the electrodes, and applied high-voltage electric pulses between the electrodes. When the gas ignited between the electrodes, it launched a plasma plume through the hole of the outer electrode up to 5 cm into the air.

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(Left) Photograph of a plasma bullet taken with an ICCD camera, illustrating the bullet’s donut shape. (Right) An externally applied dc voltage causes the plasma plume to bend in the opposite direction. Image credit: Mericam-Bourdet, et al.

The plasma plume (which is actually a train of plasma bullets) moves at a velocity of up to 100,000 meters per second - much faster than the velocity of the gas coming out of the device, which is just 8 meters per second. Although previous research has explained that photoionization could be responsible for the high velocity, Laroussi and his students at Old Dominion have now found clues to the bullets’ original formation.

In their study, the researchers found that the length of the electrically-driven plume depends mainly on two parameters: the applied voltage between the two electrodes and the helium gas flow. Also, the average bullet velocity increases when the voltage increases. By analyzing images from the ICCD camera, the scientists also found that the bullets always become extinguished when the voltage pulse ends.

By viewing the plasma bullets at multiple angles, the researchers found another surprise: the bullet is not round, but is shaped like a donut, with a hole in the middle. Based on this shape, the researchers proposed that the plasma bullets are surface waves that travel along the interface between two media - helium and ambient air.

In addition, the researchers found that they could control the initiation time and distance of the plasma bullets by applying an external dc electric field. The applied field decreased the bullets’ average velocity and distance traveled. Also, by applying the electric field perpendicular to the axis of the plasma plume, the negatively charged plume is deflected away from the negatively charged field.

As Laroussi explained, the aim of the study was to attempt to understand the physics behind the formation and propagation of these cold plasma bullets.“There has been a lot of debate as to how these bullets propagate. So we hope that we have contributed some interesting ideas to this debate,” he toldPhysOrg.com, adding that still more work needs to be done.

Laroussi also said that the plasma bullets could be used for biomedical purposes, such as dental and wound healing applications. Teaming up with microbiologists, Laroussi has already used the tiny plasma bullets to inactivate bacteria, especially those of dental relevance such asStreptococcus mutanswhich are implicated in the onset and progression of dental caries (tooth decay).

More information:Mericam-Bourdet, N.; Laroussi, M.; Begum, A.; and Karakas, E.“Experimental investigations of plasma bullets.”J. Phys. D: Appl. Phys. 42 (2009) 055207 (7pp).

Copyright 2009 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

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Physicists produce black hole plasma in the lab

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(PhysOrg.com) -- Black holes are voracious: They devour large amounts of matter from gas clouds or stars in their neighbourhood. As the incoming"food"spirals faster and faster into the abyss, it becomes denser and denser, and heats up to temperatures of many millions of degrees Celsius. Before the matter finally disappears, it emits extraordinarily intense X-rays into space. This"last cry"originates from iron, one of the elements contained in this matter. Researchers at the Max Planck Institute for Nuclear Physics in Heidelberg have collaborated with colleagues at the Helmholtz Zentrum Berlin and used the BESSY II synchrotron X-ray source to investigate what happens in this process.

In order to understand the nature of black holes, it is best to watch them feeding. The most interesting part is just before the matter disappears behind the event horizon - that is, the distance at which the mass attraction of the black hole becomes so strong that not even light can escape. This turbulent process generates X-rays, which in turn excite variouschemical elementsin the cloud of matter to emit X-rays themselves with characteristic lines ("colours"). An analysis of the lines provides information on the density, velocity and composition of the plasmas near the event horizon.

During this process iron plays an important role. Although it is not as abundant in the universe as lighter elements - mainly hydrogen and helium - it is much better at absorbing and reemitting X-rays. Thephotonsemitted thereby also have a higher energy, respectively a shorter wavelength (a different"colour"), than that of the lighter atoms.

They therefore leave behind clear fingerprints in the rainbow of the dispersed radiation: in the spectrum they reveal themselves as strong lines. The so-called K-alpha line of iron is the final visible spectral signature of matter, its"last cry", before it disappears behind theevent horizonof a black hole, never to be seen again.

The X-rays emitted are also absorbed as they pass through the medium surrounding the black hole at larger distances. And here iron again leaves behind clear fingerprints in the spectra. The radiation ionises the atoms several times and so-called photoionisation typically strips away more than half of the 26 electrons which the iron atoms usually contain. This produces ions with positive charge states that correspond to the number of stripped electrons. The end result is highly charged ions produced not by collisions but by radiation.

It is precisely this process, the stripping of further electrons from highly charged ions by incident X-rays, which researchers at the Max Planck Institute forNuclear Physicshave reproduced in the laboratory in collaboration with colleagues at BESSY II - the Berlin synchrotron X-ray source. The heart of the experiment was the EBIT electron beam ion trap designed at the Max-Planck institute. Inside the trap, iron atoms were heated up with the aid of an intense electron beam as they would be deep inside the sun or, as in this case, in the vicinity of a black hole.

Under such conditions, iron exists, for example, as the Fe¹⁴⁺ion, ionised fourteen times as it were. The experiment proceeds as follows: A cloud of these ions, only a few centimetres long and thin as a hair, is kept suspended in an ultra-high vacuum with the help of magnetic and electric fields. X-rays from the synchrotron then impact on this cloud; the photon energy of theX-raysis selected by a"monochromator"with extreme precision and directed onto the ions as a thin, focused beam.

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The researchers use EBIT, the electron beam ion trap, to reconstruct processes in the laboratory as they occur in the matter around black holes. Image: MPI for Nuclear Physics

The spectral lines measured in this experiment can be directly and easily compared with the most recent observations made by X-ray observatories, like Chandra and XMM-Newton. It turns out that most of the theoretical calculation methods used do not predict the line positions accurately enough. This is a big problem for the astrophysicists, because without accurate knowledge of the wavelengths there is no accurate determination of the so-called Doppler effect of these lines.

The Doppler effect describes the change in frequency (energy or wavelength) of the emitted light as a function of the velocity of the source (the ions in the plasma.). Anyone who listens to the siren of a passing ambulance experiences this phenomenon: as long as the vehicle approaches, the perceived pitch of the sound is higher; as it moves away, it is lower. If the frequency in the system at rest is known (ambulance is stationary), measuring the pitch makes it possible to determine the velocity of the source - in astronomy this is the plasma.

This left the scientists puzzled over the interpretation of NGC 3783, one of the active galactic nuclei which have been under investigation for the longest time. The error bars in the frequency in a rest frame calculated with the aid of different theoretical models led to such large uncertainties in the derived velocity of the emitting plasma that reliable statements on theplasmaflows were no longer possible.

The laboratory measurements of the Heidelberg-based Max-Planck researchers have now identified one theoretical method among several model calculations that provides the most accurate predictions. They also achieved the highest spectral resolution to date in this wavelength range. It had previously not been possible to experimentally check the different theories in this energy range with such high accuracy.

The novel combination of a trap for highly charged ions and brightsynchrotronradiation sources thus represents an important step and a new approach for understanding the physics in the plasmas aroundblack holesor active galactic nuclei. The researchers expect the combination of EBIT spectroscopy and brighter and brighter X-ray sources of the third (PETRA III at DESY) and fourth generation (free-electron laser XFEL, Hamburg/Germany; LCLS, Stanford, USA; SCSS, Tsukuba, Japan) to bring fresh drive to this field.

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Scientists Generate Black Hole Radiation in the Lab

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(PhysOrg.com) -- Due to their violent nature and long distance from Earth, black holes and their surroundings are very difficult to study. Currently, the main method to observe a black hole is to use an X-ray satellite to detect the X-ray fluorescence emitted by a black hole’s companion star as the star’s material falls into the black hole. But now, scientists have developed a laser-driven method to generate a flash of brilliant Planckian X-rays in the lab that can be used to simulate the X-rays that exist near black holes. The new results contrast with the generallyaccepted explanation for the origins of these astronomical features, and may also help scientists test the complex computer codes used in X-ray astronomy.

The team of researchers, Shinsuke Fujioka, et al., from Osaka University, the Chinese Academy of Sciences, the Korea Atomic Energy Research Institute, and Shanghai Jiao Tong University, have published their study on creating Planckian X-rays in the laboratory in a recent issue ofNature Physics.

In their study, the researchers used a direct laser-driven implosion to create a hot, denseplasma. They aimed 12 intense laser beams (for a total of 3 billion watts, and carrying 4.0 kJ {kilojoules} of energy) onto a micrometer-sized spherical hollow plastic shell. When the shell’s core imploded, its temperature approached 1 keV (kiloelectronvolt), creating a hot plasma. With other adjustments to the set-up, the researchers could produce a slowly expanding, cool plasma, much like the astronomical plasma observed nearblack holes. In the laboratory-generated plasma, the researchers detected the emitted X-rays and measured their spectra.

They identified two characteristic spectral peaks that closely resemble the spectral peaks observed in the binary systems Cygnus X-3 and Vela X-1. In the model of Cygnus X-3, which consists of a black hole and a companion star, the gravitational energy of the star’s accreting material is converted into thermal energy, which is the origin of the radiation emitted by the accretion disk. The X-ray spectra of Cygnus X-3 was previously observed by an X-ray spectrometer onboard the Chandra X-ray satellite.

“Astronomers use computer simulation codes to interpret their observational data, e.g. x-ray spectra and x-ray images,” Fujioka told PhysOrg.com. “Because matter near a black hole is in extreme conditions (very hot and very massive), which was difficult to be reproduced on the Earth, astronomerscould not validate their simulation results with valid experimental data; namely, astronomers were not sure whether their simulation results and their interpretations were correct or not.

“Furthermore, astronomers cannot directly measure temperature, density, and pressure of astronomical objects; there are many unknown parameters to interpret their observations. On the other hand, we can easily measure them in the laboratory. Our experimental technique offers astronomers a test bedto validate their models and simulations by comparing them to the experimental results obtained under well-characterized extreme conditions.”

Although the X-ray spectra obtained in the lab resemble those observed astronomically, their interpretations are very different, and even contradictory. Most significantly, the first spectral peak in the two binary systems is thought to be a forbidden resonance line of helium-like silicon ions. However, as Fujioka explained, these differences could help astronomers test the computer codes used in X-ray astronomy modeling.

“X-ray spectroscopy of photoionized plasma near a black hole is an important tool to study the evolution of a black hole,” Fujioka said. “Astronomers can reproduce their observational data even with incorrect or wrong models owing to adjusting the unknown parameters. If their codes are not valid,characteristics (temperature, density, mass, pressure etc.) of the binary systems may be changed. We hope that our result improves their understanding of the birth, growth, and death of a black hole.”

More information:Shinsuke Fujioka, et al.“X-ray astronomy in the laboratory with a miniature compact object produced by laser-driven implosion.”Nature Physics, Vol. 5, November 2009.Doi:10.1038/NPHYS1402

Copyright 2009 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

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Scientists unlock the secrets of exploding plasma clouds on the sun

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Twisted"ropes"of magnetic field lines erupt from the Sun and tanglewith the Earth's magnetic field.

The Sun sporadically expels trillions of tons of million-degreehydrogen gasin explosions called coronal mass ejections (CMEs). Such clouds -- an example is shown in Figure 1 -- are enormous in size (spanning millions of miles) and are made up of magnetizedplasmagases, so hot thathydrogen atomsare ionized. CMEs are rapidly accelerated by magnetic forces to speeds of hundreds of kilometers per second to upwards of 2,000 kilometers per second in several tens of minutes. CMEs are closely related to solar flares and, when they impinge on the Earth, can trigger spectacular auroral displays. They also induce strongelectric currentsin the Earth's plasma atmosphere (i.e., themagnetosphereandionosphere), leading to outages in telecommunications and GPS systems and even the collapse of electric power grids if the disturbances are very severe.

Since the first observation of asolar flarein 1859, solar eruptions ("explosions") have attracted much attention from scientists around the world and have been studied with a succession of increasingly sophisticated international satellite missions in the past three decades. A major challenge has been that enormous and complicated plasma structures accelerating away from the Sun can only be observed remotely. As a result, it has been difficult to testtheoretical modelsto establish a correct understanding of the mechanisms that cause such eruptions. But in 2006, an international twin-satellite mission called STEREO was launched to continuously observe the erupting plasma structures from the Sun to the Earth.

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This is an artist's rendition of an expanding model CME flux rope, which is about to impinge on the Earth. The dark blue represents a weak calculated magnetic field (of the order of 15 nanotesla) while red shows a strong field (of the order of 1 gauss). One representative magnetic"field line"is illustrated. Credit: J. Chen and V. Kunkel

Now, using the data from STEREO, new research by scientists at the Naval Research Laboratory (NRL) in Washington, D.C., demonstrates for the first time that the observed motion of erupting plasma clouds driven by magnetic forces can be correctly explained by a theoretical model. The work will be presented at the 52nd Annual Meeting of the APS Plasma Physics Division.

The theory, controversial when it was first proposed in 1989 by Dr. James Chen of NRL, is based on the concept that an erupting plasma cloud is a giant"magnetic flux rope,"a rope of"twisted"magnetic field linesshaped like a partial donut. Chen and Valbona Kunkel, a doctoral student at George Mason University, have applied this model to the new STEREO data of CMEs and shown that the theoretical solutions agree with the measured trajectories of the ejected clouds within the entire field of view from the Sun to the Earth.

The position of the leading edge (LE) of a CME that erupted on December 24, 2007 were tracked by the STEREO-A spacecraft from the earliest stages of eruption to its arrival at 1 AU approximately five days later. The magnetic field and plasma parameters were measured by the STEREO-B spacecraft. The agreement between theory and data is within 1 percent of the measured position of the LE. Chen and Kunkel's results show that the theoretically predicted magnetic field and plasma properties are in excellent agreement with the measurements aboard STEREO-B. This is the first model that can replicate directly observed quantities near the Sun and the Earth as well as the actual trajectories of CMEs. Prior to STEREO, the motion of CMEs in the region corresponding to HI1 and HI2 data was not observed.

Interestingly, the basic forces acting on solar flux ropes are the same as those in laboratory plasma structures such as tokamaks developed to produce controlled fusion energy. The mechanism described by the theory is also potentially applicable to eruptions on other stars.

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