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1

Is channeling of fission tracks taking place?  

CERN Multimedia

A single crystal of natural zircon which is sliced to have (010) basal plane and thinned by ion thinning is electron microscopically observed after slow neutron irradiation to ascertain whether channeling of the nuclear fission fragments is taking place or not. A fairly large number of the induced fission tracks are recognized at low magnification images where a considerable number of them are parallel to low-index lattice planes such as 100, 001, 101, 301, 103 though their directions changed some time up to several degrees. High resolution images of fission tracks often show a variety of zigzag passing of the tracks along low-index lattice planes in atomistic level. The rate of the tracks which are parallel to these low-index lattice planes is fairly high as about 45%, which strongly suggests that channeling of the fission tracks is taking place.

Yada, K

1999-01-01

2

Astrophysical Reconnection and Particle Acceleration  

CERN Document Server

Astrophysical reconnection takes place in a turbulent medium. The turbulence in most cases is pre-existing, not caused by the reconnection itself. The model of magnetic reconnection in Lazarian & Vishniac (1999) predicts that in the presence of turbulence the reconnection becomes fast, i.e. it is independent of resistivity, but dependent on the level of turbulence. Magnetic reconnection injects energy into plasmas through a turbulent outflow from the reconnection region and this outflow can enhance the level of turbulence creating bursts of reconnection. Magnetic reconnection in the presence of turbulence can accelerate energetic particles through the first order Fermi mechanism, as was discussed in Gouveia dal Pino & Lazarian (2005). We discuss new numerical results on particle acceleration in turbulent reconnection, compare the acceleration arising from turbulent reconnection to the acceleration of energetic particles in turbulent medium.

Lazarian, A; Pino, B Gouveia dal

2012-01-01

3

Third Place Learning Environments: Perspective Sharing and Perspective Taking  

Directory of Open Access Journals (Sweden)

Full Text Available In this paper we deliberate on intercultural and global communication strategies of perspective sharing and perspective taking, and potential perspective transformation. Consideration to these strategies is given within the two instances of third place learning environments: (a Role-play simulation environment in which learners develop experiment with strategies for resolving intercultural misconceptions, and (b a professional virtual learning network that may provide just-in-time support for its members encountering disorienting dilemma. The central purpose of the second environment is actually development of knowledge basis for understanding of Third Place Learning.

Mara Alagic

2009-11-01

4

Book review: Cyber war will not take place  

Digital Repository Infrastructure Vision for European Research (DRIVER)

"Cyber War Will Not Take Place." Thomas Rid. Hurst. April 2013. --- In 2005, the U.S. Air Force boasted it would now fly, fight, and win in cyberspace, the ‘fifth domain’ of warfare. This book takes stock to consider whether or not cyber war is a real threat. Thomas Rid argues that the focus on war and winning distracts from the real challenge of cyberspace: non-violent confrontation that may rival or even replace violence in surprising ways. Tracing the most significant hacks and att...

Muravska, Julia

2013-01-01

5

Third Place Learning Environments: Perspective Sharing and Perspective Taking  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this paper we deliberate on intercultural and global communication strategies of perspective sharing and perspective taking, and potential perspective transformation. Consideration to these strategies is given within the two instances of third place learning environments: (a) Role-play simulation environment in which learners develop experiment with strategies for resolving intercultural misconceptions, and (b) a professional virtual learning network that may provide just-in-time support f...

Mara Alagic; Rimmington, Glyn M.; Tatiana Orel

2009-01-01

6

Reconnection Diffusion, Star Formation and Numerical Simulations  

CERN Document Server

We consider fast magnetic reconnection that takes place within turbulent magnetic flux and show that the process results in diffusion of magnetic fields and matter, which we term reconnection diffusion. The process of reconnection diffusion is based on the model of 3D reconnection of weakly turbulent magnetic fields and is applicable to both fully ionized and partially ionized gas. The rate of reconnection diffusion does not depend on the level of ionization and therefore the usually employed ambipolar diffusion idea gets irrelevant for magnetic field transport in turbulent fluids. We claim that the reconnection diffusion process is a manifestation of the violation of flux conservation in highly conducting turbulent fluids. We discuss the consequences of reconnection diffusion for star formation and stress. We show that reconnection diffusion on large scales is independent of small scale magnetic field dynamics of magnetic fields. We conclude that numerical simulations correctly represents the diffusion of ac...

Lazarian, A

2013-01-01

7

Reconnection in Planetary Magnetospheres  

Science.gov (United States)

Current sheets in planetary magnetospheres that lie between regions of "oppositely-directed" magnetic field are either magnetopause-like, separating plasmas with different properties, or tail-like, separating plasmas of rather similar properties. The magnetopause current sheets generally have a nearly limitless supply of magnetized plasma that can reconnect, possibly setting up steady-state reconnection. In contrast, the plasma on either side of a tail current sheet is stratified so that, as reconnection occurs, the plasma properties, in particular the Alfven velocity, change. If the density drops and the magnetic field increases markedly perpendicular to the sheet, explosive reconnection can occur. Even though steady state reconnection can take place at magnetopause current sheets, the process often appears to be periodic as if a certain low average rate was demanded by the conditions but only a rapid rate was available. Reconnection of sheared fields has been postulated to create magnetic ropes in the solar corona, at the Earth's magnetopause, and in the magnetotail. However, this is not the only way to produce magnetic ropes as the Venus ionosphere shows. The geometry of the reconnecting regions and the plasma conditions both can affect the rate of reconnection. Sorting out the various controlling factors can be assisted through the examination of reconnection in planetary settings. In particular we observe similar small-scale tearing in the magnetopause current layers of the Earth, Saturn. Uranus and Neptune and the magnetodisk current sheet at Jupiter. These sites may be seeds for rapid reconnection if the reconnection site reaches a high Alfven velocity region. In the Jupiter magnetosphere this appears to be achieved with resultant substorm activity. Similar seeds may be present in the Earth's magnetotail with the first one to reach explosive growth dominating the dynamics of the tail.

Russell, C. T.

2000-01-01

8

Out in the Pinwheel Galaxy, a rare event takes place  

Science.gov (United States)

Astronomers forgo sleep; eyes fixed on star's explosionhttp://www.usatoday.com/tech/science/space/story/2011-09-07/Astronomers-forgo-sleep-eyes-fixed-on-stars-explosion/50303380/1#.TmjMWp9vWhAHow to See a Supernova From Your Backyard this Weekendhttp://www.universetoday.com/88617/how-to-see-a-supernova-from-your-backyard-this-weekend/A Stellar Explosion In The Big Dipperhttp://www.npr.org/2011/09/03/140163733/a-stellar-explosion-in-the-big-dippers-handleThe Hubble Space Telescopehttp://hubble.nasa.gov/The Pinwheel Galaxyhttp://www.ing.iac.es/PR/press/m101.htmlWhite Dwarfshttp://imagine.gsfc.nasa.gov/docs/science/know_l2/dwarfs.htmlAstronomers and others who peer into the night sky are getting quite excited about a rather rare event this Friday. A supernova (an exploding star) out in the Pinwheel Galaxy is expected to peak in brightness, and at only a mere 21 million light years away, it is the closest of its kind to be seen in 40 years. In a recent interview, Peter Nugent of the Lawrence Berkeley National Laboratory summed up the sentiments of many when he said "I'm running on adrenaline right now. A good night is four hours sleep." A number of observatories around the world are casting their telescopes out into the Pinwheel Galaxy to observe and document this rather unusual and fascinating event. This particular supernova is part of the "Type 1a" group, born from a runaway thermonuclear combustion from a white dwarf star. While the blast is quite "close" (cosmically speaking), if it had occurred in the Milky Way galaxy, the light from such an event would be visible during the daytime. Those individuals without their own personal high-end space observatory should not dismay, as a 6-inch telescope or a powerful set of binoculars will let them see part of this magnificent event. The first link will take visitors to a piece from Thursday's USA TODAY about this rather unusual and rare event. The second link will whisk users away to a great video clip from Universe Today that features astrophysicist Peter Nugent talking about how amateur astronauts can best view this event. Moving along, the third link will take users to a nice piece from NPR's Weekend Edition that provides a bit more insight into this supernova. The fourth link leads to NASA's homepage for the Hubble Space Telescope. Here visitors can learn about this technological triumph, and also read about its work examining the Pinwheel Galaxy. The fifth link leads to an amazing photograph of the Pinwheel Galaxy, courtesy of the Isaac Newton Telescope. The last link will take users to a page created by NASA's Goddard Space Flight Center that provides some background on white dwarfs.

Grinnell, Max

2011-09-16

9

Key European Grid event to take place in Geneva  

CERN Document Server

EGEE'06 is the main conference of the EGEE project, which is co-funded by the European Union and hosted by CERN. More than 90 partners all over Europe and beyond are working together in EGEE to provide researchers in both academia and industry with access to major computing resources, independent of their geographic location. The largest user community of the EGEE Grid is the High-Energy Physics community and in particular the LHC experiments, which are already making heavy use of the infrastructure to prepare for data taking. However, with the many new challenges faced by EGEE in its second phase that started in April this year, an even broader audience than at previous EGEE conferences is expected. In particular, a large number of related Grid projects will feature prominently in both plenary and parallel sessions during the 5 days of this event. Industry will also be well represented, highlighting the EGEE project's commitment to technology transfer to industry. CERN is the host of the conference, which i...

2006-01-01

10

Collisionless Magnetic Reconnection in Space Plasmas  

CERN Document Server

Magnetic reconnection requires the violation of the frozen-in condition which ties gyrating charged particles to the magnetic field inhibiting diffusion. Ongoing reconnection has been identified in near-Earth space as being responsible for the excitation of substorms, magnetic storms, generation of field aligned currents and their consequences, the wealth of auroral phenomena. Its theoretical understanding is now on the verge of being completed. Reconnection takes place in thin current sheets. Analytical concepts proceeded gradually down to the microscopic scale, the scale of the electron skin depth or inertial length, recognizing that current layers that thin do preferentially undergo spontaneous reconnection. Thick current layers start reconnecting when being forced by plasma inflow to thin. For almost half a century the physical mechanism of reconnection has remained a mystery. Spacecraft in situ observations in combination with sophisticated numerical simulations in two and three dimensions recently clari...

Treumann, R A

2014-01-01

11

Magnetic Reconnection under Anisotropic MHD Approximation  

CERN Document Server

We study the formation of slow-mode shocks in collisionless magnetic reconnection by using one- and two-dimensional collisionless MHD codes based on the double adiabatic approximation and the Landau closure model. We bridge the gap between the Petschek-type MHD reconnection model accompanied by a pair of slow shocks and the observational evidence of the rare occasion of in-situ slow shock observation. Our results showed that once magnetic reconnection takes place, a firehose-sense pressure anisotropy arises in the downstream region, and the generated slow shocks are quite weak comparing with those in an isotropic MHD. In spite of the weakness of the shocks, however, the resultant reconnection rate is 10-30% higher than that in an isotropic case. This result implies that the slow shock does not necessarily play an important role in the energy conversion in the reconnection system, and is consistent with the satellite observation in the Earth's magnetosphere.

Hirabayashi, K

2013-01-01

12

Magnetic reconnection under anisotropic magnetohydrodynamic approximation  

International Nuclear Information System (INIS)

We study the formation of slow-mode shocks in collisionless magnetic reconnection by using one- and two-dimensional collisionless MHD codes based on the double adiabatic approximation and the Landau closure model. We bridge the gap between the Petschek-type MHD reconnection model accompanied by a pair of slow shocks and the observational evidence of the rare occasion of in-situ slow shock observations. Our results showed that once magnetic reconnection takes place, a firehose-sense (p?>p?) pressure anisotropy arises in the downstream region, and the generated slow shocks are quite weak comparing with those in an isotropic MHD. In spite of the weakness of the shocks, however, the resultant reconnection rate is 10%–30% higher than that in an isotropic case. This result implies that the slow shock does not necessarily play an important role in the energy conversion in the reconnection system and is consistent with the satellite observation in the Earth's magnetosphere

2013-11-01

13

Magnetic reconnection in sheared solar magnetic arcades  

Energy Technology Data Exchange (ETDEWEB)

The evolution of solar magnetic arcades is investigated with the use of MHD simulations imposing resistivity on sheared magnetic fields. It is found that there is a critical amount of shear, over which magnetic reconnection can take place in an arcade-like field geometry to create a magnetic island. The process leading to reconnection cannot be solely attributed to a tearing instability, but rather to a reactive evolution of the magnetic arcade under resistivity. The natures of the arcade reconnection are governed by the spatial pattern of resistivity. A fast reconnection with a small shock angle can only be achieved when the diffusion region is localized. In this case, a highly collimated reconnection outflow can tear the plasmoid into a pair, and most of principal features in solar eruptive processes are reproduced.

Choe, G.S.

1996-12-31

14

Magnetic reconnection under anisotropic magnetohydrodynamic approximation  

Science.gov (United States)

We study the formation of slow-mode shocks in collisionless magnetic reconnection by using one- and two-dimensional collisionless MHD codes based on the double adiabatic approximation and the Landau closure model. We bridge the gap between the Petschek-type MHD reconnection model accompanied by a pair of slow shocks and the observational evidence of the rare occasion of in-situ slow shock observations. Our results showed that once magnetic reconnection takes place, a firehose-sense (p>p) pressure anisotropy arises in the downstream region, and the generated slow shocks are quite weak comparing with those in an isotropic MHD. In spite of the weakness of the shocks, however, the resultant reconnection rate is 10%-30% higher than that in an isotropic case. This result implies that the slow shock does not necessarily play an important role in the energy conversion in the reconnection system and is consistent with the satellite observation in the Earth's magnetosphere.

Hirabayashi, K.; Hoshino, M.

2013-11-01

15

Two- and three-dimensional magnetic reconnection observed in the Eulerian-Lagrangian analysis of magnetohydrodynamics equations.  

Science.gov (United States)

We study reconnection phenomena in magnetohydrodynamics on the basis of a magnetohydrodynamic version of the Eulerian-Lagrangian analysis. We find that the methods are useful in capturing time scales associated with magnetic reconnection both in two and three dimensions. Visualizations show that the determinants of the Jacobian determinants of the diffusive labels are small where active reconnection takes place. The resetting of the diffusive labels extracts a short time scale during reconnection. PMID:19256953

Ohkitani, K; Constantin, P

2008-12-01

16

Simulation study of magnetic reconnection  

Energy Technology Data Exchange (ETDEWEB)

Dynamical process of collisionless driven reconnection is investigated by means of a two-and-one-half-dimensional particle simulation. Magnetic reconnection develops in two steps in accordance with the formation of ion and electron current layers. The dominant triggering mechanism for electron phase changes from electron meandering motion effect to electron inertia effect as a longitudinal magnetic field increases. It is also found that the energy conversion takes place from electrons to ions through the action of an electrostatic field excited in the downstream and thus the average ion temperature becomes about 1.5 of the average electron temperature. (author)

Horiuchi, Ritoku [Theory and Computer Simulation Center, National Institute for Fusion Science, Toki, Gifu (Japan)

1998-08-01

17

Reconnection Diffusion, Star Formation, and Numerical Simulations  

Science.gov (United States)

We consider fast magnetic reconnection that takes place within turbulent magnetic flux and show that the process results in diffusion of magnetic fields and matter, which we term reconnection diffusion. The process of reconnection diffusion is based on the model of 3D reconnection of weakly turbulent magnetic fields and is applicable to both fully ionized and partially ionized gas. The rate of reconnection diffusion does not depend on the level of ionization and therefore the usually employed ambipolar diffusion idea gets irrelevant for magnetic field transport in turbulent fluids. We claim that the reconnection diffusion process is a manifestation of the violation of flux conservation in highly conducting turbulent fluids. We discuss the consequences of reconnection diffusion for star formation and stress. We show that reconnection diffusion on large scales is independent of small scale magnetic field dynamics of magnetic fields. We conclude that numerical simulations correctly represents the diffusion of actual astrophysical magnetic fields in flows with substantially larger Lundquist numbers if these simulated regions regions are turbulent.

Lazarian, A.

2013-04-01

18

Evidence of transient reconnection in the outflow jet of primary reconnection site  

Science.gov (United States)

The precise mechanism for the formation of magnetic islands in the magnetotail and the subsequent evolution are still controversial. New investigations have provided the first observational evidence of secondary reconnection in the earthward outflow jet of primary reconnection in the magnetotail. The secondary reconnection takes place 38 c/?pi earthward from the primary reconnection site and results in the birth of a magnetic island observed. This generation mechanism is different from the widely used model of multiple reconnection X-lines. The duration of the secondary reconnection was approximate one ion gyration period (5 s). The observations resemble recent numerical simulations where magnetic reconnection could spontaneously and transiently happen in the outflow jet, called secondary reconnection, which was used to explain the formation of the dipolarization fronts. Coincidentally, another magnetic island moving earthward passed through three satellites successively. By this chance we find the magnetic island was accelerated towards Earth with an acceleration of about 9 km s-2 at -19 RE in the magnetotail.

Wang, R.; Nakamura, R.; Zhang, T.; Du, A.; Baumjohann, W.; Lu, Q.; Fazakerley, A. N.

2014-03-01

19

23 CFR 636.402 - What types of information exchange may take place after the release of the RFP document?  

Science.gov (United States)

...exchange may take place after the release of the RFP document? 636.402 Section 636.402...exchange may take place after the release of the RFP document? Certain types of information...different points after the release of the RFP document. The following table...

2009-04-01

20

Magnetic reconnection: dynamics and particle acceleration  

International Nuclear Information System (INIS)

A significant fraction of the magnetic energy released during magnetic reconnection in solar flares appears as energetic electrons and protons and the observations suggest a common acceleration mechanism. How this conversion of magnetic energy takes place so efficiently has been a scientific topic of great interest. Recent developments in our understanding of reconnection have important implications for understanding energetic particle production. The onset of fast reconnection occurs only after sufficiently narrow current sheets develop. It has been suggested that the coronae of stars and accretions discs naturally evolve to a critical state close to fast reconnection onset. In flares the classical picture of the formation of a single large x-line does not seem to be viable: the narrow current layers that develop near the reconnection sites break up into secondary magnetic islands whose dynamics and size spectrum are likely to control particle acceleration. Energetic electrons are produced though the Fermi-like reflection in contracting magnetic islands rather than by parallel electric fields. Their energy gain is linked to the release of magnetic energy. The Fermi mechanism is viable only for super-Alfvenic ions so a seed mechanism for ions is required. Ion pickup in reconnection outflow exhausts is proposed as the seed mechanism. This seed model has the property that low Q/M ions gain energy faster than protons, which is consistent with observed enhancements of low Q/M ions in impulsive flares. Ion and electron acceleration in a multi-island environment remains poorly understood. (author)

2008-10-05

 
 
 
 
21

The 'taking place' of health and wellbeing: Towards non-representational theory.  

Science.gov (United States)

For the last two decades health geography has focused on the dynamics between health and place. Although the social constructivist perspective of much research has provided many insights into the meanings of health and health care arguably, mirroring progress in the parent discipline of human geography, there could be a far more serious engagement with non-representational theory and the 'taking place' of health and health care. To showcase the importance and potential of this broadly, the idea of wellbeing is re-approached. The paper reflects on the ways wellbeing has been treated in research primarily as a meaningful and relatively prescribed state of life, to the neglect of process. Based on this critique, a qualitative study then illustrates the most immediate and everyday ways wellbeing might arise through 'affect'; the pre-personal mobile energies and intensities that result from physical encounters within assemblages of bodies and objects. Indeed, theoretically the findings support the proposition that, at one level, wellbeing might not be taken from environment but instead might emerge as the affective environment. They certainly raise awareness of how much in health might originate at the surface, prior to meaning, within life's infinite spatial doings, and thus they launch some final thoughts on the wider challenges and opportunities for non-representational health geographies. PMID:24675389

Andrews, Gavin J; Chen, Sandra; Myers, Samantha

2014-05-01

22

Mechanisms of impulsive magnetic reconnection: Global and local aspects  

Energy Technology Data Exchange (ETDEWEB)

The global and local aspects of mechanisms of impulsive magnetic reconnection are discussed focusing on results from a dedicated laboratory experiment, MRX (Magnetic Reconnection Experiment), as well as fusion experiments. Possible application of the present analysis to reconnection phenomena in solar and space plasmas is also discussed. An external force which drives internal current in a fusion plasma causes magnetic flux to accumulate in a core section of the plasma (flux build-up). When the flux build-up generates a magnetic profile that satisfies a condition for a global magnetohydrodynamic instability to develop, reconnection takes place in an induced current layer generated by the instability leading to a global self-organization of the plasma. Generally the flux build-up phase is significantly longer than the reconnection time, {tau}{sub H} >> {tau}{sub Rec}, thus making the waveform of flux evolution or other plasma parameters sawtooth shaped. In the reconnection layer of collisionless plasmas, the two fluid dynamics would lead to the formation of a narrow electron current channel which tends to become unstable against micro-instabilities, leading to an unsteady or impulsive reconnection. A common feature of impulsive reconnection after flux build-up is presented.

Yamada, Masaaki [Center for Magnetic Self-Organization, Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)

2011-11-15

23

Mechanisms of impulsive magnetic reconnection: Global and local aspects  

International Nuclear Information System (INIS)

The global and local aspects of mechanisms of impulsive magnetic reconnection are discussed focusing on results from a dedicated laboratory experiment, MRX (Magnetic Reconnection Experiment), as well as fusion experiments. Possible application of the present analysis to reconnection phenomena in solar and space plasmas is also discussed. An external force which drives internal current in a fusion plasma causes magnetic flux to accumulate in a core section of the plasma (flux build-up). When the flux build-up generates a magnetic profile that satisfies a condition for a global magnetohydrodynamic instability to develop, reconnection takes place in an induced current layer generated by the instability leading to a global self-organization of the plasma. Generally the flux build-up phase is significantly longer than the reconnection time, ?H >> ?Rec, thus making the waveform of flux evolution or other plasma parameters sawtooth shaped. In the reconnection layer of collisionless plasmas, the two fluid dynamics would lead to the formation of a narrow electron current channel which tends to become unstable against micro-instabilities, leading to an unsteady or impulsive reconnection. A common feature of impulsive reconnection after flux build-up is presented.

2011-11-01

24

Optimization on Placing-in and Taking-out Operation for Railway Special Line Based on Improved Simulated Annealing Algorithm  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Placing-in and taking-out operation of railway special line is one of the key links and also is a complicated system engineering that is influenced by multitudinous factors. The intrinsic mechanism of placing-in and taking-out operation for railway radial special line was analyzed according to the characters of railway radial special line. On this basis, the whole process of placing-in and taking-out operation for railway radial special line was divided into the two operations process w...

Deyuan Liu; Changfeng Zhu; Linna Cheng; Haijun Li

2013-01-01

25

DSC studies of retrogradation and amylose lipid complex transition taking place in gamma irradiated wheat starch  

Science.gov (United States)

The effect of gamma irradiation ( 60Co) with doses of 5-30 kGy on the amylose-lipid complex transition and retrogradation occurring in gels containing ca. 50% and ca. 20% wheat starch was studied by differential scanning calorimetry (DSC) during heating-cooling-heating cycles (up to three cycles). Transition of the amylose-lipid complex occurs in all the irradiated samples at a lower temperature as compared to the non-irradiated starch. That effect was larger when the radiation dose was higher. A further thermal treatment causes a decrease of the transition temperature in the irradiated samples, with no effect or increase of that temperature observed for the non-irradiated ones. Irradiation hinders retrogradation taking place in 50% gels but facilitates the process occurring in 20% gels. The differences between the irradiated and the non-irradiated samples are more evident in the every next heating or cooling cycle as well as after storage and in the case of ca. 50% suspensions as compared to ca. 20% suspensions. The results point out to the deterioration of the structure of the complexes formed in the irradiated starch as compared to the non-irradiated one.

Cie?la, K.; Eliasson, A. C.

2007-12-01

26

Makro- and micromorphological evidence of processes taking place during Albeluvisol development in S Norway  

Science.gov (United States)

We studied two soil chronosequences in S Norway to identify processes involved in Albeluvisol formation. For this purpose, field observation of vertical and horizontal sections of soil profiles, soil chemical and mineralogical analyses were carried out, and in particular, micromorphological analysis was applied. The study area is located at the western and eastern side of the Oslofjord, S Norway, in the counties Vestfold and Østfold. This region is characterized by continuous glacio-isostatic uplift over the entire Holocene. Hence, the age of the land surface continuously increases from the coast towards higher elevations. Twelve soil profiles in loamy marine sediments were studied. Based on macro- and micromorphological observations and analytical data progressive soil formation is characterized as follows: As soon as the land surface is raised above sea level, five major processes are initiated: 1) development of deep desiccation cracks, forming a polygonal pattern; 2) compaction, taking place as soon as the coarse pores have been drained; 3) pyrite oxidation and release of sulfuric acid; 4) carbonate dissolution by acids from pyrite and iron oxidation resulting in rapid decarbonatization of the originally calcareous sediments; 5) precipitation of iron hypocoatings and coatings in the capillary fringe Soon after these very early processes have taken place, limited water permeability of the fine-textured sediments leads to horizon differentiation into Ah, Eg and Btg horizons within less than 2.1 ka. Eg horizons become lighter in colour with time. Also illuvial clay is already observed in the 2.1 ka-old soil. Soil pH in the upper part of the E horizon of this soil is already too low for significant clay mobilization. Clay illuviation is still active in all soils studied, but the upper boundary of the zone where pH favours clay mobilization is at 20-50 cm depth. Progressive clay illuviation over time is recorded in increasing thickness of clay coatings and proportion of voids having clay coatings. Clay mobilization and iron co-eluviation in the upper Eg horizon ceases within less than 2.1 ka, whereas weathering and formation of clay minerals and iron oxides continue, leading to formation of a BE horizon in the upper part of the Eg horizon. Albeluvic tongues start to form after 4.6-6.2 ka, developing preferably along desiccation cracks. Albeluvic material is washed into the cracks, and also enhanced leaching of bases and clay eluviation take place in the cracks. As both processes proceed, the albeluvic tongues get longer and wider. Clayey intercalations occur in the older soils (Stagnic Albeluvisols), and the following concept is suggested to explain their genesis: When after snow melt or a rainy period infiltrating water arrives at the lower end of an albeluvic tongue, the tongue fills up with water. Perched water accumulates also on top of the dense Btg horizon. Water, carrying suspended clay, penetrates under the pressure of the overlying water column from the tongue into the Btg horizon, where additional clay is mobilized. The clay settles when the velocity of the water decreases, forming clayey intercalations in the dense matrix of the Btg horizon.

Sauer, Daniela; Schülli-Maurer, Isabelle; Sperstad, Ragnhild; Sørensen, Rolf

2014-05-01

27

Criticism of reconnection models of the magnetosphere  

International Nuclear Information System (INIS)

Reconnection involves singular lines called X-lines on the day and night sides of the magnetosphere, and the reconnection rate is proportional to the component of the electric field along the X-line. Although there is some indirect support for this model there is no direct evidence to indicate that the reconnection process does actually take place in the magnetosphere. There are however a number of observations that provide some indirect support. In this paper it is pointed out that some recent observations provide possibilities for direct tests of the theoretical predictions. However it is shown that the direct evidence is clearly contradictory. Some of it is so compelling as to require drastic revision, even rejection, of current concepts in magnetospheric physics. (author)

1978-01-01

28

OECD Global Science Forum's Astronomy Workshop to take place in Munich  

Science.gov (United States)

On December 1 to 3, the city of Munich (Bavaria, Germany) will be the venue for a "Workshop on Large Scale Programmes and Projects in Astronomy and Astrophysics" organised by the Organisation for Economic Co-operation and Development (OECD) Global Science Forum in co-operation with the European Southern Observatory (ESO). The Workshop will be chaired by Ian Corbett (ESO). The Global Science Forum brings together science policy officials from the OECD countries. The delegates, who meet twice a year, look at a range of generic issues in science funding and seek to identify and maximise opportunities for international co-operation in basic scientific research. This Workshop was proposed by Germany and agreed by the delegates to the Global Science Forum in June. Government officials and scientists will be able to review in detail the information and the observational and technological advances needed for major progress in the field during the next 15- 20 years. The research subjects reviewed will cover the full range from planets, solar systems, life in the Universe, stars, galaxies, extreme objects to cosmology. Related technological challenges, virtual observatories and other data handling issues will also be considered. The primary objective is to specify the policy issues relating to priority-setting, planning, funding and, above all, international co-ordination and co-operation. The Workshop will focus on issues relevant to the process through which astronomy advances, and will highlight means to enhance that process in light of longer-term scientific and political trends. There will probably be a follow-up meeting early in 2004, from which a policy level report will be prepared for consideration by the Global Science Forum and so transmitted to governments. Eighteen delegations, from non-OECD as well as OECD countries, will attend, each consisting of senior programme managers from the national ministry, funding agency or research council, and one or more senior members of the national astronomical community. The International Astronomical Union (IAU) and the European Southern Observatory (ESO) are explicitly represented. Experts from the world-wide astronomy community have been invited to set the stage and provide input for the discussions. The choice by Germany and the OECD to make Munich the venue of this Global Science Forum Workshop is no coincidence. It is a recognition of the important role played by many institutions in the Munich region in the field of Astronomy and Astrophysics. They include the Ludwig-Maximilians-Universität where the Workshop will take place, the Max-Planck-Institut für Astrophysik, the Max-Planck Institut für Extraterrestrische Physik and the European Southern Observatory. These institutions are all participating in large programmes and projects in astronomy. ESO, for its part, is at the leading edge of world astronomy with its flagship facility, the Very Large Telescope in Paranal (Chile) and the newly started ALMA project at Chajnantor (Chile), being carried out in partnership between Europe and North America. Public Talks (Munich) on December 1, 2003 As a prelude to the Workshop, two public keynote presentations will take place on December 1 at the Deutsches Museum in Munich at 18:00 CET. The speakers are Malcolm Longair, Jacksonian Professor of Natural Philosophy and Head of Laboratory, Cavendish Laboratory, Cambridge (UK) and Martin Harwit, Professor Emeritus of Astronomy, Cornell University, and former Director of the National Air and Space Museum, Washington, DC (USA). The talks will be given in English and the entry to this public event is free. Professor Longair will speak on "Astrophysics and Cosmology in the Twenty-First Century" and Professor Harwit will speak on "The Growth of Understanding of our Universe". You can find more informaton on the Public Talks web page.

2003-11-01

29

ERCP in acute pancreatitis: What takes place in routine clinical practice?  

Directory of Open Access Journals (Sweden)

Full Text Available AIM: To evaluate the data from a survey carried out in Italy regarding the endoscopic approach to acute pancreatitis in order to obtain a picture of what takes place after the release of an educational project on acute pancreatitis sponsored by the Italian Association for the Study of the Pancreas.METHODS: Of the 1 173 patients enrolled in our survey, the most frequent etiological category was biliary forms (69.3% and most patients had mild pancreatitis (85.8%.RESULTS: 344/1 173 (29.3% underwent endoscopic retrograde cholangiopancreatography (ERCP. The mean interval between the onset of symptoms and ERCP was 6.7 ± 5.0 d; only 89 examinations (25.9% were performed within 72 h from the onset of symptoms. The main indications for ERCP were suspicion of common bile duct stones (90.3%, jaundice (44.5%, clinical worsening of acute pancreatitis (14.2% and cholangitis (6.1%. Biliary and pancreatic ducts were visualized in 305 patients (88.7% and in 93 patients (27.0% respectively. The success rate in obtaining a cholangiogram was statistically higher (P = 0.003 in patients with mild acute pancreatitis (90.6% than in patients with severe disease (72.2%. Biliary endoscopic sphincterotomy was performed in 295 of the 305 patients (96.7% with no difference between mild and severe disease (P = 0.985. ERCP morbidity was 6.1% and mortality was 1.7%; the mortality was due to the complications of acute pancreatitis and not the endoscopic procedure.CONCLUSION: The results of this survey, as with those carried out in other countries, indicate a lack of compliance with the guidelines for the indications for interventional endoscopy.

Armando Gabbrielli

2010-09-01

30

Particle simulation study of driven magnetic reconnection in a collisionless plasma  

International Nuclear Information System (INIS)

Driven magnetic reconnection in a collisionless plasma, 'collisionless driven reconnection', is investigated by means of a 2.5 dimensional particle simulation. Magnetic reconnection develops in two steps, i.e., slow reconnection which takes place in the early stage of the compression when the current layer is compressed as thin as the orbit amplitude of an ion meandering motion (ion current layer), and subsequent fast reconnection which takes place in the late stage when the electron current is concentrated into the narrow region with spatial scale comparable to the orbit amplitude of an electron meandering motion (electron current layer). The global dynamic evolution of magnetic reconnection is controlled by the physics of the ion current layer. The maximum reconnection rate is roughly in proportion to the driving electric field. It is also found that both ion heating and electron heating take place in accordance with the formation of two current layers and the ion temperature becomes two or more times as high as the electron temperature. (author)

1994-01-01

31

Particle simulation study of collisionless driven reconnection in a sheared magnetic field  

Energy Technology Data Exchange (ETDEWEB)

Nonlinear development of collisionless driven reconnection and the consequent energy conversion process between the field and particles in a sheared magnetic field are investigated by means of a two-and-a-half-dimensional particle simulation. Magnetic reconnection takes place in two steps irrespective of a longitudinal magnetic field, but the growth rate of reconnection field varies in proportion to the E x B drift velocity at an input boundary. It is clearly observed that the triggering mechanism of collisionless driven reconnection for the fast growing phase changes from an electron meandering dominance in a weak longitudinal field to an electron inertia dominance in a strong field. The electron acceleration and heating take place in the reconnection area under the influence of reconnection electric field, while the electron energy is converted to the ion energy through the action of electrostatic (ambipolar) field excited by magnetic compression in the downstream. It is also found that, in the presence of a longitudinal magnetic field, the electron acceleration by the reconnection field takes place effectively and the generated force-free current is maintained for a long period while forming an asymmetric spatial profile of current layer. (author)

Horiuchi, Ritoku; Sato, Tetsuya

1996-08-01

32

Particle simulation study of driven magnetic reconnection in a collisionless plasma  

International Nuclear Information System (INIS)

Driven magnetic reconnection in a collisionless plasma, ''collisionless driven reconnection,'' is investigated by means of two-and-one-half-dimensional particle simulation. Magnetic reconnection develops in two steps, i.e., slow reconnection, which takes place in the early stage of the compression when the current layer is compressed as thin as the orbit amplitude of an ion meandering motion (ion current layer), and subsequent fast reconnection, which takes place in the late stage when the electron current is concentrated into the narrow region with a spatial scale comparable to the orbit amplitude of an electron meandering motion (electron current layer). The global dynamic evolution of magnetic reconnection is controlled by the physics of the ion current layer. The maximum reconnection rate is roughly in proportion to the driving electric field. It is also found that both ion heating and electron heating take place in accordance with the formation of two current layers and the ion temperature becomes two or more times as high as the electron temperature

1994-11-01

33

Optimization on Placing-in and Taking-out Operation for Railway Special Line Based on Improved Simulated Annealing Algorithm  

Directory of Open Access Journals (Sweden)

Full Text Available Placing-in and taking-out operation of railway special line is one of the key links and also is a complicated system engineering that is influenced by multitudinous factors. The intrinsic mechanism of placing-in and taking-out operation for railway radial special line was analyzed according to the characters of railway radial special line. On this basis, the whole process of placing-in and taking-out operation for railway radial special line was divided into the two operations process which include placing-in scheduling and taking-out scheduling, then the optimization model of placing-in and taking-out operation for railway radial special line have been built considering that the time-window of each operation sites, the reliability train on-time and minimize the delay number of jobs is respectively regarded as the decision variable and objective function and optimization sequence of placing-in and taking-out operation was abstained under condition of non-through cars arriving at station. Meanwhile, corresponding optimization algorithm has also been put forward based on Improved Simulated Annealing (ISA algorithm. Finally, a case study has been carried out in order to testify validity, objectivity and applicability of this model and its algorithm and the computing results of Genetic Algorithm (GA, Simulated Annealing (SA and ISA is compared and analyzed respectively, it is shown that the results obtained by ISA are better than those obtained by SA and GA applied alone, the best solutions found so far of the ISA have less fitness value than that of the other two. This model and its algorithm can solve placing-in and taking-out operation of railway radial special line very well.

Linna Cheng

2013-01-01

34

Magnetic reconnection under anisotropic magnetohydrodynamic approximation  

Energy Technology Data Exchange (ETDEWEB)

We study the formation of slow-mode shocks in collisionless magnetic reconnection by using one- and two-dimensional collisionless MHD codes based on the double adiabatic approximation and the Landau closure model. We bridge the gap between the Petschek-type MHD reconnection model accompanied by a pair of slow shocks and the observational evidence of the rare occasion of in-situ slow shock observations. Our results showed that once magnetic reconnection takes place, a firehose-sense (p{sub ?}>p{sub ?}) pressure anisotropy arises in the downstream region, and the generated slow shocks are quite weak comparing with those in an isotropic MHD. In spite of the weakness of the shocks, however, the resultant reconnection rate is 10%–30% higher than that in an isotropic case. This result implies that the slow shock does not necessarily play an important role in the energy conversion in the reconnection system and is consistent with the satellite observation in the Earth's magnetosphere.

Hirabayashi, K.; Hoshino, M. [Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo (Japan)

2013-11-15

35

Spirit of place in science park. Take ZJ Inno-Park as an example  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Concerning the environment feature and its stabilisation as well as its development, the theory of spirit of place is used in this article to analyse the main expressing forms of the spirit of place in science park, with an example from one of the most famous science parks in China, Zhangjiang Inno-Park. The aim of this article is to search and establish the character of the place in science park as well as its humane features, and to give some practical advices for creating a vigorous, harmo...

Wang, Biao; Adolphe, Luc

2012-01-01

36

DSC studies of retrogradation and amylose-lipid transition taking place in gamma-irradiated wheat starch  

International Nuclear Information System (INIS)

It has been already shown that degradation resulting from gamma irradiation induces a decrease in order of starch granules and influences gelatinisation taking place during heating of starch and flour suspensions. In presented paper, DSC (differential scanning calorimetry) studies were carried out for wheat starch, non-irradiated and irradiated using doses in the range from 5 to 30 kGy. The influence of the conditions applied during DSC measurements on the possibility to observe differences between the amylose-lipid complex transition and retrogradation taking place in the non-irradiated and particularly irradiated starch samples was checked. The better differentiation between the amylose-lipid complex transition taking place in particular samples accompanied by the better reproducity were obtained in the case of dense suspensions as compared to the watery suspensions as well as during the first analysis performed for the recrystallised gels

2006-01-01

37

NEW SOLAR TELESCOPE OBSERVATIONS OF MAGNETIC RECONNECTION OCCURRING IN THE CHROMOSPHERE OF THE QUIET SUN  

International Nuclear Information System (INIS)

Magnetic reconnection is a process in which field-line connectivity changes in a magnetized plasma. On the solar surface, it often occurs with the cancellation of two magnetic fragments of opposite polarity. Using the 1.6 m New Solar Telescope, we observed the morphology and dynamics of plasma visible in the H? line, which is associated with a canceling magnetic feature (CMF) in the quiet Sun. The region can be divided into four magnetic domains: two pre-reconnection and two post-reconnection. In one post-reconnection domain, a small cloud erupted, with a plane-of-sky speed of 10 km s-1, while in the other one, brightening began at points and then tiny bright loops appeared and subsequently shrank. These features support the notion that magnetic reconnection taking place in the chromosphere is responsible for CMFs.

2010-04-10

38

An Experimental Investigation of the Process of Isotope Exchange that Takes Place when Heavy Water Is Exposed to the Atmosphere  

Science.gov (United States)

We have used the recently developed method for rapid measurement of maximum density temperature to determine the rate at which hydrogen and deuterium isotope exchange takes place when a sample of heavy water is exposed to the atmosphere. We also provide a simple explanation for the observed linear rate of transition. (Contains 2 figures.)

Deeney, F. A.; O'Leary, J. P.

2009-01-01

39

Magnetohydrodynamic modeling of two-dimensional reconnection in the Magnetic Reconnection Experiment  

International Nuclear Information System (INIS)

A two-dimensional magnetohydrodynamics (MHD) code is used to investigate the dynamical evolution of driven reconnection in the Magnetic Reconnection Experiment (MRX) [M. Yamada et al., Phys. Plasmas 7, 1781 (2000)]. The initial conditions and dimensionless parameters of the simulation are set to be similar to the experimental values. Many features of the time-evolution of magnetic configurations for both co- and counter-helicity reconnection in MRX are successfully reproduced in the framework of resistive MHD. The resistive MHD model is then augmented by the addition of a 'model Hall' term to begin to assess the importance of two-fluid physics in the experiment. The effective decoupling of the ion fluid from the reconnecting magnetic field due to the model Hall term is shown to be important during the early dynamic X-phase of MRX reconnection, while effectively negligible during the late 'steady-state' Y-phase, when plasma heating takes place. These results are consistent with the available experimental evidence. Based on simple symmetry considerations, an experiment to directly measure the Hall effect in MRX configuration is proposed and numerical evidence for the expected outcome is given

2003-08-01

40

Time window for magnetic reconnection in plasma configurations with velocity shear.  

Science.gov (United States)

It is shown that the rate of magnetic field line reconnection can be clocked by the evolution of the large-scale processes that are responsible for the formation of the current layers where reconnection can take place. In unsteady plasma configurations, such as those produced by the onset of the Kelvin-Helmholtz instability in a plasma with a velocity shear, qualitatively different magnetic structures are produced depending on how fast the reconnection process develops on the external clock set by the evolving large-scale configuration. PMID:18999757

Faganello, M; Califano, F; Pegoraro, F

2008-10-24

 
 
 
 
41

Magnetic reconnection  

International Nuclear Information System (INIS)

The fundamental physics of magnetic reconnection in laboratory and space plasmas is reviewed by discussing results from theory, numerical simulations, observations from space satellites, and recent results from laboratory plasma experiments. After a brief review of the well-known early work, representative recent experimental and theoretical works are discussed and the essence of significant modern findings are interpreted. In the area of local reconnection physics, many findings have been made with regard to two-fluid physics and are related to the cause of fast reconnection. Profiles of the neutral sheet, Hall currents, and the effects of guide field, collisions, and microturbulence are discussed to understand the fundamental processes in a local reconnection layer in both space and laboratory plasmas. While the understanding of the global reconnection dynamics is less developed, notable findings have been made on this issue through detailed documentation of magnetic self-organization phenomena in fusion plasmas. Application of magnetic reconnection physics to astrophysical plasmas is also discussed.

2010-01-01

42

Barrier breakers : women battling the odds to take places in engineering and oil  

Energy Technology Data Exchange (ETDEWEB)

The future role of women in Canada's engineering and petroleum industry was discussed. Women make up almost half of Canada's labour force, but they occupy only 24.2 per cent of the petroleum sector. This article briefly discussed some of the complex reasons why women continue to be under-represented in the oil and gas sector. In Alberta, job opportunities in engineering and the petroleum industry are alluring to both genders. Profiles of some young women just entering the work force after finishing their university education were also presented. Work experience, internships and networking were considered to be major factors in succeeding in male-dominated fields. It was suggested that it takes both genders to create the diverse thinking and experience needed to move forward technologically.

Rucker, D.

2001-04-02

43

A Study on the Place Attachment Differences of Residents in Tourism Destination: Take Gulangyu Island as an Example  

Directory of Open Access Journals (Sweden)

Full Text Available Place attachment is a long time research topic in tourism geography. However, when Chinese people do tourism planning and manage the destination, most of them also pay attention to the management of real enviroment or recreation faclilities. Few people study the place attachment relationship between the resident and the destination. This study takes Gulangyu as an example. By a large number of questionnaires, using relevant statistical software and methematical analysis, the paper analyzes the relationship between place attachment and the background, ways of tourism and frequency of visitation of local residents, the result shows that such as gender, cultural level, living time, occupation and whether the local people have an impact on the place attachment of residents. However,such as age and activities have no impact on the place attachment of residents, some differences of residents' place attachment are found. On the basis of the study, the paper analyzes the residents cluster basing on the difference of place attachment. Four types of resident are identified:"the daily life", "the emotion approval", "the sparsely leaving" and "the vital function".

YUAN Shu-ai

2011-11-01

44

Scaling of magnetic reconnection processes from MRX to astrophysical plasmas  

Science.gov (United States)

We discuss how the MRX (Magnetic Reconnection Experiment) physics results scale to space astrophysical plasmas. When the collisionality is reduced to satisfy the relationship c/?pi>?SP between the ion skin depth (c/?pi) and the Sweet-Parker width ?SP, a fast reconnection rate is observed in MRX [1], and the results are verified by numerical simulations. Since (c/?pi)/?SP is roughly equal to 5 (?mfp/L)^1/2, this relationship suggests that two-fluid effects become dominant even when the electron mean free path is one order of magnitude smaller than the system size [1]. The reconnection rate is found to increase rapidly as the ratio of the electron mean free path to the scale length increases. This result is attributed primarily to the large Hall electric field in the reconnection layer except near the X point where dissipative processes caused by electron pressure gradients and high frequency turbulence take place. Finally, a fast local reconnection generally leads to an impulsive global topology change or global magnetic self-organization phenomena. We also discuss how our local analysis can be applied to variety of magnetic reconnection phenomena in space astrophysical plasmas [2]. [1]M. Yamada, Phys. Plasmas, v. 14, 058102 (2007)[2]D. Uzdensky, Ap. J v.671, 2139 (2007)

Yamada, M.; Kulsrud, R.; Ji, H.; Uzdensky, D.; Zweibel, E.

2008-11-01

45

The study of magnetic reconnection in solar spicules  

CERN Document Server

This work is devoted to study the magnetic reconnection instability under solar spicule conditions. Numerical study of the resistive tearing instability in a current sheet is presented by considering the magnetohydrodynamic (MHD) framework. To investigate the effect of this instability in a stratified atmosphere of solar spicules, we solve linear and non-ideal MHD equations in the x-z plane. In the linear analysis it is assumed that resistivity is only important within the current sheet, and the exponential growth of energies takes place faster as plasma resistivity increases. We are interested to see the occurrence of magnetic reconnection during the lifetime of a typical solar spicule.

Fazel, Z

2014-01-01

46

Taking the High Ground: Geothermal's Place in the Revolving Energy Market  

Energy Technology Data Exchange (ETDEWEB)

It's a genuine privilege for me to be here today. As Dr. Mock mentioned, I have been President of California Energy for not yet three months and have a total tenure in the industry of only one year. As a newcomer to the industry, I am honored to address this group and share my views on ''The Opportunities and Challenges for Expanding Geothermal Energy''. You will see that my outlook for our industry is generally optimistic, shaped in part, perhaps by a newcomer's enthusiasm, but largely I think by my analysis of the opportunities which are open to us as an industry. Many of you and your predecessors over the last 20 years pioneered the geothermal industry in the United States. The risks were great, the results sometimes rewarding, sometimes disappointing. Government and the private sector forged an alliance that moved the industry ahead. Developers, utilities and federal land managers worked together to bring projects on line. Government helped identify geothermal areas, in many cases doing exploration work. The geothermal pioneers had to form entirely new, multi-disciplinary teams to solve problems unique to this resource. From discovery of fields, to environmental mitigation, to management of reservoirs and all of the steps in between, new teams had to be assembled. Geologists, geochemists, hydrologists, reservoir engineers and drilling technologists now apply their skills. Even anthropologists and biologists routinely get into the act in the environmental assessment phase of development. The care that our industry is taking today to do the job right reflects a maturing industry with high standards of performance. To be sure, mistakes were made in the early years, but the industry learned from them. We all know the value of responsible development and resource management to the long-term future of our industry. Improvements in technology and more efficient operations have helped lower our costs and improve our competitiveness. Our industry's progress has also been affected by outside factors. The price of and demand for electric power has fluctuated through economic cycles and changes in fuel prices. As our industry evolved and matured, we experienced a shakeout of ownership, with new companies arriving on the scene. We can be encouraged that today, some stable companies with solid projects lead in the development of the earth's natural steam. As more geothermal companies offer projects in competitive bidding, their names are becoming familiar to utility executives. Names like UNOCAL, Magma Power, Oxbow, Calpine, OESI, and yes, my company, California Energy. We compete, but we also benefit from one another's successes. Well-run, cost-effective geothermal plants elevate our small industry. We have matured from experimenting with emerging technologies to providing an established, reliable source of power.

Jaros, Richard

1992-03-24

47

Magnetic reconnection during magnetospheric substorms  

Science.gov (United States)

The near earth reconnection model of substorms represents an attempt to place a broad range of observations into a consistent framework. The roles and requirements of reconnection are discussed. High speed plasma sheet flows, thin current sheet instability, substorm triggering, plasmoids and flux ropes in the distant tail, and magnetohydrodynamic simulations are discussed. Substorms are global, coherent sequences of processes involving solar wind/magnetosphere/ionosphere interaction. Magnetic reconnection is required to explain different dayside and polar cap phenomena, which required nightside reconnection. The modification and expansion of the standard near earth neutral line (NENL) model can integrate breakup arcs, current disruption, current wedge features, and localized plasma flows into the magnetic reconnection framework.

Baker, Daniel N.

1996-01-01

48

Separatrices: the crux of reconnection  

CERN Document Server

Reconnection is one of the key processes in astrophysical and laboratory plasmas: it is the opposite of a dynamo. Looking at energy, a dynamo transforms kinetic energy in magnetic energy while reconnection takes magnetic energy and returns is to its kinetic form. Most plasma processes at their core involve first storing magnetic energy accumulated over time and then releasing it suddenly. We focus here on this release. A key concept in analysing reconnection is that of the separatrix, a surface (line in 2D) that separates the fresh unperturbed plasma embedded in magnetic field lines not yet reconnected with the hotter exhaust embedded in reconnected field lines. In kinetic physics, the separatrices become a layer where many key processes develop. We present here new results relative to the processes at the separatrices that regulate the plasma flow, the energisation of the species, the electromagnetic fields and the instabilities developing at the separatrices.

Lapenta, Giovanni; Divin, Andrey; Newman, David; Goldman, Martin

2014-01-01

49

Electromagnetic energy conversion at reconnection fronts.  

Science.gov (United States)

Earth's magnetotail contains magnetic energy derived from the kinetic energy of the solar wind. Conversion of that energy back to particle energy ultimately powers Earth's auroras, heats the magnetospheric plasma, and energizes the Van Allen radiation belts. Where and how such electromagnetic energy conversion occurs has been unclear. Using a conjunction between eight spacecraft, we show that this conversion takes place within fronts of recently reconnected magnetic flux, predominantly at 1- to 10-electron inertial length scale, intense electrical current sheets (tens to hundreds of nanoamperes per square meter). Launched continually during intervals of geomagnetic activity, these reconnection outflow flux fronts convert ~10 to 100 gigawatts per square Earth radius of power, consistent with local magnetic flux transport, and a few times 10(15) joules of magnetic energy, consistent with global magnetotail flux reduction. PMID:24072917

Angelopoulos, V; Runov, A; Zhou, X-Z; Turner, D L; Kiehas, S A; Li, S-S; Shinohara, I

2013-09-27

50

Magnetic Reconnection  

International Nuclear Information System (INIS)

We review the fundamental physics of magnetic reconnection in laboratory and space plasmas, by discussing results from theory, numerical simulations, observations from space satellites, and the recent results from laboratory plasma experiments. After a brief review of the well-known early work, we discuss representative recent experimental and theoretical work and attempt to interpret the essence of significant modern findings. In the area of local reconnection physics, many significant findings have been made with regard to two-fluid physics and are related to the cause of fast reconnection. Profiles of the neutral sheet, Hall currents, and the effects of guide field, collisions, and micro-turbulence are discussed to understand the fundamental processes in a local reconnection layer both in space and laboratory plasmas. While the understanding of the global reconnection dynamics is less developed, notable findings have been made on this issue through detailed documentation of magnetic self-organization phenomena in fusion plasmas. Application of magnetic reconnection physics to astrophysical plasmas is also briefly discussed.

2009-01-01

51

Magnetic Reconnection  

Energy Technology Data Exchange (ETDEWEB)

We review the fundamental physics of magnetic reconnection in laboratory and space plasmas, by discussing results from theory, numerical simulations, observations from space satellites, and the recent results from laboratory plasma experiments. After a brief review of the well-known early work, we discuss representative recent experimental and theoretical work and attempt to interpret the essence of significant modern findings. In the area of local reconnection physics, many significant findings have been made with regard to two- uid physics and are related to the cause of fast reconnection. Profiles of the neutral sheet, Hall currents, and the effects of guide field, collisions, and micro-turbulence are discussed to understand the fundamental processes in a local reconnection layer both in space and laboratory plasmas. While the understanding of the global reconnection dynamics is less developed, notable findings have been made on this issue through detailed documentation of magnetic self-organization phenomena in fusion plasmas. Application of magnetic reconnection physics to astrophysical plasmas is also brie y discussed.

Masaaki Yamada, Russell Kulsrud and Hantao Ji

2009-09-17

52

ON THE NATURE OF RECONNECTION AT A SOLAR CORONAL NULL POINT ABOVE A SEPARATRIX DOME  

Energy Technology Data Exchange (ETDEWEB)

Three-dimensional magnetic null points are ubiquitous in the solar corona and in any generic mixed-polarity magnetic field. We consider magnetic reconnection at an isolated coronal null point whose fan field lines form a dome structure. Using analytical and computational models, we demonstrate several features of spine-fan reconnection at such a null, including the fact that substantial magnetic flux transfer from one region of field line connectivity to another can occur. The flux transfer occurs across the current sheet that forms around the null point during spine-fan reconnection, and there is no separator present. Also, flipping of magnetic field lines takes place in a manner similar to that observed in the quasi-separatrix layer or slip-running reconnection.

Pontin, D. I. [Division of Mathematics, University of Dundee, Dundee DD1 4HN (United Kingdom); Priest, E. R. [School of Mathematics and Statistics, University of St Andrews, Fife KY16 9SS (United Kingdom); Galsgaard, K., E-mail: dpontin@maths.dundee.ac.uk [Niels Bohr Institute, Copenhagen DK-2100 (Denmark)

2013-09-10

53

On the nature of reconnection at a solar coronal null point above a separatrix dome  

CERN Document Server

Three-dimensional magnetic null points are ubiquitous in the solar corona, and in any generic mixed-polarity magnetic field. We consider magnetic reconnection at an isolated coronal null point, whose fan field lines form a dome structure. We demonstrate using analytical and computational models several features of spine-fan reconnection at such a null, including the fact that substantial magnetic flux transfer from one region of field line connectivity to another can occur. The flux transfer occurs across the current sheet that forms around the null point during spine-fan reconnection, and there is no separator present. Also, flipping of magnetic field lines takes place in a manner similar to that observed in quasi-separatrix layer or slip-running reconnection.

Pontin, D I; Galsgaard, K

2013-01-01

54

Hall MHD Modeling of Two-dimensional Reconnection: Application to MRX Experiment  

International Nuclear Information System (INIS)

Two-dimensional resistive Hall magnetohydrodynamics (MHD) code is used to investigate the dynamical evolution of driven reconnection in the Magnetic Reconnection Experiment (MRX). The initial conditions and dimensionless parameters of the simulation are set to be similar to the experimental values. We successfully reproduce many features of the time evolution of magnetic configurations for both co- and counter-helicity reconnection in MRX. The Hall effect is shown to be important during the early dynamic X-phase of MRX reconnection, while effectively negligible during the late ''steady-state'' Y-phase, when plasma heating takes place. Based on simple symmetry considerations, an experiment to directly measure the Hall effect in MRX configuration is proposed and numerical evidence for the expected outcome is given

2003-01-01

55

Magnetic reconnection driven by filament eruption in the 7 June 2011 event  

Science.gov (United States)

During an unusually massive filament eruption on 7 June 2011, SDO/AIA imaged for the first time significant EUV emission around a magnetic reconnection region in the solar corona. The reconnection occurred between magnetic fields of the laterally expanding CME and a neighbouring active region. A pre-existing quasi-separatrix layer was activated in the process. This scenario is supported by data-constrained numerical simulations of the eruption. Observations show that dense cool filament plasma was re-directed and heated in situ, producing coronal-temperature emission around the reconnection region. These results provide the first direct observational evidence, supported by MHD simulations and magnetic modelling, that a large-scale re-configuration of the coronal magnetic field takes place during solar eruptions via the process of magnetic reconnection.

van Driel-Gesztelyi, L.; Baker, D.; Török, T.; Pariat, E.; Green, L. M.; Williams, D. R.; Carlyle, J.; Valori, G.; Démoulin, P.; Matthews, S. A.; Kliem, B.; Malherbe, J.-M.

2014-01-01

56

A MAGNETIC RECONNECTION ORIGIN FOR THE SOFT X-RAY EXCESS IN AN ACTIVE GALACTIC NUCLEUS  

International Nuclear Information System (INIS)

We present a new scenario to explain the soft X-ray excess in an active galactic nucleus (AGN). Magnetic reconnection could happen in a thin layer on the surface of an accretion disk. Electrons are accelerated by a shock wave and turbulence is triggered by magnetic reconnection. Inverse Compton scattering then takes place above the accretion disk, producing soft X-rays. Based on the standard disk model, we estimate the magnetic field strength and the energy released by magnetic reconnection along the accretion disk and find that the luminosity arising from magnetic reconnection is mostly emitted in the inner disk, which is dominated by radiation pressure. We then apply the model to fit the spectra of AGNs with strong soft X-ray excess

2013-08-10

57

A magnetic reconnection origin for the soft X-ray excess in AGN  

CERN Document Server

We present a new scenario to explain the soft X-ray excess in Active Galactic Nucleus. The magnetic reconnection could happen in a thin layer on the surface of accretion disk. Electrons are accelerated by shock wave and turbulence triggered by magnetic reconnection, then they take place inverse Compton scattering above accretion disk which contributes soft X-rays. Based on standard disk model, we estimate the magnetic field strength and the energy released by magnetic reconnection along accretion disk, and find that the luminosity caused by magnetic reconnection mainly emits in the inner disk which is dominated by radiation pressure. We then apply the model to fit the spectra of AGNs with strong soft X-ray excess.

Zhong, Xiaogu

2013-01-01

58

A MAGNETIC RECONNECTION ORIGIN FOR THE SOFT X-RAY EXCESS IN AN ACTIVE GALACTIC NUCLEUS  

Energy Technology Data Exchange (ETDEWEB)

We present a new scenario to explain the soft X-ray excess in an active galactic nucleus (AGN). Magnetic reconnection could happen in a thin layer on the surface of an accretion disk. Electrons are accelerated by a shock wave and turbulence is triggered by magnetic reconnection. Inverse Compton scattering then takes place above the accretion disk, producing soft X-rays. Based on the standard disk model, we estimate the magnetic field strength and the energy released by magnetic reconnection along the accretion disk and find that the luminosity arising from magnetic reconnection is mostly emitted in the inner disk, which is dominated by radiation pressure. We then apply the model to fit the spectra of AGNs with strong soft X-ray excess.

Zhong Xiaogu; Wang Jiancheng, E-mail: guqian29@ynao.ac.cn [National Astronomical Observatories, Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011 (China)

2013-08-10

59

DSC Studies of Retrogradation and Amylose-Lipid Complex Transition Taking Place in Gamma Irradiated Wheat Starch  

International Nuclear Information System (INIS)

Degradation resulting from gamma irradiation induces decrease in order of starch granules and influences the processes occurring in starch-water system. Differential scanning calorimetry (DSC) was applied at present for studying the effect of radiation with doses of 5 - 30 kGy on amylose-lipid complex transition and retrogradation occurring in wheat starch gels. Influence of the conditions applied during DSC measurements and intermediate storage was tested on the possibility to observe radiation effect. Wheat starch was irradiated with 60Co gamma rays in a gamma cell Issledovatiel placed in the Department of Radiation Chemistry, INCT. DSC measurements were performed for ca. 50% and ca. 20% gels during heating - cooling - heating cycles (up to 3 cycles) in the temperature range 10 - 150 degree at heating and cooling rates of 10, 5 and 2.5 degree min-1. The Seiko DSC 6200 calorimeter was used. Decrease in amylose-lipid complex transition temperature was found already after irradiation of wheat starch with a dose of 5 kGy showing modificatin of the complex structure. The differences between the irradiated and the non-irradiated samples became the easier seen in the every foregoing heating or cooling cycle as compared to the preceeding one. It is because that thermal treatment causes decrease of transition temperature in all the irradiated samples, with no effect or increase of that temperature observed in the non-irradiated ones. Irradiation hinders retrogradation taking place in ca. 50% gels but facilitates retrogradation occurring in ca. 20 % gels. Moreover, the expanded differences between the amylose-lipid complex formed in the irradiated and non-irradiated gels result due to their recrystallisation. Storage of the gels induces decrease in the temperature of the complex transition as compared to the last cycle of the first analysis. That decrease was, however, more significant in the case of all the irradiated samples than in the case of the initial sample. In result, the differences between the irradiated and the non-irradiated samples are easier detected after storage. The better differentiation between the amylose-lipid complex transition taking place in particular samples accompanied by the better reproducity were obtained in the case of ca. 50% suspensions as compared to ca. 20% suspensions submitted to the same treatment. The results are discussed in terms of the structural changes resulting in starch due to irradiation. The work was sponsored in the frame of research grant 2P06T 026 27 of Polish Ministry of Scientific Research and Information Technology

2006-09-23

60

Magnetic reconnection  

International Nuclear Information System (INIS)

A review is given of the theory of magnetic reconnection in the framework of resistive magnetohydrodynamics (MHD). While most of the material refers to two-dimensional systems, the final sections give a brief outlook of problems arising in fully three-dimensional configurations. (orig.)

1991-01-01

 
 
 
 
61

Human mitochondrial RNA decay mediated by PNPase-hSuv3 complex takes place in distinct foci.  

Science.gov (United States)

RNA decay is usually mediated by protein complexes and can occur in specific foci such as P-bodies in the cytoplasm of eukaryotes. In human mitochondria nothing is known about the spatial organization of the RNA decay machinery, and the ribonuclease responsible for RNA degradation has not been identified. We demonstrate that silencing of human polynucleotide phosphorylase (PNPase) causes accumulation of RNA decay intermediates and increases the half-life of mitochondrial transcripts. A combination of fluorescence lifetime imaging microscopy with Förster resonance energy transfer and bimolecular fluorescence complementation (BiFC) experiments prove that PNPase and hSuv3 helicase (Suv3, hSuv3p and SUPV3L1) form the RNA-degrading complex in vivo in human mitochondria. This complex, referred to as the degradosome, is formed only in specific foci (named D-foci), which co-localize with mitochondrial RNA and nucleoids. Notably, interaction between PNPase and hSuv3 is essential for efficient mitochondrial RNA degradation. This provides indirect evidence that degradosome-dependent mitochondrial RNA decay takes place in foci. PMID:23221631

Borowski, Lukasz S; Dziembowski, Andrzej; Hejnowicz, Monika S; Stepien, Piotr P; Szczesny, Roman J

2013-01-01

62

DSC studies of retrogradation and amylose-lipid complex transition taking place in gamma irradiated wheat starch  

International Nuclear Information System (INIS)

The effect of gamma irradiation (60Co) with doses of 5-30 kGy on the amylose-lipid complex transition and retrogradation occurring in gels containing ca. 50% and ca. 20% wheat starch was studied by differential scanning calorimetry (DSC) during heating-cooling-heating cycles (up to three cycles). Transition of the amylose-lipid complex occurs in all the irradiated samples at a lower temperature as compared to the non-irradiated starch. That effect was larger when the radiation dose was higher. A further thermal treatment causes a decrease of the transition temperature in the irradiated samples, with no effect or increase of that temperature observed for the non-irradiated ones. Irradiation hinders retrogradation taking place in 50% gels but facilitates the process occurring in 20% gels. The differences between the irradiated and the non-irradiated samples are more evident in the every next heating or cooling cycle as well as after storage and in the case of ca. 50% suspensions as compared to ca. 20% suspensions. The results point out to the deterioration of the structure of the complexes formed in the irradiated starch as compared to the non-irradiated one

2007-12-01

63

DSC studies of retrogradation and amylose-lipid complex transition taking place in gamma irradiated wheat starch  

Energy Technology Data Exchange (ETDEWEB)

The effect of gamma irradiation ({sup 60}Co) with doses of 5-30 kGy on the amylose-lipid complex transition and retrogradation occurring in gels containing ca. 50% and ca. 20% wheat starch was studied by differential scanning calorimetry (DSC) during heating-cooling-heating cycles (up to three cycles). Transition of the amylose-lipid complex occurs in all the irradiated samples at a lower temperature as compared to the non-irradiated starch. That effect was larger when the radiation dose was higher. A further thermal treatment causes a decrease of the transition temperature in the irradiated samples, with no effect or increase of that temperature observed for the non-irradiated ones. Irradiation hinders retrogradation taking place in 50% gels but facilitates the process occurring in 20% gels. The differences between the irradiated and the non-irradiated samples are more evident in the every next heating or cooling cycle as well as after storage and in the case of ca. 50% suspensions as compared to ca. 20% suspensions. The results point out to the deterioration of the structure of the complexes formed in the irradiated starch as compared to the non-irradiated one.

Ciesla, K. [Institute of Nuclear Chemistry and Technology, Dorodna 16 str., 03-195 Warsaw (Poland)], E-mail: kciesla@orange.ichtj.waw.pl; Eliasson, A.C. [Department of Food Technology Engineering and Nutrition, Division of Food Technology, University of Lund, P.O. Box 124, S-221 00 Lund (Sweden)

2007-12-15

64

The structure of the magnetic reconnection exhaust boundary  

Science.gov (United States)

Switch-off slow shocks (SSS) are the key structure of driving the outflow in Petschek's reconnection model. Observations of reconnection in the solar wind in particular seem to suggest that reconnection X-lines and associated exhausts grow to very large scales and resemble the open outflow geometry predicted by Petschek. However, direct observations of SSSs in the Earth's magnetosphere and the solar wind are infrequent. Since it is the release of magnetic energy downstream from the X-line that ultimately drives the outflow rather than the dynamics close to the X-line, the absence of the SSS in observations and kinetic simulations calls into question the conjecture that fast collisionless reconnection actually can scale to very large systems. Thus, a key requirement for demonstrating the fast energy release of reconnection that takes place in large systems is to pin down the specific mechanism driving the Alfvenic outflow. We present a large 2-D reconnection simulation and its companion Riemann problem using a Particle-In-Cell code. The self-generated firehose-sense temperature anisotropy (i.e., T| > T) by counterstreaming ions is found to be important in determining the structure of reconnection exhausts. This temperature anisotropy slows down the intermediate mode while speeds up the slow mode, and consequently prevents the formation of classical Switch-off Slow shocks in Petschek's model. Instead, the nonlinear coupling between the slow and intermediate waves constitutes the shock transition. A plateau of the firehose stability parameter 1-(?|-?)/2 at value 0.25 is observed inside these hybrid waves, which should also be observable in Earth's magnetotail and the solar wind. This special value is significant because it is the degeneracy point of slow and intermediate waves in anisotropic plasmas. The anisotropic Rankine-Hugoniot jump conditions are derived and compared with our simulations, while the pseudo-potentials of shocks are analyzed to explain the dynamics of forming these transition structures. The Wal'en relation is shown to fail at the core of reconnection exhausts, where the firehose instability is unstable. (Ref: Yi-Hsin Liu, J. F. Drake and M. Swisdak, The structure of the magnetic reconnection exhaust boundary, Phys. of Plasmas, 19, 022110, 2012)

Liu, Yi-Hsin

2012-10-01

65

Study of Magnetic Reconnection.  

Science.gov (United States)

This research studied magnetic reconnection in a laboratory setting. (Magnetic reconnection is considered to be the primary cause of substorms.) It was found possible to trigger magnetic reconnection through the ion tearing mode and associated magnetic an...

J. M. Urrutia R. L. Stenzel W. Gekelman

1988-01-01

66

Ion Heating and Acceleration During Magnetic Reconnection Relevant to the Corona  

Science.gov (United States)

The heating and acceleration of ions during magnetic reconnection relevant to coronal heating and flares is explored via particle-in-cell (PIC) simulations and analytic modeling. We show that the dominant heating mechanism of sub-Alvénic ions during reconnection with a guide field, the case of greatest relevance to the corona, results from pickup behavior during the entry into reconnection exhausts, which produces effective thermal speeds of the order of the Alfvén velocity based on the reconnecting magnetic field. There is a mass-to-charge ( M/ Q) threshold for pickup behavior that favors the heating of high- M/ Q ions. Ions below the threshold gain little energy beyond that associated with convective flow. PIC simulations with protons and alphas confirm the pickup threshold. The enhanced heating of high M/ Q ions is consistent with observations of abundance enhancements of such ions in impulsive flares. In contrast to anti-parallel reconnection, the temperature increment during ion pickup is dominantly transverse, rather than parallel, to the local magnetic field. The simulations reveal the dominance of perpendicular heating, which is also consistent with observations. We suggest that the acceleration of ions to energies well above that associated with the Alfvén speed takes place during the interaction with many magnetic islands, which spontaneously develop during 3-D guide-field reconnection. The exploration of particle acceleration in a full 3-D multi-island system remains computationally intractable. Instead we explore ion acceleration in a multi-current layer system with low initial ?. Ion energy gain takes place due to Fermi reflection in contracting and merging magnetic islands. Particle acceleration continues until the available magnetic free-energy is significantly depleted so that the pressure of energetic ions approaches that of the reconnecting field. Depending on the strength of the ambient guide field and in spite of the low initial plasma ?, the dominance of parallel heating can cause significant regions of the plasma to exceed the marginal firehose condition.

Drake, J. F.; Swisdak, M.

2012-11-01

67

RECONNECTION ELECTRIC FIELD AND HARDNESS OF X-RAY EMISSION OF SOLAR FLARES  

International Nuclear Information System (INIS)

Magnetic reconnection is believed to be the prime mechanism that triggers solar flares and accelerates electrons up to energies of MeV. In the classical two-dimensional reconnection model, the separation motion of chromospheric ribbons, manifests the successive reconnection that takes place higher up in the corona. Meanwhile, downward traveling energetic electrons bombard the dense chromosphere and create hard X-ray (HXR) emissions, which provide a valuable diagnostic of electron acceleration. Analyses of ribbon dynamics and the HXR spectrum have been carried out separately. In this Letter, we report a study of the comparison of reconnection electric field measured from ribbon motion and hardness (spectral index) of X-ray emission derived from X-ray spectrum. Our survey of the maximum average reconnection electric field and the minimum overall spectral index for 13 two-ribbon flares shows that they are strongly anticorrelated. The former is also strongly correlated with flare magnitude measured using the peak flux of soft X-ray emissions. These provide strong support for electron acceleration models based on the electric field generated at reconnecting current sheet during flares.

2009-05-01

68

In-Situ Observations of Reconnection in Space  

Science.gov (United States)

This paper gives an overview of the insights into the magnetic reconnection process obtained by in-situ measurements across current sheets found in planetary magnetospheres and the solar wind. Emphasis is placed on results that might be of interest to the study of reconnection in regions where no in-situ observations are available. These results include the role of symmetric versus asymmetric boundary conditions, the identification of the onset conditions, the reconnection rates, and the spatial and temporal scales. Special attention is paid to observations in the so-called diffusion region surrounding the reconnection sites, where ions and eventually also electrons become demagnetized and reconnection is initiated.

Paschmann, Götz; Øieroset, Marit; Phan, Tai

69

Forced magnetic reconnection due to boundary perturbation  

International Nuclear Information System (INIS)

Boundary layer analysis of forced magnetic reconnection due to an externally imposed boundary perturbation is revised. This revised analysis introduces correct asymptotic matching to take into account the effect of inertia in the inner layer precisely, and adopts a time dependent boundary perturbation which is suitable for this analysis. The revised analysis demonstrates a new reconnection process and clarifies the role of stability against the tearing modes in the process. The initial evolution of this new reconnection process is characterized by some significant features. One is that the reconnected flux increases on the same time scale as the boundary perturbation, which excludes the Sweet-Parker time scale obtained by use of the invalid constant-? asymptotic matching. Another is that an induced surface current on a resonant surface is in such a direction as to oppose the progress of the reconnection, because the equilibrium is stable against the tearing modes in the absence of the boundary perturbation. (author)

2000-06-01

70

Forced magnetic reconnection due to boundary perturbation  

Energy Technology Data Exchange (ETDEWEB)

Boundary layer analysis of forced magnetic reconnection due to an externally imposed boundary perturbation is revised. This revised analysis introduces correct asymptotic matching to take into account the effect of inertia in the inner layer precisely, and adopts a time dependent boundary perturbation which is suitable for this analysis. The revised analysis demonstrates a new reconnection process and clarifies the role of stability against the tearing modes in the process. The initial evolution of this new reconnection process is characterized by some significant features. One is that the reconnected flux increases on the same time scale as the boundary perturbation, which excludes the Sweet-Parker time scale obtained by use of the invalid constant-{psi} asymptotic matching. Another is that an induced surface current on a resonant surface is in such a direction as to oppose the progress of the reconnection, because the equilibrium is stable against the tearing modes in the absence of the boundary perturbation. (author)

Ishizawa, Akihiro; Tokuda, Shinji [Japan Atomic Energy Research Inst., Naka, Ibaraki (Japan). Naka Fusion Research Establishment

2000-06-01

71

Research of Place-based 3D Augmented Community-Taking The 3D Virtual Campus as an Example  

Directory of Open Access Journals (Sweden)

Full Text Available Place-based virtual community is the trend of recent researches on pervasive computing. The purpose is to enable users in a physical place to receive ubiquitous services from the environment while they communicate with each other unwittingly. The paper further promotes this idea by allowing remote users to join such a virtual community as well as to interact with members on site and calls this type of community as the place-based 3D augmented (PDA community. With the help of the augmented reality technique, on-the-spot member can visually sense the remote users by their representing avatars. To achieve this goal, the ambient communication environment is required to support message flow among the remote users and people on site. Besides, this environment should be able to discover context passing among members of this community to provide proper services. The context issues and context-awareness approaches of PDA community are fully discussed in the paper. Finally, the infrastructure of this PDA community is also presented along with preliminary result of the prototyping environment.

Chung-Hsien Tsai

2011-05-01

72

Solar flare mechanism based on magnetic arcade reconnection and island merging  

Energy Technology Data Exchange (ETDEWEB)

The authors propose a model describing physical processes of solar flares based on resistive reconnection of magnetic field subject to continuous increase of magnetic shear in the arcade. The individual flaring process consists of magnetic reconnection of arcade field lines, generation of magnetic islands in the magnetic arcade, and coalescence of magnetic islands. When a magnetic arcade is sheared (either by foot point motion or by flux emergence), a current sheet is formed and magnetic reconnection can take place to form a magnetic island. A continuing increase of magnetic shear can trigger a new reconnection process and create a new island in the under lying arcade below the magnetic island. The new born island rises faster than the preceding island and merges with it to form one island. Before completing the island merging process, the new born island exhibits two phases of rising motion: a first phase with a slower rising speed and a second phase with a faster rising speed. The flare plasma heating occurs mainly due to magnetic reconnection in the current sheet under the new born island. The new born island represents the X-ray plasma ejecta which shows two phases of rising motion observed by Yohkoh [Ohyama and Shibata (1997)]. The first phase with slower new born island rising speed corresponds to the early phase of reconnection of line-tied field in the underlying current sheet and is considered as the preflare phase. In the second phase, the island coalescence takes place, and the underlying current sheet is elongated so that the line-tied arcade field reconnection rate is enhanced. This phase is interpreted as the impulsive phase or the flash phase of flares. The obtained reconnection electric field is large enough to accelerate electrons to an energy level higher than 10 keV, which is necessary for observed hard X-ray emissions. After merging of the islands is completed, magnetic reconnection continues in the current sheet under the integrated island for a longer period, which is considered as the main phase of flares. The sequence of all these processes is repeated with some time interval while a shear-increasing motion continues. The authors propose that these repetitive flaring processes constitute a set of homologous flares.

C.Z. Chen; G.S. Choe

2000-06-15

73

Explosive Turbulent Magnetic Reconnection  

CERN Document Server

We report simulation results for turbulent magnetic reconnection obtained using a newly developed Reynolds-averaged magnetohydrodynamics model. We find that the initial Harris current sheet develops in three ways, depending on the strength of turbulence: laminar reconnection, turbulent reconnection, and turbulent diffusion. The turbulent reconnection explosively converts the magnetic field energy into both kinetic and thermal energy of plasmas, and generates open fast reconnection jets. This fast turbulent reconnection is achieved by the localization of turbulent diffusion. Additionally, localized structure forms through the interaction of the mean field and turbulence.

Higashimori, Katsuaki; Hoshino, Masahiro

2013-01-01

74

Explosive turbulent magnetic reconnection.  

Science.gov (United States)

We report simulation results for turbulent magnetic reconnection obtained using a newly developed Reynolds-averaged magnetohydrodynamics model. We find that the initial Harris current sheet develops in three ways, depending on the strength of turbulence: laminar reconnection, turbulent reconnection, and turbulent diffusion. The turbulent reconnection explosively converts the magnetic field energy into both kinetic and thermal energy of plasmas, and generates open fast reconnection jets. This fast turbulent reconnection is achieved by the localization of turbulent diffusion. Additionally, localized structure forms through the interaction of the mean field and turbulence. PMID:23829741

Higashimori, K; Yokoi, N; Hoshino, M

2013-06-21

75

Magnetic reconnection in astrophysics  

International Nuclear Information System (INIS)

Magnetic reconnection has been invoked to explain important transport phenomena and the activity of space and astrophysical plasmas. Two major classes of reconnection are generally distinguished. If time dependence is not essential, steady state reconnection schemes may be applicable. The time-dependent reconnection may either be predominantly spontaneous or predominantly driven. A few aspects that are essential in current research in this field are mentioned and the general trend in favour of the time-dependent reconnection is emphasized. The key role of in-situ space probe measurements is accounted for. A satisfactory theoretical understanding of reconnection requires a deeper insight into collective dissipation processes. (J.U.)

1984-08-27

76

Evidence of Particle Acceleration and Plasma Heating in Magnetic Reconnection Outflows in an Eruptive Solar Flare  

Science.gov (United States)

Where particle acceleration and plasma heating take place in relation to magnetic reconnection is a fundamental question for solar flares. We present here analysis of an M7.7 flare on 2012 July 19 observed by SDO/AIA and RHESSI that sheds new light on this question (Liu, Chen, & Petrosian, 2013, ApJ). Bi-directional outflows in forms of plasmoid ejections and contracting cusp-shaped loops originate between an erupting flux rope (Patsourakos et al. 2013, ApJ) and underlying flare loops at speeds of typically 200-300 km/s up to 1050 km/s. These outflows are associated with spatially separated double coronal X-ray sources with their centroid separation decreasing with energy. The highest temperature is located near the nonthermal X-ray loop-top source, well below the original heights of contracting cusps near the inferred reconnection site. These observations suggest that the primary loci of particle acceleration and plasma heating are in the reconnection outflow regions, rather than the reconnection site itself. We stress that models with this ingredient were proposed long ago (e.g., Forbes & Priest 1983) and backed by recent numerical simulations (e.g., Drake & Swisdak 2012), but solid observational evidence as presented here has been lacking. In addition, there is an initial ascent of the X-ray and EUV loop-top source prior to its recently recognized descent, which we ascribe to the interplay among multiple processes including the upward development of reconnection and the downward contractions of reconnected loops. The impulsive phase onset coincides with the rapid speed increases of the upward plasmoids, the individual loop shrinkages, and the overall loop-top descent, suggestive of an intimate relation of the energy release rate and the reconnection outflow speed.Abstract (2,250 Maximum Characters): Where particle acceleration and plasma heating take place in relation to magnetic reconnection is a fundamental question for solar flares. We present here analysis of an M7.7 flare on 2012 July 19 observed by SDO/AIA and RHESSI that sheds new light on this question (Liu, Chen, & Petrosian, 2013, ApJ). Bi-directional outflows in forms of plasmoid ejections and contracting cusp-shaped loops originate between an erupting flux rope (Patsourakos et al. 2013, ApJ) and underlying flare loops at speeds of typically 200-300 km/s up to 1050 km/s. These outflows are associated with spatially separated double coronal X-ray sources with their centroid separation decreasing with energy. The highest temperature is located near the nonthermal X-ray loop-top source, well below the original heights of contracting cusps near the inferred reconnection site. These observations suggest that the primary loci of particle acceleration and plasma heating are in the reconnection outflow regions, rather than the reconnection site itself. We stress that models with this ingredient were proposed long ago (e.g., Forbes & Priest 1983) and backed by recent numerical simulations (e.g., Drake & Swisdak 2012), but solid observational evidence as presented here has been lacking. In addition, there is an initial ascent of the X-ray and EUV loop-top source prior to its recently recognized descent, which we ascribe to the interplay among multiple processes including the upward development of reconnection and the downward contractions of reconnected loops. The impulsive phase onset coincides with the rapid speed increases of the upward plasmoids, the individual loop shrinkages, and the overall loop-top descent, suggestive of an intimate relation of the energy release rate and the reconnection outflow speed.

Liu, Wei; Chen, Q.; Petrosian, V.

2013-07-01

77

Solar wind interaction with the Earth's magnetosphere: the role of reconnection in the presence of a large scale sheared flow  

Directory of Open Access Journals (Sweden)

Full Text Available The Earth's magnetosphere and solar wind environment is a laboratory of excellence for the study of the physics of collisionless magnetic reconnection. At low latitude magnetopause, magnetic reconnection develops as a secondary instability due to the stretching of magnetic field lines advected by large scale Kelvin-Helmholtz vortices. In particular, reconnection takes place in the sheared magnetic layer that forms between adjacent vortices during vortex pairing. The process generates magnetic islands with typical size of the order of the ion inertial length, much smaller than the MHD scale of the vortices and much larger than the electron inertial length. The process of reconnection and island formation sets up spontaneously, without any need for special boundary conditions or initial conditions, and independently of the initial in-plane magnetic field topology, whether homogeneous or sheared.

F. Califano

2009-01-01

78

Placing the power of real options analysis into the hands of natural resource managers - taking the next step.  

Science.gov (United States)

This paper explores heuristic methods with potential to place the analytical power of real options analysis into the hands of natural resource managers. The complexity of real options analysis has led to patchy or ephemeral adoption even by corporate managers familiar with the financial-market origins of valuation methods. Intuitively accessible methods for estimating the value of real options have begun to evolve, but their evaluation has mostly been limited to researcher-driven applications. In this paper we work closely with Bush Heritage Australia to evaluate the potential of real options analysis to support the intuitive judgement of conservation estate managers in covenanting land with uncertain future conservation value due to climate change. The results show that modified decision trees have potential to estimate the option value of covenanting individual properties while time and ongoing research resolves their future conservation value. Complementing this, Luehrman's option space has potential to assist managers with limited budgets to increase the portfolio value of multiple properties with different conservation attributes. PMID:23702285

Nelson, Rohan; Howden, Mark; Hayman, Peter

2013-07-30

79

Stuck between a ROC and a hard place? Barriers to the take up of green energy in the UK  

International Nuclear Information System (INIS)

This paper examines the UK mechanisms for ensuring future investment in renewable energy through consumer adoption of green energy tariffs and the Renewable Obligation Certificate (ROC) system. Using a national survey and focus groups the stated willingness by UK customers to pay a premium for renewable or green energy and actual take up of such tariffs is assessed. Substantial differences between willingness to pay for and the adoption of green energy tariffs are reported. This disparity is linked to a range of factors including consumer confusion, lack of supply, complexities of constructing 'green source' tariffs under the ROC system and a lack of customer trust. It is concluded that the re-definition of the green energy market in favour of 'green source' tariffs, greater direct compliance with the Renewable Obligation by addressing supply constraints, and efforts in providing clearer information and choices for consumers via a compulsory green energy accreditation scheme are required if willing consumers' are to contribute to investment in renewable energy. (author)

2008-08-01

80

Vortex Ring Reconnections  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We investigate numerically the Navier-Stokes dynamics of reconnecting vortex rings at small $Re$ number. We find that reconnections are dissipative due to the smoothing of vorticity gradients at reconnection kinks and to the formation of secondary structures of stretched anti-parallel vorticity which transfer kinetic energy to small scales where it is subsequently dissipated efficiently. In addition, the relaxation of the reconnection kinks excites Kelvin waves which due to ...

Chatelain, Philippe; Kivotides, Demosthenes; Leonard, Anthony

2002-01-01

 
 
 
 
81

Cognitive Distance in and Between COP’s and Firms: Where do Exploitation and Exploration take Place, and How are they Connected?  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This paper contributes to the analysis of where and how both exploitation and exploration may take place inside and between communities and organizations. It connects with the discussion of differences between communities of practice and epistemic communities. The analysis allows for differences in cognition within communities of practice (‘cognitive distance’). Such distance yields potential novelty but creates problems in utilizing that potential. In communities of practice and epistemi...

Nooteboom, B.

2007-01-01

82

RELAP5-3D code validation in the neutron-dynamic analysis of transient processes taking place in RBMK-1500 reactors  

Energy Technology Data Exchange (ETDEWEB)

The paper presents an evaluation of RELAP5-3D code suitability to model-specific transients that take place during RBMK-1500 reactor operation, where the neutronic response of the core is important. Certain RELAP5-3D transient calculation results were benchmarked against calculation results obtained using the Russian complex neutronic-thermal-hydraulic code STEPAN/KOBRA, specially designed for RBMK reactor analysis. Comparison of the results obtained, using the RELAP5-3D and STEPAN/KOBRA codes, showed reasonable mutual agreement of the calculation results of both codes and their reasonable agreement with the real plant data.

Uspuras, E.; Bubelis, E. E-mail: evaldas@isag.lei.lt

2003-10-01

83

Asymmetric Magnetic Reconnection in Partially Ionized Chromospheric Plasmas  

Science.gov (United States)

Magnetic reconnection is a ubiquitous process in the solar chromosphere. Realistic models of chromospheric reconnection must take into account that the plasma is partially ionized. Asymmetric reconnection in the chromosphere may occur when newly emerged flux interacts with pre-existing, overlying flux. We present simulations of asymmetric reconnection in weakly ionized, reacting plasmas where the magnetic field strengths, densities, and temperatures are different in each upstream region. The simulations show considerable thinning of the current sheet, asymmetric decoupling of ions and neutrals in the inflow regions, and plasmoid formation late in time. We will discuss these simulations in the context of newly available observations from the Interface Region Imaging Spectrograph (IRIS).

Murphy, Nicholas Arnold; Lukin, Vyacheslav; Raymond, John C.

2014-06-01

84

Reversible collisionless magnetic reconnection  

International Nuclear Information System (INIS)

Reversible magnetic reconnection is demonstrated for the first time by means of gyrokinetic numerical simulations of a collisionless magnetized plasma. Growth of a current-driven instability in a sheared magnetic field is accompanied by magnetic reconnection due to electron inertia effects. Following the instability growth, the collisionless reconnection is accelerated with development of a cross-shaped structure of current density, and then all field lines are reconnected. The fully reconnected state is followed by the secondary reconnection resulting in a weakly turbulent state. A time-reversed simulation starting from the turbulent state manifests that the collisionless reconnection process proceeds inversely leading to the initial state. During the reversed reconnection, the kinetic energy is reconverted into the original magnetic field energy. In order to understand the stability of reversed process, an external perturbation is added to the fully reconnected state, and it is found that the accelerated reconnection is reversible when the deviation of the E × B streamlines due to the perturbation is comparable with or smaller than a current layer width

2013-10-01

85

Understanding the structural changes that take place in a polypyrrole film during its oxi-reduction process: a molecular dynamics simulation study  

Science.gov (United States)

Oxi-reduction processes of conducting polymer are the base of a great number of technological developments in the fields of polymeric actuators (artificial muscles) or smart windows. Hence, the understanding the structural changes that take place in the polymer as a function of its oxidation seems to be crucial for a proper understanding of these complicated systems. In this sense, a model with atomic detail has been simulated by Molecular Dynamics Simulation, which provides an insight of how the electrical response of the system depends of the structural changes that take place inside the polymer. In this regard, the conducting polymer, water and counterions were modeled with atomic detail with the goal of obtaining an insight of the ring orientation and reorientational relaxation time of the pyrrole rings at different oxidation states of the polymer. In addition, we studied how the above properties are greatly affected by the oxidation state of the polymer and the variation these properties changes from the polypyrrole/water interface to the polypyrrole bulk. Finally, we correlated the reorientational dynamics of pyrrole rings with the oxidation kinetic observed from a macroscopic point of view.

Lopez Cascales, J. J.; Otero, T. F.

2005-06-01

86

Magnetic reconnection in space  

International Nuclear Information System (INIS)

Models of magnetic reconnection in space plasmas generally consider only a segment of the magnetic field lines. The consideration of only a segment of the lines is shown to lead to paradoxical results in which reconnection can be impossible even in a magnetic field constrained to be curl free or can be at an Alfvén rate even when the plasma is a perfect conductor. A model of reconnecting magnetic fields is developed which shows the smallness of the interdiffusion distance ?d of magnetic field lines does not limit the speed of reconnection but does provide a reconnection trigger. When the reconnection region has a natural length Lr, the spatial scale of the gradient of magnetic field across the magnetic field lines must reach Lg?0.3Lr/ln(Lr/?d) for fast reconnection to be triggered, which implies a current density j?B/?0Lg that is far lower than that usually thought required for fast reconnection. The relation between magnetic reconnection in space and in toroidal laboratory plasmas is also discussed.

2012-09-01

87

Magnetic reconnection in solar atmosphere observed by Hinode  

International Nuclear Information System (INIS)

Complete text of publication follows. The Hinode spacecraft was launched on 2006 September 22 UT. It is a Japanese mission collaborating with US and UK with three instruments on board; the Solar Optical Telescope (SOT), the X-Ray Telescope (XRT) and EUV Imaging Spectrometer (EIS). Hinode reveals the three-dimensional structure and dynamics in the various activities of the Sun. One of the most interesting topics in solar physics is magnetic reconnection, because magnetic reconnection is one of the rapidest processes of energy conversion from stored magnetic energy to thermal energy and kinetic energy or non-thermal particle energy. In this talk, we present Hinode observation related to magnetic reconnection. One of the most interesting/astonishing Hinode's findings is that the magnetic reconnection can be taken place everywhere in solar atmosphere. We can clearly see the observational evidence of magnetic reconnection in not only solar corona but also chromosphere. SOT can observe the photospheric/chromospheric dynamics, and XRT/EIS can observe coronal dynamics. With those three telescopes, we can discuss magnetic reconnections from photosphere to upper corona. Generally the physical conditions of plasma are quite different between solar corona and chromosphere (for example, temperature, density, and so on). Thus, we can compare the magnetic reconnection in different physical condition and discuss the fundamental characteristics of magnetic reconnection with Hinode. We will discuss the major difference of the magnetic reconnection in the solar corona and photosphere/chromosphere in this talk.

2009-08-23

88

Some aspects of structural transformations taking place in organic mass of Ukrainian coals during heating. Part 1. Study of structural transformations when heating coals of different caking capacity  

Energy Technology Data Exchange (ETDEWEB)

The structure of the plastic layer in coals of different caking capacity was studied using the X-ray method and the influence of the plastic layer structure on the mechanism of coke formation was determined. It is shown that the transportation of the plastic mass in the gas-saturated zone of the plastic layer has a decisive influence on the decrease in volume of the coal charge and on obtaining a denser residue during carbonization. When heating poorly caking and non-caking coals an increase in the charge volume takes place. Using the quantitative X-ray phase analysis an ordered phase amount (C{sub cryst}) was found in solid residues of carbonization and the parameters d{sub 002}, L{sub c} and L{sub a} were determined. It is shown that the gas-saturated zone is generated in the plastic layer only when structural transformations in coals take place at the pre-plastic stage without changing the ratio between the number of carbon atoms in the ordered and non-ordered phases. The transition of well caking coal into the plastic state is accompanied by the activation of segmental and conformal movement of side chains and separate macromolecular fragments of the coal organic mass. In the course of grain swelling of non-caking coal its crystallites degrade. The conclusions drawn on the basis of X-ray studies were confirmed by the EPR-spectroscopy of residues corresponding to plastic zones in coals of different caking capacity. 36 refs., 17 figs., 1 tab.

Valentina V. Zubkova [Jan Kochanowski University, Kielce (Poland)

2005-04-01

89

Astrophysical reconnection and collisionless dissipation  

Energy Technology Data Exchange (ETDEWEB)

Magnetic reconnection and collisionless dissipation are common phenomena of astrophysical and fusion plasmas. While reconnection is responsible for disruptions of a fusion confinement, it causes flare explosions at the Sun and stars, in galaxies, planetary magnetospheres, and it causes aurorae and structure formation in the Universe as well as penetration through magnetic boundaries. Due to the weak coupling in astrophysical and fusion plasmas, dissipation is due to collective phenomena such as plasma waves and micro-turbulence rather than direct particle-particle collisions. Since astrophysical plasmas usually are not directly observable, laboratory investigations may help to verify theoretical plasma astrophysical predictions but for the transfer of knowledge one has to take into account some specifics of astroplasmas, their density, temperature, currents and magnetic field strengths, geometry and even topology. As an example we discuss magnetic reconnection in the solar corona which requires collisionless dissipation. Both are highly nonlinear processes that occur at totally different scales. Hence, we refer to numerical simulations. Finally, we list the most urgent open questions in plasma astrophysics which should be addressed in the near future.

Buechner, J [Max-Planck-Institut fuer Sonnensystemforschung, 37191 Katlenburg-Lindau (Germany)

2007-12-15

90

A THEMIS Survey of Flux Ropes and Traveling Compression Regions: Location of the Near-Earth Reconnection Site During Solar Minimum  

Science.gov (United States)

A statistical study of flux ropes and traveling compression regions (TCRs) during the Time History of Events and Macroscale Interactions during Substorms (THEMIS) second tail season has been performed. A combined total of 135 flux ropes and TCRs in the range GSM X approx -14 to -31 R(sub E) were identified, many of these occurring in series of two or more events separated by a few tens of seconds. Those occurring within 10 min of each other were combined into aggregated reconnection events. For the purposes of this survey, these are most likely the products of reconnect ion occurring simultaneously at multiple, closely spaced x-lines as opposed to statistically independent episodes of reconnection. The 135 flux ropes and TCRs were grouped into 87 reconnection events; of these, 28 were moving tailward and 59 were moving Earthward. The average location of the near-Earth x-line determined from statistical analysis of these reconnection events is (X(sub GSM), Y*(sub GSM)) = (-30R(sub E), 5R(sub E)), where Y* includes a correction for the solar aberration angle. A strong east-west asymmetry is present in the tailward events, with >80% being observed at GSM Y* > O. Our results indicate that the Earthward flows are similarly asymmetric in the midtail region, becoming more symmetric inside - 18 R(sub E). Superposed epoch analyses indicate that the occurrence of reconnection closer to the Earth, i.e., X > -20 R(sub E), is associated with elevated solar wind velocity and enhanced negative interplanetary magnetic field B(sub z). Reconnection events taking place closer to the Earth are also far more effective in producing geomagnetic activity, judged by the AL index, than reconnection initiated beyond X approx -25 R(sub E).

Imber, S. M.; Slavin, J. A.; Auster, H. U.; Angelopoulos, V.

2011-01-01

91

On Turbulent Reconnection  

CERN Document Server

We examine the dynamics of turbulent reconnection in 2D and 3D reduced MHD by calculating the effective dissipation due to coupling between small-scale fluctuations and large-scale magnetic fields. Sweet-Parker type balance relations are then used to calculate the global reconnection rate. Two approaches are employed -- quasi-linear closure and an eddy-damped fluid model. Results indicate that despite the presence of turbulence, the reconnection rate remains inversely proportional to $\\sqrt{R_m}$, as in the Sweet-Parker analysis. In 2D, the global reconnection rate is shown to be enhanced over the Sweet-Parker result by a factor of magnetic Mach number. These results are the consequences of the constraint imposed on the global reconnection rate by the requirement of mean square magnetic potential balance. The incompatibility of turbulent fluid-magnetic energy equipartition and stationarity of mean square magnetic potential is demonstrated.

Kim, E J; Kim, Eun-Jin

2001-01-01

92

Quantum vortex reconnections  

CERN Document Server

We study reconnections of quantum vortices by numerically solving the governing Gross-Pitaevskii equation. We find that the minimum distance between vortices scales differently with time before and after the vortex reconnection. We also compute vortex reconnections using the Biot-Savart law for vortex filaments of infinitesimal thickness, and find that, in this model, reconnection are time-symmetric. We argue that the likely cause of the difference between the Gross-Pitaevskii model and the Biot-Savart model is the intense rarefaction wave which is radiated away from a Gross-Pitaeveskii reconnection. Finally we compare our results to experimental observations in superfluid helium, and discuss the different length scales probed by the two models and by experiments.

Zuccher, S; Baggaley, A W; Barenghi, C F

2012-01-01

93

Simulation of the 3-D Evolution of Electron Scale Magnetic Reconnection - Motivated by Laboratory Experiments Predictions for MMS  

Science.gov (United States)

The four s/c of the Magnetospheric Multiscale (MMS) mission, to be launched in 2014, will use the Earth's magnetosphere as a laboratory to study the microphysics of three fundamental plasma processes. One of them is magnetic reconnection, an essentially multi-scale process. While laboratory experiments and past theoretical investigations have shown that important processes necessary to understand magnetic reconnection take place at electron scales the MMS mission for the first time will be able to resolve these scales by in space observations. For the measurement strategy of MMS it is important to make specific predictions of the behavior of current sheets with a thickness of the order of the electron skin depth which play an important role in the evolution of collisionless magnetic reconnection. Since these processes are highly nonlinear and non-local numerical simulation is needed to specify the current sheet evolution. Here we present new results about the nonlinear evolution of electron-scale current sheets starting from the linear stage and using 3-D electron-magnetohydrodynamic (EMHD) simulations. The growth rates of the simulated instabilities compared well with the growth rates obtained from linear theory. Mechanisms and conditions of the formation of flux ropes and of current filamentation will be discussed in comparison with the results of fully kinetic simulations. In 3D the X- and O-point configurations of the magnetic field formed in reconnection planes alternate along the out-of-reconnection-plane direction with the wavelength of the unstable mode. In the presence of multiple reconnection sites, the out-of-plane magnetic field can develop nested structure of quadrupoles in reconnection planes, similar to the 2-D case, but now with variations in the out-of-plane direction. The structures of the electron flow and magnetic field in 3-D simulations will be compared with those in 2-D simulations to discriminate the essentially 3D features. We also discuss the influence of guide fields, as in the magnetopause case and show how the 3-D evolution of an electron current sheet is influenced the strength of the guide field. This is unlike the 2-D case where reconnection takes place only in a plane. This work was partially funded by the Max-Planck/Princeton Center for Plasma Physics and the National Science Foundation.

Buechner, J.; Jain, N.; Sharma, A.

2013-12-01

94

Nonlinear driven reconnection  

International Nuclear Information System (INIS)

Characteristics of driven reconnection are explained with emphasis on the distinction from spontaneous reconnection. Numerical simulations indicate that driven reconnection is almost independent of resistivity but is largely controlled by driving plasma flow, this making a clear contrast with spontaneous reconnection. Four different examples of driven reconnection are studied by 3D MHD simulations. The first one is the case where two identical plasmas with anti-parallel fields are driven to collide in an open system. A typical example is the stretched magnetotail neutral sheet. Simulations indicate that slow mode shocks are formed whereby plasma is explosively accelerated. The second example is the case where a high-beta plasma collides against a low-beta plasma with an arbitrary field angle. The solar wind-magnetosphere interaction is a typical example - Results indicate that no prominent plasma acceleration is observed in this case but the high-beta plasma continuously erodes the low-beta plasma. The fine structure in the vicinity of the reconnection line is disclosed. The third example is the merging process of two spheromaks. It is shown that merging is an energy relaxation process. The final example is the self-reversal process in the reversed field pinch. It is shown that the self reversal is a relaxation process caused by nonlinear driven reconnection

1984-07-03

95

Mathematical Modeling of a Cs(I – Sr(II – Bentonite – Magnetite Sorption System, Simulating the Processes Taking Place in a Deep Geological Repository  

Directory of Open Access Journals (Sweden)

Full Text Available The derivation of mathematical models of systems consisting of Cs(I or Sr(II and of bentonite (B, magnetite (M or their mixtures (B+M are described. The paper deals especially with modeling of the protonation and sorption processes occurring on the functional groups of the solid phase, namely on so called edge sites and layer sites. The two types of sites have different properties and, as a result, three types of Surface Complexation Models (SCM are used for edge sites, viz. two electrostatic SCMs: the Constant Capacitance Model (CCM and the Diffusion Double Layer Model (DLM, and one without electrostatic correction: the Chemical Model (CEM. The processes taking place on the layer sites are described by means of the Ion Exchange Model (IExM. In the course of modeling, the speciation of the given metal in the liquid (aqueous phase has to be taken into account. In principle, the model of protonation or sorption processes is based on the reactions occurring in the aqueous phase and on the surface of the solid phase, and comprises not only the equations of the equilibrium constants of the individual reactions, but also the mass and charge balance equations. The algorithm of the numerical solution is compatible with FAMULUS 3.5 (a Czech software product quite extensively used at Czech universities in the last decade, the bookcase codes of which are utilized. 

H. Filipská

2005-01-01

96

Three-dimensional steady-state magnetic reconnection  

International Nuclear Information System (INIS)

A family of three-dimensional models of reconnection is presented in which the different members of the family are characterized by the vorticity with which plasma flows towards the reconnection site. The nature of this inflow also determines the size and speed of the outflow jet that carries reconnected field lines away from the reconnection site, and the shape of the MHD shocks that bound it. Flows with positive vorticity are of a flux pile-up type, for which the outflow jet is fastest and narrowest. Among those with negative vorticity is the three-dimensional analogue of Petschek reconnection. Not all combinations of vorticity and reconnection rate are possible; for those solutions with negative vorticity, there is a maximum reconnection rate. As the magnetic Reynolds number R_m_e or the current density is increased, this maximum is reduced and the possible types of solution become more polarized towards the two extremes of flux pile-up and slow compression regimes. Given a distribution of vorticities and inflow speeds, these models give the corresponding distribution of possible steady-state reconnection rates. As an illustrative example, we take Gaussian distributions of both to show that the resulting distribution is dominated by the flux pile-up regime. (author)

1994-06-01

97

Magnetic Reconnection in Astrophysical Environments  

CERN Document Server

Magnetic reconnection is a process that changes magnetic field topology in highly conducting fluids. Traditionally, magnetic reconnection was associated mostly with solar flares. In reality, the process must be ubiquitous as astrophysical fluids are magnetized and motions of fluid elements necessarily entail crossing of magnetic frozen in field lines and magnetic reconnection. We consider magnetic reconnection in realistic 3D geometry in the presence of turbulence. This turbulence in most astrophysical settings is of pre-existing nature, but it also can be induced by magnetic reconnection itself. In this situation turbulent magnetic field wandering opens up reconnection outflow regions, making reconnection fast. We discuss Lazarian \\& Vishniac (1999) model of turbulent reconnection, its numerical and observational testings, as well as its connection to the modern understanding of the Lagrangian properties of turbulent fluids. We show that the predicted dependences of the reconnection rates on the level of...

Lazarian, A; Vishniac, E; Kowal, G

2014-01-01

98

Model for magnetic reconnection  

International Nuclear Information System (INIS)

A forced reconnection problem was modeled by two infinite wires that are embedded in a plasma which carry parallel currents. They are brought together at a specified rate. The distance between the wires is taken as 2a(1-e/sup ?t/). For small displacements, the hydromagnetic equations can be linearized and solved asymptotically. For larger displacements, the plasma behavior can be estimated by use of scaling arguments. We determine a local velocity of magnetic reconnection and show that it is essentially equal to the maximum possible reconnection velocity (that of the corresponding vacuum case) up to the time when this velocity approaches the local Alfven speed. We compare the details of our solution with the Sweet-Parker and Petschek reconnection theories

1978-01-01

99

Catastrophic eruption of magnetic flux rope in the corona and solar wind with and without magnetic reconnection  

CERN Document Server

It is generally believed that the magnetic free energy accumulated in the corona serves as a main energy source for solar explosions such as coronal mass ejections (CMEs). In the framework of the flux rope catastrophe model for CMEs, the energy may be abruptly released either by an ideal magnetohydrodynamic (MHD) catastrophe, which belongs to a global magnetic topological instability of the system, or by a fast magnetic reconnection across preexisting or rapidly-developing electric current sheets. Both ways of magnetic energy release are thought to be important to CME dynamics. To disentangle their contributions, we construct a flux rope catastrophe model in the corona and solar wind and compare different cases in which we either prohibit or allow magnetic reconnection to take place across rapidly-growing current sheets during the eruption. It is demonstrated that CMEs, even fast ones, can be produced taking the ideal MHD catastrophe as the only process of magnetic energy release. Nevertheless, the eruptive s...

Chen, Y; Sun, S J

2007-01-01

100

EHD transport processes and electric reconnection  

International Nuclear Information System (INIS)

There are a variety of dusty or dirty plasmas containing charged dust grains or aerosols in the laboratory and in space. The former examples are nuclear fusion devices with impurity ions and atoms, unipolar arcing, electric discharge, and plasma synthesis for recent industrial applications, while the latter ones are the terrestrial, planetary, and cometary atmospheres and interstellar dark space. In such environments, electric rather than magnetic phenomena are taking place predominantly involving electric charging and discharge, ionization and recombination, particle disruption and coalescence, and space charge transport. Space charges are carried on an underlying stream, convection or diffusion in a variety of forms of charged streams and/or vortices in external and internal electric fields. It is newly shown that the conversion from electric to kinetic or flow energy also causes significant atmospheric phenomena such as lightnings by electric field line merging-reconnection in the EHD regime. This concept has been introduced by the present author for the first time and its theory is newly presented on the basis of the equation of electric field transport in relation to the Kelvin-Helmholtz theorem, particularly introducing a new quantity, the electric Reynolds number analogous to the Reynolds and magnetic Reynolds numbers, mathematically, and at the same time on the basis of a new but more basic space-charge related frozen-in field concept besides the conventional source-free frozen-in concept

1993-06-07

 
 
 
 
101

Spontaneous non-steady magnetic reconnection within the solar environment  

CERN Document Server

This work presents a 2.5-dimensional simulation study of the instability of current-sheets located in a medium with a strong density variation along the current layer. The initial force-free configuration is observed to undergo a two-stage evolution consisting of an abrupt regime transition from a slow to a fast reconnection process leading the system to a final chaotic configuration. Yet, the onset of the fast phase is not determined by the presence of any anomalous enhancement in plasma's local resistivity, but rather is the result of a new mechanism discovered in Lapenta (2008)* and captured only when sufficient resolution is present. Hence, the effects of the global resistivity, the global viscosity and the plasma beta on the overall dynamics are considered. This mechanism allowing the transition from slow to fast reconnection provides a simple but effective model of several processes taking place within the solar atmosphere from the high chromosphere up to the low corona. In fact, the understanding of a ...

Bettarini, Lapo

2009-01-01

102

Magnetic flipping: Reconnection in three-dimensions without null points  

International Nuclear Information System (INIS)

In three dimensions, magnetic reconnection may take place in a sheared magnetic field at any singular field line, where the nearby field has X-type topology in planes perpendicular to the field line and where an electric field is present parallel to the field line. In the ideal region around the singular line there will, in general, be singularities in the plasma flow and electric field, both at the singular line and at magnetic flipping layers, which are remnants of local magnetic separatrices. In the absence of a three-dimensional magnetic point or null point, reconnection of field lines can still occur by a process of magnetic flipping, in which the plasma crosses the flipping layers but the field lines rapidly flip along them by magnetic diffusion. Depending on the boundary conditions, there may be two or four flipping layers which converge on the singular line. A boundary layer analysis of a flipping layer is given, in which the magnetic field parallel to the layer decreases as one crosses it while the plasma pressure (or magnetic pressure associated with the field along the singular line) increases. The width of the flipping layer decreases with distance from the singular line

1992-02-01

103

Evolution of anisotropic turbulence in nonlinear magnetic reconnection.  

Science.gov (United States)

The anisotropy properties of magnetohydrodynamic turbulence in a sheared magnetic field are analyzed through a three-dimensional numerical simulation that reproduces the linear and nonlinear stage of a tearing instability. Far from the current sheet, the energy spectrum develops perpendicularly to the local magnetic field, as in homogeneous configurations. Within the current sheet, the spectrum anisotropy is also affected by the structure of unstable modes. With increasing time, the configuration becomes more turbulent, the former effect disappears, and the energy cascade takes place perpendicularly to the local magnetic field. The local spectrum becomes increasingly anisotropic while the spatially integrated spectrum tends to isotropize. There is the possibility that these properties could be used to identify the nonlinear stage of magnetic reconnection in space and laboratory plasmas, as well as to identify the particle transport regime in the considered magnetic configuration. PMID:18764062

Onofri, M; Malara, F

2008-07-01

104

Externally driven magnetic reconnection  

International Nuclear Information System (INIS)

A model is presented in which externaly driven reconnection is simulated by solving the MHD equations in an initially plane current sheet. Magnetic reconnection in the earth's magnetotail is widely believed to be the direct cause of magnetospheric substorms. Both 2-D and 3-D versions of the model have been developed. It is postulated that connection in the tail is triggered by a local compression of the plasma sheet which results from an invasion of the solar wind into the magnetotail. Thus, the simulation is started by introducing flow from the lobes normal to the plasma sheet. When resistivity is generated in a local region of the neutral sheet, reconnection develops and magnetic energy is converted into plasma bulk flow. Although the driven reconnection model is highly simplified, it can aid in understanding many features of substorms in the tail; in particular, results show that rapid flows both earthward and tailward of the neutral line and the nightside substorm current system are natural consequences of driven magnetic reconnection. 34 references

1984-01-01

105

Simulation and Analysis of Magnetic Reconnection in an Experimental Geometry  

Science.gov (United States)

The process of magnetic reconnection is important in space, laboratory, and astrophysical plasmas. The Magnetic Reconnection Experiment (MRX) is designed to study controlled reconnection in collisional and marginally collisionless plasmas (Yamada et al. 1997). We present single and two-fluid simulations of MRX using the NIMROD extended MHD code (Sovinec et al. 2004). These simulations highlight the interrelationship between the small-scale physics of the reconnection layer and the global magnetic field geometry. The communication between small and large scales is dominated by pressure gradients that result from a pileup of reconnection outflow. Toroidicity leads to asymmetry in either the inflow direction or the outflow direction, depending on the experimental mode of operation. To explain effects observed during reconnection with asymmetry in the outflow direction, we present an extension of the Sweet-Parker model that takes into account asymmetric downstream pressure. This model is applicable to reconnection in coronal mass ejections, the Earth's magnetotail, and in circumstellar disks present in hot star winds. This research is supported by the NSF Center for Magnetic Self-Organization in Laboratory and Astrophysical Plasmas.

Murphy, Nicholas Arnold; Sovinec, C. R.; Cassak, P. A.

2009-01-01

106

Collisionless driven magnetic reconnection  

Energy Technology Data Exchange (ETDEWEB)

Driven magnetic reconnection in a collisionless plasma is investigated by means of a two-and-one-half dimensional particle simulation. The dynamical compression by plasma inflow forms a peaked profile of current density in the neutral sheet. When the width of current layer is compressed as thin as the ion Larmor radius, the charge separation becomes distinct abruptly at the center of the current layer due to the finite ion Larmor radius effect. The charge separation in the central current region and the subsequent spatial modification of the current profile result in excitation of collisionless driven magnetic reconnection. In the cause of collisionless driven magnetic reconnection an efficient energy conversion from field energy to particle energy is observed. (author).

Horiuchi, Ritoku; Sato, Tetsuya

1993-06-01

107

Collisionless driven magnetic reconnection  

International Nuclear Information System (INIS)

Driven magnetic reconnection in a collisionless plasma is investigated by means of a two-and-one-half dimensional particle simulation. The dynamical compression by plasma inflow forms a peaked profile of current density in the neutral sheet. When the width of current layer is compressed as thin as the ion Larmor radius, the charge separation becomes distinct abruptly at the center of the current layer due to the finite ion Larmor radius effect. The charge separation in the central current region and the subsequent spatial modification of the current profile result in excitation of collisionless driven magnetic reconnection. In the cause of collisionless driven magnetic reconnection an efficient energy conversion from field energy to particle energy is observed. (author)

1993-01-01

108

Reconnection in tokamaks  

International Nuclear Information System (INIS)

Calculations with several different computer codes based on the resistive MHD equations have shown that (m = 1, n = 1) tearing modes in tokamak plasmas grow by magnetic reconnection. The observable behavior predicted by the codes has been confirmed in detail from the waveforms of signals from x-ray detectors and recently by x-ray tomographic imaging

1983-10-03

109

Magnetic reconnection of plasma toroids with co- and counter-helicity  

Energy Technology Data Exchange (ETDEWEB)

Magnetic reconnection phenomena are investigated taking into account all three vector components of the magnetic field in a laboratory experiment. Two toroidal magnetized plasmas carrying identical toroidal currents and poloidal field configurations are made to collide, thereby inducing magnetic reconnections, The directions of the toroidal field play an important role in the merging process. It is found that plasmas of anti-parallel helicity merge much faster than those of parallel helicity. It is also found that the reconnection rate is proportional to the initial relative velocity of the two plasma tori, suggesting that magnetic reconnection, in the present experiment, is forced phenomenon. 16 refs., 5 figs.

Yamada, M.; Ono, Y.; Hayakawa, A.; Katsurai, M. (Tokyo Univ. (Japan). Dept. of Electrical Engineering); Perkins, F.W. (Princeton Univ., NJ (USA). Plasma Physics Lab.)

1990-07-01

110

Three-dimensional magnetic reconnection  

International Nuclear Information System (INIS)

Complete text of publication follows. Three-dimensional reconnection is much more diverse than two-dimensional reconnection. In deed, the characteristics of these two types of reconnection are very different. For instance, three-dimensional reconnection can occur both in the vicinity of null points, as well as in the absence of null points. It occurs continuously and continually throughout a diffusion region, as opposed to at a single point, as it does in two dimensions. This means that in three-dimensions field lines do not reconnect in pairs of lines or even in sets of surfaces making understanding three-dimensional reconnection difficult. One important location for three-dimensional reconnection is at separators, special field lines that connect pairs of null points and lie along the intersection of the two separatrix surfaces emanating from the null points. By focussing on a series of three-dimensional resistive MHD experiments involving separator reconnection I reveal the local requirements and nature of reconnection along separators, as well as describing some of the global consequences of reconnection at multiple separators.

2009-08-23

111

Turbulent Reconnection in the Magnetic Reconnection Experiment (MRX)  

Science.gov (United States)

One of the key open questions in Magnetic Reconnection is the nature of the mechanism that governs the reconnection rate in real astrophysical and laboratory systems. For collisonless plasmas, the Hall effect removes an important bottleneck to fast reconnection as the heavier ions exit the reconnection layer over a broader region [1]. However, the Hall term cannot balance the reconnection electric field at the layer center, and the 2-D, collisionless expression for the electric field due to particle dynamics [2] has been shown to be insufficient in the Magnetic Reconnection Experiment (MRX) [1,3]. Turbulent 3-D effects such as lower hybrid frequency range fluctuations [4] may play an important role in fast reconnection in MRX. These electromagnetic fluctuations tend to be associated with high local currents and a rapid local reconnection rate. The precise relation of these fluctuations and associated 3-D asymmetries to fast reconnection is a topic of active investigations; the most up to date results will be discussed. This work was supported by NDSEG, DOE, NASA, and NSF.[4pt] [1] Y. Ren, et al., Phys. Plasmas 15, 082113 (2008). [2] M. Hesse, et al., Phys. Plasmas, 6:1781 (1999). [3] S. Dorfman, et al., Phys. Plasmas 15, 102107 (2008). [4] H. Ji, et al., Phys.Rev.Lett. 92 (2004) 115001.

Dorfman, S.; Ji, H.; Yamada, M.; Oz, E.; Yoo, J.; Daughton, W.; Roytershteyn, V.

2009-11-01

112

Reconnection rate in collisionless magnetic reconnection under open boundary conditions  

International Nuclear Information System (INIS)

Collisionless magnetic reconnection is studied by using two-dimensional Darwin particle-in-cell simulations with different types of open boundary conditions. The simulation results indicate that reconnection rates are strongly dependent on the imposed boundary conditions of the magnetic field Bx in the inward side. Under the zero-gradient Bx boundary condition, the reconnection rate quickly decreases after reaching its maximum and no steady-state is found. Under both electromagnetic and magnetosonic boundary conditions, the system can reach a quasi-steady state. However, the reconnection rate Er=0.08 under the electromagnetic boundary condition is weaker than Er=0.13 under the magnetosonic boundary condition. (authors)

2008-05-01

113

Three-Dimensional Magnetic Reconnection  

CERN Multimedia

The importance of magnetic reconnection as an energy release mechanism in many solar, stellar, magnetospheric and astrophysical phenomena has long been recognised. Reconnection is the only mechanism by which magnetic fields can globally restructure, enabling them to access a lower energy state. Over the past decade, there have been some major advances in our understanding of three-dimensional reconnection. In particular, the key characteristics of 3D magnetohydrodynamic (MHD) reconnection have been determined. For instance, 3D reconnection (i) occurs with or without nulls, (ii) occurs continuously and continually throughout a diffusion region and (iii) is driven by counter rotating flows. Furthermore, analysis of resistive 3D MHD magnetic experiments have revealed some intriguing effects relating to where and how reconnection occurs. To illustrate these new features, a series of constant-resistivity experiments, involving the interaction of two opposite-polarity magnetic sources in an overlying field, are con...

Parnell, Clare E

2009-01-01

114

The Role of Compressibility in Energy Release by Magnetic Reconnection  

Science.gov (United States)

Using resistive compressible magnetohydrodynamics, we investigate the energy release and transfer by magnetic reconnection in finite (closed or periodic) systems. The emphasis is on the magnitude of energy released and transferred to plasma heating in configurations that range from highly compressible to incompressible, based on the magnitude of the background beta (ratio of plasma pressure over magnetic pressure) and of a guide field in two-dimensional reconnection. As expected, the system becomes more incompressible, and the role of compressional heating diminishes, with increasing beta or increasing guide field. Nevertheless, compressional heating may dominate over Joule heating for values of the guide field of 2 or 3 (in relation to the reconnecting magnetic field component) and beta of 5-10. This result stems from the strong localization of the dissipation near the reconnection site, which is modeled based on particle simulation results. Imposing uniform resistivity, corresponding to a Lundquist number of 10(exp 3) to 10(exp 4), leads to significantly larger Ohmic heating. Increasing incompressibility greatly reduces the magnetic flux transfer and the amount of energy released, from approx. 10% of the energy associated with the reconnecting field component, for zero guide field and low beta, to approx. 0.2%-0.4% for large values of the guide field B(sub y0) > 5 or large beta. The results demonstrate the importance of taking into account plasma compressibility and localization of dissipation in investigations of heating by turbulent reconnection, possibly relevant for solar wind or coronal heating.

Birn, J.; Borovosky, J. E.; Hesse, M.

2012-01-01

115

The role of lateral magnetic reconnection in solar eruptive events  

Directory of Open Access Journals (Sweden)

Full Text Available On 10–11 December 2005 a slow CME occurred in between two coronal streamers in the Western Hemisphere. SOHO/MDI magnetograms show a multipolar magnetic configuration at the photosphere consisting of a complex of active regions located at the CME source and two bipoles at the base of the lateral coronal streamers. White light observations reveal that the expanding CME affects both of the lateral streamers and induces the release of plasma within or close to them. These transient phenomena are possibly due to magnetic reconnections induced by the CME expansion that occurs either inside the streamer current sheet or between the CME flanks and the streamer. Our observations show that CMEs can be associated to not only a single reconnection process at a single location in the corona, but also to many reconnection processes occurring at different times and locations around the flux rope. Numerical simulations are used to demonstrate that the observed lateral reconnections can be reproduced. The observed secondary reconnections associated to CMEs may facilitate the CME release by globally decreasing the magnetic tension of the corona. Future CME models should therefore take into account the lateral reconnection effect.

A. Soenen

2009-10-01

116

Reconnection of colliding vortex rings.  

Science.gov (United States)

We investigate numerically the Navier-Stokes dynamics of reconnecting vortex rings at small Reynolds number for a variety of configurations. We find that reconnections are dissipative due to the smoothing of vorticity gradients at reconnection kinks and to the formation of secondary structures of stretched antiparallel vorticity which transfer kinetic energy to small scales where it is subsequently dissipated efficiently. In addition, the relaxation of the reconnection kinks excites Kelvin waves which due to strong damping are of low wave number and affect directly only large scale properties of the flow. PMID:12633362

Chatelain, Philippe; Kivotides, Demosthenes; Leonard, Anthony

2003-02-01

117

Nonstationary reconnection of crossed magnetic fields  

Science.gov (United States)

The problem of the nonstationary reconnection of crosd magnetic fields with different intensities and finite length of the reconnection line is solved. As a result of reconnection, the reconnected magnetic flux tubes are extended as they move along the magnetopause. The reconnected tubes carry accelerated and heated plasma and reconnected flux. The reconnection process is accompanied by current-sheet oscillations and, in the case of antiparallel reconecting components of different size, by erosion of the magnetopause. It is further shown that reconnection can occur only in a sheet which is stable with respect to the Kelvin-Helmholtz instability.

Semenov, V. S.; Sidneva, M. V.; Kubyshkin, I. V.; Lebedeva, V. V.

118

Reconnecting to the Biosphere  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Humanity has emerged as a major force in the operation of the biosphere, with a significant imprint on the Earth System, challenging social–ecological resilience. This new situation calls for a fundamental shift in perspectives, world views, and institutions. Human development and progress must be reconnected to the capacity of the biosphere and essential ecosystem services to be sustained. Governance challenges include a highly interconnected and faster world, cascading social–ecological...

Folke, Carl; Jansson, A?sa; Rockstro?m, Johan; Olsson, Per; Carpenter, Stephen R.; Chapin, F. Stuart; Cre?pin, Anne-sophie; Daily, Gretchen; Danell, Kjell; Ebbesson, Jonas; Elmqvist, Thomas; Galaz, Victor; Moberg, Fredrik; Nilsson, Ma?ns; O?sterblom, Henrik

2011-01-01

119

Theoretical analysis of the magnetic reconnection experiment, MRX  

Energy Technology Data Exchange (ETDEWEB)

In the MRX experiment two identical spheromaks with a common major axis are driven together. Their poloidal fields are oriented so that at the point of contact reconnection occurs. Their toroidal fields are oriented either parallel or antiparallel. The general theoretical picture of the physics of the experiment is discussed. It is believed that an axisymmetric current layer forms between the two spheromaks, in which the reconnection occurs. In this layer the electron temperature is high due to ohmic heating, and there is considerable magnetic tension due to the merging poloidal field. In addition, in the counterhelicity case, there is magnetic tension in the toroidal direction. As a result of these forces large velocities develop in the layer. These velocities take the plasma out of the reconnection region, and into a thin separatrix region that lies, between the regions of unreconnected flux and common flux. In this separatrix region the motion quickly develops into heat. We first describe the experiment from a global point of view. At any time the plasma is in magnetostatic equilibrium everywhere except in the reconnection and separatrix regions. Across these regions the sum of magnetic pressure and the gas pressure is continuous. The high pressure in the region of common flux results from the dissipation of kinetic energy, and can be found by energy conservation since it really comes from dissipation of poloidal and, in the counterhelicity case, toroidal field energy. Thus, from the global point of view a unique sequence of equilibria is given. Once the global situation is determined the proper boundary conditions and geometry are available to treat the local behavior in the reconnection region by asymptotic analysis. The rate of reconnection determines the rate of passage through the sequence of equilibria. We attempt to carry out the inner analysis for a variety of reconnection rates ranging from the Sweet-Parker rate to the Petschek maximum reconnection rate.

Uzdensky, D.; Kulsrud, R.; Yamada, M. [Princeton Plasma Physics Lab., NJ (United States)

1996-12-31

120

Theoretical analysis of the magnetic reconnection experiment, MRX  

International Nuclear Information System (INIS)

In the MRX experiment two identical spheromaks with a common major axis are driven together. Their poloidal fields are oriented so that at the point of contact reconnection occurs. Their toroidal fields are oriented either parallel or antiparallel. The general theoretical picture of the physics of the experiment is discussed. It is believed that an axisymmetric current layer forms between the two spheromaks, in which the reconnection occurs. In this layer the electron temperature is high due to ohmic heating, and there is considerable magnetic tension due to the merging poloidal field. In addition, in the counterhelicity case, there is magnetic tension in the toroidal direction. As a result of these forces large velocities develop in the layer. These velocities take the plasma out of the reconnection region, and into a thin separatrix region that lies, between the regions of unreconnected flux and common flux. In this separatrix region the motion quickly develops into heat. We first describe the experiment from a global point of view. At any time the plasma is in magnetostatic equilibrium everywhere except in the reconnection and separatrix regions. Across these regions the sum of magnetic pressure and the gas pressure is continuous. The high pressure in the region of common flux results from the dissipation of kinetic energy, and can be found by energy conservation since it really comes from dissipation of poloidal and, in the counterhelicity case, toroidal field energy. Thus, from the global point of view a unique sequence of equilibria is given. Once the global situation is determined the proper boundary conditions and geometry are available to treat the local behavior in the reconnection region by asymptotic analysis. The rate of reconnection determines the rate of passage through the sequence of equilibria. We attempt to carry out the inner analysis for a variety of reconnection rates ranging from the Sweet-Parker rate to the Petschek maximum reconnection rate

1996-03-18

 
 
 
 
121

NS [Nuclear Safety] update. Current safety and security activities and developments taking place in the Department of Nuclear Safety and Security, Issue no. 6, March 2008  

International Nuclear Information System (INIS)

The current issue presents information about the following activities: 1) International Conference on Illicit Nuclear Trafficking which took place in November 2007 in Edinburgh. The principal aim of the conference was to examine the threat and context of illicit nuclear trafficking of radioactive material, specifically, what is being done to combat such trafficking and where more needs to be done. The conference was also to consider how the obligations and commitments of the legally binding and non-binding international instruments could be and are being implemented by various States. 2) INSAG Message on Nuclear Safety Infrastructure in which the INSAG Chairman Richard Meserve addressed nuclear safety in the current context and various issues that warrant special attention. 3) approved for publication the Safety Requirements publication on Safety of Nuclear Fuel Cycle Facilities. 4) The Asian Nuclear Safety Network (ANSN)

2008-01-01

122

NS [Nuclear Safety] update. Current safety and security activities and developments taking place in the Department of Nuclear Safety and Security, Issue no. 8, September 2008  

International Nuclear Information System (INIS)

The current issue presents information about the following activities: 1) International Workshops on Denial of Shipments raise awareness of suppliers, recipients, regulators, carriers/consignors and international organizations of the problems relating to denials of radioactive shipments to determine effective measures to prevent or reduce the instances of shipment denials and delays. 2) Communication and knowledge Management in the Department of Nuclear Safety and Security (NS). 3) Nuclear Security at the Beijing Olympics - an excellent example of the IAEA's work in protecting large scale public events. 4) The Incident and Emergency Centre's Participation in the ConvEx 3 Exercise, 9-10 July 2008, which took place at the Laguna Verde nuclear power plant in Mexico. During the 43 hour long exercise, the Incident and Emergency Centre (IEC) was fully activated. Staff members participating in the exercise represented different departments within the IAEA and the diversity of their knowledge and experience ensured an effective response

2008-01-01

123

Analysis of the chemical stability of the 1% sodium hypochlorite solution taking in consideration the place of storage and the amount of present solution in the bottle  

Directory of Open Access Journals (Sweden)

Full Text Available Introduction and objective: This study had as objective to analyze theloss of the chlorine text of the 1% sodium hypochlorite solution stored in coolant and ambient temperature and in bottles of plastic amber and cloudy white plastic, leading in consideration the amount of existing solution in the bottles. Material and methods: 24 liters of solution had been used, which had been divided in two groups: group 1 (6 bottles of plastic amber and 6 white plastic bottles filled with 1.000 mL of the 1% sodium hypochlorite solution and group 2 (6 bottles of plastic amber and 6 white plastic bottles filled with 800 mL of solution.In the second group had been removed 50 mL of solution of each bottle on each week, while the bottles of group 1 had always remained full. The analysis of the chlorine text was carried through in the beginning and in the final period of 10 weeks through the method of titulometria of oxi-reduction or iodometria. Results and conclusion:For the analysis statistics it was used analysis of the variance (Anovafollowed by the test of Tukey, to the level of significance of 5%, where it can be verified that the amount of present solution in the interior of the bottles contributed for the instability of the solution, whatever the place and the bottle of storage, and the full bottles had kept the chlorinetext of the solutions higher.

Graziele BORIN

2008-12-01

124

Plasmoid Ejections and Loop Contractions in an Eruptive M7.7 Solar Flare: Evidence of Particle Acceleration and Heating in Magnetic Reconnection Outflows  

CERN Document Server

Where particle acceleration and plasma heating take place in relation to magnetic reconnection is a fundamental question for solar flares. We report analysis of an M7.7 flare on 2012 July 19 observed by SDO/AIA and RHESSI. Bi-directional outflows in forms of plasmoid ejections and contracting cusp-shaped loops originate between an erupting flux rope and underlying flare loops at speeds of typically 200-300 km/s up to 1050 km/s. These outflows are associated with spatially separated double coronal X-ray sources with centroid separation decreasing with energy. The highest temperature is located near the nonthermal X-ray loop-top source well below the original heights of contracting cusps near the inferred reconnection site. These observations suggest that the primary loci of particle acceleration and plasma heating are in the reconnection outflow regions, rather than the reconnection site itself. In addition, there is an initial ascent of the X-ray and EUV loop-top source prior to its recently recognized descen...

Liu, Wei; Petrosian, Vahe'

2013-01-01

125

Principles of retrospective reconstruction of absorbed doses of external gamma radiation and beta particles for persons taking part in the ChNPP accident effect elimination according to the data on radiation situation and route places  

International Nuclear Information System (INIS)

The principles of retrospective reconstruction of observed doses of external gamma radiation and beta particles for persons taking part in accident effect elimination at initial stage of reconstruction works are developed. The method is based on the data on radiation situation and concrete route places, which were visited by these persons. The method is built on probabilistic estimation of the real situation reconstruction. Axiomatic interpretation of the probability from the measure theory viewpoint is used

1992-05-15

126

Magnetic blowout during collisionless reconnection  

Science.gov (United States)

Analytic calculations and simulations of the steady-state structure of the dissipation region during collisionless reconnection are described. Ions are treated as particles and electrons as a dissipative fluid. A limiting reconnection rate results as the ions 'blowout' the magnetic field in the dissipation area. The implications for comprehending substorm dynamics are discussed.

Drake, J. F.; Burkhart, G. R.

1992-01-01

127

Nonthermal acceleration from reconnection shocks  

Energy Technology Data Exchange (ETDEWEB)

Reconnection shocks in a magnetically dominated plasma must be compressive. Nonthermal ion acceleration can occur across built-in slow shocks, and across outflow fast shocks when the outflow is supermagnetc and the field is line yield. Electron acceleration may be initiated by injection from the dissipation region. Reconnection and shock acceleration thus cooperate and nonthermal acceleration should be a characteristic feature.

Blackman, E.G.; Field, G.B. (Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138 (United States))

1994-12-05

128

The Magnetic Reconnection Code: Center for Magnetic Reconnection Studies  

Energy Technology Data Exchange (ETDEWEB)

Understanding magnetic reconnection is one of the principal challenges in plasma physics. Reconnection is a process by which magnetic fields reconfigure themselves, releasing energy that can be converted to particle energies and bulk flows. Thanks to the availability of sophisticated diagnostics in fusion and laboratory experiments, in situ probing of magnetospheric and solar wind plasmas, and X-ray emission measurements from solar and stellar plasmas, theoretical models of magnetic reconnection can now be constrained by stringent observational tests. The members of the CMRS comprise an interdisciplinary group drawn from applied mathematics, astrophysics, computer science, fluid dynamics, plasma physics, and space science communities.

Amitava Bhattacharjee

2007-04-20

129

Solar wind magnetosphere interaction as simulated by a 3-D EM particle code : A 3-D reconnection at the magnetopause  

DEFF Research Database (Denmark)

We have studied the solar wind-magnetosphere interaction with a 3-D electromagnetic particle code. The results for an unmagnetized solar wind plasma streaming past a dipole magnetic field show the formation of a magnetopause and a magnetotail, the penetration of energetic particles into cusps and radiation belt and dawn-dusk asymmetries. The effects of interplanetary magnetic field (IMF) have been investigated in a similar way as done by MHD simulations. The simulation results with a southward IMF show the shrunk magnetosphere with great particle entry into the cusps and nightside magnetosphere. This is a signature of a magnetic reconnection at the dayside magnetopause. On the other hand, in the case where a solar wind with a northward IMF is switched on, the significant changes take place in the magnetotail. The waving motion was seen in the magnetotail and its length was shortened, This phenomena are consistent with the reconnections which occur at the high latitude magnetopause. In our simulations kinetic effects will determine the self-consistent anomalous resistivity in the magnetopause that causes reconnections.

Nishikawa, K.-I; Neubert, Torsten

1996-01-01

130

Collisionless Kelvin-Helmholtz instability and vortex-induced reconnection in the external region of the Earth magnetotail  

International Nuclear Information System (INIS)

In a magnetized plasma streaming with a non uniform velocity, the Kelvin-Helmholtz instability plays a major role in mixing different plasma regions and in stretching the magnetic field lines leading to the formation of layers with a sheared magnetic field where magnetic field line reconnection can take place. A relevant example is provided by the formation of a mixing layer between the Earth's magnetosphere and the solar wind at low latitudes during northward periods. In the considered configuration, in the presence of a magnetic field nearly perpendicular to the plane defined by the velocity field and its inhomogeneity direction, velocity shear drives a Kelvin-Helmholtz instability which advects and distorts the magnetic field configuration. If the Alfven velocity associated to the in-plane magnetic field is sufficiently weak with respect to the variation of the fluid velocity in the plasma, the Kelvin-Helmholtz instability generates fully rolled-up vortices which advect the magnetic field lines into a complex configuration, causing the formation of current layers along the inversion curves of the in-plane magnetic field component. Pairing of the vortices generated by the Kelvin-Helmholtz instability is a well know phenomenon in two-dimensional hydrodynamics. Here we investigate the development of magnetic reconnection during the vortex pairing process and show that completely different magnetic structures are produced depending on how fast the reconnection process develops on the time scale set by the pairing process.

2008-10-01

131

Effect of interchange instability on magnetic reconnection  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present here the results of a study of interacting magnetic fields that involves a force normal to the reconnection layer. In the presence of such force, the reconnection layer becomes unstable to interchange disturbances. The interchange instability results in formation of tongues of heated plasma that leaves the reconnection layer through its wide surface rather than through its narrow ends, as is the case in traditional magnetic reconnection models. This plasma flow out of the reconnect...

Lyatsky, W.; Goldstein, M. L.

2013-01-01

132

Reconnection In The Interstellar Medium  

CERN Document Server

We discuss the role of ambipolar diffusion for simple reconnection in a partially ionized gas, following the reconnection geometry of Parker and Sweet. When the recombination time is short the mobility and reconnection of the magnetic field is substantially enhanced as matter escapes from the reconnection region via ambipolar diffusion. Our analysis shows that in the interstellar medium it is the recombination rate that usually limits the rate of reconnection. We show that heating effects can reduce this rate by increasing the recombination time and raising the local ion pressure. In the colder parts of the ISM, when temperatures are or the order of 100K or less, we obtain a significant enhancement over the usual Sweet-Parker rate, but only in dense molecular clouds will the reconnection velocity exceed 0.001 times the Alfvén speed. The ratio of the ion orbital radius to the reconnection layer thickness is typically a few percent, except in dense molecular clouds where it can approach unity. We briefly discu...

Vishniac, E T; Vishniac, Ethan T.

1999-01-01

133

Reconnection of colliding cosmic strings  

International Nuclear Information System (INIS)

For vortex strings in the abelian Higgs model and D-strings in superstring theory, both of which can be regarded as cosmic strings, we give analytical study of reconnection (recombination, inter-commutation) when they collide, by using effective field theories on the strings. First, for the vortex strings, via a string sigma model, we verify analytically that the reconnection is classically inevitable for small collision velocity and small relative angle. Evolution of the shape of the reconnected strings provides an upper bound on the collision velocity in order for the reconnection to occur. These analytical results are in agreement with previous numerical results. On the other hand, reconnection of the D-strings is not classical but probabilistic. We show that a quantum calculation of the reconnection probability using a D-string action reproduces the nonperturbative nature of the worldsheet results by Jackson, Jones and Polchinski. The difference on the reconnection - classically inevitable for the vortex strings while quantum mechanical for the D-strings - is suggested to originate from the difference between the effective field theories on the strings

2005-06-01

134

Intuitive approach to magnetic reconnection  

International Nuclear Information System (INIS)

Two reconnection problems are considered. The first problem concerns global physics. The plasma in the global reconnection region is in magnetostatic equilibrium. It is shown that this equilibrium can be uniquely characterized by a set of constraints. During reconnection and independently of the local reconnection physics, these constraints can be uniquely evolved from any initial state. The second problem concerns Petschek reconnection. Petschek's model for fast reconnection, which is governed by resistive MHD equations with constant resistivity is not validated by numerical simulations. Malyshkin et al.[Phys. Plasmas 12, 102920 (2005)], showed that the reason for the discrepancy is that Petschek did not employ Ohm's law throughout the local diffusion region, but only at the X-point. A derivation of Petschek reconnection, including Ohm's law throughout the entire diffusion region, removes the discrepancy. This derivation is based largely on Petschek's original 1964 calculation [in AAS-NASA Symposium on Solar Flares (National Aeronautics and Space Administration, Washington, D.C., 1964), NASA SP50, p. 425]. A useful physical interpretation of the role which Ohm's law plays in the diffusion region is presented.

2011-11-01

135

Reconnection rates of magnetic fields  

Energy Technology Data Exchange (ETDEWEB)

The Sweet-Parker and Petschek scalings of magnetic reconnection rate are modified to include the effect of the viscosity. The modified scalings show that the viscous effect can be important in high-..beta.. plasmas. The theoretical reconnection scalings are compared with numerical simulation results in a tokamak geometry for three different cases: a forced reconnection driven by external coils, the nonlinear m = 1 resistive internal kink, and the nonlinear m = 2 tearing mode. In the first two cases, the numerical reconnection rate agrees well with the modified Sweet-Parker scaling, when the viscosity is sufficiently large. When the viscosity is negligible, a steady state which was assumed in the derivation of the reconnection scalings is not reached and the current sheet in the reconnection layer either remains stable through sloshing motions of the plasma or breaks up to higher m modes. When the current sheet remains stable, a rough comparison with the Sweet-Parker scaling is obtained. In the nonlinear m = 2 tearing mode case where the instability is purely resistive, the reconnection occurs on the slower dissipation time scale (Psi/sub s/ approx. eta). In addition, experimental data of the nonlinear m = 1 resistive internal kink in tokamak discharges are analyzed and are found to give reasonable agreement with the modified Sweet-Parker scaling.

Park, W.; Monticello, D.A.; White, R.B.

1983-05-01

136

Reconnection rates of magnetic fields  

International Nuclear Information System (INIS)

The Sweet-Parker and Petschek scalings of magnetic reconnection rate are modified to include the effect of the viscosity. The modified scalings show that the viscous effect can be important in high-? plasmas. The theoretical reconnection scalings are compared with numerical simulation results in a tokamak geometry for three different cases: a forced reconnection driven by external coils, the nonlinear m = 1 resistive internal kink, and the nonlinear m = 2 tearing mode. In the first two cases, the numerical reconnection rate agrees well with the modified Sweet-Parker scaling, when the viscosity is sufficiently large. When the viscosity is negligible, a steady state which was assumed in the derivation of the reconnection scalings is not reached and the current sheet in the reconnection layer either remains stable through sloshing motions of the plasma or breaks up to higher m modes. When the current sheet remains stable, a rough comparison with the Sweet-Parker scaling is obtained. In the nonlinear m = 2 tearing mode case where the instability is purely resistive, the reconnection occurs on the slower dissipation time scale (Psi/sub s/ approx. eta). In addition, experimental data of the nonlinear m = 1 resistive internal kink in tokamak discharges are analyzed and are found to give reasonable agreement with the modified Sweet-Parker scaling

1983-01-01

137

Effect of interchange instability on magnetic reconnection  

Directory of Open Access Journals (Sweden)

Full Text Available We present here the results of a study of interacting magnetic fields that involves a force normal to the reconnection layer. In the presence of such force, the reconnection layer becomes unstable to interchange disturbances. The interchange instability results in formation of tongues of heated plasma that leaves the reconnection layer through its wide surface rather than through its narrow ends, as is the case in traditional magnetic reconnection models. This plasma flow out of the reconnection layer facilitates the removal of plasma from the layer and leads to fast reconnection. The proposed mechanism provides fast reconnection of interacting magnetic fields and does not depend on the thickness of the reconnection layer. This instability explains the strong turbulence and bidirectional streaming of plasma that is directed toward and away from the reconnection layer that is observed frequently above reconnection layers. The force normal to the reconnection layer also accelerates the removal of plasma islands appearing in the reconnection layer during turbulent reconnection. In the presence of this force normal to the reconnection layer, these islands are removed from the reconnection layer by the "buoyancy force", as happens in the case of interchange instability that arises due to the polarization electric field generated at the boundaries of the islands.

W. Lyatsky

2013-06-01

138

Can amorphization take place in nanoscale interconnects?  

International Nuclear Information System (INIS)

The trend of miniaturization has highlighted the problems of heat dissipation and electromigration in nanoelectronic device interconnects, but not amorphization. While amorphization is known to be a high pressure and/or temperature phenomenon, we argue that defect density is the key factor, while temperature and pressure are only the means. For nanoscale interconnects carrying modest current density, large vacancy concentrations may be generated without the necessity of high temperature or pressure due to the large fraction of grain boundaries and triple points. To investigate this hypothesis, we performed in situ transmission electron microscope (TEM) experiments on 200 nm thick (80 nm average grain size) aluminum specimens. Electron diffraction patterns indicate partial amorphization at modest current density of about 105 A cm?2, which is too low to trigger electromigration. Since amorphization results in drastic decrease in mechanical ductility as well as electrical and thermal conductivity, further increase in current density to about 7 × 105 A cm?2 resulted in brittle fracture failure. Our molecular dynamics (MD) simulations predict the formation of amorphous regions in response to large mechanical stresses (due to nanoscale grain size) and excess vacancies at the cathode side of the thin films. The findings of this study suggest that amorphization can precede electromigration and thereby play a vital role in the reliability of micro/nanoelectronic devices. (paper)

2012-03-09

139

Reconnection of magnetic field lines  

International Nuclear Information System (INIS)

Magnetic field line diffusion in a plasma is studied on the basis of the non-linear boundary layer equations of dissipative, incompressible magnetohydrodynamics. Non-linear steady state solutions for a class of plasma parameters have been obtained which are consistent with the boundary conditions appropriate for reconnection. The solutions are self-consistent in connecting a stagnation point flow of a plasma with reconnecting magnetic field lines. The range of the validity of the solutions, their relation to other fluid models of reconnection, and their possible applications to space plasma configurations are pointed out. (Author)

1990-07-16

140

Reconnection Rate in Collisionless Magnetic Reconnection under Open Boundary Conditions  

International Nuclear Information System (INIS)

Collisionless magnetic reconnection is studied by using two-dimensional Darwin particle-in-cell simulations with different types of open boundary conditions. The simulation results indicate that reconnection rates are strongly dependent on the imposed boundary conditions of the magnetic field Bx in the inward side. Under the zero- gradient Bx boundary condition, the reconnection rate quickly decreases after reaching its maximum and no steady-state is found. Under both electromagnetic and magnetosonic boundary conditions, the system can reach a quasi-steady state. However, the reconnection rate Er ? 0.08 under the electromagnetic boundary condition is weaker than Er ? 0.13 under the magnetosonic boundary condition. (physics of gases, plasmas, and electric discharges)

2008-05-01

 
 
 
 
141

Can magnetopause reconnection drive Saturn's magnetosphere?  

Science.gov (United States)

solar wind-driven compression of Saturn's magnetosphere is an important trigger of magnetospheric dynamics, the importance of magnetopause reconnection has been the subject of debate. Here we use Cassini observations at Saturn's magnetopause to address this open issue. Measured conditions at the boundary suggest a typical reconnection electric field strength of order 0.01 mV m-1. Although the strongest reconnection electric fields correspond to a compressed magnetosphere, compressed conditions do not guarantee a relatively strong reconnection electric field at the magnetopause location sampled by the spacecraft. By considering northward Interplanetary Magnetic Field (IMF), we predict reconnection voltages (open magnetic flux production rates) for the strongest driving of Saturn's magnetosphere by magnetopause reconnection. The typical northward IMF reconnection voltage is less than 100 kV for a wide range of reconnection X line lengths. This suggests that magnetopause reconnection is not a major driver of dynamics in Saturn's magnetosphere, except possibly on rare occasions.

Masters, A.; Fujimoto, M.; Hasegawa, H.; Russell, C. T.; Coates, A. J.; Dougherty, M. K.

2014-03-01

142

Flux closure during magnetotail reconnection  

Science.gov (United States)

The ability to store magnetic energy from the solar wind for later release is a crucial part of magnetotail dynamics. Under which conditions is the magnetotail able to store energy, and how do the subsequent release of energy influence the dynamics in the tail? To address these questions we have studied 13 reconnection event with in-situ Cluster observations from the current sheet and the reconnection region. We find that the most common feature in the current sheet before reconnection onset, is a gradual thinning from 22000 km to 11000 km in about 50 minutes. This thinning seems to occur whether or not there is a total pressure increase or a current sheet stretching in the same time interval. The decrease of the lobe magnetic field during the reconnection events vary between 3~nT and 41~nT, and the magnitude of the unloading increases with about 1.2~nT per unit of the initial lobe magnetic field before reconnection. Furthermore, there is a correlation of 94~% between the decrease of the lobe magnetic field and the estimated decrease of magnetic flux in the magnetotail. We also study how the amount of energy conversion during the 13 reconnection events affect local parameters in the outflow region like velocity, mass and flux transport, particle fluxes and field aligned currents.

Snekvik, K.; Tanskanen, E. I.; Ostgaard, N.

2010-12-01

143

Magnetic reconnection via current sheets  

International Nuclear Information System (INIS)

A general picture of magnetic reconnection in the frame work of 2D incompressible resistive magnetohydrodynamic theory is presented. Numerical studies of (quasi-) steady state driven reconnection reveal current sheet formation for Mach numbers M = u/v_A exceeding the Sweet-Parker reconnection rate M_S_P = ?/Lv_A)"1"/"2. Since the thickness ? of the current sheet is found to be invariant to a change of the resistivity ?, its length ? increases rapidly with decreasing ? or increasing M, which can be written in the form ? ? (M/M_S_P)"4, so that ? reaches the global system size L within a short range of the parameter M/M_S_P. The reconnection process is therefore rather slow. This picture agrees in essence with Syrovatsky's theory of current sheets and disproves Petschek's mechanism of fast magnetic reconnection. A theory of the solution in the external and in the diffusion region is developed and analytical expressions in agreement with the simulation results are obtained by means of a variational principle. For sufficiently long current sheets the tearing mode becomes unstable in spite of the stabilizing effect of the inhomogeneous flow. The tearing mode contributes to the overall reconnection process, but a general assessment of this effect in the asymptotic regime of almost vanishing ? is difficult

1986-01-01

144

Properties of asymmetric magnetic reconnection  

International Nuclear Information System (INIS)

Properties of magnetic reconnection are investigated in two-dimensional, resistive magnetohydrodynamic (MHD) simulations of current sheets separating plasmas with different magnetic field strengths and densities. Specific emphasis is on the influence of the external parameters on the reconnection rate. The effect of the dissipation in the resistive MHD model is separated from this influence by evaluating resistivity dependence together with the dependence on the background parameters. Two scenarios are considered, which may be distinguished as driven and nondriven reconnection. In either scenario, the maximum reconnection rate (electric field) is found to depend on appropriate hybrid expressions based on a magnetic field strength and an Alfven speed derived from the characteristic values in the two inflow regions. The scaling compares favorably with an analytic formula derived recently by Cassak and Shay [Phys. Plasmas 14, 102114 (2007)] applied to the regime of fast reconnection. An investigation of the energy flow and conversion in the vicinity of the reconnection site revealed a significant role of enthalpy flux generation, in addition to the expected conversion of Poynting flux to kinetic energy flux. This enthalpy flux generation results from Ohmic heating as well as adiabatic, that is, compressional heating. The latter is found more important when the magnetic field strengths in the two inflow regions are comparable in magnitude

2008-03-01

145

Laboratory Measurements of Guide Field Reconnection  

Science.gov (United States)

The presence of a guide field can significantly alter the dynamics of magnetic reconnection in laboratory and astrophysical plasmas. Experiments which vary the guide field from zero to several times the reconnecting field have shown that increasing guide field tends to reduce the reconnection rate. Contrarily, during sawtooth activity in fusion plasmas, reconnection occurs in the presence of very strong guide fields on very fast time scales. Here, we investigate guide field reconnection in the Magnetic Reconnection Experiment (MRX) and compare to previous measurements of reconnection in the Madison Symmetric Torus (MST) reversed field pinch. In MRX, guide field dynamics can be studied either by varying control currents within the primary drive circuits, or by specifically applying a guide field using a set of dedicated steady state guide-field coils. In MST fusion plasmas, reconnection occurs spontaneously and nonlinear effects dominate the plasma dynamics.

Tharp, T. D.; Dorfman, S.; Jara-Almonte, J.; Ji, H.; Lawrence, E.; Myers, C.; Yamada, M.; Yoo, J.

2010-11-01

146

Fast reconnection does not explain internal disruption  

International Nuclear Information System (INIS)

It is shown that a fast reconnection in non viscous plasmas converts a significant part of the liberated magnetic energy into kinetic eddies: such a process cannot persist long enough to allow complete reconnection

1986-01-01

147

Plasmoid Ejections and Loop Contractions in an Eruptive M7.7 Solar Flare: Evidence of Particle Acceleration and Heating in Magnetic Reconnection Outflows  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Where particle acceleration and plasma heating take place in relation to magnetic reconnection is a fundamental question for solar flares. We report analysis of an M7.7 flare on 2012 July 19 observed by SDO/AIA and RHESSI. Bi-directional outflows in forms of plasmoid ejections and contracting cusp-shaped loops originate between an erupting flux rope and underlying flare loops at speeds of typically 200-300 km/s up to 1050 km/s. These outflows are associated with spatially se...

Liu, Wei; Chen, Qingrong; Petrosian, Vahe

2013-01-01

148

Fast Reconnection and Reconnection Diffusion: Implications for Star Formation  

CERN Document Server

Fast reconnection of magnetic field in turbulent fluids allows magnetic fields change their topology and connections. As a result the traditional concept of magnetic field being frozen into plasma is no more applicable. Plasma which is at one instance can be associated with a given magnetic field lines at the next instant is distributed along a different set of magnetic field lines. This diffusion is enabled by reconnection and therefore is termed "reconnection diffusion". The astrophysical implications of this concept include many astrophysical phenomena, e.g. heat transfer in plasmas, advection of metals in plasmas etc. However, the most dramatic implications of the concept are related to star formation process. The reason for that is that the existing theory of star formation was developed assuming that the decoupling of mass and magnetic field is due to neutrals drifting in respect to magnetic field with entrained ions, i.e. through the process of ambipolar diffusion. This implies that if the ionization o...

Lazarian, A

2011-01-01

149

Helicity, Reconnection, and Dynamo Effects  

Energy Technology Data Exchange (ETDEWEB)

The inter-relationships between magnetic helicity, magnetic reconnection, and dynamo effects are discussed. In laboratory experiments, where two plasmas are driven to merge, the helicity content of each plasma strongly affects the reconnection rate, as well as the shape of the diffusion region. Conversely, magnetic reconnection events also strongly affect the global helicity, resulting in efficient helicity cancellation (but not dissipation) during counter-helicity reconnection and a finite helicity increase or decrease (but less efficiently than dissipation of magnetic energy) during co-helicity reconnection. Close relationships also exist between magnetic helicity and dynamo effects. The turbulent electromotive force along the mean magnetic field (alpha-effect), due to either electrostatic turbulence or the electron diamagnetic effect, transports mean-field helicity across space without dissipation. This has been supported by direct measurements of helicity flux in a laboratory plasma. When the dynamo effect is driven by electromagnetic turbulence, helicity in the turbulent field is converted to mean-field helicity. In all cases, however, dynamo processes conserve total helicity except for a small battery effect, consistent with the observation that the helicity is approximately conserved during magnetic relaxation.

Ji, Hantao

1998-11-01

150

Magnetic Reconnection in Astrophysical Systems  

CERN Multimedia

The main subject of my talk is the question: in what kind of astrophysical systems magnetic reconnection is interesting and/or important? To address this question, I first put forward three general criteria for selecting the relevant astrophysical environments. Namely, reconnection should be: fast; energetically important; and observable. From this, I deduce that the gas density should be low, so that the plasma is: collisionless; force-free; and optically thin. Thus, for example, the requirement that reconnection is fast implies that Petschek's reconnection mechanism must be operating, which is possible, apparently, only in the collisionless regime. Next, I argue that the force-free condition implies that the magnetic field be produced in, and anchored by, a nearby dense massive object, e.g., a star or a disk, strongly stratified by gravity. I then stress the importance of field-line opening (e.g., by differential rotation) as a means to form a reconnecting current sheet. Correspondingly, I suggest the Y-poi...

Uzdensky, D A

2006-01-01

151

Multiple Spacecraft Study of the Impact of Turbulence on Reconnection Rates  

Science.gov (United States)

Magnetic turbulence and secondary island formation have reemerged as possible explanations for fast reconnection. Recent three-dimensional simulations reveal the formation of secondary islands that serve to shorten the current sheet and increase the accelerating electric field, while both simulations and observations witness electron holes whose collapse energizes electrons. However, few data studies have explicitly investigated the effect of turbulence and islands on the reconnection rate. We present a more comprehensive analysis of the effect of turbulence and islands on reconnection rates observed in space. Our approach takes advantage of multiple spacecraft to find the location of the spacecraft relative to the inflow and the outflow, to estimate the reconnection electric field, to indicate the presence and size of islands, and to determine wave vectors indicating turbulence. A superposed epoch analysis provides independent estimates of spatial scales and a reconnection electric field. We apply k-filtering and a new method adopted from seismological analyses to identify the wavevectors. From several case studies of reconnection events, we obtain preliminary estimates of the spectral scaling law, identify wave modes, and present a method for finding the reconnection electric field associated with the wave modes.

Wendel, Deirdre; Goldstein, Melvyn; Figueroa-Vinas, Adolfo; Adrian, Mark; Sahraoui, Fouad

2011-01-01

152

Particle Acceleration by Magnetic Reconnection  

CERN Document Server

Observational data require a rich variety of mechanisms to accelerate fast particles in astrophysical environments operating under different conditions. The mechanisms discussed in the literature include varying magnetic fields in compact sources, stochastic processes in turbulent environments, and acceleration behind shocks. An alternative, much less explored mechanism involves particle acceleration within magnetic reconnection sites. In this chapter we discuss this mechanism and show that particles can be efficiently accelerated by reconnection through a first order Fermi process within large scale current sheets (specially when in the presence of local turbulence which speeds up the reconnection and make the acceleration region thicker) and also through a second order Fermi process in pure MHD turbulent environments.

Pino, Elisabete M de Gouveia Dal

2013-01-01

153

Study of effects of external drive on MRX reconnection  

Science.gov (United States)

The Magnetic Reconnection Experiment (MRX) studies driven reconnection utilizing two toroidal flux cores [1]. One active topic of research is the relationship between global plasma parameters and local reconnection physics. External drive is determined by the rate at which poloidal magnetic field is pulled back into the flux cores. Findings from the TS-3 experiment [2] and recent 2-D simulations [3] have shown a linear scaling between driving parameters and reconnection rate. This study investigates the relationship of external drive to the out-of-plane electric field and the MHD inflow velocity in MRX. Initial results show a linear scaling between external drive and out-of-place electric field at low fill pressure and reduced dependence at higher fill pressure. Further analysis of the effect of external drive on other relevant plasma parameters and comparisons to 2-D kinetic simulations will be reported. [1] M. Yamada, et al., Phys. Plasmas 4(5),1936 (1997). [2] M. Yamada, et al., Physical Review Letters 65(6),721 (1990). [3] S. Dorfman, et al., Submitted to Phys. Plasmas. This work was supported by DOE, NASA, and NSF.

Schroeder, J.; Dorfman, S.; Yamada, M.; Ji, H.; McGeehan, B.; Oz, E.; Williams, N.; Daughton, W.; Roytershteyn, V.

2008-11-01

154

Electromagnetic Perturbations in the Reconnecting Current Sheet in MRX  

International Nuclear Information System (INIS)

Magnetic reconnection is a fundamental plasma process in which magnetic field lines break and reconnect, converting magnetic field energy into particle kinetic energy. Electromagnetic fluctuations, which may play a role in fast reconnection, are studied from both an experimental and theoretical standpoint. The waves, which are in the lower hybrid range of frequencies, may be produced by a plasma instability known as the oblique lower hybrid drift instability. When the electron drift velocity is large, the theory predicts coupling between whistler and acoustic waves in the ion frame that may lead to an instability in the vicinity of the current sheet. On the experimental side, an antenna placed in the Magnetic Reconnection Experiment (MRX) at the Princeton Plasma Physics Laboratory is used to apply perturbations, and their propagation characteristics are measured. Results from a 2mm diameter antenna indicate that any induced fluctuations are confined to the current sheet and are preferentially excited in the direction of electron flow within the layer. Preliminary data from a 2cm diameter antenna shows a wave propagating in the electron flow direction at the local electron drift velocity. Thus electron drift appears to play a crucial role in the appearance of fluctuations

2006-11-30

155

Transition to whistler mediated magnetic reconnection  

Science.gov (United States)

The transition in the magnetic reconnection rate from the resistive magnetohydrodynamic (MHD) regime where the Alfen wave controls reconnection to a regime in which the ions become unmagnetized and the whistler wave mediates reconnection is explored with 2-D hybrid simulations. In the whistler regime the electrons carry the currents while the ions provide a neutralizing background. A simple physical picture is presented illustrating the role of the whistler mediated reconnection is calculated analytically. The development of an out-of-plane component of the magnetic field is an observable signature of whistler driven reconnection.

Mandt, M. E.; Denton, R. E.; Drake, J. F.

1994-01-01

156

Interaction behaviours of solitoffs: fission, fusion, reconnection and annihilation  

Science.gov (United States)

The interactions between solitoffs are extensively investigated. Besides the known solitoff fission and fusion interactions, two new types of solitoff interactions are discovered, named the solitoff reconnection and the solitoff annihilation. Taking the asymmetric Nizhnik-Novikov-Veselov equation as an illustrative system, five types of solitoff interactions are graphically revealed on the basis of the analytical solution obtained by the modified tanh function expansion method.

Li, Jun-Min; Liang, Zu-Feng; Tang, Xiao-Yan

2010-10-01

157

Interaction behaviours of solitoffs: fission, fusion, reconnection and annihilation  

International Nuclear Information System (INIS)

The interactions between solitoffs are extensively investigated. Besides the known solitoff fission and fusion interactions, two new types of solitoff interactions are discovered, named the solitoff reconnection and the solitoff annihilation. Taking the asymmetric Nizhnik-Novikov-Veselov equation as an illustrative system, five types of solitoff interactions are graphically revealed on the basis of the analytical solution obtained by the modified tanh function expansion method. (general)

2010-10-01

158

Magnetopause reconnection and interlinked flux tubes  

Science.gov (United States)

Magnetic reconnection can be a continuous or a transient process. Global magnetohydrodynamics (MHD) simulations are important tools to understand the relevant magnetic reconnection mechanisms and the resulting magnetic structures. We have studied magnetopause reconnection using a global 3D MHD simulation in which the interplanetary magnetic field (IMF) has been set to large positive By and large negative Bz components, i.e., a south-duskward direction. Flux tubes have been observed even during these constant solar wind conditions. We have focused on the interlinked flux tubes event resulting from time-dependent, patchy and multiple reconnection. At the event onset, two reconnection modes seem to occur simultaneously: a time-dependent, patchy and multiple reconnection for the subsolar region; and, a steady and large-scale reconnection for the regions far from the subsolar site.

Cardoso, F. R.; Gonzalez, W. D.; Sibeck, D. G.; Kuznetsova, M. M.; Koga, D.

2013-12-01

159

Relation of Astrophysical Turbulence and Magnetic Reconnection  

CERN Document Server

Astrophysical fluids are generically turbulent and this must be taken into account for most transport processes. We discuss how the preexisting turbulence modifies magnetic reconnection and how magnetic reconnection affects the MHD turbulent cascade. We show the intrinsic interdependence and interrelation of magnetic turbulence and magnetic reconnection, in particular, that strong magnetic turbulence in 3D requires reconnection and 3D magnetic turbulence entails fast reconnection. We follow the approach in Eyink, Lazarian & Vishniac 2011 to show that the expressions of fast magnetic reconnection in Lazarian & Vishniac 1999 can be recovered if Richardson diffusion of turbulent flows is used instead of ordinary Ohmic diffusion. This does not revive, however, the concept of magnetic turbulent diffusion which assumes that magnetic fields can be mixed up in a passive way down to a very small dissipation scales. On the contrary, we are dealing the reconnection of dynamically important magnetic field bundles...

Lazarian, A; Vishniac, E

2011-01-01

160

Magnetopause reconnection and interlinked flux tubes  

Directory of Open Access Journals (Sweden)

Full Text Available Magnetic reconnection can be a continuous or a transient process. Global magnetohydrodynamics (MHD simulations are important tools to understand the relevant magnetic reconnection mechanisms and the resulting magnetic structures. We have studied magnetopause reconnection using a global 3-D MHD simulation in which the interplanetary magnetic field (IMF has been set to large positive By and large negative Bz components, i.e., a south-duskward direction. Flux tubes have been observed even during these constant solar wind conditions. We have focused on the interlinked flux tubes event resulting from time-dependent, patchy and multiple reconnection. At the event onset, two reconnection modes seem to occur simultaneously: a time-dependent, patchy and multiple reconnection for the subsolar region; and, a steady and large-scale reconnection for the regions far from the subsolar site.

F. R. Cardoso

2013-10-01

 
 
 
 
161

Women take the island: nation, profession, place Women take the island: nation, profession, place  

Directory of Open Access Journals (Sweden)

Full Text Available The Tempest has been one of Shakespeare’s most adapted plays. Its stage history is concomitantly a history of the British theatre, from regularized comedy to semi-opera to pantomime to opera. It has had other lives, too, from its position in romantic ideas of Shakespeare’s biography and his so-called farewell to the stage, to a supporting role as witness for the nineteenth-century Darwinians’ idea of the missing link, to a veritable efflorescence of walk-on parts, cameos, and star vehicles in twentieth-century psychoanalytic and social arguments about European expansion.2 The play has given us individual poems and paintings, not to speak of screen-plays for several film adaptations. The Tempest has been one of Shakespeare’s most adapted plays. Its stage history is concomitantly a history of the British theatre, from regularized comedy to semi-opera to pantomime to opera. It has had other lives, too, from its position in romantic ideas of Shakespeare’s biography and his so-called farewell to the stage, to a supporting role as witness for the nineteenth-century Darwinians’ idea of the missing link, to a veritable efflorescence of walk-on parts, cameos, and star vehicles in twentieth-century psychoanalytic and social arguments about European expansion.2 The play has given us individual poems and paintings, not to speak of screen-plays for several film adaptations.

Ruth Morse

2008-04-01

162

NUMERICAL STUDIES OF WEAKLY STOCHASTIC MAGNETIC RECONNECTION  

Directory of Open Access Journals (Sweden)

Full Text Available We study the e ects of turbulence on magnetic reconnection using three-dimensional numerical simulations.This is the rst attempt to test the model of fast magnetic reconnection proposed by Lazarian & Vishniac (1999, which assumes the presence of weak, small-scale magnetic eld structure near the current sheet. This a ects the rate of reconnection by reducing the transverse scale for reconnection ows and by allowing many independent ux reconnection events to occur simultaneously. We performed a number of simulations to test the dependencies of the reconnection speed, de ned as the ratio of the in ow velocity to the Alfv n speed, on the turbulence power, the injection scale and resistivity. Our results show that turbulence signi cantly a ects the topology of magnetic eld near the di usion region and increases the thickness of the out ow region. We con rm the predictions of the Lazarian & Vishniac model. In particular, we report the growth of the reconnection speed proportional to V 2 l , where Vl is the amplitude of velocity at the injection scale. It depends on the injection scale linj as (linj=L2=3, where L is the size of the system, which is somewhat faster but still roughly consistent with the theoretical expectations. We also show that for 3D reconnection the Ohmic resistivity is important in the local reconnection events only, and the global reconnection rate in the presence of turbulence does not depend on it.

G. Kowal

2009-01-01

163

OBSERVATIONAL ANALYSIS OF MAGNETIC RECONNECTION SEQUENCE  

International Nuclear Information System (INIS)

We conduct comprehensive analysis of an X2.0 flare to derive quantities indicative of magnetic reconnection in solar corona by following temporally and spatially resolved flare ribbon evolution in the lower atmosphere. The analysis reveals a macroscopically distinctive two-stage reconnection marked by a clear division in the morphological evolution, reconnection rate, and energy release rate. During the first stage, the flare brightening starts at and primarily spreads along the polarity inversion line (PIL) with the maximum apparent speed comparable to the local Alfven speed. The second stage is dominated by ribbon expansion perpendicular to the PIL at a fraction of the local Alfven speed. We further develop a data analysis approach, namely reconnection sequence analysis, to determine the connectivity and reconnection flux during the flare between a dozen magnetic sources defined from partitioning the photospheric magnetogram. It is found that magnetic reconnection proceeds sequentially between magnetic cells, and the observationally measured reconnection flux in major cells compare favorably with computations by a topological model of magnetic reconnection. The three-dimensional evolution of magnetic reconnection is discussed with respect to its implication on helicity transfer and energy release through reconnection.

2009-02-20

164

On phase diagrams of magnetic reconnection  

International Nuclear Information System (INIS)

Recently, “phase diagrams” of magnetic reconnection were developed to graphically organize the present knowledge of what type, or phase, of reconnection is dominant in systems with given characteristic plasma parameters. Here, a number of considerations that require caution in using the diagrams are pointed out. First, two known properties of reconnection are omitted from the diagrams: the history dependence of reconnection and the absence of reconnection for small Lundquist number. Second, the phase diagrams mask a number of features. For one, the predicted transition to Hall reconnection should be thought of as an upper bound on the Lundquist number, and it may happen for considerably smaller values. Second, reconnection is never “slow,” it is always “fast” in the sense that the normalized reconnection rate is always at least 0.01. This has important implications for reconnection onset models. Finally, the definition of the relevant Lundquist number is nuanced and may differ greatly from the value based on characteristic scales. These considerations are important for applications of the phase diagrams. This is demonstrated by example for solar flares, where it is argued that it is unlikely that collisional reconnection can occur in the corona

2013-06-01

165

Whistler dominated quasi-collisionless magnetic reconnection  

International Nuclear Information System (INIS)

A theory of fast quasi-collisionless reconnection is presented. For spatial scales smaller than the ion inertia length the electrons decouple from the ions and the dynamics is described by electron magnetohydrodynamics (EMHD). A qualitative analysis of the reconnection region is obtained, which is corroborated by numerical simulations. The main results are that in contrast to resistive reconnection no macroscopic current sheet is generated, and the reconnection rate is independent of the smallness parameters of the system, i.e. the electron inertia length and the dissipation coefficients. At larger scales the coupling to the ions is important, which, however, does not change the small-scale dynamics. The reconnection rate is only limited by ion inertia being independent of the electron inertia scale and the dissipation coefficients. Reconnection is much faster than in the absence of the whistler mode. (orig.)

1995-01-01

166

The plasmaspheric plume and magnetopause reconnection  

Science.gov (United States)

We present near-simultaneous measurements from two THEMIS spacecraft at the dayside magnetopause with a 1.5 h separation in local time. One spacecraft observes a high-density plasmaspheric plume while the other does not. Both spacecraft observe signatures of magnetic reconnection, providing a test for the changes to reconnection in local time along the magnetopause as well as the impact of high densities on the reconnection process. When the plume is present and the magnetospheric density exceeds that in the magnetosheath, the reconnection jet velocity decreases, the density within the jet increases, and the location of the faster jet is primarily on field lines with magnetosheath orientation. Slower jet velocities indicate that reconnection is occurring less efficiently. In the localized region where the plume contacts the magnetopause, the high-density plume may impede the solar wind-magnetosphere coupling by mass loading the reconnection site.

Walsh, B. M.; Phan, T. D.; Sibeck, D. G.; Souza, V. M.

2014-01-01

167

On the Rate of Spontaneous Magnetic Reconnection  

CERN Document Server

Magnetic reconnection is a topological rearrangement of the magnetic field lines, leading to the release of magnetic energy, which is thought to be associated with solar flares, coronal mass ejections and magnetospheric storms. Despite magnetic field lines are supposed to be frozen into the well-conducting plasma, the reconnection observed in nature is, typically, fast, so that the rate of convergence of the magnetic field lines is the fraction of the Alfven speed, v_A. The Sweet-Parker solution predicts reconnection rates which are negligible for the solar or astrophysical conditions, this have prompted research into collisionless reconnection. The stochasticity of magnetic field lines due to ambient turbulence leads to fast reconnection and the rate was predicted to be proportional to kinetic energy density of ambient turbulence. Also, tearing instability of the thin current sheet was proposed as a driver of resistivity-independent reconnection, which was shown to be consistent with two-dimensional simulati...

Beresnyak, Andrey

2013-01-01

168

Indeterminacy and instability in Petschek reconnection  

Energy Technology Data Exchange (ETDEWEB)

We explain two puzzling aspects of Petschek's model for fast reconnection. One is its failure to occur in plasma simulations with uniform resistivity. The other is its inability to provide anything more than an upper limit for the reconnection rate. We have found that previously published analytical solutions based on Petschek's model are structurally unstable if the electrical resistivity is uniform. The structural instability is associated with the presence of an essential singularity at the X-line that is unphysical. By requiring that such a singularity does not exist, we obtain a formula that predicts a specific rate of reconnection. For uniform resistivity, reconnection can only occur at the slow, Sweet-Parker rate. For nonuniform resistivity, reconnection can occur at a much faster rate provided that the resistivity profile is not too flat near the X-line. If this condition is satisfied, then the scale length of the nonuniformity determines the reconnection rate.

Forbes, Terry G. [Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, New Hampshire 03824 (United States); Priest, Eric R. [Institute of Mathematics, University of St. Andrews, Fife KY16 9SS, Scotland (United Kingdom); Seaton, Daniel B. [SIDC-Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels (Belgium); Litvinenko, Yuri E. [Department of Mathematics, University of Waikato, P.O. 3105, Hamilton (New Zealand)

2013-05-15

169

Fast Magnetic Reconnection and Energetic Particle Acceleration  

CERN Document Server

Our numerical simulations show that the reconnection of magnetic field becomes fast in the presence of weak turbulence in the way consistent with the Lazarian and Vishniac (1999) model of fast reconnection. We trace particles within our numerical simulations and show that the particles can be efficiently accelerated via the first order Fermi acceleration. We discuss the acceleration arising from reconnection as a possible origin of the anomalous cosmic rays measured by Voyagers.

Lazarian, A; Vishniac, E; Pino, E de Gouveia dal

2010-01-01

170

Impulsive nature in collisional driven reconnection  

Energy Technology Data Exchange (ETDEWEB)

Compressible magnetohydrodynamic simulation is carried out in order to investigate energy relaxation process of the driven magnetic reconnection in an open finite system through a long time calculation. It is found that a very impulsive energy release occurs in an intermittent fashion through magnetic reconnection for a continuous magnetic flux injection on the boundary. In the impulsive phase, the reconnection rate is remarkably enhanced up to more than ten times of the driving rate on the boundary. (author).

Kitabata, Hideyuki; Hayashi, Takaya; Sato, Tetsuya

1995-11-01

171

Magnetopause reconnection and interlinked flux tubes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Magnetic reconnection can be a continuous or a transient process. Global magnetohydrodynamics (MHD) simulations are important tools to understand the relevant magnetic reconnection mechanisms and the resulting magnetic structures. We have studied magnetopause reconnection using a global 3-D MHD simulation in which the interplanetary magnetic field (IMF) has been set to large positive By and large negative Bz components, i.e., a south-duskward direction. Flu...

Cardoso, F. R.; Gonzalez, W. D.; Sibeck, D. G.; Kuznetsova, M.; Koga, D.

2013-01-01

172

Impulsive nature in magnetohydrodynamic driven reconnection  

International Nuclear Information System (INIS)

Compressible magnetohydrodynamic simulation is carried out in order to investigate energy relaxation process of the driven magnetic reconnection in an open finite system through a long time calculation. It is found that a very impulsive energy release occurs in an intermittent fashion through magnetic reconnection for a continuous magnetic flux injection on the boundary. In the impulsive phase, the reconnection rate is remarkably enhanced up to more than ten times of the driving rate on the boundary. (author)

1996-10-01

173

Solar flares: an extremum of reconnection  

Energy Technology Data Exchange (ETDEWEB)

Three points are emphasized: that the solar flare is that particular astrophysical phenomenon that is the extremum of reconnection, no other phenomenon demands as rapid magnetic flux annihilation as is seen in the solar flare; that plasma physics experiments can and should be performed in the laboratory that model reconnection as we observe it in astrophysics; and that stochastic field lines derived from something similar to Alfven wave turbulence are a necessary part of reconnection.

Colgate, S.A.

1983-12-22

174

Gravitational Wave Bursts from Cosmic Superstring Reconnections  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We compute the gravitational waveform produced by cosmic superstring reconnections. This is done by first constructing the superstring reconnection trajectory, which closely resembles that of classical, instantaneous reconnection but with the singularities smoothed out due to the string path integral. We then evaluate the graviton vertex operator in this background to obtain the burst amplitude. The result is compared to the detection threshold for current and future gravita...

Jackson, Mark G.; Siemens, Xavier

2009-01-01

175

Impulsive nature in collisional driven reconnection  

International Nuclear Information System (INIS)

Compressible magnetohydrodynamic simulation is carried out in order to investigate energy relaxation process of the driven magnetic reconnection in an open finite system through a long time calculation. It is found that a very impulsive energy release occurs in an intermittent fashion through magnetic reconnection for a continuous magnetic flux injection on the boundary. In the impulsive phase, the reconnection rate is remarkably enhanced up to more than ten times of the driving rate on the boundary. (author)

1995-01-01

176

Turbulent Magnetic Reconnection in Two Dimensions  

CERN Document Server

Two-dimensional numerical simulations of the effect of background turbulence on 2D resistive magnetic reconnection are presented. For sufficiently small values of the resistivity ($\\eta$) and moderate values of the turbulent power ($\\epsilon$), the reconnection rate is found to have a much weaker dependence on $\\eta$ than the Sweet-Parker scaling of $\\eta^{1/2}$ and is even consistent with an $\\eta-$independent value. For a given value of $\\eta$, the dependence of the reconnection rate on the turbulent power exhibits a critical threshold in $\\epsilon$ above which the reconnection rate is significantly enhanced.

Loureiro, N F; Schekochihin, A A; Cowley, S C; Yousef, T A

2009-01-01

177

Gravitational Wave Bursts from Cosmic Superstring Reconnections  

CERN Document Server

We compute the gravitational waveform produced by cosmic superstring reconnections. This is done by first constructing the superstring reconnection trajectory, which closely resembles that of classical, instantaneous reconnection but with the singularities smoothed out due to the string path integral. We then evaluate the graviton vertex operator in this background to obtain the burst amplitude. The result is compared to the detection threshold for current and future gravitational wave detectors, finding that neither bursts nor the stochastic background would be detectable by Advanced LIGO. This disappointing but anticipated conclusion holds even for the most optimistic values of the reconnection probability and loop sizes.

Jackson, Mark G

2009-01-01

178

Kinematics of relativistic magnetic reconnection  

Energy Technology Data Exchange (ETDEWEB)

We study the relativistic generalizations of two-dimensional Sweet-Parker and Petschek reconnection models in the context of a relativistic pair plasma. The solutions show that if the outflow velocity from the resistive region approaches the relativistic Alfven speed, the outflow density increase from Lorentz contraction allows a much faster inflow and thus a faster rate of magnetic energy dissipation than in the nonrelativistic regime. We briefly suggest applications of this result.

Blackman, E.G.; Field, G.B. (Harvard University, Cambridge, Massachusetts 02138 (United States) Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138 (United States))

1994-01-24

179

Relation of astrophysical turbulence and magnetic reconnection  

International Nuclear Information System (INIS)

Astrophysical fluids are generically turbulent and this must be taken into account for most transport processes. We discuss how the preexisting turbulence modifies magnetic reconnection and how magnetic reconnection affects the MHD turbulent cascade. We show the intrinsic interdependence and interrelation of magnetic turbulence and magnetic reconnection, in particular, that strong magnetic turbulence in 3D requires reconnection and 3D magnetic turbulence entails fast reconnection. We follow the approach in Eyink et al.[Astrophys. J. 743, 51 (2011)] to show that the expressions of fast magnetic reconnection in A. Lazarian and E. T. Vishniac [Astrophys. J. 517, 700 (1999)] can be recovered if Richardson diffusion of turbulent flows is used instead of ordinary Ohmic diffusion. This does not revive, however, the concept of magnetic turbulent diffusion which assumes that magnetic fields can be mixed up in a passive way down to a very small dissipation scales. On the contrary, we are dealing the reconnection of dynamically important magnetic field bundles which strongly resist bending and have well defined mean direction weakly perturbed by turbulence. We argue that in the presence of turbulence the very concept of flux-freezing requires modification. The diffusion that arises from magnetic turbulence can be called reconnection diffusion as it based on reconnection of magnetic field lines. The reconnection diffusion has important implications for the continuous transport processes in magnetized plasmas and for star formation. In addition, fast magnetic reconnection in turbulent media induces the First order Fermi acceleration of energetic particles, can explain solar flares and gamma ray bursts. However, the most dramatic consequence of these developments is the fact that the standard flux freezing concept must be radically modified in the presence of turbulence.

2012-01-01

180

Relation of astrophysical turbulence and magnetic reconnection  

Energy Technology Data Exchange (ETDEWEB)

Astrophysical fluids are generically turbulent and this must be taken into account for most transport processes. We discuss how the preexisting turbulence modifies magnetic reconnection and how magnetic reconnection affects the MHD turbulent cascade. We show the intrinsic interdependence and interrelation of magnetic turbulence and magnetic reconnection, in particular, that strong magnetic turbulence in 3D requires reconnection and 3D magnetic turbulence entails fast reconnection. We follow the approach in Eyink et al.[Astrophys. J. 743, 51 (2011)] to show that the expressions of fast magnetic reconnection in A. Lazarian and E. T. Vishniac [Astrophys. J. 517, 700 (1999)] can be recovered if Richardson diffusion of turbulent flows is used instead of ordinary Ohmic diffusion. This does not revive, however, the concept of magnetic turbulent diffusion which assumes that magnetic fields can be mixed up in a passive way down to a very small dissipation scales. On the contrary, we are dealing the reconnection of dynamically important magnetic field bundles which strongly resist bending and have well defined mean direction weakly perturbed by turbulence. We argue that in the presence of turbulence the very concept of flux-freezing requires modification. The diffusion that arises from magnetic turbulence can be called reconnection diffusion as it based on reconnection of magnetic field lines. The reconnection diffusion has important implications for the continuous transport processes in magnetized plasmas and for star formation. In addition, fast magnetic reconnection in turbulent media induces the First order Fermi acceleration of energetic particles, can explain solar flares and gamma ray bursts. However, the most dramatic consequence of these developments is the fact that the standard flux freezing concept must be radically modified in the presence of turbulence.

Lazarian, A. [Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, Wisconsin 53706 (United States); Eyink, Gregory L. [Department of Applied Mathematics and Statistics, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Vishniac, E. T. [Department of Physics and Astronomy, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1 (Canada)

2012-01-15

 
 
 
 
181

Three-dimensional reconnection from a global viewpoint  

International Nuclear Information System (INIS)

Three-dimensional reconnection is defined in terms of changes in a magnetic field topology, even in the absence of true separatrices. Global magnetic helicity conservation at magnetopause flux transfer events is also discused. When people talk about 'field topology', they usually mean the separtrix topology. Consider for example coronal fieldlines with two endpoints in the solar photosphere. Such fieldlines generate a mapping of the photosphere. Such fieldlines generate a mapping of the photosphere to itself. This mapping is often only piecewise continuous, and the separatix surfaces separate the flux regions associated with each continuous piece. Reconnection can be defined in terms of flux transfer across the separatrices. However, there can still be considerable structure between the separatrices, such as braiding and shearing. A fieldline topology is defined which recognizes this structure. Even in the absence of separatrices, the fieldline mapping can develop sharp gradients because of flux localization or because of stagnation points in the photospheric flow. The this regions where these gradients occur can be employed in place of separatrices in a definition of reconnection. (author). 23 refs.; 2 figs

1988-09-05

182

Magnetic reconnection in partially ionized plasmas  

Energy Technology Data Exchange (ETDEWEB)

We review the theory of magnetic reconnection in weakly ionized gases. The theory is relevant to reconnection in the interstellar medium, protostellar and protoplanetary disks, the outer envelopes of cool stars, and a new laboratory experiment. In general, partial ionization introduces three effects beyond the obvious one: increased resistivity due to electron-neutral collisions. First, magnetic neutral sheets are steepened by plasma-neutral drift, setting up the conditions for reconnection. Second, when ion-neutral friction is strong, the effective ion mass is increased by {rho}/{rho}{sub i}, the ratio of total to plasma mass density. This reduces the Alfven speed v{sub A} by a factor of {radical}({rho}/{rho}{sub i}) and increases the ion skin depth {delta}{sub i} by {radical}({rho}/{rho}{sub i}). As a result, entrainment of neutrals slows MHD reconnection but permits the onset of fast collisionless reconnection at a larger Lundquist number S, or for a longer current sheet, than in the fully ionized plasma case. These effects, taken together, promote fast collisionless reconnection when the ionization fraction is of order 10% to 1%, but reconnection is slowed down for much smaller ionization fractions. Finally, ion-neutral friction can be a strong heating mechanism throughout the inflow and outflow regions. These effects are under study at the Magnetic Reconnection Experiment (MRX).

Zweibel, Ellen G. [Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, Wisconsin 53706 (United States); Lawrence, Eric; Yoo, Jongsoo; Ji Hantao; Yamada, Masaaki [Princeton Plasma Physics Laboratory, P. O. Box 451, Princeton, New Jersey 08543 (United States); Malyshkin, Leonid M. [Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637 (United States)

2011-11-15

183

Magnetic reconnection in partially ionized plasmas  

Science.gov (United States)

We review the theory of magnetic reconnection in weakly ionized gases. The theory is relevant to reconnection in the interstellar medium, protostellar and protoplanetary disks, the outer envelopes of cool stars, and a new laboratory experiment. In general, partial ionization introduces three effects beyond the obvious one: increased resistivity due to electron-neutral collisions. First, magnetic neutral sheets are steepened by plasma-neutral drift, setting up the conditions for reconnection. Second, when ion-neutral friction is strong, the effective ion mass is increased by ?/?i, the ratio of total to plasma mass density. This reduces the Alfven speed vA by a factor of ?/?i and increases the ion skin depth ?i by ?/?i. As a result, entrainment of neutrals slows MHD reconnection but permits the onset of fast collisionless reconnection at a larger Lundquist number S, or for a longer current sheet, than in the fully ionized plasma case. These effects, taken together, promote fast collisionless reconnection when the ionization fraction is of order 10% to 1%, but reconnection is slowed down for much smaller ionization fractions. Finally, ion-neutral friction can be a strong heating mechanism throughout the inflow and outflow regions. These effects are under study at the Magnetic Reconnection Experiment (MRX).

Zweibel, Ellen G.; Lawrence, Eric; Yoo, Jongsoo; Ji, Hantao; Yamada, Masaaki; Malyshkin, Leonid M.

2011-11-01

184

On the cessation of magnetic reconnection  

Directory of Open Access Journals (Sweden)

Full Text Available Kinetic simulations of collisionless magnetic reconnection are used to study the effect on the reconnection rate of ion density enhancements in the inflow region. The goal of the investigation is to study a candidate mechanism for the slow-down of magnetic reconnection. The calculations involve either proton or oxygen additions in the inflow region, initially located at two distances from the current sheet. Protons are found to be much more tightly coupled into the evolution of the reconnecting system and, therefore, they effect an immediate slowdown of the reconnection process, as soon as the flux tubes they reside on become involved. Oxygen, on the other hand, has, within the limits of the calculations, a much less pronounced effect on the reconnection electric field. The difference is attributed to the lack of tight coupling to the magnetic field of the oxygen populations. Last, a study of proton and oxygen acceleration finds that protons respond primarily to the reconnection electric field, whereas the main oxygen electric field is achieved by Hall-type electric fields at the plasma sheet boundary.

Key words. Space plasma physics (magnetic reconnection; numerical simulation studies; numerical simulation studies

M. Hesse

2004-01-01

185

Theoretical analysis of driven magnetic reconnection experiments  

International Nuclear Information System (INIS)

In this paper the authors develop a theoretical framework for the Magnetic Reconnection Experiment (MRX) in order to understand the basic physics of the experiment, including the effect of the external driving force, and the difference between co and counterhelicity cases of the experiment. In order to simplify the problem they reduce it to a 1-D resistive MHD model. Also, they define a special class of holonomic boundary conditions under which a unique sequence of global equilibria can be obtained, independent of the rate of reconnection. This enables them to break the whole problem into two parts: a global problem for the ideal region, and a local problem for the resistive reconnection layer. The authors carry out the calculations and obtain the global solution for the ideal region in one particular case of holonomic constraints, the so called 'constant force'' regime, for both the co and counterhelicity cases. After the sequence of equilibria in the ideal region is found, they tackle the problem of the rate of reconnection in the resistive reconnection region. This rate tells how fast they proceed through the sequence of global equilibria but does not affects the sequence itself. Assuming the Sweet-Parker model for the reconnection layer, they calculate the reconnection rate, and demonstrate the difference between the co and counterhelicity cases, as well as the role of the external forces. The authors find their results to be in reasonable agreement with the experiment. Magnetic reconnection is important both in laboratory experiments and in astrophysics

1995-01-01

186

Theoretical analysis of driven magnetic reconnection experiments  

Energy Technology Data Exchange (ETDEWEB)

In this paper the authors develop a theoretical framework for the Magnetic Reconnection Experiment (MRX) in order to understand the basic physics of the experiment, including the effect of the external driving force, and the difference between co and counterhelicity cases of the experiment. In order to simplify the problem they reduce it to a 1-D resistive MHD model. Also, they define a special class of holonomic boundary conditions under which a unique sequence of global equilibria can be obtained, independent of the rate of reconnection. This enables them to break the whole problem into two parts: a global problem for the ideal region, and a local problem for the resistive reconnection layer. The authors carry out the calculations and obtain the global solution for the ideal region in one particular case of holonomic constraints, the so called `constant force`` regime, for both the co and counterhelicity cases. After the sequence of equilibria in the ideal region is found, they tackle the problem of the rate of reconnection in the resistive reconnection region. This rate tells how fast they proceed through the sequence of global equilibria but does not affects the sequence itself. Assuming the Sweet-Parker model for the reconnection layer, they calculate the reconnection rate, and demonstrate the difference between the co and counterhelicity cases, as well as the role of the external forces. The authors find their results to be in reasonable agreement with the experiment. Magnetic reconnection is important both in laboratory experiments and in astrophysics.

Uzdensky, D.A.; Kulsrud, R.M.; Yamada, Masaaki [Princeton Univ., NJ (United States)

1995-11-01

187

Magnetic reconnection from a multiscale instability cascade.  

Science.gov (United States)

Magnetic reconnection, the process whereby magnetic field lines break and then reconnect to form a different topology, underlies critical dynamics of magnetically confined plasmas in both nature and the laboratory. Magnetic reconnection involves localized diffusion of the magnetic field across plasma, yet observed reconnection rates are typically much higher than can be accounted for using classical electrical resistivity. It is generally proposed that the field diffusion underlying fast reconnection results instead from some combination of non-magnetohydrodynamic processes that become important on the 'microscopic' scale of the ion Larmor radius or the ion skin depth. A recent laboratory experiment demonstrated a transition from slow to fast magnetic reconnection when a current channel narrowed to a microscopic scale, but did not address how a macroscopic magnetohydrodynamic system accesses the microscale. Recent theoretical models and numerical simulations suggest that a macroscopic, two-dimensional magnetohydrodynamic current sheet might do this through a sequence of repetitive tearing and thinning into two-dimensional magnetized plasma structures having successively finer scales. Here we report observations demonstrating a cascade of instabilities from a distinct, macroscopic-scale magnetohydrodynamic instability to a distinct, microscopic-scale (ion skin depth) instability associated with fast magnetic reconnection. These observations resolve the full three-dimensional dynamics and give insight into the frequently impulsive nature of reconnection in space and laboratory plasmas. PMID:22337058

Moser, Auna L; Bellan, Paul M

2012-02-16

188

Magnetic reconnection in partially ionized plasmas  

International Nuclear Information System (INIS)

We review the theory of magnetic reconnection in weakly ionized gases. The theory is relevant to reconnection in the interstellar medium, protostellar and protoplanetary disks, the outer envelopes of cool stars, and a new laboratory experiment. In general, partial ionization introduces three effects beyond the obvious one: increased resistivity due to electron-neutral collisions. First, magnetic neutral sheets are steepened by plasma-neutral drift, setting up the conditions for reconnection. Second, when ion-neutral friction is strong, the effective ion mass is increased by ?/?i, the ratio of total to plasma mass density. This reduces the Alfven speed vA by a factor of ?(?/?i) and increases the ion skin depth ?i by ?(?/?i). As a result, entrainment of neutrals slows MHD reconnection but permits the onset of fast collisionless reconnection at a larger Lundquist number S, or for a longer current sheet, than in the fully ionized plasma case. These effects, taken together, promote fast collisionless reconnection when the ionization fraction is of order 10% to 1%, but reconnection is slowed down for much smaller ionization fractions. Finally, ion-neutral friction can be a strong heating mechanism throughout the inflow and outflow regions. These effects are under study at the Magnetic Reconnection Experiment (MRX).

2011-11-01

189

Computer Modeling of Fast Collisionless Reconnection.  

Science.gov (United States)

Particle simulations of collisionless tearing, reconnection and coalescence of magnetic fields for a sheet-pinch configuration show that reconnection is Sweet-Parker like in the tearing and island formation phase. It is much faster to explosive in the isl...

J. N. Leboeuf F. Brunel T. Tajima J. Sakai C. C. Wu

1984-01-01

190

Understanding the Dynamics of Magnetic Reconnection Layer  

Science.gov (United States)

We review progress in understanding the dynamics of a typical magnetic reconnection layer by describing the historical development of theory and the recent findings and discoveries in space and laboratory plasmas. The emphasis is on the dynamics of electrons moving with respect to ions in the collision-free neutral sheet. We make a detailed comparison of experimental results from the Magnetic Reconnection Experiment (MRX) with those from theory and numerical simulations. The collaboration between space and laboratory scientists on reconnection research has recently reached a point where we can compare measurements of the reconnection layer profile in detail with support from numerical simulations. In spite of the large difference in physical scales by 106-107, we find remarkable commonalities in the features of the magnetic reconnection region in laboratory and magnetospheric plasmas. A newly planned laboratory experiment, in which a current sheet is swept in the way a magnetosphere current sheet crosses space satellites, is also described.

Yamada, Masaaki

2011-10-01

191

Collisionless magnetic reconnection in a plasmoid chain  

CERN Multimedia

The kinetic features of plasmoid chain formation and evolution are investigated by two dimensional Particle-in-Cell simulations. Magnetic reconnection is initiated in multiple X points by the tearing instability. Plasmoids form and grow in size by continuously coalescing. Each chain plasmoid exhibits a strong out-of plane core magnetic field and an out-of-plane electron current that drives the coalescing process. The disappearance of the X points in the coalescence process are due to anti-reconnection, a magnetic reconnection where the plasma inflow and outflow are reversed with respect to the original reconnection flow pattern. Anti-reconnection is characterized by the Hall magnetic field quadrupole signature. Two new kinetic features, not reported by previous studies of plasmoid chain evolution, are here revealed. First, intense electric fields develop in-plane normally to the separatrices and drive the ion dynamics in the plasmoids. Second, several bipolar electric field structures are localized in proximi...

Markidis, Stefano; Lapenta, Giovanni; Divin, Andrey; Goldman, Martin V; Newman, David; Eriksson, Stefan

2012-01-01

192

Magnetic reconnection in space and laboratory plasmas  

International Nuclear Information System (INIS)

An important kind of plasma instabilities is the magnetic reconnection, when the topology of magnetic field lines changes suddenly, new field lines occur and reconnect. This phenomenon is often accompanied with fast variation of the magnetic field strength, burst-like acceleration of charged particles and fast plasma heating effects. The energy of magnetic field is transformed into heat and kinetic energy. The physical conditions of magnetic reconnection instability are investigated in detail. If the condition of freezing in of the magnetic field lines are not valid, the resistive diffusion of field lines can lead to the magnetic reconnection. The formation and explosive instability of current sheets are in close connection with magnetic reconnection processes. This phenomenon is important in laboratory, e.g. in fusion plasma experiments, and in the astrophysics, as the possible mechanism of solar flares. (D.Gy.)

1986-03-01

193

A theoretical foundation of general magnetic reconnection  

Energy Technology Data Exchange (ETDEWEB)

This paper deals with the theoretical background of magnetic reconnection including systems where the magnetic field does not vanish (general magnetic reconnection). The magnetic field is represented by Euler potentials. The time evolution of the Euler potentials as seen by the moving plasma provides an appropriate formulation of the properties of general magnetic reconnection. A critical review of the concept of magnetic merging is given, and it is shown that in certain situations there may be ideal plasma flow across a separatrix which does not involve nonideal effects. It is shown that such problems do not arise within the concept of general magnetic reconnection. It is demonstrated that general magnetic reconnection with nonvanishing magnetic field crucially depends on properties of the parallel electric field.

Hesse, M.; Schindler, K. (Ruhr-Univ. Bochum (West Germany))

1988-06-01

194

Taking Medication  

Medline Plus

Full Text Available ... or labels with you when you go to health appointments. Ask a family member to go to an appointment with you adn take notes so your not confused when you get home. Also, ask them to remind you to take your medications or labels when you go for any medical appointment.

195

Quantitative, Comprehensive, Analytical Model for Magnetic Reconnection in Hall Magnetohydrodynamics  

International Nuclear Information System (INIS)

Dissipation-independent, or 'fast', magnetic reconnection has been observed computationally in Hall magnetohydrodynamics (MHD) and predicted analytically in electron MHD. However, a quantitative analytical theory of reconnection valid for arbitrary ion inertial lengths, di, has been lacking and is proposed here for the first time. The theory describes a two-dimensional reconnection diffusion region, provides expressions for reconnection rates, and derives a formal criterion for fast reconnection in terms of dissipation parameters and di. It also confirms the electron MHD prediction that both open and elongated diffusion regions allow fast reconnection, and reveals strong dependence of the reconnection rates on di

2008-09-05

196

Scaling of the magnetic reconnection rate with symmetric shear flow  

International Nuclear Information System (INIS)

The scaling of the reconnection rate during (fast) Hall magnetic reconnection in the presence of an oppositely directed bulk shear flow parallel to the reconnecting magnetic field is studied using two-dimensional numerical simulations of Hall reconnection with two different codes. Previous studies noted that the reconnection rate falls with increasing flow speed and shuts off entirely for super-Alfvenic flow, but no quantitative expression for the reconnection rate in sub-Alfvenic shear flows is known. An expression for the scaling of the reconnection rate is presented.

2011-07-01

197

Quantitative, comprehensive, analytical model for magnetic reconnection in Hall magnetohydrodynamics.  

Science.gov (United States)

Dissipation-independent, or "fast", magnetic reconnection has been observed computationally in Hall magnetohydrodynamics (MHD) and predicted analytically in electron MHD. However, a quantitative analytical theory of reconnection valid for arbitrary ion inertial lengths, d{i}, has been lacking and is proposed here for the first time. The theory describes a two-dimensional reconnection diffusion region, provides expressions for reconnection rates, and derives a formal criterion for fast reconnection in terms of dissipation parameters and d{i}. It also confirms the electron MHD prediction that both open and elongated diffusion regions allow fast reconnection, and reveals strong dependence of the reconnection rates on d{i}. PMID:18851221

Simakov, Andrei N; Chacón, L

2008-09-01

198

Cause of Sudden Magnetic Reconnection in a Laboratory Plasma  

International Nuclear Information System (INIS)

The cause for sudden reconnection in reversed field pinch plasmas is determined experimentally for two cases: large reconnection events (the sawtooth crash) and small reconnection events during improved confinement. We measure the term in the MHD equations which represents the driving (or damping) of edge tearing modes due to the axisymmetric magnetic field. The term is negative for large reconnection events (the modes are stable, implying that reconnection may be driven by nonlinear coupling to other modes) and positive for small reconnection events (modes are unstable, reconnection is spontaneous)

2006-04-14

199

Magnetic reconnection in the heliosheath and the generation of anomalous cosmic rays  

Science.gov (United States)

The recent observations of the anomalous cosmic ray (ACR) energy spectrum as Voyagers 1 and 2 crossed the heliospheric termination shock have called into question the conventional shock source of these energetic particles. We suggest that the sectored heliospheric magnetic field, which results from the flapping of the heliospheric current sheet, compresses across the termination shock and reconnects in the subsonic flow of the heliosheath. A number of Voyager observations support the hypothesis that the heliosheath sectored field has reconnected. Particle-in-cell (PIC) simulations in 2-D suggest that the sectors break up into a bath of elongated magnetic islands and that most of the magnetic energy released goes into the pickup ions. The most energetic ions gain energy as they circulate in contracting and merging magnetic islands, a first order Fermi process. The firehose condition plays an essential role in the reconnection dynamics and particle acceleration. The simulations are being extended to 3-D where ions circulating within islands have a finite lifetime. Measured energy spectra are similar to those in 2-D. We present a new analytic model of particle acceleration in a multi-island reconnecting system that describes the energy spectrum of ions parallel and perpendicular to the local magnetic field. Including anisotropy is essential to describe reconnection driven particle acceleration since Fermi acceleration during reconnection drives anisotropy, which is self-consistently limited by scattering and the approach to firehose marginal stability, which is now explicitly evaluated from the anisotropic spectrum. The limiting ACR differential energy spectrum takes the form of a power law with a spectral index of 1.5, a result which was obtained earlier in a much more primitive model. The new transport equation for the particle energy spectrum is suitable for calculating the global distribution of reconnection driven energetic particles in the heliosphere.

Drake, J. F.; Opher, M.; Schoeffler, K. M.; Swisdak, M. M.; Dahlin, J.; Fermo, R. L.

2012-12-01

200

Three-dimensional inverse energy transfer induced by vortex reconnections  

Science.gov (United States)

In low-temperature superfluid helium, viscosity is zero and vorticity takes the form of discrete vortex filaments of fixed circulation and atomic thickness. We present numerical evidence of three-dimensional inverse energy transfer from small length scales to large length scales in superfluid turbulence generated by a flow of vortex rings. We argue that the effect arises from the anisotropy of the flow, which favors vortex reconnections of vortex loops of the same polarity, and that it has been indirectly observed in the laboratory. The effect opens questions about analogies with related processes in ordinary turbulence.

Baggaley, Andrew W.; Barenghi, Carlo F.; Sergeev, Yuri A.

2014-01-01

 
 
 
 
201

Magnetic reconnection and magnetic activity  

International Nuclear Information System (INIS)

A large-scale magnetic field extending through a highly conducting tenuous fluid may become distorted on a small scale as a consequence of slow small-scale shuffling of the magnetic lines of force at the boundaries of the tenuous fluid. Any slow wrapping and winding introduced at the boundaries is distributed along the field (at the Alfven speed). It is a curious and little-known fact that such wrapping and winding possesses no static equilibrium (except for a set of solutions of extreme symmetry). The result is neutral-point reconnection of the strains in the field, rapidly dissipating the wrapping and winding. It is suggested that this is the principal cause of the extreme heating that produces the active corona of the sun and other stars. The shuffling of the footpoints of the magnetic field in the photospheric turbulence introduces small-scale wrapping and twisting into the coronal loops. The work done by the turbulence in twisting the fields is dissipated within a matter 10-20 hours by neutral-point reconnection, introducing heat into the corona at a rate of about 10 Mergs/sq cm sec for photospheric turbulence of 0.5 km/sec. It is suggested that this is the basic cause of the X-ray corona. 32 references

1984-01-01

202

Reconnection: where is the party?  

Science.gov (United States)

Kinetic reconnection is often described in the form of two concentric boxes, the inner electron diffusion region and an outer ion diffusion regions. The meaning is the electrons become decoupled in the inner regions and the ions in the outer region. But is it true that all electrons and all ions involved in the process of kinetic reconnection have to go through those two regions? Or the more fluid-like point of view of Petscheck that reconneciton might be on a much larger area where most particles do not even have to go through the central part is in some form revitalised in the kinetic picture? We present evidence to the latter: a small fraction of electrons go through their little central box, or even through the extended jets frm it more recently discovered. Most cross the separatrices at far more distant regions. There is the party: a localised strong field deflects, energises and radnomises the electrons conveying them toward an outflowing plasma region charactereised by very different energetics and turbulence.

Lapenta, Giovanni; Markidis, Stefano; Vapirev, Alex; Goldman, Martin; Newman, David

2012-10-01

203

Taking Medication  

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Full Text Available ... Access My Learning Access AADE7 System Find a Diabetes Educator Questions, Comments, Concerns? 800.338.3633 , ext. 100 Taking Medication Diabetes is a progressive condition. Depending on what type ...

204

Taking Medication  

Science.gov (United States)

... Access My Learning Access AADE7 System Find a Diabetes Educator Questions, Comments, Concerns? 800.338.3633 , ext. 100 Taking Medication Diabetes is a progressive condition. Depending on what type ...

205

Taking Medication  

Medline Plus

Full Text Available ... schedule. Be sure to bring all medications or labels with you when you go to health appointments. ... to remind you to take your medications or labels when you go for any medical appointment.

206

Magnetic reconnection as an element of turbulence  

Directory of Open Access Journals (Sweden)

Full Text Available In this work, recent advances on the study of reconnection in turbulence are reviewed. Using direct numerical simulations of decaying incompressible two-dimensional magnetohydrodynamics (MHD, it was found that in fully developed turbulence complex processes of reconnection locally occur (Servidio et al., 2009, 2010a. In this complex scenario, reconnection is spontaneous but locally driven by the fields, with the boundary conditions provided by the turbulence. Matching classical turbulence analysis with a generalized Sweet-Parker theory, the statistical features of these multiple-reconnection events have been identified. A discussion on the accuracy of our algorithms is provided, highlighting the necessity of adequate spatial resolution. Applications to the study of solar wind discontinuities are reviewed, comparing simulations to spacecraft observations. New results are shown, studying the time evolution of these local reconnection events. A preliminary study on the comparison between MHD and Hall MHD is reported. Our new approach to the study of reconnection as an element of turbulence has broad applications to space plasmas, shedding a new light on the study of magnetic reconnection in nature.

S. Servidio

2011-10-01

207

Physics of Reconnection and MMS Mission  

Science.gov (United States)

Reconnection is the most important process driving the Earth's magnetosphere. Key to the success of the MMS science plan is the coupling of theory and observation. Determining the kinetic processes occurring in the diffusion region and physical parameters that control the rate of magnetic reconnection are among primary objectives of the MMS mission. Analysis of the role played by particle inertial effects in the diffusion region where the plasma is unmagnetized will be presented. The reconnection electric field in he diffusion region is supported primarily by particle non-gyrotropic effects. At the quasi-steady stage the reconnection electric field serves to accelerate and heat the incoming plasma population to maintain the current flow in the diffusion region the pressure balance. The primary mechanism controlling the dissipation in the vicinity of the reconnection site is incorporated into the fluid description in terms of non-gyrotropic corrections to the. induction and energy equations. The results of kinetic and fluid simulations illustrating the physics of magnetic reconnection will be presented. We will dem:tistrate that kinetic nongyrotropic effects can significantly alter the global magnetosphere evolution and location of reconnection sites.

Kuznetsova, M. M.; Hesse, M.; Gombosi, T.

2009-01-01

208

Evolution of magnetic helicity under kinetic magnetic reconnection: Part II B ? 0 reconnection  

Directory of Open Access Journals (Sweden)

Full Text Available We investigate the evolution of magnetic helicity under kinetic magnetic reconnection in thin current sheets. We use Harris sheet equilibria and superimpose an external magnetic guide field. Consequently, the classical 2D magnetic neutral line becomes a field line here, causing a B ? 0 reconnection. While without a guide field, the Hall effect leads to a quadrupolar structure in the perpendicular magnetic field and the helicity density, this effect vanishes in the B ? 0 reconnection. The reason is that electrons are magnetized in the guide field and the Hall current does not occur. While a B = 0 reconnection leads just to a bending of the field lines in the reconnection area, thus conserving the helicity, the initial helicity is reduced for a B ? 0 reconnection. The helicity reduction is, however, slower than the magnetic field dissipation. The simulations have been carried out by the numerical integration of the Vlasov-equation.

T. Wiegelmann

2002-01-01

209

The role of the Weibel instability at the reconnection jet front in relativistic pair plasma reconnection  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The role of the Weibel instability is investigated for the first time in the context of the large-scale magnetic reconnection problem. A late-time evolution of magnetic reconnection in relativistic pair plasmas is demonstrated by particle-in-cell (PIC) simulations. In the outflow regions, powerful reconnection jet piles up the magnetic fields and then a tangential discontinuity appears there. Further downstream, it is found that the two-dimensional extension of the relativis...

Zenitani, S.; Hesse, M.

2007-01-01

210

Vortex-induced magnetic reconnection and single X line reconnection at the magnetopause  

Energy Technology Data Exchange (ETDEWEB)

The authors present the results of two-dimensional MHD simulations of two different models of magnetic reconnection, a vortex-induced magnetic reconnection, and a bursty single X line reconnection. They look at the implications of the magnetic topolgy of the magnetopause for the occurrence of conditions conducive to these two processes. They also discuss the physical implications which could be derived from these two models.

Fu, S.Y.; Pu, Z.Y. [Peking Univ., Beijing (China); Liu, Z.X. [Academia Sinica, Beijing (China)

1995-04-01

211

Evolution of magnetic helicity under kinetic magnetic reconnection: Part II B ? 0 reconnection  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We investigate the evolution of magnetic helicity under kinetic magnetic reconnection in thin current sheets. We use Harris sheet equilibria and superimpose an external magnetic guide field. Consequently, the classical 2D magnetic neutral line becomes a field line here, causing a B ? 0 reconnection. While without a guide field, the Hall effect leads to a quadrupolar structure in the perpendicular magnetic field and the helicity density, this effect vanishes in the B ? 0 reconnect...

2002-01-01

212

Magnetic reconnection in a space plasma  

International Nuclear Information System (INIS)

A review is presented of reconnection in a space plasma of collisionless magnetic field lines with special regard to the earth's magnetosphere. The collisionless tearing mode is considered to be the main mechanism for the merging of magnetic field lines. It is shown that the difference between the nose and tail reconnection is related to the difference in the geometries of magnetic field lines. Non-linear analysis of the collisionless tearing mode provides an estimate of the reconnection rate of interplanetary and geomagnetic field lines. Magnetospheric tail instability during substorms is discussed in terms of the tearing-mode development. (author)

1977-04-09

213

Magnetic Reconnection Sweet-Parker Versus Petschek  

CERN Document Server

The two theories for magnetic reconnection, one of Sweet and Parker, and the other of Petschek, are reconciled by exhibiting an extra condition in that of Petschek which reduces his theory to that of Sweet and Parker, provided that the resistivity is constant in space. On the other hand, if the resistivity is enhanced by instabilities, then the reconnection rate of both theories is increased substantially, but Petschek's rate can be faster. A different formula from the usual one is presented for enhanced Petschek reconnection.

Kulsrud, R M

2000-01-01

214

Magnetic reconnection in the terrestrial magnetosphere  

Energy Technology Data Exchange (ETDEWEB)

An overview is given of quantitative comparisons between measured phenomena in the terrestrial magnetosphere thought to be associated with magnetic reconnection, and related theoretical predictions based on Petschek's simple model. Although such a comparison cannot be comprehensive because of the extended nature of the process and the relatively few in situ multipoint measurements made to date, the agreement is impressive where comparisons have been possible. This result leaves little doubt that magnetic reconnection does indeed occur in the terrestrial magnetosphere. The maximum reconnection rate, expressed in terms of the inflow Mach number, M/sub A/, is measured to be M/sub A/ = 0.2 +- 0.1.

Feldman, W.C.

1984-01-01

215

Magnetic reconnection in the terrestrial magnetosphere  

Energy Technology Data Exchange (ETDEWEB)

An overview is given of quantitative comparisons between measured phenomena in the terrestrial magnetosphere thought to be associated with magnetic reconnection, and related theoretical predictions based on Petschek's simple model. Although such a comparison cannot be comprehensive because of the extended nature of the process and the relatively few in situ multipoint measurements made to date, the agreement is impressive where comparisons have been possible. This result leaves little doubt that magnetic reconnection does indeed occur in the terrestrial magnetosphere. The maximum reconnection rate, expressed in terms of the inflow Mach number, M/sub A/, is measured to be M/sub A/ = 0.2 +- 0.1

Feldman, W.C.

1986-06-30

216

Collisionless magnetic reconnection via Alfvén eigenmodes.  

Science.gov (United States)

We propose an analytic approach to the problem of collisionless magnetic reconnection formulated as a process of Alfvén eigenmodes' generation and dissipation. Alfvén eigenmodes are confined by the current sheet in the same way that quantum mechanical waves are confined by the tanh;{2} potential. The dynamical time scale of reconnection is the system scale divided by the eigenvalue propagation velocity of the n = 1 mode. The prediction of the n = 1 mode shows good agreement with the in situ measurement of the reconnection-associated Hall fields. PMID:19659017

Dai, Lei

2009-06-19

217

New electric field in asymmetric magnetic reconnection.  

Science.gov (United States)

We present a theory and numerical evidence for the existence of a previously unexplored in-plane electric field in collisionless asymmetric magnetic reconnection. This electric field, dubbed the "Larmor electric field," is associated with finite Larmor radius effects and is distinct from the known Hall electric field. Potentially, it could be an important indicator for the upcoming Magnetospheric Multiscale mission to locate reconnection sites as we expect it to appear on the magnetospheric side, pointing earthward, at the dayside magnetopause reconnection site. PMID:24116786

Malakit, K; Shay, M A; Cassak, P A; Ruffolo, D

2013-09-27

218

Places to Go: Moodle  

Science.gov (United States)

Educators are becoming increasingly interested in alternatives to learning management systems (LMS) Blackboard and WebCT. Stephen Downes's column Places to Go turns to one internationally popular open source LMS--Moodle. Downes takes the reader through Moodle's Web site, which is simultaneously a Web site about its LMS and an example of what its…

Downes, Stephen

2006-01-01

219

Interaction of magnetic reconnection and Kelvin-Helmholtz modes for large magnetic shear: 2. Reconnection trigger  

Science.gov (United States)

A typical property of magnetopause reconnection is a significant perpendicular shear flow due to the fast streaming magnetosheath plasma. Therefore, the magnetopause represents a large magnetic and flow shear boundary during periods of southward interplanetary magnetic field, which can be unstable to Kelvin-Helmholtz (KH) modes and to magnetic reconnection. A series of local three-dimensional MHD and Hall MHD simulations is carried out to investigate the interaction of reconnection and nonlinear KH waves considering magnetic reconnection as the primary process. It is demonstrated that the onset reconnection causes a thinning of the shear flow layer, thereby generating small wavelength KH modes. In turn, the growing KH modes modify the current layer width, which modulate the diffusion regions, increase the local reconnection rates, and generate field-aligned currents. The simulation results imply a limitation of total amount of open flux likely caused by nonlinear saturation of KH growth and the associated diffusion. It is also demonstrated that the reconnection rate maximizes for conditions that allow a strong nonlinear evolution of KH waves, i.e., fast shear flow and limited guide magnetic field. The presence of Hall physics increases the reconnection rate in the early stage; however, the maximum reconnection rate and the total amount of open flux at saturation are the same as in the MHD case.

Ma, Xuanye; Otto, Antonius; Delamere, Peter A.

2014-02-01

220

Places available**  

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If you wish to participate in one of the following courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at: http://www.cern.ch/Training/ or fill in an "application for training" form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of their receipt. TECHNICAL TRAINING Monique Duval tel. 74924 technical.training@cern.ch ** The number of places available may vary. Please check our Web site to find out the current availability. Places are available in the following courses: ACCESS 2000 - niveau 1 : 13 & 14.11.03 (2 jours) C++ for Particle Physicists : 17 ? 21.11.03 (6 X 3-hour lectures) Programmation automate Schneider TSX Premium ? niveau 2 : 18 ? 21.11.03 (4 jours) JAVA 2 Enterprise Edition ? Part 1 : WEB Applications : 20 & ...

2003-01-01

 
 
 
 
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Places available  

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If you wish to participate in one of the following courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at: http://www.cern.ch/Training/ or fill in an "application for training" form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of their receipt. Places available The number of places available may vary. Please check our Web site to find out the current availability. Places are available in the following courses : Introduction à Outlook : 19.8.2004 (1 journée) Outlook (short course I) : E-mail : 31.8.2004 (2 hours, morning) Outlook (short course II) : Calendar, Tasks and Notes : 31.8.2004 (2 hours, afternoon) Instructor-led WBTechT Study or Follow-up for Microsoft Applications : 7.9.2004 (morning) Outlook (short course III) : Meetings and Delegation : 7.9.2004 (2 hours, afternoon) Introduction ...

2004-01-01

222

Interchange reconnection in a turbulent Corona  

CERN Document Server

Magnetic reconnection at the interface between coronal holes and loops, so-called interchange reconnection, can release the hotter, denser plasma from magnetically confined regions into the heliosphere, contributing to the formation of the highly variable slow solar wind. The interchange process is often thought to develop at the apex of streamers or pseudo-streamers, near Y and X-type neutral points, but slow streams with loop composition have been recently observed along fanlike open field lines adjacent to closed regions, far from the apex. However, coronal heating models, with magnetic field lines shuffled by convective motions, show that reconnection can occur continuously in unipolar magnetic field regions with no neutral points: photospheric motions induce a magnetohydrodynamic turbulent cascade in the coronal field that creates the necessary small scales, where a sheared magnetic field component orthogonal to the strong axial field is created locally and can reconnect. We propose that a similar mechan...

Rappazzo, A F; Ruffolo, D; Servidio, S; Velli, M

2012-01-01

223

Integral formulation of collisionless reconnecting modes  

Energy Technology Data Exchange (ETDEWEB)

The problem of collisionless reconnecting modes is solved by using an integral formulation that includes finite-ion-gyro-radius effects to all orders. Numerical study of this solution reveals a strong stabilizing effect associated with a finite temperature gradient.

Crew, G.B.; Antonsen, T.M. Jr.; Coppi, B. (Massachusetts Inst. of Tech., Cambridge (USA). Dept. of Physics)

1982-01-01

224

Fast Shocks From Magnetic Reconnection Outflows  

CERN Document Server

Magnetic reconnection is commonly perceived to drive flow and particle acceleration in flares of solar, stellar, and astrophysical disk coronae but the relative roles of different acceleration mecha- nisms in a given reconnection environment are not well understood. We show via direct numerical simulations that reconnection outflows produce weak fast shocks, when conditions for fast recon- nection are met and the outflows encounter an obstacle. The associated compression ratios lead to a Fermi acceleration particle spectrum that is significantly steeper than the strong fast shocks commonly studied, but consistent with the demands of solar flares. While this is not the only acceleration mechanism operating in a reconnection environment, it is plausibly a ubiquitous one.

Workman, Jared C; Ren, Chuang

2011-01-01

225

The Role of Geometry in Magnetic Reconnection  

Science.gov (United States)

Magnetic reconnection is arguably the most effective energy conversion and transport process in plasmas. Reconnection is subject to topological considerations in two ways. First, the process itself involves a change in topology of the combined plasma-magnetic field system. This change in topology transcends that of the magnetic field alone and accounts for flux transport relative to the motion of the plasma in the system under investigation. The second way topology is important to magnetic reconnection is through modifications of the diffUSion/dissipation physics brought about by the structure of the reconnecting system. This presentation will present an overview and summary of both past and recent results pertaining to both aspects.

Hesse, Michael; Aunai, Nicholas; Birn, Joachim; Zenitani, Seiji

2012-01-01

226

The Inner Workings of Magnetic Reconnection  

Science.gov (United States)

Magnetic reconnection is arguably the most efficient transport and energy conversion mechanism in almost ideal plasmas. Reconnection controls the overall dynamics in space and astrophysics plasmas, as well as in many laboratory plasma systems. Reconnection operates by means of a localized diffusion region, where deviations from the plasma idealness condition generate electric fields and permit plasma transport even far away from the diffusion region itself. Recent advances in analytic theory and computer modeling have begun to shed light on the internal dynamics of the diffusion region. In particular, we begin to understand the delicate nature of the force balance in the inner diffusion region, where particles can become unmagnetized and where electric field forces are important. This presentation will provide a brief introduction of the reconnection process and its applications. This introduction will be followed by a detailed analysis of the current understanding of dissipation region physics, and by an outlook toward future research.

Hesse, Michael; Zenitani, S.

2007-01-01

227

Resistive Magnetohydrodynamic Simulations of Relativistic Magnetic Reconnection  

Science.gov (United States)

Resistive relativistic magnetohydrodynamic (RRMHD) simulations are applied to investigate the system evolution of relativistic magnetic reconnection. A time-split Harten-Lan-van Leer method is employed. Under a localized resistivity, the system exhibits a fast reconnection jet with an Alfv enic Lorentz factor inside a narrow Petschek-type exhaust. Various shock structures are resolved in and around the plasmoid such as the post-plasmoid vertical shocks and the "diamond-chain" structure due to multiple shock reflections. Under a uniform resistivity, Sweet-Parker-type reconnection slowly evolves. Under a current-dependent resistivity, plasmoids are repeatedly formed in an elongated current sheet. It is concluded that the resistivity model is of critical importance for RRMHD modeling of relativistic magnetic reconnection.

Zenitani, Seiji; Hesse, Michael; Klimas, Alex

2010-01-01

228

Magnetic Reconnection in the Earth's Magnetosphere  

Science.gov (United States)

The process of magnetic reconnection plays an important role during the interaction of the solar wind with the Earth's magnetosphere which leads to the exchange of mass, momentum, and energy between these two highly conducting plasmas.

Tsurutani, B. T.; Lakhina, G. S.

1997-01-01

229

The Dissipation Mechanism of Magnetic Reconnection  

Science.gov (United States)

Magnetic reconnection is arguably the most efficient transport and energy conversion mechanism in almost ideal plasmas. Reconnection controls the overall dynamics in space and astrophysics plasmas, as well as in many laboratory plasma systems. Reconnection operates by means of a localized diffusion region, where deviations from the plasma idealness condition generate electric fields and permit plasma transport even far away from the diffusion region itself. Recent advances in analytic theory and computer modeling have begun to shed light on the internal dynamics of the diffusion region. In particular, we begin to understand the delicate nature of the force balance in the inner diffusion region, where particles can become unmagnetized and where electric field forces are important. This presentation will provide a brief introduction of the reconnection process and its applications. This introduction will be followed by a detailed analysis of the current understanding of dissipation region physics, and by an outlook toward future research.

Hesse, Michael

2008-01-01

230

Computer Simulation of Reconnection in Planetary Magnetospheres.  

Science.gov (United States)

The earth's magnetosphere provides an ideal opportunity to model reconnection in well known geometries that are close enough to the idealized analytic models to make a comparison of the computer models with analytic theory meaningful. In addition more det...

J. Birn

1983-01-01

231

Resistive Magnetohydrodynamic Simulations of Relativistic Magnetic Reconnection  

CERN Multimedia

Resistive relativistic magnetohydrodynamic (RRMHD) simulations are applied to investigate the system evolution of relativistic magnetic reconnection. A time-split Harten--Lan--van Leer (HLL) method is employed. Under a localized resistivity, the system exhibits a fast reconnection jet with an Alfv\\'{e}nic Lorentz factor inside a narrow Petschek-type exhaust. Various shock structures are resolved in and around the plasmoid such as the post-plasmoid vertical shocks and the "diamond--chain" structure due to multiple shock reflections. Under a uniform resistivity, Sweet--Parker-type reconnection slowly evolves. Under a current-dependent resistivity, plasmoids are repeatedly formed in an elongated current sheet. It is concluded that the resistivity model is of critical importance for RRMHD modeling of relativistic magnetic reconnection.

Zenitani, Seiji; Klimas, Alex

2010-01-01

232

Helicity transfer during quantised vortex reconnection  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We consider the reconnection of two untwisted, linked quantised vortex rings in a Bose-Einstein condensate. We show that the reconnection is capable of transferring helicity, from the links present in the initial configuration, to a twisting of the resulting vortex ring, and hence a rotation of the phase plane along the vortex ring. As velocities in a quantum fluid are the gradient of the phase, a twisting of the phase along the vortices leads to an axial flow along the vort...

Baggaley, Andrew W.

2014-01-01

233

Collisionless Magnetic Reconnection via Alfven Eigenmodes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We propose an analytic approach to the problem of collisionless magnetic reconnection formulated as a process of Alfven eigenmodes' generation and dissipation. Alfven eigenmodes are confined by the current sheet in the same way that quantum mechanical waves are confined by the tanh^2 potential. The dynamical time scale of reconnection is the system scale divided by the eigenvalue propagation velocity of the n=1 mode. The prediction of the n=1 mode shows good agreement with t...

Dai, Lei

2009-01-01

234

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2003-01-01

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2004-01-01

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2003-01-01

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If you wish to participate in one of the following courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at: http://www.cern.ch/Training/ or fill in an "application for training" form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of their receipt. TECHNICAL TRAINING Monique Duval tel. 74924 technical.training@cern.ch ** The number of places available may vary. Please check our Web site to find out the current availability. Places are available in the following courses: MATLAB Fundamentals and Programming Techniques (ML01) :2 & 3.12.03 (2 days) Oracle 8i : SQL : 3 - 5.12.03 (3 days) The EDMS MTF in practice : 5.12.03 (afternoon, free of charge) Modeling Dynamic Systems with Simulink (SL01) : 8 & 9.12.03 (2 days) Signal Processing with MATLAB (SG01) : 11 & ...

2003-01-01

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2003-01-01

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2004-01-01

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2003-01-01

 
 
 
 
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If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at: http://www.cern.ch/Training/ or fill in an "application for training" form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of their receipt. ** The number of places available may vary. Please check our Web site to find out the current availability. Places are available in the following courses : EXCEL 2000 - niveau 1 : 20 & 22.10.03 (2 jours) CLEAN-2002 : Working in a Cleanroom (free of charge) : 23.10.03 (half day) The EDMS-MTF in practice (free of charge) :  28 -  30.10.03 (6 half-day sessions) AutoCAD 2002 - Level 1 : 3, 4, 12, 13.11.03 (4 days) LabVIEW TestStand ver. 3 : 4 & 5.11.03 (2 days) Introduction to Pspice : 4.11.03 p.m. (half-day) Hands-on Introduction to Python Programm...

2003-01-01

242

Stochastic sawtooth reconnection in ASDEX Upgrade  

International Nuclear Information System (INIS)

In this paper we investigate non-complete sawtooth reconnection in the ASDEX Upgrade tokamak. Such reconnection phenomena are associated with internal m/n = 1/1 kink mode which does not vanish after the crash phase (as would be the case for complete reconnection). It is shown that this sawtooth cannot be fully described by pure m/n = 1/1 mode and that higher harmonics play an important role during the sawtooth crash phase. We employ the Hamiltonian formalism and reconstructed perturbations to model incomplete sawtooth reconnection. It is demonstrated that stochastization appears due to the excitation of low-order resonances which are present in the corresponding q-profiles inside the q = 1 surface which reflects the key role of the q0 value. Depending on this value two completely different situations are possible for one and the same mode perturbations: (i) the resonant surfaces are present in the q-profile leading to stochasticity and sawtooth crash (q0 ? 0.7 ± 0.1); (ii) the resonant surfaces are not present, which means no stochasticity in the system and no crash event (q0 ? 0.9 ± 0.05). Accordingly the central safety factor value is always less than unity in the case of a non-complete sawtooth reconnection. Our investigations show that the stochastic model agrees well with the experimental observations and can be proposed as a promising candidate for an explanation of the sawtooth reconnection

2007-01-01

243

Driven magnetic reconnection near the Dreicer limit  

Science.gov (United States)

The influence of Coulomb collisions on the dynamics of driven magnetic reconnection in geometry mimicking the Magnetic Reconnection eXperiment (MRX) [M. Yamada et al., Phys. Plasmas 4, 1936 (1997)] is investigated using two-dimensional (2D) fully kinetic simulations with a Monte Carlo treatment of the collision operator. For values of collisionality typical of MRX, the reconnection mechanism is shown to be a combination of collisionless effects, represented by off-diagonal terms in the electron stress tensor, and collisional momentum exchange between electrons and ions. The ratio of the reconnection electric field ER to the critical runaway field Ecrit provides a convenient measure of the relative importance of these two mechanisms. The structure of electron-scale reconnection layers in the presence of collisions is investigated in light of the previously reported [S. Dorfman et al., Phys. Plasmas 15, 102107 (2008)] discrepancy in the width of the electron reconnection layers between collisionless simulations and experimental observations. It is demonstrated that the width of the layer increases in the presence of collisions, but does not substantially deviate from its collisionless values, given by the electron crossing orbit width, unless ERMRX observations demonstrates that the layer width in 2D simulations with Coulomb collisions is substantially smaller than the value observed in the low-density experiments with ER<~Ecrit, indicating that physical mechanisms beyond those included in the simulations control the structure of the electron layers in these experiments.

Roytershteyn, V.; Daughton, W.; Dorfman, S.; Ren, Y.; Ji, H.; Yamada, M.; Karimabadi, H.; Yin, L.; Albright, B. J.; Bowers, K. J.

2010-05-01

244

Multiscale Modeling of Solar Coronal Magnetic Reconnection  

Science.gov (United States)

Magnetic reconnection is widely believed to be the primary process by which the magnetic field releases energy to plasma in the Sun's corona. For example, in the breakout model for the initiation of coronal mass ejections/eruptive flares, reconnection is responsible for the catastrophic destabilizing of magnetic force balance in the corona, leading to explosive energy release. A critical requirement for the reconnection is that it have a "switch-on' nature in that the reconnection stays off until a large store of magnetic free energy has built up, and then it turn on abruptly and stay on until most of this free energy has been released. We discuss the implications of this requirement for reconnection in the context of the breakout model for CMEs/flares. We argue that it imposes stringent constraints on the properties of the flux breaking mechanism, which is expected to operate in the corona on kinetic scales. We present numerical simulations demonstrating how the reconnection and the eruption depend on the effective resistivity, i.e., the effective Lundquist number, and propose a model for incorporating kinetic flux-breaking mechanisms into MHO calculation of CMEs/flares.

Antiochos, Spiro K.; Karpen, Judith T.; DeVore, C. Richard

2010-01-01

245

Collisionless magnetic reconnection in a plasmoid chain  

Directory of Open Access Journals (Sweden)

Full Text Available The kinetic features of plasmoid chain formation and evolution are investigated by two dimensional Particle-in-Cell simulations. Magnetic reconnection is initiated in multiple X points by the tearing instability. Plasmoids form and grow in size by continuously coalescing. Each chain plasmoid exhibits a strong out-of plane core magnetic field and an out-of-plane electron current that drives the coalescing process. The disappearance of the X points in the coalescence process are due to anti-reconnection, a magnetic reconnection where the plasma inflow and outflow are reversed with respect to the original reconnection flow pattern. Anti-reconnection is characterized by the Hall magnetic field quadrupole signature. Two new kinetic features, not reported by previous studies of plasmoid chain evolution, are here revealed. First, intense electric fields develop in-plane normally to the separatrices and drive the ion dynamics in the plasmoids. Second, several bipolar electric field structures are localized in proximity of the plasmoid chain. The analysis of the electron distribution function and phase space reveals the presence of counter-streaming electron beams, unstable to the two stream instability, and phase space electron holes along the reconnection separatrices.

S. Markidis

2012-02-01

246

Asymmetric Magnetic Reconnection in the Solar Atmosphere  

Science.gov (United States)

Models of solar flares and coronal mass ejections typically predict the development of an elongated current sheet in the wake behind the rising flux rope. In reality, reconnection in these current sheets will be asymmetric along the inflow, outflow, and out-of-plane directions. We perform resistive MHD simulations to investigate the consequences of asymmetry during solar reconnection. We predict several observational signatures of asymmetric reconnection, including flare loops with a skewed candle flame shape, slow drifting of the current sheet into the strong field upstream region, asymmetric footpoint speeds and hard X-ray emission, and rolling motions within the erupting flux rope. There is net plasma flow across the magnetic field null along both the inflow and outflow directions. We compare simulations to SDO/AIA, Hinode/XRT, and STEREO observations of flare loop shapes, current sheet drifting, and rolling motions during prominence eruptions. Simulations of the plasm! oid instability with different upstream magnetic fields show that the reconnection rate remains enhanced even during the asymmetric case. The islands preferentially grow into the weak field upstream region. The islands develop net vorticity because the outflow jets impact them obliquely rather than directly. Asymmetric reconnection in the chromosphere occurs when emerging flux interacts with pre-existing overlying flux. We present initial results on asymmetric reconnection in partially ionized chromospheric plasmas. Finally, we discuss how comparisons to observations are necessary to understand the role of three-dimensional effects.

Murphy, N. A.; Miralles, M. P.; Ranquist, D. A.; Pope, C. L.; Raymond, J. C.; Lukin, V. S.; McKillop, S. C.; Shen, C.; Winter, H. D.; Reeves, K. K.; Lin, J.

2013-12-01

247

Achieving Fast Reconnection in Resistive MHD Models via Turbulent Means  

CERN Multimedia

Astrophysical fluids are generally turbulent and this preexisting turbulence must be taken into account for the models of magnetic reconnection which are attepmted to be applied to astrophysical, solar or heliospheric environments. In addition, reconnection itself induces turbulence which provides an important feedback on the reconnection process. In this paper we discuss both theoretical model and numerical evidence that magnetic reconnection gets fast in the approximation of resistive MHD. We consider the relation between the Lazarian & Vishniac turbulent reconnection theory and Lapenta's numerical experiments testifying of the spontaneous onset of turbulent reconnection in systems which are initially laminar.

Lapenta, Giovanni

2011-01-01

248

Achieving fast reconnection in resistive MHD models via turbulent means  

Directory of Open Access Journals (Sweden)

Full Text Available Astrophysical fluids are generally turbulent and this preexisting turbulence must be taken into account for models of magnetic reconnection in astrophysical, solar or heliospheric environments. In addition, reconnection itself induces turbulence which provides an important feedback on the reconnection process. In this paper we discuss both the theoretical model and numerical evidence that magnetic reconnection becomes fast in the approximation of resistive MHD. We consider the relation between the Lazarian and Vishniac turbulent reconnection theory and Lapenta's numerical experiments testifying of the spontaneous onset of turbulent reconnection in systems which are initially laminar.

G. Lapenta

2012-04-01

249

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Monique Duval

2002-01-01

250

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Monique Duval

2002-01-01

251

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Technical Training; Tel. 74924

2001-01-01

252

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Places are available in the following courses: Introduction to Databases :  3 - 4.7.01 (2 days) The JAVA programming language Level 2 : 4 - 6.7.01 (3 days) Enterprise JavaBeans :  9 - 11.7.01 (3 days) Design Patterns :  10 - 12.7.01 (3 days) C++ for Particle Physicists :  23 - 27.7.01 (6 3-hour lectures) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : http://www.cern.ch/Training/ or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of their receipt.

Technical Training; Tel. 74924

2001-01-01

253

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CERN Multimedia

Places are available in the following courses:   LabView hands-on 13.11.00 4 hours LabView Basics 1 14 - 16.11.00 3 days C++ for Particle Physicists 20 - 24.11.00 6 lectures Develop PL/SQL Program Units 20 - 22.11.00 3 days The JAVA programming Language level 2 27 - 29.11.00.00 3 days If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : http://www.cern.ch/Training/ or fill in an ?application for training? form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of their receipt.

Enseignement Technique; Technical Training; Monique Duval - Tel. 74924

2000-01-01

254

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CERN Multimedia

Places are available in the following courses: Introduction to Perl 5 : 2 - 3.7.01 (2 days) Introduction to Databases :  3 - 4.7.01 (2 days) JAVA programming language Level 2 : 4 - 6.7.01 (3 days) Enterprise JavaBeans :  9 - 11.7.01 (3 days) Design Patterns :  10 - 12.7.01 (3 days) C++ for Particle Physicists :  23 - 27.7.01 (6 3-hour lectures) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : http://www.cern.ch/Training/ or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of their receipt.

Technical Training; Tel. 74924

2001-01-01

255

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CERN Document Server

Places are available in the following courses: The JAVA programming language level 1: 8 - 9.2.01 (2 days) AutoCAD 2D niveau 1 : 12 - 16.2.01 (5 jours) The JAVA programming language level 2: 19 - 21.2.01 (3 days) C++ for Particle Physicists: 5 - 9.3.01 (20 hrs on 5 days) Contract Follow-up : 12.3.01 (3 heures) The JAVA programming language level 2: 12 - 14.3.01 (3 days) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : http://www.cern.ch/Training/ or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of their receipt.

TECHNICAL TRAINING; Tel. 74460

2001-01-01

256

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CERN Document Server

Places are available in the following courses: The Java programming language (Level 1) : 8 - 9.2.01 (2 days) Architecture d'automatisme : 20 - 21.2.01 (2 jours) Programmation TSX Premium 1 (Schneider) : 26.2 - 2.3.01 (5 jours) C++ for Particle Physicists : 5 - 9.3.01 (6*3 hour lectures) The Java programming language (Level 2) : 12 - 14.3.2001 (3 days) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : http://www.cern.ch/Training/ or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of their receipt.

TECHNICAL TRAINING; Tel. 74460

2001-01-01

257

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CERN Multimedia

Places are available in the following courses: December 2002   PCAD Schémas - Débutants :  5 & 6.12.02  (2 jours) PCAD PCB - Débutants :  9 - 11.12.02  (3 jours) FrontPage 2000 - level 1:  9 & 10.12.02  (2 days) Introduction à la CAO Cadence (cours gratuit) :  10 & 11.12.02  (2 jours) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : Technical Training or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of their receipt. Technical Training Monique Duval Tel.74924 monique.duval@cern.ch

Monique Duval

2002-01-01

258

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CERN Multimedia

Places are available in the following courses: November 2002   Hands-on Object-Oriented Design and Programming with C++:  19 - 21.11.02  (3 days)  December 2002   LabVIEW - DSC (English) :  2 - 3.12.02  (2 days) AutoCAD 2002 - niveau 2 :  2 & 3.12.02  (2 jours) FileMaker (Français) :  2 - 5.12.02  (4 jours) PCAD Schémas - Débutants :  5 & 6.12.02  (2 jours) PCAD PCB - Débutants :  9 - 11.12.02  (3 jours) FrontPage 2000 - level 1:  9 & 10.12.02  (2 days) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : Technical Training or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisiona...

Monique Duval

2002-01-01

259

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Places are available in the following courses: November 2002   Introduction to PVSS (free of charge): 11.11.02  (afternoon) EXCEL 2000 - niveau 1 :  12 & 13.11.02  (2 jours) CLEAN-2002: Working in a Cleanroom (English, free of charge):  13.11.2002  (afternoon) AutoCAD 2002 - niveau 1 :  14, 15, 21, 22.11.02  (4 jours) Hands-on Object-Oriented Design and Programming with C++:  19 - 21.11.02  (3 days)  EXCEL 2000 - niveau 2 :  25 & 26.11.02  (2 jours) FrontPage 2000 - niveau 1 :  27 & 28.11.02  (2 jours) December 2002   LabVIEW - DSC (English) :  2 - 3.12.02  (2 days) AutoCAD 2002 - niveau 2 :  2 & 3.12.02  (2 jours) FileMaker (Français) :  2 - 5.12.02  (4 jours) PCAD Schémas - Débutants :  5 & 6.12.02 ...

Monique Duval

2002-01-01

260

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Places are available in the following courses: October 2002   Introduction to the CERN Engineering Data Management System (free of charge):  29.10.2002  (1 day) The CERN EDMS for Advanced users (free of charge):  30.10.2002  (1 day) November 2002   LabView hands-on (bilingue/bilingual): 5.11.02 (matin/morning) LabView DAQ hands-on (bilingue/bilingual):  5.11.02  (après-midi afternoon) Introduction au PC et Windows 2000 au CERN :  6 & 7.11.02  (2 jours) Oracle 8i : Access the Database with Java:  7 & 8.11.02  (2 days) AutoCAD 2002 - niveau 2 :  7 & 8.11.02  (2 jours) Introduction to PVSS (free of charge):  11.11.2002 pm  (1/2 day) Basic PVSS:  12 - 14.11.02  (3 days) EXCEL 2000 - niveau 1 :  12 & 13.11.02  (2 jours) CLEAN-2002: Working in a Cleanroom (English, free ...

Monique Duval

2002-01-01

 
 
 
 
261

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CERN Multimedia

Places are available in the following courses: November 2002   Java Programming Language level 1 :  28 & 29.11.02  (2 days) December 2002   LabVIEW - DSC (English) :  2 - 3.12.02  (2 days) FileMaker (Français) :  2 - 5.12.02  (4 jours) PCAD Schémas - Débutants :  5 & 6.12.02  (2 jours) PCAD PCB - Débutants :  9 - 11.12.02  (3 jours) FrontPage 2000 - level 1:  9 & 10.12.02  (2 days) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : Technical Training or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of their receipt. Technical Training M...

Monique Duval

2002-01-01

262

Self-generated Three Dimensional Turbulence in Magnetic Reconnection Layers Sharply Increases Reconnection Rates  

Science.gov (United States)

Magnetic reconnection is a fundamental plasma process in which magnetic field lines change topology and rapidly convert magnetic energy into thermal energy, which is often directly radiated and thus astrophysically observable. However, the rate at which this process occurs in the classical picture is orders of magnitude too slow to explain solar flares. The recent identification of the plasmoid instability, a super-Alfvenic, high wavenumber instability has fundamentally altered our understanding of reconnection theory by providing a mechanism to greatly speed up reconnection. However, the majority of the work done to date has focused on 2D reconnection layers, assuming symmetry in the plane of the current sheet itself. The plasmoid instability is inherently multi-scale, with a large separation between the global scale of the reconnection layer and the resistive length where the instability grows, making 3D simulations impractical before now. We have begun to use the 3D adaptive mesh refinement code Enzo to resolve the reconnection layer. We show the growth of a secondary instability in the plane of the current sheet that drives a huge increase in the rate of reconnection. Understanding how the saturation of this instability controls the global, 3D structure of reconnection regions is required to predict the observable properties of flares, the mass loading of coronal mass ejections, and the acceleration of charged particles in the corona. This research was partly supported by NSF grant AST10-09802, and used computational resources provided under XSEDE grant TG-AST120045.

Oishi, Jeffrey S.; Mac Low, M.; Collins, D. C.

2014-01-01

263

Coupling between reconnection and Kelvin-Helmholtz instabilities in collisionless plasmas  

Directory of Open Access Journals (Sweden)

Full Text Available In a collisionless plasma, when reconnection instability takes place, strong shear flows may develop. Under appropriate conditions these shear flows become unstable to the Kelvin-Helmholtz instability. Here, we investigate the coupling between these instabilities in the framework of a four-field model. Firstly, we recover the known results in the low ? limit, ? being the ratio between the plasma and the magnetic pressure. We concentrate our attention on the dynamical evolution of the current density and vorticity sheets which evolve coupled together according to a laminar or a turbulent regime. A three-dimensional extension in this limit is also discussed. Secondly, we consider finite values of the ? parameter, allowing for compression of the magnetic and velocity fields along the ignorable direction. We find that the current density and vorticity sheets now evolve separately. The Kelvin-Helmholtz instability involves only the vorticity field, which ends up in a turbulent regime, while the current density maintains a laminar structure.

D. Grasso

2009-04-01

264

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Monique Duval

2002-01-01

265

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CERN Document Server

Places are available in the following courses: Utilisation du simulateur Simplorer : 30.5 - 1.6.01 (3 jours) JAVA programming language level 1: 11-12.6.01 (2 days) LabView hands-on F ou E : 11.6.01 (1/2 journée) Comprehensive VHDL for EPLD/FPGA Design : 11 - 15.6.01 (5 days) Introduction au Langage C : 13 - 15.6.01 (3 jours) LabView Base 1 : 12 - 14.6.01 (3 jours) Habilitation électrique : superviseurs : 2 sessions d'une demi-journée les 12 et 19.6.01 Migration de LabVIEW 5 vers LabVIEW 6i Migration from LabVIEW 5 to LabVIEW 6I :  15.6.01 (1/2 journée/half-day) Introduction to Perl 5 : 2 - 3.7.01 (2 days) JAVA programming language level 2 : 4 - 6.7.01 (3 days) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : http://www.cern.ch/Training/ or fill in an 'application for training' form available from ...

Technical Training; Tel. 74924

2001-01-01

266

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CERN Multimedia

Places are available in the following courses: PROFIBUS : 25 - 26.9.01 (2 jours) PROFIBUS : 27 - 28.9.01 (2 days) Automates et réseaux de terrain : 3 - 4.10.2001 (2 jours) PCAD Schémas - débutants : 4 - 5.10.01 (2 jours) PCAD PCB - débutants : 8 - 10.10.01 (3 jours) Programmation TSX Premium 1 : 15 - 19.10.01 (5 jours) Programmation TSX Premium 1 : 22 - 26.10.01 (5 jours) Programming TSX Premium 2: 19 - 23.11.01 (5 days) Programmation TSX Premium 2 : 26 - 30.11.01 (5 jours) Autocad Migration support courses: a detailed calendar will be published shortly for this series of sessions which will start on 15.10.2001. Registration is already open AutoCAD : Mise à jour AutoCAD r-14 vers 2002 (2 jours) AutoCAD Mechanical PowerPack 6 basé sur AutoCAD 2002 (5 jours) The following LabView courses will be given in either English or French according to demand LabVIEW - Base 1 / LabVIEW - Basics 1 : 10 - 12.9.01 (3 jours / 3 days)...

Technical training; Tel. 74924

2001-01-01

267

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Places are available in the following courses: PVSS Basics : 20 - 24.8.01 (5 days) PROFIBUS : 25 - 26.9.01 (2 jours) PROFIBUS : 27 - 28.9.01 (2 days) PCAD Schémas - débutants : 4 - 5.10.01 (2 jours) PCAD PCB - débutants : 8 - 10.10.01 (3 jours) Programming TSX Premium 1: 15 - 19.10.01 (5 days) Programmation TSX Premium 1 : 22 - 26.10.01 (5 jours) Programming TSX Premium 2: 19 - 23.11.01 (5 days) Programmation TSX Premium 2 : 26 - 30.11.01 (5 jours) The following LabView courses will be given in either English or French according to demand LabVIEW - Base 1 / LabVIEW - Basics 1 : 10 - 12.9.01 (3 jours / 3 days) LabVIEW - DAQ / LabVIEW - DAQ : 13 - 14.9.01 (2 jours / 2 days) LabVIEW - Base 1 / LabVIEW - Basics 1 : 15 - 17.10.01 (3 jours / 3 days) LabVIEW - Base 2 / LabVIEW - Basics 2 : 18 - 19.10.01 (2 jours / 2 days) LabVIEW - Base 1 / LabVIEW - Basics 1 : 12 - 14.11.01 (3 jours / 3 days) LabVIEW - DAQ / LabVIEW - DAQ : 15 - 16.11.01 (2 jours / 2...

Technical Training; Tel. 74924

2001-01-01

268

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CERN Document Server

Places are available in the following courses: Introduction à Windows 2000 au CERN : 2 sessions de _ journée les 24 et 25.9.01 PROFIBUS : 25 - 26.9.01 (2 jours) PROFIBUS : 27 - 28.9.01 (2 days) PowerPoint 2000 : 1 et 2.10.01 (2 jours) EXCEL 2000 - niveau 1 : 3 et 4.10.01 (2 jours) Automates et réseaux de terrain : 3 - 4.10.2001 (2 jours) PCAD Schémas - débutants : 4 - 5.10.01 (2 jours) Introduction à Outlook : 5.10.01 (1 journée) Frontpage 2000 - niveau 1 : 8 et 9.10.01 (2 jours) PCAD PCB - débutants : 8 - 10.10.01 (3 jours) C++ for Particle Physicists : 8 - 12.10.01 (6 3-hour lectures) MS-Project 2000 - niveau 1 : 15 - 18.10.01 (4 demi-journées) LabView Basics 1 :  15 - 17.10.01  (3 days) Programmation TSX Premium 1 : 15 - 19.10.01 (5 jours) WORD 2000 : importer et manipuler des images : 19.10.01 (1 journée) Programmation TSX Premium 1 : 22 - 26.10.01...

Technical Training; Tel. 74924

2001-01-01

269

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Places are available in the following courses: Cadence Board Design tools : Upgrading to release 14 :  3 1-day sessions on 9, 10 & 11.10.01 MS-Project 2000 - niveau 1 : 15 - 18.10.01 (4 demi-journées) LabView Base 2 : 18 & 19.10.01 (2 jours) WORD 2000 : importer et manipuler des images : 19.10.01 (1 journée) Contract Follow-up (F) :  30.10.01 (1/2 journée) The CERN Engineering Data Management System for Electronics Design :  30.10.01 (1 day) UNIX pour non-programmeurs : 5 - 7.11.01 (3 jours) The Java programming language Level 1: 8 - 9.11.01 (2 days) LabView Base 1 : 12 - 14.11.01 (3 jours) Introduction to PERL 5 :  15 - 16.11.01  (2 days) Introduction to XML :  19 - 20.11.01 (2 days) Programming TSX Premium 1 :  19 - 23.11.01  (5 days) Introduction to C Programming :  21- 23.11.01 (3 days) The Java programming language Level 2:  26 - 28.11.01 (...

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2001-01-01

270

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Places are available in the following courses: Contract Follow-up (F) : 30.10.01 (1/2 journée) The CERN Engineering Data Management System for Electronics Design :  30.10.01 (1 day) UNIX pour non-programmeurs : 5 - 7.11.01 (3 jours) Nouveautés d'EXCEL : 5.11.01 (1/2 journée) Introduction a Windows 2000 au CERN : 6.11.01 (1/2 journée) The Java programming language Level 1: 8 - 9.11.01 (2 days) LabView Base 1 : 12 - 14.11.01 (3 jours) Automates et réseaux de terrain : 13 & 14.11.01 (2 jours) Introduction to PERL 5 :  15 - 16.11.01  (2 days) Introduction to XML :  19 - 20.11.01 (2 days) Programming TSX Premium 1 :  19 - 23.11.01  (5 days) Introduction to C Programming :  21- 23.11.01 (3 days) The Java programming language Level 2:  26 - 28.11.01 (3 days) Programmation TSX Premium 2 : 26 - 30.11.01 (5 jours) Autocad Migration support courses: a detail...

Technical Training; Tel. 74924

2001-01-01

271

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Places are available in the following courses: PVSS Basics : 20 - 24.8.01 (5 days) PROFIBUS : 25 - 26.9.01 (2 jours) PROFIBUS : 27 - 28.9.01 (2 days) PCAD Schémas - débutants : 4 - 5.10.01 (2 jours) PCAD PCB - débutants : 8 - 10.10.01 (3 jours) Programming TSX Premium 1: 15 - 19.10.01 (5 days) Programmation TSX Premium 1 : 22 - 26.10.01 (5 jours) Programming TSX Premium 2: 19 - 23.11.01 (5 days) Programmation TSX Premium 2 : 26 - 30.11.01 (5 jours) The following LabView courses will be given in either English or French according to demand LabVIEW - Base 1 / LabVIEW - Basics 1 : 10 - 12.9.01 (3 jours / 3 days) LabVIEW - DAQ / LabVIEW - DAQ : 13 - 14.9.01 (2 jours / 2 days) LabVIEW - Base 1 / LabVIEW - Basics 1 : 15 - 17.10.01 (3 jours / 3 days) LabVIEW - Base 2 / LabVIEW - Basics 2 : 18 - 19.10.01 (2 jours / 2 days) LabVIEW - Base 1 / LabVIEW - Basics 1 : 12 - 14.11.01 (3 jours / 3 days) LabVIEW - DAQ / LabVIEW - DAQ : 15 - 16.11.01 (2 jours / 2...

Technical training; Tel. 74924

2001-01-01

272

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CERN Multimedia

Places are available in the following courses: Introduction à Windows 2000 au CERN : 2 sessions de _ journée les 24 et 25.9.01 PROFIBUS : 25 - 26.9.01 (2 jours) PROFIBUS : 27 - 28.9.01 (2 days) EXCEL 2000 - niveau 1 : 3 et 4.10.01 (2 jours) Automates et réseaux de terrain : 3 - 4.10.2001 (2 jours) Introduction à Outlook : 5.10.01 (1 journée) Frontpage 2000 - niveau 1 : 8 et 9.10.01 (2 jours) C++ for Particle Physicists : 8 - 12.10.01 (6 lectures) MS-Project 2000 - niveau 1 : 15 - 18.10.01 (4 demi-journées) Programmation TSX Premium 1 : 15 - 19.10.01 (5 jours) WORD 2000 : importer et manipuler des images : 19.10.01 (1 journée) Programmation TSX Premium 1 : 22 - 26.10.01 (5 jours) UNIX pour non-programmeurs : 5 - 7.11.01 (3 jours) The Java programming language Level 1: 8 - 9.11.01 (2 days) Introduction to PERL 5 :  15 - 16.11.01  (2 days) Introduction to XML :  19 - 20.11.01 (2...

Technical Training; Tel. 74924

2001-01-01

273

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CERN Multimedia

Places are available in the following courses: EXCEL 2000 - niveau 1 : 3 et 4.10.01 (2 jours) Automates et réseaux de terrain : 3 - 4.10.2001 (2 jours) Introduction à Outlook : 5.10.01 (1 journée) C++ for Particle Physicists : 8 - 12.10.01 (6 lectures) Cadence Board Design tools : Upgrading to release 14 : 3 1-day sessions on 9, 10 & 11.10.01 MS-Project 2000 - niveau 1 : 15 - 18.10.01 (4 demi-journées) LabView Base 2 : 18 & 19.10.01 (2 jours) WORD 2000 : importer et manipuler des images : 19.10.01 (1 journée) The CERN Engineering Data Management System for Electronics Design :  30.10.01 (1 day) UNIX pour non-programmeurs : 5 - 7.11.01 (3 jours) The Java programming language Level 1: 8 - 9.11.01 (2 days) Introduction to PERL 5 :  15 - 16.11.01  (2 days) Introduction to XML :  19 - 20.11.01 (2 days) Programming TSX Premium 1 :  19 - 23.11.01  (5 days) Introd...

Technical Training; Tel. 74924

2001-01-01

274

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CERN Document Server

Places are available in the following courses: MS-Project 2000 - niveau 1 : 15 - 18.10.01 (4 demi-journées) LabView Base 2 : 18 & 19.10.01 (2 jours) WORD 2000 : importer et manipuler des images : 19.10.01 (1 journée) Contract Follow-up (F) : 30.10.01 (1/2 journée) The CERN Engineering Data Management System for Electronics Design :  30.10.01 (1 day) UNIX pour non-programmeurs : 5 - 7.11.01 (3 jours) The Java programming language Level 1: 8 - 9.11.01 (2 days) LabView Base 1 : 12 - 14.11.01 (3 jours) Automates et réseaux de terrain : 13 & 14.11.01 (2 jours) Introduction to PERL 5 :  15 - 16.11.01  (2 days) Introduction to XML :  19 - 20.11.01 (2 days) Programming TSX Premium 1 :  19 - 23.11.01  (5 days) Introduction to C Programming :  21- 23.11.01 (3 days) The Java programming language Level 2:  26 - 28.11.01 (3 days) Programmation TSX Premium 2 : 26 ...

Technical Training; Tel. 74924

2001-01-01

275

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CERN Multimedia

Places are available in the following courses: LabVIEW Basics 2: 13 & 14.5.02 (2 days) WorldFIP - Généralités : 14.5.2002 (1/2 journée) WorldFIP - Développer avec MicroFIP HANDLER : 14.5 - après-midi, 15.5.02 - matin (1 jour) WorldFIP - FullFIP FDM : FIP Device Manager (F) : 15.5 - après-midi, 16.5.02 - matin (1 jour) LabVIEW DAQ (F) : 15 & 16.5.02 (2 jours) EXCEL 2000 - niveau 2 : 22 & 23.5.02 (2 jours) The CERN Engineering Data Management System for Advanced users:  30.5.02  (1 day) LabVIEW Basics 1:  3 - 5.6.02  (3 days) AutoCAD 2002 - condensé : 4 - 6.6.02 (3 jours) LabVIEW DAQ (E):  6 & 7.6.02  (2 days) AutoCAD 2002 - Level 1:  10 - 12 and 24 - 26.6.02  (6 days) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the c...

Monique Duval

2002-01-01

276

PLACES AVAILABLE  

CERN Document Server

Places are available in the following courses: Introduction to the CERN Engineering Data Management System:  7.5.02  (1 day) LabVIEW Basics 2: 13 & 14.5.02 (2 days) AutoCAD Mechanical 6 PowerPack (F) : 13-14, 17, 21, 27-28.5.02 (6 jours) WorldFIP - Généralités : 14.5.2002 (1/2 journée) WorldFIP - Développer avec MicroFIP HANDLER : 14.5 - après-midi, 15.5.02 - matin (1 jour) WorldFIP - FullFIP FDM : FIP Device Manager (F) : 15.5 - après-midi, 16.5.02 - matin (1 jour) LabVIEW DAQ (F) : 15 & 16.5.02 (2 jours) EXCEL 2000 - niveau 2 : 22 & 23.5.02 (2 jours) The CERN Engineering Data Management System for Advanced users:  30.5.02  (1 day) LabVIEW Basics 1:  3 - 5.6.02  (3 days) AutoCAD 2002 - condensé : 4 - 6.6.02 (3 jours) LabVIEW DAQ (E):  6 & 7.6.02  (2 days) AutoCAD 2002 - Level 1:  10 - ...

Monique Duval

2002-01-01

277

PLACES AVAILABLE  

CERN Document Server

Places are available in the following courses: Nouveautés d'EXCEL : 5.11.01 (1/2 journée) Introduction a Windows 2000 au CERN : 6.11.01 (1/2 journée) UNIX pour non-programmeurs : 5 - 7.11.01 (3 jours) Design Patterns :  7 - 8.11.01 (2 days) The Java programming language Level 1: 8 - 9.11.01 (2 days) Automates et réseaux de terrain : 13 & 14.11.01 (3 jours) Introduction à Windows 2000 au CERN : 12 - 14.11.01 (1/2 journée) Introduction to Windows 2000 at CERN :  14.11.01  (half-day) Introduction to PERL 5 :  15 - 16.11.01  (2 days) Introduction to C Programming :  21- 23.11.01 (3 days) Programmation TSX Premium 2 : 26 - 30.11.01 (5 jours) Contract Follow-up (F) : 26.11.01 (1/2 journée) Object-Oriented Analysis and Design :  27 - 30.11.2001  (4 days) Hands-on Object-Oriented Design and Programming with C++ :  11 - 13.12.2...

Technical Training; Tel. 74924

2001-01-01

278

Places available**  

CERN Multimedia

Places are available in the following courses : FrontPage 2000 - niveau 1: 20 & 21.5.03 (2 jours) PIPES-2003 : Pratique du sertissage de tubes métalliques et multicouches: 21.5.03 (1 jour) Introduction à la CAO Cadence: de la saisie de schéma Concept-HDL au PCB : 20 & 22.5.03 (2 jours) AutoCAD Mechanical 6 PowerPack (E): 5, 6, 12, 13, 26, 27.6.03 (6 days) EXCEL 2000 - niveau 1: 10 & 11.6.03 (2 jours) Conception de PCB rapides dans le flot Cadence: 11.6.03 (matin) EXCEL 2000 - level 1: 12 & 13.6.03 (2 days) Introduction to PVSS: 16.6.03 (half-day, pm) Basic PVSS: 17 - 19.6.03 (3 days) Réalisation de PCB rapides dans le flot Cadence: 17.6.03 (matin) LabView DSC (language to be defined): 19 & 20.6.03 PVSS - JCOP Framework Tutorial: 20.6.03 (1 day) EXCEL 2000 - niveau 2: 24 & 25.6.03 (2 jours) Siemens SIMATIC Training: Introduction to STEP7: 3 & 4.6.03 (2 days) STEP7 Programming: 16 - 20.6.03 (5 days) Simatic Net Network: 26 & 27.6.03 (2 days) These courses will be given...

2003-01-01

279

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Introduction à la CAO CADENCE : 20 & 21.2.02 (2 jours) LabView Basics 1 :  4 - 6.3.02  (3 days) Introduction au VHDL et utilisation du simulateur de CADENCE : 6 & 7.3.02 (2 jours) CLEAN-2002 : Working in a Clean Room :  7.3.2002  (1 day) LabView Base 2 : 11 & 12.3.02 (2 jours) C++ for Particle Physicists :  11 - 15.3.2002  (6 * 3 hour lectures) LabView Advanced :  13 - 15.3.02 (3 days) Cours sur la migration AutoCAD :   AutoCAD : Mise à jour AutoCAD r-14 vers 2002 (2 jours) AutoCAD Mechanical PowerPack 6 basé sur AutoCAD 2002 (5 jours) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : Technical Training or fill in an 'application for training' form available from your Divisiona...

Monique Duval

2002-01-01

280

PLACES AVAILABLE  

CERN Document Server

Places are available in the following courses: ELEC-2002 : Spring Term :  9, 11, 16, 18, 23, 25, 30.4.02 (7 * 2.5 hours) Object-Oriented Analysis & Design: 16 - 19.4.02  (4 days) The CERN Engineering Data Management System for Advanced users:  16.4.02  (1 day) Migration from AutoCAD 14 towards AutoCAD Mechanical6 PowerPack:  17 - 19.4 and 2 &3.5.02  (5 days) AutoCAD - niveau 1 : 22, 23, 29, 30.4 et 6, 7.5.02 (6 jours) LabVIEW base 1 : 22 - 24.4.02 (3 jours) CLEAN 2002 : working in a cleanroom:  24.4.02  (half-day, pm) LabVIEW DSC (F) 25 & 26.4.02 (2 jours) AutoCAD : Mise à jour AutoCAD r-14 vers 2002 : 25 & 26.4.02 (2 jours) LabVIEW Basics 2 : 13 & 14.5.02 (2 days) EXCEL 2000 - niveau 1 : 15 & 16.5.02 (2 jours) LabVIEW DAQ (F) : 15 & 16.5.02 (2 jours) EXCEL 2000 - niveau 2 : 22 & 23.5.02 (2 jours) LabVIEW Basics 1:  3 - 5.6.02&a...

Monique Duval

2002-01-01

 
 
 
 
281

PLACES AVAILABLE  

CERN Document Server

Places are available in the following courses: LabView Basics 1 :  4 - 6.3.02  (3 days) CLEAN-2002 : Working in a Clean Room :  7.3.2002  (half day) LabView Base 2 : 11 & 12.3.02 (2 jours) C++ for Particle Physicists :  11 - 15.3.2002  (6 * 3 hour lectures) Programming the Web for Control Applications : 11, 12, 18, 19.3.2002  (4 * 2 hour lectures) Habilitation électrique : recyclage HT/BT (Français) : 13 - 14.3.2002 (2 * 2 heures) LabView Advanced :  13 - 15.3.02 (3 days) Introduction to the CERN Engineering Data Management System (EDMS) :  20.3.2002  (1 day) The CERN (EDMS) for Advanced Users :  21.3.2002  (1 day) LabVIEW DSC : 25 - 26.4.2002 (2 jours) LabVIEW DAQ : 15 - 16.5.2002 (2 jours) Cours sur la migration AutoCAD :   AutoCAD : Mise à jour AutoCAD r-14 vers 2002 (2 jours) AutoCAD Mechanical PowerPack 6 basé ...

Monique DUVAL

2002-01-01

282

PLACES AVAILABLE  

CERN Document Server

Places are available in the following courses: LabView Hands-on (bilingue/bilingual - gratuit/free of charge) : 13.9.02 (a.m.) LabView DAQ Hands-on (bilingue/bilingual - gratuit/free of charge) : 13.9.02 (p.m.) AutoCAD 2002 - niveau 1 : 19, 20, 26, 27.9.02 (4 jours) LabView Base 1 : 23 - 25.9.02 (3 jours) LabView DAQ (E) : 26 - 27.9.02 (2 days) AutoCAD Mechanical 6 PowerPack (F) : 30.9, 1, 2, 9, 10, 11.10.02 (6 jours) CLEAN-2002 : Working in a Cleanroom (free of charge) : 10.10.02 (half-day, p.m.) AutoCAD 2002 - niveau 2 : 14 - 15.10.02 (2 jours) AutoCAD 2002 - Level 1 : 17, 18, 24, 25.10.02 (4 days) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : Technical Training or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisional Training Of...

Monique Duval

2002-01-01

283

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: LabVIEW base 1 : 22 - 24.4.02 (3 jours) CLEAN 2002 : working in a cleanroom:  24.4.02  (half-day, pm) LabVIEW DSC (F) 25 & 26.4.02 (2 jours) AutoCAD : Mise à jour AutoCAD r-14 vers 2002 : 25 & 26.4.02 (2 jours) Cotations selon les normes GPS de l'ISO : 29 - 30.4.02 (2 jours) Introduction to the CERN Engineering Data Management System:  7.5.02  (1 day) LabVIEW Basics 2: 13 & 14.5.02 (2 days) AutoCAD Mechanical 6 PowerPack (F) : 13-14, 17, 21, 27-28.5.02 (6 jours) WorldFIP - Généralités : 14.5.2002 (1/2 journée) WorldFIP - Développer avec MicroFIP HANDLER : 14.5 - après-midi, 15.5.02 - matin (1 jour) WorldFIP - FullFIP FDM : FIP Device Manager (F) : 15.5 - après-midi, 16.5.02 - matin (1 jour) LabVIEW DAQ (F) : 15 & 16.5.02 (2 jours) EXCEL 2000 - niveau 2 : 22 & 23.5.02 (2 jours)...

Monique Duval

2002-01-01

284

Places available**  

CERN Multimedia

Places are available in the following courses: PIPES-2003 - Pratique du sertissage de tubes métalliques et multicouches :26.8.03(stage pratique) The CERN EDMS for Engineers (free of charge) : 27.8.03 (1 day) CLEAN-2002 : Travailler en salle blanche (séminaire gratuit) : 4.9.03(une demi-journée) The CERN EDMS for Local Administrators (free of charge) : 24 & 25.9.03 (2 days) HeREF-2003 : Techniques de la réfrigération Hélium (cours en français avec support en anglais) : 6 - 10.10.2003 (7 demi-journées) The Java Programming Language Level 1 : 6 - 7.10.2003 (2 days) Java 2 Enterprise Edition - Part 2 : Enterprise JavaBeans : 8 - 10.10.2003 (3 days) FileMaker - niveau 1 : 9 & 10.10.03 (2 jours) EXCEL 2000 - niveau 1 : 20 & 22.10.03 (2 jours) AutoCAD 2002 - niveau 1 : 20, 21, 27, 28.10.03 (4 jours) CLEAN-2002 : Working in a Cleanroom (free of charge) : 23.10.03 (half day) AutoCAD Mechanical 6 PowerPack (E) : 23, 24, 30, 31.10 & 12, 13.11.03 (6 days) AutoCAD 2002 - niveau 2...

2003-01-01

285

Places available**  

CERN Multimedia

Places are available in the following courses: The CERN EDMS for Local Administrators : 24 & 25.9.03 (2 days, free of charge) HeREF-2003 : Techniques de la réfrigération Hélium cours en français avec support en anglais) : 6 - 10.10.2003 (7 demi-journées) The Java Programming Language Level 1 : 6 - 7.10.2003 (2 days) Java 2 Enterprise Edition - Part 2 : Enterprise JavaBeans : 8 - 10.10.2003 (3 days) FileMaker - niveau 1 : 9 & 10.10.03 (2 jours) EXCEL 2000 - niveau 1 : 20 & 22.10.03 (2 jours) AutoCAD 2002 - niveau 1 : 20, 21, 27, 28.10.03 (4 jours) CLEAN-2002 : Working in a Cleanroom : 23.10.03 (half day, free of charge) AutoCAD 2002 - Level 1 : 3, 4, 12, 13.11.03 (4 days) AutoCAD 2002 - niveau 2 : 10 & 11.11.03 (2 jours) ACCESS 2000 - niveau 1 : 13 & 14.11.03 (2 jours) AutoCAD Mechanical 6 PowerPack (E) : 17, 18, 24, 25.11 & 1, 2.12.03 (6 days) FrontPage 2000 - niveau 1 : 20 & 21.11.03 (2 jours) MAGNE-03 : Magnétisme pour l'électrotechnique : 25 - 27.11.03 (3 jours) ...

2003-01-01

286

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Introduction to C Programming :  21- 23.11.01 (3 days) Programmation TSX Premium 2 : 26 - 30.11.01 (5 jours) Contract Follow-up (F) : 26.11.01 (1/2 journée) Habilitation électrique : électriciens network : 27 - 29.11.2001 (3 jours) Object-Oriented Analysis and Design :  27 - 30.11.2001  (4 days) Introduction to the CERN Engineering Data Management System :  30.11.2001 (1 day) Electromagnetic Compatibility (EMC): Introduction (bilingual) :  3.12.01 (half-day) Introduction to the CERN Engineering Data Management System : 07.12.2001 (1 day) LabVIEW - Basics 1 :  10 - 12.12.01 (3 days) LabVIEW - Basics 2 :  13 - 14.12.01 (2 days) EXCEL 2000 - niveau 2 : 15 - 16.1.02 (2 jours) C++ Programming Level 2 - Traps and Pitfalls :  15 - 18.1.2002  (4 days) Nouveautés de WORD 2000 : 18.1.02 (1/2 journée) FileMaker P...

Technical Training; Tel. 74924

2001-01-01

287

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Electromagnetic Compatibility (EMC): Introduction (bilingual) :  3.12.01 (half-day) Habilitation électrique : superviseurs : 5.12.01 (1/2 journée) Introduction to the CERN Engineering Data Management System : 07.12.2001 (1 day) LabVIEW - Basics 1 :  10 - 12.12.01 (3 days) Introduction au PC et Windows 2000 : 12 & 14.12.01 (2 jours) LabVIEW - Basics 2 :  13 - 14.12.01 (2 days) Habilitation électrique : superviseurs : 17.12.2001 (1/2 journée) EXCEL 2000 - niveau 2 : 15 - 16.1.02 (2 jours) C++ Programming Level 2 - Traps and Pitfalls :  15 - 18.1.2002  (4 days) Nouveautés de WORD 2000 : 18.1.02 (1/2 journée) LabView hands-on : 21.01.02 (1/2 journée) LabView DAQ hands-on : 21.01.02 (1/2 journée) FileMaker Pro : 22 - 25.1.02 (4 jours) Introduction au PC et à Windows 2000 au CERN : 29 - 30.1....

Technical Traininf; Tel. 74924

2001-01-01

288

Places available**  

CERN Document Server

Places are available in the following courses: CLEAN-2002 : Travailler en salle blanche (séminaire gratuit) : 4.9.03 (une demi-journée) The CERN EDMS for Local Administrators (free of charge) : 24 & 25.9.03 (2 days) HeREF-2003 : Techniques de la réfrigération Hélium (cours en français avec support en anglais) : 6 - 10.10.2003 (7 demi-journées) The Java Programming Language Level 1 : 6 - 7.10.2003 (2 days) Java 2 Enterprise Edition - Part 2 : Enterprise JavaBeans : 8 - 10.10.2003 (3 days) FileMaker - niveau 1 : 9 & 10.10.03 (2 jours) EXCEL 2000 - niveau 1 : 20 & 22.10.03 (2 jours) AutoCAD 2002 - niveau 1 : 20, 21, 27, 28.10.03 (4 jours) CLEAN-2002 : Working in a Cleanroom (free of charge) : 23.10.03 (half day) AutoCAD Mechanical 6 PowerPack (E) : 23, 24, 30, 31.10 & 12, 13.11.03 (6 days) AutoCAD 2002 - niveau 2 : 10 & 11.11.03 (2 jours)...

2003-01-01

289

Places available**  

CERN Document Server

Places are available in the following courses : FrontPage 2000 - niveau 1 : 20 & 21.5.03 (2 jours) PIPES-2003 : Pratique du sertissage de tubes métalliques et multicouches : 21.5.03 (1 jour) Introduction à la CAO Cadence : de la saisie de schéma Concept-HDL au PCB : 20 & 22.5.03 (2 jours) AutoCAD 2002 - niveau 2 : 3 & 4.6.03 (2 jours) AutoCAD Mechanical 6 PowerPack (F) : 5, 6, 12, 13, 26, 27.6.03 (6 jours) EXCEL 2000 - niveau 1 : 10 & 11.6.03 (2 jours) Conception de PCB rapides dans le flot Cadence : 11.6.03 (matin) EXCEL 2000 - level 1 : 12 & 13.6.03 (2 days) PowerPoint 2000 (F) : 17 & 18.6.03 (2 jours) Réalisation de PCB rapides dans le flot Cadence : 17.6.03 (matin) FrontPage 2000 - niveau 2 : 19 & 20.6.03 (2 jours) LabView DSC (langue à décider/language to be defined) : 19 & 20.6.03 EXCEL 2000 - niveau 2 : 24 & 25.6.03 (2 jours) Siemens SIMATIC Training: Introduction to STEP7 : 3 & 4.6.03 (2 days) STEP7 Programming : 16 - 20.6.03 (5 days) Simatic...

2003-01-01

290

Places available**  

CERN Multimedia

Places are available in the following courses : EXCEL 2000 - niveau 1 : 10 & 11.6.03 (2 jours) Conception de PCB rapides dans le flot Cadence : 11.6.03 (matin) EXCEL 2000 - level 1 : 12 & 13.6.03 (2 days) Introduction to PVSS : 16.6.03 (p.m.) Basic PVSS : 17 - 19.6.03 (3 days) Réalisation de PCB rapides dans le flot Cadence : 17.6.03 (matin) PVSS - JCOP Framework Tutorial : 20.6.03 (1 day) EXCEL 2000 - niveau 2 : 24 & 25.6.03 (2 jours) Siemens SIMATIC Training : Introduction to STEP7 : 3 & 4.6.03 (2 jours/2 days) STEP7 Programming : 16 - 20.6.03 (5 jours/5 days) Simatic Net Network : 26 & 27.6.03 (2 jours/2 days) These courses will be given in French or English following the requests. Programmation automate Schneider : Programmation automate Schneider TSX Premium - 1er niveau : 10 - 13.6.03 (4 jours) - audience : toute personne qui veux maitriser la msie en uvre et la programmation d'un automate TSX Premium - objectifs : maitriser la mise en uvre et la programmation d'un autom...

2003-01-01

291

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Introduction à PowerPoint : 26.2.01 (1 journée) Programmation TSX Premium 1 : 26.2 - 2.3.01 (5 jours) Premiers pas avec votre PC : 27.2 - 2.3.01 (4 matins) C++ for Particle Physicists :  5 - 9.3.01 (6*3 hour lectures) The CERN Engineering Data Management System for Electronic Design : 6.3.01 (1 day) The CERN Engineering Data Management System for Electronic Design : 7.3.01 (1 day) EXCEL : 6, 7 et 13, 14.3.01 (4 jours) The JAVA programming language level 2 : 12 - 14.3.01 (3 days) Nouveautés de FileMaker : 20 - 23.03.01 (4 matins) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : http://www.cern.ch/Training/ or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be acc...

Technical Training; Tel. 74460

2001-01-01

292

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: The JAVA programming language level 1 : 22 - 23.1.01 (2 days) Introduction to Databases : 23 - 24.1.01 (2 days) EXCEL : 24 - 25.1.01  et 1 - 2.2.01 (4 jours) Advanced and Modern Databases : 25 - 26.01.01 (2 days) UNIX pour non-programmeurs : 31.1 - 2.2.01 (3 jours) JAVA for non-programmers : 5 - 7.2.01 (3 days) Publier sur le Web :  6 - 8.2.01 (3 demi-journées) Contract Follow-up : 12.2.01 (3 heures) Introduction to Oracle SQL and PL/SQL : 12 - 16.2.01 (5 days) The JAVA programming language level 2 : 19 - 21.2.01 (3 days) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : http://www.cern.ch/Training/ or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order...

Technical Training; Tel. 74460

2001-01-01

293

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Introduction to Databases : 23 - 24.1.01 (2 days) Advanced and Modern Databases : 25 - 26.01.01 (2 days) UNIX pour non-programmeurs : 31.1 - 2.2.01 (3 jours) JAVA for non-programmers : 5 - 7.2.01 (3 days) Contract Follow-up : 12.2.01 (3 heures) Introduction to Oracle SQL and PL/SQL : 12 - 16.2.01 (5 days) AutoCAD 2D niveau I : 12 - 16.2.02 (5 jours) The JAVA programming language level 2 : 19 - 21.2.2001 (3 days) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : http://www.cern.ch/Training/ or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of their receipt.

TECHNICAL TRAINING; Tel. 74460

2001-01-01

294

PLACES AVAILABLE  

CERN Document Server

Places are available in the following courses: MS-Project 1er niveau : 20 - 23.2.01 (4 matins) Architecture d'automatisme : 20 - 21.2.01 (2 jours) Introduction à PowerPoint : 26.2.01 (1 journée) Programmation TSX Premium 1 (Schneider) : 26.2 - 2.3.01 (5 jours) Premiers pas avec votre PC : 27.2 - 2.3.01 (4 matins) C++ for Particle Physicists : 5 - 9.3.01 (6*3 hour lectures) EXCEL : 6, 7 et 13, 14.3.01 (4 jours) The JAVA programming language level 2 :  12 - 14.3.01 (3 days) Nouveautés de FileMaker :  20 - 23.03.01 (4 matins) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : http://www.cern.ch/Training/ or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of their receipt.

TECHNICAL TRAINING; Tel. 74460

2001-01-01

295

PLACES AVAILABLES  

CERN Multimedia

Places are available in the following courses:   C++ for Particle Physicists 20 - 24.11.00 6 lectures CANbus 20.11.00 1 journée CANopen 21 et 22.11.00 2 jours Sécutiré dans les installations cryogéniques 21 et 22.11.00 2 demi-journées The JAVA programming language level 2 27 ­ 29.11.00 3 days Contract Follow-up 27.11.00 3 heures 1/2 Cryogénie (introduction) 4 ­ 8.12.00 ANSYS Introduction : langue a décider suivant majorité 5 ­ 7.12.00 3 jours EXCEL 7, 8, 13 et 14.12.00 4 jours Contract Follow-up 15.12.00 3 heures 1/2 If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : http://www.cern.ch/Training/ or fill in an ?application for training? form available from your Divisional Secretariat or from your DTO (Divisional Training Officer)....

Technical Training; Tel. 74924

2000-01-01

296

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: LabView hands-on (bilingue/bilingual): 5.11.02 (matin/morning) LabView DAQ hands-on (bilingue/bilingual):  5.11.02  (après-midi afternoon) Introduction au PC et Windows 2000 au CERN:  6 & 7.11.02  (2 jours) Oracle 8i : Access the Database with Java:  7 & 8.11.02  (2 days) AutoCAD 2002 - niveau 2:  7 & 8.11.02  (2 jours) Introduction to PVSS (free of charge):  11.11.2002 pm  (1/2 day) Basic PVSS:  12 - 14.11.02  (3 days) EXCEL 2000 - niveau 1:  12 & 13.11.02  (2 jours) CLEAN-2002: Working in a Cleanroom (English, free of charge):  13.11.2002  (afternoon) LabView Base 1 :  13 - 15.11.02  (3 jours) AutoCAD 2002 - Level 1:  14, 15, 21, 22.11.2002  (4 days) LabVIEW - Advanced:  18 - 20.11.02  (3 days) Auto...

Monique Duval

2002-01-01

297

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Introduction à DesignSpace :  16.10.02  (1 journée) AutoCAD Mechanical 6 PowerPack (F) :  21, 22, 23.10 et 4, 5, 6.11.02  (6 jours) Introduction à ANSYS 21 - 25.10.02  (5 jours/days) HREF-2002: Helium Refrigeration Techniques (English-French, bilingual) :  21 - 25.10.2002  (7 half days) LabVIEW Basics 1 (English):  21 - 23.10.02  (3 days) LabVIEW Basics 2 (English):  24 & 25.10.02  (2 days) Oracle 8i : Access the Database with Java:  7 & 8.11.02  (2 days) AutoCAD 2002 - niveau 2 :  7 & 8.11.02  (2 jours) AutoCAD 2002 - Level 1:  14, 15, 21, 22.11.02  (4 days) LabVIEW - Advanced (English) :  18 - 20.11.2002  (3 days) AutoCAD 2002 - niveau 1 :  19, 20, 25, 26.11.02 (4 jours) Oracle iDS Designer: First Class:&...

Monique Duval

2002-01-01

298

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Introduction to Oracle 8i : SQL and PL/SQL:  7 - 11.10.02  (5 days) CLEAN-2002 : Working in a Cleanroom (free of charge):  10.10.02  (half-day, p.m.) LabView Hands-on (bilingue/bilingual) : 10.10.02 (matin/morning) LabView DAQ Hands-on (bilingue/bilingual)  10.10.02 (après-midi /afternoon) Introduction à DesignSpace :  16.10.02  (1 journée) Introduction to DesignSpace:  17.10.02  (1 day) AutoCAD Mechanical 6 PowerPack (F) :  21, 22, 23.10 et 4, 5, 6.11.02  (6 jours) Introduction à ANSYS/Introduction to ANSYS (langue à définir suivant demande/ Language to be chosen according to demand):  21 - 25.10.02  (5 jours/days) HREF-2002: Helium Refrigeration Techniques (English-French, bilingual) :  21 - 25.10.2002  (7 half days) HREF-2002: Techniques de la...

Monique Duval

2002-01-01

299

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Habilitation électrique : recyclage HT/BT : 11 - 15.3.2002  (2 * 2 heures) PVSS Basics :  8 - 12.4.02  (5 days) ELEC-2002 : Spring Term :  9, 11, 16, 18, 23, 25, 30.4.02 (7 * 2.5 hours) LabVIEW base 1 : 22 - 24.4.02 (3 jours) LabVIEW DSC (F) 25 & 26.4.02 (2 jours) LabVIEW Basics 2 : 13 & 14.5.02 (2 days) LabVIEW DAQ (F) : 15 & 16.5.02 (2 jours) Cours sur la migration AutoCAD :   AutoCAD : Mise à jour AutoCAD r-14 vers 2002 (2 jours) AutoCAD Mechanical PowerPack 6 basé sur AutoCAD 2002 (5 jours) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : Technical Training or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applica...

Monique Duval

2002-01-01

300

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Introduction to Oracle 8i : SQL and PL/SQL:  7 - 11.10.02  (5 days) CLEAN-2002 : Working in a Cleanroom (free of charge):  10.10.02  (half-day, p.m.) AutoCAD 2002 - niveau 2 :  14 - 15.10.02  (2 jours) Introduction à DesignSpace :  16.10.02  (1 journée) Introduction to DesignSpace:  17.10.02  (1 day) AutoCAD 2002 - Level 1:  17, 18, 24, 25.10.02  (4 days) AutoCAD Mechanical 6 PowerPack (F) :  21, 22, 23.10 et 4, 5, 6.11.02  (6 jours) Introduction à ANSYS/Introduction to ANSYS (langue à définir suivant demande/ Language to be chosen according to demand):  21 - 25.10.02  (5 jours/days) HREF-2002: Helium Refrigeration Techniques (English-French, bilingual) :  21 - 25.10.2002  (7 half days) HREF-2002: Techniques de la Réfri...

Monique Duval

2002-01-01

 
 
 
 
301

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: November 2002   LabView hands-on (bilingue/bilingual): 5.11.02 (matin/morning) LabView DAQ hands-on (bilingue/bilingual):  5.11.02  (après-midi afternoon) PCAD Schémas - Débutants :  5 & 6.11.02  (2 jours) PCAD PCB - Débutants :  9 - 11.11.02  (3 jours) Introduction au PC et Windows 2000 au CERN :  6 & 7.11.02  (2 jours) Oracle 8i : Access the Database with Java :  7 & 8.11.02  (2 days) Introduction to PVSS (free of charge):  11.11.2002 pm  (1/2 day) Basic PVSS:  12 - 14.11.02  (3 days) EXCEL 2000 - niveau 1 :  12 & 13.11.02  (2 jours) CLEAN-2002: Working in a Cleanroom (English, free of charge):  13.11.2002  (afternoon) LabView Base 1 :  13 - 15.11.02  (3 jours) AutoCAD 2002 - niveau 1 :  14, 15, 21, 22.11.02  (4 jours) LabVIEW - Advanced:  18 - 20.11.02  (3 days) Hands-on Object-Oriented Design and Programming with C++ :  19 - 21.11.02  (3 days)  LabVIEW - Basics 2:  21 - 22.11.02 ...

Monique Duval

2002-01-01

302

Places available**  

CERN Multimedia

Places are available in the following courses : DISP-2003 - Spring II Term : Advanced Digital Signal Processing : 30.4, 7, 14, 21.5.03 (4 X 2-hour lectures) Oracle iDS Reports : Build Internet Reports : 5 - 9.5.03 (5 days) LabView DAQ (language to be defined) : 8 & 9.5.03 AutoCAD Mechanical 6 PowerPack (F) : 12, 13, 20, 21, 27 & 28.5.03 (6 jours) AutoCAD 2002 - niveau 2 : 3 & 4.6.03 (2 jours) LabView DSC (language to be defined) : 19 & 20.6.03 Siemens SIMATIC Training : Introduction to STEP7 : 3 & 4.6.03 (2 days) STEP7 Programming : 16 - 20.6.03 (5 days) Simatic Net Network : 15 & 16.4.03 / 26 & 27.6.03 (sessions of 2 days) These courses will be given in French or English following the requests. Cours de sécurité : Etre TSO au CERN : Prochaines sessions : 24, 25 & 27.6.03 - 4, 5 & 7.11.03 (session de 3 jours) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description ...

2003-01-01

303

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: C++ for Particle Physicists :  11 - 15.3.2002  (6 * 3 hour lectures) Programming the Web for Control Applications : 11, 12, 18, 19.3.2002  (4 * 2 hour lectures) Habilitation électrique : recyclage HT/BT (Français) : 13 - 14.3.2002 (2 * 2 heures) Introduction à la CAO CADENCE : 19 & 20.3.02 (2 jours) LabVIEW base 1 : 22 - 24.4.02 (3 jours) LabVIEW DSC (F) 25 & 26.4.02 (2 jours) LabVIEW Basics 2 : 13 & 14.5.02 (2 days) LabVIEW DAQ (F) : 15 & 16.5.02 (2 jours) Cours sur la migration AutoCAD :   AutoCAD : Mise à jour AutoCAD r-14 vers 2002 (2 jours) AutoCAD Mechanical PowerPack 6 basé sur AutoCAD 2002 (5 jours) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : Technical Training or fil...

Monique Duval

2002-01-01

304

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: The CERN Engineering Data Management System for Advanced users : 16.4.02  (1 day) Migration from AutoCAD 14 towards AutoCAD Mechanical6 PowerPack:  17 - 19.4 and 2 &3.5.02  (5 days) AutoCAD - niveau 1 : 22, 23, 29, 30.4 et 6, 7.5.02 (6 jours) LabVIEW base 1 : 22 - 24.4.02 (3 jours) CLEAN 2002 : working in a cleanroom:  24.4.02  (half-day, pm) LabVIEW DSC (F) 25 & 26.4.02 (2 jours) AutoCAD : Mise à jour AutoCAD r-14 vers 2002 : 25 & 26.4.02 (2 jours) Cotations selon les normes GPS de l'ISO : 29 - 30.4.02 (2 jours) Introduction to the CERN Engineering Data Management System:  7.5.02  (1 day) LabVIEW Basics 2: 13 & 14.5.02 (2 days) AutoCAD Mechanical 6 PowerPack (F) : 13-14, 17, 21, 27-28.5.02 (6 jours) WorldFIP - Généralités : 14.5.2002 (1/2 journée) WorldFIP - Développer avec Micr...

Monique Duval

2002-01-01

305

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: ELEC-2002 : Spring Term :  9, 11, 16, 18, 23, 25, 30.4.02 (7 * 2.5 hours) Object-Oriented Analysis & Design: 16 - 19.4.02  (4 days) The CERN Engineering Data Management System for Advanced users:  16.4.02  (1 day) Migration from AutoCAD 14 towards AutoCAD Mechanical6 PowerPack:  17 - 19.4 and 2 &3.5.02  (5 days) AutoCAD - niveau 1 : 22, 23, 29, 30.4 et 6, 7.5.02 (6 jours) LabVIEW base 1 : 22 - 24.4.02 (3 jours) CLEAN 2002 : working in a cleanroom:  24.4.02  (half-day, pm) LabVIEW DSC (F) 25 & 26.4.02 (2 jours) AutoCAD : Mise à jour AutoCAD r-14 vers 2002 : 25 & 26.4.02 (2 jours) Cotations selon les normes GPS de l'ISO : 29 - 30.4.02 (2 jours) Introduction to the CERN Engineering Data Management System:  7.5.02  (1 day) LabVIEW Basics 2 : 13 & 14.5.02 (2 days) AutoCAD Mechanical 6 PowerPack (F) : 13-...

Monique Duval

2002-01-01

306

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: PVSS Basics :  8 - 12.4.02  (5 days) AutoCAD : Mise à jour AutoCAD r-14 vers 2002 : 25 & 26.4.02 (2 jours) ELEC-2002 : Spring Term :  9, 11, 16, 18, 23, 25, 30.4.02 (7 * 2.5 hours) Object-Oriented Analysis & Design: 16 - 19.4.02  (4 days) Migration from AutoCAD 14 towards AutoCAD Mechanical6 PowerPack:  17 - 19.4 and 2 &3.5.02  (5 days) LabVIEW base 1 : 22 - 24.4.02 (3 jours) LabVIEW DSC (F) 25 & 26.4.02 (2 jours) LabVIEW Basics 2 : 13 & 14.5.02 (2 days) EXCEL 2000 - niveau 2 : 22 & 23.5.02 (2 jours) LabVIEW DAQ (F) : 15 & 16.5.02 (2 jours) LabVIEW Basics 1:  3 - 5.6.02  (3 days) LabVIEW DAQ (E):  6 & 7.6.02  (2 days) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that...

Monique Duval

2002-01-01

307

Places available**  

CERN Multimedia

Places are available in the following courses: The CERN EDMS for Local Administrators (free of charge) : 24 & 25.9.03 (2 days) HeREF-2003 : Techniques de la réfrigération Hélium (cours en français avec support en anglais) : 6 - 10.10.2003 (7 demi-journées) The Java Programming Language Level 1 : 6 - 7.10.2003 (2 days) Java 2 Enterprise Edition - Part 2 : Enterprise JavaBeans : 8 - 10.10.2003 (3 days) FileMaker - niveau 1 : 9 & 10.10.03 (2 jours) EXCEL 2000 - niveau 1 : 20 & 22.10.03 (2 jours) AutoCAD 2002 - niveau 1 : 20, 21, 27, 28.10.03 (4 jours) CLEAN-2002 : Working in a Cleanroom (free of charge) : 23.10.03 (half day) AutoCAD Mechanical 6 PowerPack (E) : 23, 24, 30, 31.10 & 12, 13.11.03 (6 days) AutoCAD 2002 - niveau 2 : 10 & 11.11.03 (2 jours) ACCESS 2000 - niveau 1 : 13 & 14.11.03 (2 jours) FrontPage 2000 - niveau 1 : 20...

2003-01-01

308

Places available**  

CERN Multimedia

Places are available in the following courses : The CERN EDMS for Local Administrators : 24 & 25.9.03 (2 days, free of charge) HeREF-2003 : Techniques de la réfrigération Hélium (cours en français avec support en anglais) : 6 - 10.10.2003 (7 demi-journées) The Java Programming Language Level 1 : 6 - 7.10.2003 (2 days) Java 2 Enterprise Edition - Part 2 : Enterprise JavaBeans : 8 - 10.10.2003 (3 days) FileMaker - niveau 1 : 9 & 10.10.03 (2 jours) EXCEL 2000 - niveau 1 : 20 & 22.10.03 (2 jours) AutoCAD 2002 - niveau 1 : 20, 21, 27, 28.10.03 (4 jours) CLEAN-2002 : Working in a Cleanroom : 23.10.03 (half day, free of charge) AutoCAD 2002 - Level 1 : 3, 4, 12, 13.11.03 (4 days) AutoCAD 2002 - niveau 2 : 10 & 11.11.03 (2 jours) ACCESS 2000 - niveau 1 : 13 & 14.11.03 (2 jours) AutoCAD Mechanical 6 PowerPack (E) : 17, 18, 24, 25.11 & 1, 2.12.03 (6...

2003-01-01

309

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Contract Follow-up (F) : 30.10.01 (1/2 journée) The CERN Engineering Data Management System for Electronics Design :  30.10.01 (1 day) Nouveautés d'Excel 2000 : 5.11.01 (1/2 journée) UNIX pour non-programmeurs : 5 - 7.11.01 (3 jours) Introduction à Windows 2000 au CERN : 6.11.01 (1/2 journée) The Java programming language Level 1: 8 - 9.11.01 (2 days) LabView Base 1 : 12 - 14.11.01 (3 jours) LabVIEW DAQ (F) : 15 & 16.11.01 (2 jours) Automates et réseaux de terrain : 13 & 14.11.01 (2 jours) Introduction to PERL 5 :  15 - 16.11.01  (2 days) LabVIEW - DAQ : 15 - 16.11.01 (2 jours) Introduction to XML :  19 - 20.11.01 (2 days) Introduction to C Programming :  21- 23.11.01 (3 days) Programmation TSX Premium 2 : 26 - 30.11.01 (5 jours) Object-Oriented Analysis and Design :  27 - 30.11.2001 (4 days) Hands...

Technical Training; Tel. 74924

2001-01-01

310

Preferential acceleration of heavy ions in the reconnection outflow region. Drift and surfatron ion acceleration  

Science.gov (United States)

Context. Many observations show that heating in the solar corona should be more effective for heavy ions than for protons. Moreover, the efficiency of particle heating also seems to be larger for a larger particle electric charge. The transient magnetic reconnection is one of the most natural mechanisms of charged particle acceleration in the solar corona. However, the role of this process in preferential acceleration of heavy ions has still yet to be investigated. Aims: In this paper, we consider charged particle acceleration in the reconnection outflow region. We investigate the dependence of efficiency of various mechanisms of particle acceleration on particle charge and mass. Methods: We take into account recent in situ spacecraft observations of the nonlinear magnetic waves that have originated in the magnetic reconnection. We use analytical estimates and test-particle trajectories to study resonant and nonresonant particle acceleration by these nonlinear waves. Results: We show that resonant acceleration of heavy ions by nonlinear magnetic waves in the reconnection outflow region is more effective for heavy ions and/or for ions with a larger electric charge. Nonresonant acceleration can be considered as a combination of particle reflections from the front of the nonlinear waves. Energy gain for a single reflection is proportional to the particle mass, while the maximum possible gain of energy corresponds to the classical betatron heating. Conclusions: Small-scale transient magnetic reconnections produce nonlinear magnetic waves propagating away from the reconnection region. These waves can effectively accelerate heavy ions in the solar corona via resonant and nonresonnat regimes of interactions. This mechanism of acceleration is more effective for ions with a larger mass and/or with a larger electric charge.

Artemyev, A. V.; Zimbardo, G.; Ukhorskiy, A. Y.; Fujimoto, M.

2014-02-01

311

Numerical Tests of Fast Reconnection in Weakly Stochastic Magnetic Fields  

CERN Document Server

We study the effects of turbulence on magnetic reconnection using 3D numerical simulations. This is the first attempt to test a model of fast magnetic reconnection in the presence of weak turbulence proposed by Lazarian & Vishniac (1999). This model predicts that weak turbulence, generically present in most of astrophysical systems, enhances the rate of reconnection by reducing the transverse scale for reconnection events and by allowing many independent flux reconnection events to occur simultaneously. As a result the reconnection speed becomes independent of Ohmic resistivity and is determined by the magnetic field wandering induced by turbulence. To quantify the reconnection speed we use both an intuitive definition, i.e. the speed of the reconnected flux inflow, as well as a more sophisticated definition based on a formally derived analytical expression. Our results confirm the predictions of the Lazarian & Vishniac model. In particular, we find that Vrec Pinj^(1/2), as predicted by the model. The...

Kowal, G; Vishniac, E T; Otmianowska-Mazur, K

2009-01-01

312

Magnetic Reconnection in Turbulent Plasmas and Gamma Ray Bursts  

CERN Multimedia

We discuss how the model of magnetic reconnection in the presence of turbulence proposed inLazarian & Vishniac 1999 makes the reconnection rate independent either of resistivity or microscopic plasma effects, but determined entirely by the magnetic field line wandering induced by turbulence. We explain that the model accounts for both fast and slow regimes of reconnection and that this property naturally induces flares of reconnection in low beta plasma environments. In addition, we show that the model involves volume reconnection which can convert a substantial part of the energy into energetic particles. It is important that the reconnection induces an efficient acceleration of the first order Fermi type. Finally, we relate the properties of the reconnection with the observed properties of gamma ray bursts and provide evidence supporting the explanation of gamma ray bursts based on energy release via reconnection.

Lazarian, A

2013-01-01

313

Quantitative Analytical Model for Magnetic Reconnection in Hall Magnetohydrodynamics  

International Nuclear Information System (INIS)

Magnetic reconnection is of fundamental importance for laboratory and naturally occurring plasmas. Reconnection usually develops on time scales which are much shorter than those associated with classical collisional dissipation processes, and which are not fully understood. While such dissipation-independent (or 'fast') reconnection rates have been observed in particle and Hall magnetohydrodynamics (MHD) simulations and predicted analytically in electron MHD, a quantitative analytical theory of fast reconnection valid for arbitrary ion inertial lengths d(i) has been lacking. Here we propose such a theory without a guide field. The theory describes two-dimensional magnetic field diffusion regions, provides expressions for the reconnection rates, and derives a formal criterion for fast reconnection in terms of dissipation parameters and d(i). It also demonstrates that both open X-point and elongated diffusion regions allow dissipation-independent reconnection and reveals a possibility of strong dependence of the reconnection rates on d(i).

2008-11-17

314

Quantitative analytical model for magnetic reconnection in Hall magnetohydrodynamics  

International Nuclear Information System (INIS)

Magnetic reconnection is of fundamental importance for laboratory and naturally occurring plasmas. Reconnection usually develops on time scales which are much shorter than those associated with classical collisional dissipation processes, and which are not fully understood. While such dissipation-independent (or 'fast') reconnection rates have been observed in particle and Hall magnetohydrodynamics (MHD) simulations and predicted analytically in electron MHD, a quantitative analytical theory of fast reconnection valid for arbitrary ion inertial lengths di has been lacking. Here we propose such a theory without a guide field. The theory describes two-dimensional magnetic field diffusion regions, provides expressions for the reconnection rates, and derives a formal criterion for fast reconnection in terms of dissipation parameters and di. It also demonstrates that both open X-point and elongated diffusion regions allow dissipation-independent reconnection and reveals a possibility of strong dependence of the reconnection rates on di.

2009-05-01

315

Turbulent Reconnection Rates from Cluster Observations in the Magnetosheath  

Science.gov (United States)

The role of turbulence in producing fast reconnection rates is an important unresolved question. Scant in situ analyses exist. We apply multiple spacecraft techniques to a case of nonlinear turbulent reconnection in the magnetosheath to test various theoretical results for turbulent reconnection rates. To date, in situ estimates of the contribution of turbulence to reconnection rates have been calculated from an effective electric field derived through linear wave theory. However, estimates of reconnection rates based on fully nonlinear turbulence theories and simulations exist that are amenable to multiple spacecraft analyses. Here we present the linear and nonlinear theories and apply some of the nonlinear rates to Cluster observations of reconnecting, turbulent current sheets in the magnetosheath. We compare the results to the net reconnection rate found from the inflow speed. Ultimately, we intend to test and compare linear and nonlinear estimates of the turbulent contribution to reconnection rates and to measure the relative contributions of turbulence and the Hall effect.

Wendel, Deirdre

2011-01-01

316

Reconnection events in two-dimensional Hall magnetohydrodynamic turbulence  

Energy Technology Data Exchange (ETDEWEB)

The statistical study of magnetic reconnection events in two-dimensional turbulence has been performed by comparing numerical simulations of magnetohydrodynamics (MHD) and Hall magnetohydrodynamics (HMHD). The analysis reveals that the Hall term plays an important role in turbulence, in which magnetic islands simultaneously reconnect in a complex way. In particular, an increase of the Hall parameter, the ratio of ion skin depth to system size, broadens the distribution of reconnection rates relative to the MHD case. Moreover, in HMHD the local geometry of the reconnection region changes, manifesting bifurcated current sheets and quadrupolar magnetic field structures in analogy to laminar studies, leading locally to faster reconnection processes in this case of reconnection embedded in turbulence. This study supports the idea that the global rate of energy dissipation is controlled by the large scale turbulence, but suggests that the distribution of the reconnection rates within the turbulent system is sensitive to the microphysics at the reconnection sites.

Donato, S.; Servidio, S.; Carbone, V. [Dipartimento di Fisica, Universita della Calabria, I-87036 Cosenza (Italy); Dmitruk, P. [Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and Instituto de Fisica de Buenos Aires, CONICET, Buenos Aires (Argentina); Shay, M. A.; Matthaeus, W. H. [Bartol Research Institute and Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716 (United States); Cassak, P. A. [Department of Physics, West Virginia University, Morgantown, West Virginia 26506 (United States)

2012-09-15

317

Externally driven magnetic reconnection in a collisionless plasma  

Energy Technology Data Exchange (ETDEWEB)

Driven magnetic reconnection in a collisionless plasma, `collisionless driven reconnection`, is investigated by means of two-and-one-half dimensional particle simulation. Magnetic reconnection develops in two steps in accordance with the formation of two current layers, i.e., an ion current layer and an electron current layer. It is found that the global dynamical evolution of magnetic reconnection is controlled by the physics of the ion current layer. (author). 5 refs, 3 figs.

Horiuchi, R.; Sato, T. [National Inst. for Fusion Science, Nagoya (Japan)

1994-12-31

318

Achieving fast reconnection in resistive MHD models via turbulent means  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Astrophysical fluids are generally turbulent and this preexisting turbulence must be taken into account for models of magnetic reconnection in astrophysical, solar or heliospheric environments. In addition, reconnection itself induces turbulence which provides an important feedback on the reconnection process. In this paper we discuss both the theoretical model and numerical evidence that magnetic reconnection becomes fast in the approximation of resistive MHD. We consider the relation betwee...

Lapenta, G.; Lazarian, A.

2012-01-01

319

The Dissipation Mechanism in Collisionless Magnetic Reconnection  

Science.gov (United States)

The dissipation mechanism of magnetic reconnection remains a subject of intense scientific interest. On one hand, one set of recent studies have shown that particle inertia-based processes, which include thermal and bulk inertial effects, provide the reconnection electric field in the diffusion region. On the other hand, a second set of studies emphasizes the role of wave-particle interactions in providing anomalous resistivity in the diffusion region. In this presentation, we present analytical theory results, as well as PIC simulations of guide-field magnetic reconnection. We will show that the thermal electron inertia-based dissipation mechanism, expressed through nongyrotropic electron pressure tensors, remains viable in three dimensions. We will demonstrate the thermal inertia effect through studies of electron distribution functions. Furthermore, we will show that the reconnection electric field provides a transient acceleration on particles traversing the inner reconnection region. This inertial effect can be described as a diffusion-like term of the current density, which matches key features of electron distribution functions.

Hesse, Michael; Kuznetsova, M.; Birn, J.; Schindler, K.

2006-01-01

320

Flow-turbulence interaction in magnetic reconnection  

Energy Technology Data Exchange (ETDEWEB)

Roles of turbulence in the context of magnetic reconnection are investigated with special emphasis on the mutual interaction between flow (large-scale inhomogeneous structure) and turbulence. In order to evaluate the effective transport due to turbulence, in addition to the intensity information of turbulence represented by the turbulent energy, the structure information represented by pseudoscalar statistical quantities (helicities) is important. On the basis of the evolution equation, mechanisms that provide turbulence with cross helicity are presented. Magnetic-flux freezing in highly turbulent media is considered with special emphasis on the spatial distribution of the turbulent cross helicity. The cross-helicity effects in the context of magnetic reconnection are also investigated. It is shown that the large-scale flow and magnetic-field configurations favorable for the cross-helicity generation is compatible with the fast reconnection. Difference between the spatial distributions of the turbulent MHD energy and cross helicity plays an essential role for localizing the reconnection region. In this sense, turbulence and large-scale structures promote magnetic reconnection mediated by the turbulent cross helicity.

Yokoi, N. [Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505 (Japan); Hoshino, M. [Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033 (Japan)

2011-11-15

 
 
 
 
321

Flow-turbulence interaction in magnetic reconnection  

International Nuclear Information System (INIS)

Roles of turbulence in the context of magnetic reconnection are investigated with special emphasis on the mutual interaction between flow (large-scale inhomogeneous structure) and turbulence. In order to evaluate the effective transport due to turbulence, in addition to the intensity information of turbulence represented by the turbulent energy, the structure information represented by pseudoscalar statistical quantities (helicities) is important. On the basis of the evolution equation, mechanisms that provide turbulence with cross helicity are presented. Magnetic-flux freezing in highly turbulent media is considered with special emphasis on the spatial distribution of the turbulent cross helicity. The cross-helicity effects in the context of magnetic reconnection are also investigated. It is shown that the large-scale flow and magnetic-field configurations favorable for the cross-helicity generation is compatible with the fast reconnection. Difference between the spatial distributions of the turbulent MHD energy and cross helicity plays an essential role for localizing the reconnection region. In this sense, turbulence and large-scale structures promote magnetic reconnection mediated by the turbulent cross helicity.

2011-11-01

322

Vortex reconnections between coreless vortices in binary condensates  

Science.gov (United States)

Vortex reconnections plays an important role in the turbulent flows associated with the superfluids. To understand the dynamics, we examine the reconnections of vortex rings in the superfluids of dilute atomic gases confined in trapping potentials using Gross-Petaevskii equation. Further more we study the reconnection dynamics of coreless vortex rings, where one of the species can act as a tracer.

Gautam, S.; Suthar, K.; Angom, D.

2014-02-01

323

Hall Reconnection in Partially Ionized Plasmas in the Magnetic Reconnection Experiment  

Science.gov (United States)

In many space and astrophysical plasmas, such as the solar chromosphere and protoplanetary disks, the degree of ionization can be quite low; often 1% or less. In addition, magnetic reconnection is thought to be a fundamental process in these plasmas. The presence of a large neutral atom population has at least two effects relevant to magnetic reconnection. First, electron-neutral collisions enhance resistive dissipation. Second, strong ion-neutral collisions increase effective ion inertia. This may increase the length scales on which fast Hall reconnection is predicted to occur. By using high gas fill pressures in the Magnetic Reconnection Experiment (MRX), we can study reconnection in partially or weakly ionized plasmas (nn/ne= 1--200). A newly constructed magnetic probe array allows us to make magnetic measurements of the reconnection region with high spatial resolution and large spatial extent. This will allow us to diagnose, for example, the structure of the Hall quadrupole field in these conditions. Langmuir and spectroscopic diagnostics will also provide insight into how neutrals affect the reconnection process. These results will also be discussed in the context of ongoing theoretical work.

Lawrence, Eric; Ji, Hantao; Yamada, Masaaki; Yoo, Jongsoo

2011-11-01

324

Cooperative Ecology & Place: Development of a Pedagogy of Place Curriculum.  

Science.gov (United States)

The major tenets of a pedagogy of place are that nature teaches; understanding place is indispensable to community; where and how a student learns is as vital as what a student learns; and respect is integral to learning. Environmental literacy is the capacity to perceive and interpret the relative health of environmental systems and to take

Lewicki, James

325

The structure of the magnetic reconnection exhaust boundary  

CERN Document Server

The structure of shocks that form at the exhaust boundaries during collisionless reconnection of anti-parallel fields is studied using particle-in-cell (PIC) simulations and modeling based on the anisotropic magnetohydrodynamic equations. Large-scale PIC simulations of reconnection and companion Riemann simulations of shock development demonstrate that the pressure anisotropy produced by counterstreaming ions within the exhaust prevents the development of classical Petschek switch-off-slow shocks (SSS). The shock structure that does develop is controlled by the firehose stability parameter epsilon=1-mu_0(P_parallel-P_perpendicular)/ B^2 through its influence on the speed order of the intermediate and slow waves. Here P_parallel and P_perpendicular are the pressure parallel and perpendicular to the local magnetic field. The exhaust boundary is made up of a series of two shocks and a rotational wave. The first shock takes epsilon from unity upstream to a plateau of 0.25 downstream. The condition epsilon =0.25 i...

Liu, Yi-Hsin; Swisdak, M

2011-01-01

326

Take heart!  

CERN Multimedia

Recently, ten new semi-automatic defibrillators were installed at various locations around CERN. This is a preventive measure intended to provide cardiac arrest victims with the best possible response. The first responder could be you!   The Director-General has welcomed the initiative of the Medical Service and Fire Brigade for the installation of ten new semi-automatic defibrillators. You have probably seen them on your way to the restaurant, for example:  brand new semi-automatic defibrillators, ready for an emergency. Housed in a white wall-mounted case, the bright red defibrillators are marked with a white heart symbol crossed by a lightning bolt (see photo). The defibrillator is designed so that anyone can use it. “Anyone can use it, you don’t need to be a health professional,” says Dr Reymond from CERN's Medical Service. Together with the CERN Fire Brigade, he is behind the initiative to have these units put in place. And with good reason, as the unit...

Alizée Dauvergne

2010-01-01

327

What is taking place in science classrooms?: A case study analysis of teaching and learning in seventh-grade science of one Alabama school and its impact on African American student learning  

Science.gov (United States)

This qualitative case study investigated the teaching strategies that improve science learning of African American students. This research study further sought the extent the identified teaching strategies that are used to improve African American science learning reflect culturally responsive teaching. Best teaching strategies and culturally responsive teaching have been researched, but there has been minimal research on the impact that both have on science learning, with an emphasis on the African American population. Consequently, the Black-White achievement gap in science persists. The findings revealed the following teaching strategies have a positive impact on African American science learning: (a) lecture-discussion, (b) notetaking, (c) reading strategies, (d) graphic organizers, (e) hands-on activities, (f) laboratory experiences, and (g) cooperative learning. Culturally responsive teaching strategies were evident in the seventh-grade science classrooms observed. Seven themes emerged from this research data: (1) The participating teachers based their research-based teaching strategies used in the classroom on all of the students' learning styles, abilities, attitudes towards science, and motivational levels about learning science, with no emphasis on the African American student population; (2) The participating teachers taught the state content standards simultaneously using the same instructional model daily, incorporating other content areas when possible; (3) The participating African American students believed their seventh-grade science teachers used a variety of teaching strategies to ensure science learning took place, that science learning was fun, and that science learning was engaging; (4) The participating African American students genuinely liked their teacher; (5) The participating African American students revealed high self-efficacy; (6) The African American student participants' parents value education and moved to Success Middle School district for better educational opportunities; and (7) Teachers were not familiar with the term "culturally responsive teaching," but there was evidence that several aspects of it were present in the seventh-grade science classroom environment. Critical Race Theory (CRT) was the framework for analysis and interpretation of this research study. The findings support the following tenets of CRT: (a) racism is normal, (b) interest-convergence or colorblindness, (c) contextual-historical analysis, (d) storytelling or counterstorytelling, and (e) social transformation. These findings indicate that racial inequalities remain an issue in the underachievement of African Americans and may be the solution to improving science learning of African Americans. The outcome of this study contributes to the limited research on utilizing culturally responsive teaching along with best teaching strategies to improve academic achievement of African American students, and CRT exposes the issues that contribute to the Black-White achievement gap in science widening.

Norman, Lashaunda Renea

328

Computer simulation of reconnection in planetary magnetospheres  

International Nuclear Information System (INIS)

The earth's magnetosphere provides an ideal opportunity to model reconnection in well known geometries that are close enough to the idealized analytic models to make a comparison of the computer models with analytic theory meaningful. In addition more detailed, even three-dimensional, models can be used for a comparison with extended data from in situ observations. The computer studies have basically confirmed the reconnection picture that was based on two-dimensional steady state models and linear analytic theory. The three-dimensional models in particular have also added a lot more information on the reconnection process and the structure of flow, magnetic fields, and currents including many features that are consistent with observations and empirical models of geomagnetic substorms

1983-08-08

329

Magnetic Reconnection in a Weakly Ionized Plasma  

CERN Multimedia

Magnetic reconnection in partially ionized plasmas is a ubiquitous phenomenon spanning the range from laboratory to intergalactic scales, yet it remains poorly understood and relatively little studied. Here, we present results from a self-consistent multi-fluid simulation of magnetic reconnection in a weakly ionized reacting plasma with a particular focus on the parameter regime of the solar chromosphere. The numerical model includes collisional transport, interaction and reactions between the species, and optically thin radiative losses. This model improves upon our previous work in Leake et al. 2012 \\cite{Leake2012} by considering realistic chromospheric transport coefficients, and by solving a generalized Ohm's law that accounts for finite ion-inertia and electron-neutral drag. We find that during the two dimensional reconnection of a Harris current sheet with an initial width larger than the neutral-ion collisional coupling scale, the current sheet thins until its width becomes less than this coupling sca...

Leake, James E; Linton, Mark G

2013-01-01

330

Particle Demagnetization in Collisionless Magnetic Reconnection  

Science.gov (United States)

The dissipation mechanism of magnetic reconnection remains a subject of intense scientific interest. On one hand, one set of recent studies have shown that particle inertia-based processes, which include thermal and bulk inertial effects, provide the reconnection electric field in the diffusion region. In this presentation, we present analytical theory results, as well as 2.5 and three-dimensional PIC simulations of guide field magnetic reconnection. We will show that diffusion region scale sizes in moderate and large guide field cases are determined by electron Larmor radii, and that analytical estimates of diffusion region dimensions need to include description of the heat flux tensor. The dominant electron dissipation process appears to be based on thermal electron inertia, expressed through nongyrotropic electron pressure tensors. We will argue that this process remains viable in three dimensions by means of a detailed comparison of high resolution particle-in-cell simulations.

Hesse, Michael

2006-01-01

331

Flow-turbulence interaction in magnetic reconnection  

CERN Document Server

Roles of turbulence in the context of magnetic reconnection are investigated with special emphasis on the mutual interaction between flow (large-scale inhomogeneous structure) and turbulence. In order to evaluate the effective transport due to turbulence, in addition to the {\\it intensity} information of turbulence represented by the turbulent energy, the {\\it structure} information represented by pseudoscalar statistical quantities (helicities) is important. On the basis of the evolution equation, mechanisms that provide turbulence with cross helicity are presented. Magnetic-flux freezing in highly turbulent media is considered with special emphasis on the spatial distribution of the turbulent cross helicity. The cross-helicity effects in the context of magnetic reconnection are also investigated. It is shown that the large-scale flow and magnetic-field configurations favorable for the cross-helicity generation is compatible with the fast reconnection. In this sense, turbulence and large-scale structures pro...

Yokoi, Nobumitsu

2011-01-01

332

Computer simulation of reconnection in planetary magnetospheres  

Energy Technology Data Exchange (ETDEWEB)

The earth's magnetosphere provides an ideal opportunity to model reconnection in well known geometries that are close enough to the idealized analytic models to make a comparison of the computer models with analytic theory meaningful. In addition more detailed, even three-dimensional, models can be used for a comparison with extended data from in situ observations. The computer studies have basically confirmed the reconnection picture that was based on two-dimensional steady state models and linear analytic theory. The three-dimensional models in particular have also added a lot more information on the reconnection process and the structure of flow, magnetic fields, and currents including many features that are consistent with observations and empirical models of geomagnetic substorms.

Birn, J.

1983-01-01

333

Gyro-induced acceleration of magnetic reconnection  

CERN Multimedia

The linear and nonlinear evolution of magnetic reconnection in collisionless high-temperature plasmas with a strong guide field is analyzed on the basis of a two-dimensional gyrofluid model. The linear growth rate of the reconnecting instability is compared to analytical calculations over the whole spectrum of linearly unstable wave numbers. In the strongly unstable regime (large \\Delta '), the nonlinear evolution of the reconnecting instability is found to undergo two distinctive acceleration phases separated by a stall phase in which the instantaneous growth rate decreases. The first acceleration phase is caused by the formation of strong electric fields close to the X-point due to ion gyration, while the second acceleration phase is driven by the development of an open Petschek-like configuration due to both ion and electron temperature effects. Furthermore, the maximum instantaneous growth rate is found to increase dramatically over its linear value for decreasing diffusion layers. This is a consequence o...

Comisso, Luca; Waelbroeck, François L; Borgogno, Dario

2013-01-01

334

Computer modeling of fast collisionless reconnection  

Energy Technology Data Exchange (ETDEWEB)

Particle simulations of collisionless tearing, reconnection and coalescence of magnetic fields for a sheet-pinch configuration show that reconnection is Sweet-Parker like in the tearing and island formation phase. It is much faster to explosive in the island coalescence state. Island coalescence is the most energetic process and leads to large ion temperature increase and oscillations in the merged state. Similar phenomena have been observed in equivalent MHD simulations. Coalescence and its effects, as observed in our simulations, may explain many of the features of solar flares and coronal x-ray brightening.

Leboeuf, J.N.; Brunel, F.; Tajima, T.; Sakai, J.; Wu, C.C.; Dawson, J.M.

1984-01-01

335

Dynamical plasma response during driven magnetic reconnection  

International Nuclear Information System (INIS)

Direct measurements of a collisionless current channel during driven magnetic reconnection are obtained for the first time on the Versatile Toroidal Facility. The size of the diffusion region is found to scale with the electron drift orbit width, independent of the ion mass and plasma density. Based on experimental observations, analytic expressions governing the dynamical evolution of the current profile and the formation of the electrostatic potential that develops in response to the externally imposed reconnection drive are established. This time response is closely linked to the presence of ion polarization currents

2003-04-04

336

Dynamical plasma response during driven magnetic reconnection.  

Science.gov (United States)

Direct measurements of a collisionless current channel during driven magnetic reconnection are obtained for the first time on the Versatile Toroidal Facility. The size of the diffusion region is found to scale with the electron drift orbit width, independent of the ion mass and plasma density. Based on experimental observations, analytic expressions governing the dynamical evolution of the current profile and the formation of the electrostatic potential that develops in response to the externally imposed reconnection drive are established. This time response is closely linked to the presence of ion polarization currents. PMID:12689297

Egedal, J; Fasoli, A; Nazemi, J

2003-04-01

337

Observations of turbulence generated by magnetic reconnection.  

Science.gov (United States)

Spacecraft observations of turbulence within a magnetic reconnection (guide field approximately 0) ion diffusion region are presented. In the inertial subrange, electric and magnetic fluctuations both followed a -5/3 power law; at higher frequencies, the spectral indices were -1 and -8/3, respectively. The dispersion relation was found to be consistent with fast-mode-whistler waves rather than kinetic Alfvén-ion cyclotron waves. Lower hybrid waves, which could be enhanced by whistler mode conversion, were observed, but the associated anomalous resistivity was not found to significantly modify the reconnection rate. PMID:19257361

Eastwood, J P; Phan, T D; Bale, S D; Tjulin, A

2009-01-23

338

Effects of color reconnection on $t\\bar{t}$ final states at the LHC  

CERN Document Server

The modeling of color reconnection has become one of the dominant sources of systematic uncertainty in the top mass determination at hadron colliders. The uncertainty on the top mass due to color reconnection is conventionally estimated by taking the difference in the predictions of a model with and a model without color reconnection. We show that this procedure underestimates the uncertainty when applied to the existing models in {\\sc Pythia}~8. We introduce two new classes of color reconnection models, each containing several variants, which encompass a variety of scenarios that could be realized in nature and we study how they affect the reconstruction of the top mass. After tuning the new models to existing LHC data, the remaining spread of predictions is used to derive a more realistic uncertainty for the top mass, which is found to be around 500 MeV. We also propose how future LHC measurements with $t\\bar{t}$ events can be used to further constrain these models and reduce the associated modeling uncerta...

Argyropoulos, Spyros

2014-01-01

339

Fast magnetic reconnection in laser-produced plasma bubbles  

CERN Multimedia

Recent experiments have observed magnetic reconnection in high-energy-density, laser-produced plasma bubbles, with reconnection rates observed to be much higher than can be explained by classical theory. Based on fully kinetic particle simulations we find that fast reconnection in these strongly driven systems can be explained by magnetic flux pile-up at the shoulder of the current sheet and subsequent fast reconnection via two-fluid, collisionless mechanisms. In the strong drive regime with two-fluid effects, we find that the ultimate reconnection time is insensitive to the nominal system Alfven time.

Fox, W; Germaschewski, K

2011-01-01

340

Fast magnetic reconnection in laser-produced plasma bubbles.  

Science.gov (United States)

Recent experiments have observed magnetic reconnection in high-energy-density, laser-produced plasma bubbles, with reconnection rates observed to be much higher than can be explained by classical theory. Based on fully kinetic particle simulations we find that fast reconnection in these strongly driven systems can be explained by magnetic flux pileup at the shoulder of the current sheet and subsequent fast reconnection via two-fluid, collisionless mechanisms. In the strong drive regime with two-fluid effects, we find that the ultimate reconnection time is insensitive to the nominal system Alfvén time. PMID:21699307

Fox, W; Bhattacharjee, A; Germaschewski, K

2011-05-27

 
 
 
 
341

Fast Magnetic Reconnection in Laser-Produced Plasma Bubbles  

International Nuclear Information System (INIS)

Recent experiments have observed magnetic reconnection in high-energy-density, laser-produced plasma bubbles, with reconnection rates observed to be much higher than can be explained by classical theory. Based on fully kinetic particle simulations we find that fast reconnection in these strongly driven systems can be explained by magnetic flux pileup at the shoulder of the current sheet and subsequent fast reconnection via two-fluid, collisionless mechanisms. In the strong drive regime with two-fluid effects, we find that the ultimate reconnection time is insensitive to the nominal system Alfven time.

2011-05-27

342

Magnetic Reconnection: Theoretical and Observational Perspectives: Preface  

Science.gov (United States)

Magnetic reconnection is a fundamental plasma-physical process by which energy stored in a magnetic field is converted, often explosively, into heat and the kinetic energy of the charged particles that constitute the plasma. It occurs in a variety of astrophysical settings, ranging from the solar corona to pulsar magnetospheres and winds, as well as in laboratory fusion experiments, where it is responsible for sawtooth crashes. First proposed by R.G. Giovanelli in the late I 940s as the mechanism responsible for solar flares, magnetic reconnection was invoked at the beginning of the space age to explain not just solar flares but also the transfer of energy, mass, and momentum from the solar wind to Earth's magnetosphere and the subsequent storage and release of the transferred energy in the magnetotai\\. During the half century or so that has followed the seminal theoretical works by J.W. Dungey, P.A. Sweet, E.N. Parker, and H.E. Petschek, in-situ measurements by Earth-orbiting satellites and remote-sensing observations of the solar corona have provided a growing body of evidence for the occurrence of reconnection at the Sun, in the solar wind, and in the near-Earth space environment. The last thirty years have also seen the development of laboratory reconnection experiments at a number of institutions. In parallel with the efforts of experimentalists in both space and laboratory plasma physics, theorists have investigated, analytically and with the help of increasingly powerful MHD, hybrid, and kinetic numerical simulations, the structure of the diffusion region, the factors controlling the rate, onset, and cessation of reconnection, and the detailed physics that enables the demagnetization of the ions and electrons and the topological reconfiguration of the magnetic field. Moreover, the scope of theoretical reconnection studies has been extended well beyond solar system and laboratory plasmas to include more exotic astrophysical plasma systems whose strong (10(exp 14)-10(exp 15) G) magnetic fields require that models of reconnection in these systems incorporate quantum electrodynamical, special relativistic, and radiative effects. The papers collected in this topical issue of Space Science Reviews cover different aspects of recent theoretical and observational work on magnetic reconnection in solar and space physics, astrophysics, and laboratory plasma physics. They derive from presentations given at a workshop on magnetic reconnection held in the Yosemite National Park, February 8-12,2010. The intent of the workshop was to stimulate, through a combination of tutorial talks, shorter focused talks, and extensive informal discussions, an interdisciplinary dialogue among members of the different research communities working on the problem of magnetic reconnection. One of the motivating considerations for holding the workshop was its relevance to NASA's Magnetospheric Multiscale (MMS) mission, scheduled for launch in 2014. The four identically instrumented MMS spacecraft are designed to study reconnect ion in Earth's magnetosphere and, specifically, to probe the electron diffusion region in order to determine the microphysical processes that enable the change in the topology of the magnetic field. Building on the achievements of the multi spacecraft Cluster and THEMIS missions, MMS will use the magnetosphere as an astrophysical plasma laboratory in which to test, through in-situ measurement of the plasma, energetic particles, and electric and magnetic fields, various models and theories that have emerged during the past twenty years, a period of extraordinarily productive theoretical and observational work.

Lewis, W. S.; Antiochos, S. K,; Drake, J. F.

2011-01-01

343

Study of the effects of guide field on Hall reconnection  

International Nuclear Information System (INIS)

The results from guide field studies on the Magnetic Reconnection Experiment (MRX) are compared with results from Hall magnetohydrodynamic (HMHD) reconnection simulation with guide field. The quadrupole field, a signature of two-fluid reconnection at zero guide field, is modified by the presence of a finite guide field in a manner consistent with HMHD simulation. The modified Hall current profile contains reduced electron flows in the reconnection plane, which quantitatively explains the observed reduction of the reconnection rate. The present results are consistent with the hypothesis that the local reconnection dynamics is dominated by Hall effects in the collisionless regime of the MRX plasmas. While very good agreement is seen between experiment and simulations, we note that an important global feature of the experiments, a compression of the guide field by the reconnecting plasma, is not represented in the simulations

2013-05-01

344

Study of the effects of guide field on Hall reconnection  

Energy Technology Data Exchange (ETDEWEB)

The results from guide field studies on the Magnetic Reconnection Experiment (MRX) are compared with results from Hall magnetohydrodynamic (HMHD) reconnection simulation with guide field. The quadrupole field, a signature of two-fluid reconnection at zero guide field, is modified by the presence of a finite guide field in a manner consistent with HMHD simulation. The modified Hall current profile contains reduced electron flows in the reconnection plane, which quantitatively explains the observed reduction of the reconnection rate. The present results are consistent with the hypothesis that the local reconnection dynamics is dominated by Hall effects in the collisionless regime of the MRX plasmas. While very good agreement is seen between experiment and simulations, we note that an important global feature of the experiments, a compression of the guide field by the reconnecting plasma, is not represented in the simulations.

Tharp, T. D.; Yamada, M.; Ji, H.; Lawrence, E.; Dorfman, S.; Myers, C.; Yoo, J. [Center for Magnetic Self-Organization, Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543-0451 (United States); Huang, Y.-M.; Bhattacharjee, A. [Space Science Center, University of New Hampshire and Max Planck-Princeton Research Center for Plasma Physics, Princeton University, P.O. Box 451, Princeton, New Jersey 08543-0451 (United States)

2013-05-15

345

Study of the effects of guide field on Hall reconnection  

Science.gov (United States)

The results from guide field studies on the Magnetic Reconnection Experiment (MRX) are compared with results from Hall magnetohydrodynamic (HMHD) reconnection simulation with guide field. The quadrupole field, a signature of two-fluid reconnection at zero guide field, is modified by the presence of a finite guide field in a manner consistent with HMHD simulation. The modified Hall current profile contains reduced electron flows in the reconnection plane, which quantitatively explains the observed reduction of the reconnection rate. The present results are consistent with the hypothesis that the local reconnection dynamics is dominated by Hall effects in the collisionless regime of the MRX plasmas. While very good agreement is seen between experiment and simulations, we note that an important global feature of the experiments, a compression of the guide field by the reconnecting plasma, is not represented in the simulations.

Tharp, T. D.; Yamada, M.; Ji, H.; Lawrence, E.; Dorfman, S.; Myers, C.; Yoo, J.; Huang, Y.-M.; Bhattacharjee, A.

2013-05-01

346

Magnetic reconnection with radiative cooling. I. Optically thin regime  

International Nuclear Information System (INIS)

Magnetic reconnection processes in many high-energy-density astrophysical and laboratory plasma systems are significantly affected by radiation; hence traditional, nonradiative reconnection models are not applicable to these systems. Motivated by this observation, the present paper develops a Sweet-Parker-like theory of resistive magnetic reconnection with strong radiative cooling. It is found that, in the case with zero guide field, intense radiative cooling leads to a strong plasma compression, resulting in a higher reconnection rate. The compression ratio and the reconnection layer temperature are determined by the balance between ohmic heating and radiative cooling. The lower temperature in a radiatively cooled layer leads to a higher Spitzer resistivity and, hence, a higher reconnection rate. Several specific radiative processes (bremsstrahlung, cyclotron, and inverse Compton) in the optically thin regime are considered for both the zero- and strong-guide-field cases, and concrete expressions for the reconnection parameters are derived, along with the applicability conditions.

2011-04-01

347

MAGNETIC RECONNECTION, HELICITY DYNAMICS, AND HYPER-DIFFUSION  

International Nuclear Information System (INIS)

We examine the influence of noise and Alfvén wave turbulence on magnetic reconnection in a reduced magnetohydrodynamics model. We focus on the dynamics of magnetic helicity density. Helicity conservation is then used to calculate the global reconnection rate in terms of the helicity density flux. Two specific scenarios are explored—noisy reconnection and Alfvén wave turbulent reconnection. For noisy reconnection, the current sheet is assumed to sit in a noisy state, marginal to plasmoid formation instability. The scaling of the reconnection rate in the presence of noise is proportional to (S 20/VAL 2)1/11, where S 20/VAL 2 is the relative amplitude of the noise. We obtain this prediction using a symmetry analysis of the helicity density flux. For Alfvén wave turbulent reconnection, a mean field closure scheme is applied. A reconnection rate proportional to (2>/2)1/8 is obtained, where 2>/2 and (B) are the relative energy of Alfvén wave turbulence and the reconnecting field. The constraint on reconnection rate enforced mean-square magnetic potential conservation is reexamined. A critical magnetic Reynolds number Rm,c is identified. For Rm >> Rm,c, the reconnection rate becomes independent of Spitzer resistivity and thus can be higher than the Sweet-Parker model prediction. Both cases exhibit a weak dependence of the reconnection rate on the amplitude of the turbulence. Therefore, even noise or weak turbulence can trigger fast reconnection if the system is marginally stable. The important distinction between turbulent reconnection and turbulent dissipation of magnetic energy is also discussed.

2012-10-01

348

A Next Generation Magnetic Reconnection Experiment: Accessing ``Reconnection Phase Diagrams'' for Space and Astrophysical Relevances  

Science.gov (United States)

Ongoing dedicated laboratory experiments, such as Magnetic Reconnection Experiment (MRX), have been productive in providing original and valuable data in achieving much needed understanding of fast reconnection and associated processes. However, further critical contributions to astrophysical plasmas are limited by the achievable parameters. In this paper, we discuss results from our ongoing effortsfootnotetextH. Ji et al., APS 51st DPP Annual Meeting (November, 2009), http://meetings.aps.org/link/BAPS.2009.DPP.TP8.111 to develop plans for a next-generation reconnection experiment based on MRX. Most recent results from two-dimentional, large-scale numerical simulations suggest the existence of a reconnection phase diagram'', which illustrates phase transitions'' between different states'' or regimes. They include collisional MHD without plasmoids regime'', collisional MHD with plasmoids regime'', kinetic and MHD hybrid regime'', and collisionless regime''. The latter three regimes are considered to be relevant to reconnection in solar tachocline, solar corona, and Earth's magnetosphere. A natural goal for the next generation of reconnection experiments is the ability to access all of these regimes so that phase transitions can be studied in a controlled environment and the results are potentially applicable to astrophysical plasmas. Experimental requirements, aided by numerical simulations, will be discussed in detail.

Ji, H.; Yamada, M.; Prager, S.; Daughton, W.; Roytershteyn, V.

2010-11-01

349

Magnetic reconnection with large separatrix angles  

Science.gov (United States)

The magnetic reconnection process is studied here using incompressible MHD simulations with different inflow boundary conditions and different magnetic Reynolds numbers R(m). The angle between the magnetic separatrices is in steady state reconnection depends mainly on the normal magnetic field on the inflow boundary. In steady state nonuniform reconnection with large separatrix angles, field-aligned plasma jets appear slightly downstream of the magnetic separatrices. The field-aligned plasma jet are stronger when R(m) is larger. Each field-aligned plasma jet consists of two parts: a slow shock and a fast-mode compressional wave. The slow shock converts the magnetic energy into plasma kinetic energy by acceleration and heating. The fast-mode compressional wave decelerates the plasma to a smaller outflow speed and heats it further. Nearly all the magnetic energy flowing into the diffusion region is converted into other forms. The length and width of the diffusion region depend on the values of the reconnection rate, R(m), and the normal magnetic field on the inflow boundary.

Yan, M.; Lee, L. C.; Priest, E. R.

1993-01-01

350

Gyro-induced acceleration of magnetic reconnection  

Energy Technology Data Exchange (ETDEWEB)

The linear and nonlinear evolution of magnetic reconnection in collisionless high-temperature plasmas with a strong guide field is analyzed on the basis of a two-dimensional gyrofluid model. The linear growth rate of the reconnecting instability is compared to analytical calculations over the whole spectrum of linearly unstable wave numbers. In the strongly unstable regime (large ??), the nonlinear evolution of the reconnecting instability is found to undergo two distinctive acceleration phases separated by a stall phase in which the instantaneous growth rate decreases. The first acceleration phase is caused by the formation of strong electric fields close to the X-point due to ion gyration, while the second acceleration phase is driven by the development of an open Petschek-like configuration due to both ion and electron temperature effects. Furthermore, the maximum instantaneous growth rate is found to increase dramatically over its linear value for decreasing diffusion layers. This is a consequence of the fact that the peak instantaneous growth rate becomes weakly dependent on the microscopic plasma parameters if the diffusion region thickness is sufficiently smaller than the equilibrium magnetic field scale length. When this condition is satisfied, the peak reconnection rate asymptotes to a constant value.

Comisso, L.; Grasso, D. [Dipartimento Energia, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino (Italy); Istituto dei Sistemi Complessi - CNR, Via dei Taurini 19, 00185 Roma (Italy); Waelbroeck, F. L. [Institute for Fusion Studies, The University of Texas at Austin, Austin, Texas 78712-1060 (United States); Borgogno, D. [Dipartimento Energia, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino (Italy)

2013-09-15

351

Percussion Discussion: Using Drums To Reconnect Youth.  

Science.gov (United States)

Reports on a therapeutic program for juvenile offenders that uses drum playing and drum building to provide alternatives for youth activities. Drums play five important roles for youth: creating a sense of community, reconnecting with history and heritage, promoting healing, educating, and celebrating victories or rites of passage. Provides…

Wilbur, John; Harris, Tom

1998-01-01

352

The relation between reconnected flux, the parallel electric field, and the reconnection rate in a three-dimensional kinetic simulation of magnetic reconnection  

International Nuclear Information System (INIS)

We investigate the distribution of parallel electric fields and their relationship to the location and rate of magnetic reconnection in a large particle-in-cell simulation of 3D turbulent magnetic reconnection with open boundary conditions. The simulation's guide field geometry inhibits the formation of simple topological features such as null points. Therefore, we derive the location of potential changes in magnetic connectivity by finding the field lines that experience a large relative change between their endpoints, i.e., the quasi-separatrix layer. We find a good correspondence between the locus of changes in magnetic connectivity or the quasi-separatrix layer and the map of large gradients in the integrated parallel electric field (or quasi-potential). Furthermore, we investigate the distribution of the parallel electric field along the reconnecting field lines. We find the reconnection rate is controlled by only the low-amplitude, zeroth and first–order trends in the parallel electric field while the contribution from fluctuations of the parallel electric field, such as electron holes, is negligible. The results impact the determination of reconnection sites and reconnection rates in models and in situ spacecraft observations of 3D turbulent reconnection. It is difficult through direct observation to isolate the loci of the reconnection parallel electric field amidst the large amplitude fluctuations. However, we demonstrate that a positive slope of the running sum of the parallel electric field along the field line as a function of field line length indicates where reconnection is occurring along the field line

2013-12-01

353

ASYMMETRIC MAGNETIC RECONNECTION IN SOLAR FLARE AND CORONAL MASS EJECTION CURRENT SHEETS  

Energy Technology Data Exchange (ETDEWEB)

We present two-dimensional resistive magnetohydrodynamic simulations of line-tied asymmetric magnetic reconnection in the context of solar flare and coronal mass ejection current sheets. The reconnection process is made asymmetric along the inflow direction by allowing the initial upstream magnetic field strengths and densities to differ, and along the outflow direction by placing the initial perturbation near a conducting wall boundary that represents the photosphere. When the upstream magnetic fields are asymmetric, the post-flare loop structure is distorted into a characteristic skewed candle flame shape. The simulations can thus be used to provide constraints on the reconnection asymmetry in post-flare loops. More hard X-ray emission is expected to occur at the footpoint on the weak magnetic field side because energetic particles are more likely to escape the magnetic mirror there than at the strong magnetic field footpoint. The footpoint on the weak magnetic field side is predicted to move more quickly because of the requirement in two dimensions that equal amounts of flux must be reconnected from each upstream region. The X-line drifts away from the conducting wall in all simulations with asymmetric outflow and into the strong magnetic field region during most of the simulations with asymmetric inflow. There is net plasma flow across the X-line for both the inflow and outflow directions. The reconnection exhaust directed away from the obstructing wall is significantly faster than the exhaust directed toward it. The asymmetric inflow condition allows net vorticity in the rising outflow plasmoid which would appear as rolling motions about the flux rope axis.

Murphy, N. A.; Miralles, M. P.; Pope, C. L.; Raymond, J. C.; Winter, H. D.; Reeves, K. K.; Van Ballegooijen, A. A.; Lin, J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Seaton, D. B. [SIDC-Royal Observatory of Belgium, Avenue Circulaire 3, 1180 Brussels (Belgium)

2012-05-20

354

Asymmetric Magnetic Reconnection in Solar Flare and Coronal Mass Ejection Current Sheets  

Science.gov (United States)

We present two-dimensional resistive magnetohydrodynamic simulations of line-tied asymmetric magnetic reconnection in the context of solar flare and coronal mass ejection current sheets. The reconnection process is made asymmetric along the inflow direction by allowing the initial upstream magnetic field strengths and densities to differ, and along the outflow direction by placing the initial perturbation near a conducting wall boundary that represents the photosphere. When the upstream magnetic fields are asymmetric, the post-flare loop structure is distorted into a characteristic skewed candle flame shape. The simulations can thus be used to provide constraints on the reconnection asymmetry in post-flare loops. More hard X-ray emission is expected to occur at the footpoint on the weak magnetic field side because energetic particles are more likely to escape the magnetic mirror there than at the strong magnetic field footpoint. The footpoint on the weak magnetic field side is predicted to move more quickly because of the requirement in two dimensions that equal amounts of flux must be reconnected from each upstream region. The X-line drifts away from the conducting wall in all simulations with asymmetric outflow and into the strong magnetic field region during most of the simulations with asymmetric inflow. There is net plasma flow across the X-line for both the inflow and outflow directions. The reconnection exhaust directed away from the obstructing wall is significantly faster than the exhaust directed toward it. The asymmetric inflow condition allows net vorticity in the rising outflow plasmoid which would appear as rolling motions about the flux rope axis.

Murphy, N. A.; Miralles, M. P.; Pope, C. L.; Raymond, J. C.; Winter, H. D.; Reeves, K. K.; Seaton, D. B.; van Ballegooijen, A. A.; Lin, J.

2012-05-01

355

Space Place: Taking the Search Out of Search and Rescue  

Science.gov (United States)

Presented in a story format, this article illustrates the use and value of Search and Rescue Satellite-Aided Tracking (SARSAT). Two links are included, one provides a detailed explanation of the SARSAT rescue process and the other presents an authentic rescue videotaped testimonial. The article is targeted to children ages 10-12.

356

BP-Mobil partnership. The common network takes place  

International Nuclear Information System (INIS)

After the partnership between BP and Mobil was signed, the program of transformation of the petrol stations network started in November 1996 in the UK and concern 3300 stations in Europe and 800 stations in France. About 9100 stations will be transformed by the end of 1998. BP France is the operator for petroleum products (petrol, fuel, bitumens, LPG..) with a 70% share holding (30% for Mobil) while Mobil is the major shareholder (51%) for the lubricants and special products activities. The chemical, aviation nd maritime activities are not concerned. Thanks to the fusion of their down-file activities in Europe, the benefits of the partnership should reach 600 to 700 million of US Dollars each year. However the restructuring cost should reach 740 millions of US Dollars in two years, which doubles the initial estimation. Short paper. (J.S.)

1997-01-01

357

Taking Care: Community, Family, and Dying in Place  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Medicine, and cancer medicine particularly, exists on the interface of the human condition and science. The profession is distinguished by its human side, yet it is science that informs and complements patient interaction.

2011-01-01

358

A MAGNETIC RECONNECTION MECHANISM FOR THE GENERATION OF ANOMALOUS COSMIC RAYS  

International Nuclear Information System (INIS)

The recent observations of the anomalous cosmic ray (ACR) energy spectrum as Voyager 1 and Voyager 2 crossed the heliospheric termination shock have called into question the conventional shock source of these energetic particles. We suggest that the sectored heliospheric magnetic field, which results from the flapping of the heliospheric current sheet, piles up as it approaches the heliopause, narrowing the current sheets that separate the sectors and triggering the onset of collisionless magnetic reconnection. Particle-in-cell simulations reveal that most of the magnetic energy is released and most of this energy goes into energetic ions with significant but smaller amounts of energy going into electrons. The energy gain of the most energetic ions results from their reflection from the ends of contracting magnetic islands, a first-order Fermi process. The energy gain of the ions in contracting islands increases their parallel (to the magnetic field B) pressure p|| until the marginal fire-hose condition is reached, causing magnetic reconnection and associated particle acceleration to shut down. Thus, the feedback of the self-consistent development of the energetic ion pressure on reconnection is a crucial element of any reconnection-based, particle-acceleration model. The model calls into question the strong scattering assumption used to derive the Parker transport equation and therefore the absence of first-order Fermi acceleration in incompressible flows. A simple one-dimensional model for particle energy gain and loss is presented in which the feedback of the energetic particles on the reconnection drive is included. The ACR differential energy spectrum takes the form of a power law with a spectral index slightly above 1.5. The model has the potential to explain several key Voyager observations, including the similarities in the spectra of different ion species.

2010-02-01

359

Laboratory Observation of Fast Collisionless Magnetic Reconnection  

Science.gov (United States)

Magnetic reconnection in the collisionless regime is studied on the Versatile Toroidal Facility (VTF). The detailed evolution of the profiles of plasma density, current density, and electrostatic potential at the onset of driven reconnection is reconstructed experimentally. Despite a constant, externally imposed reconnection drive, we show that the reconnection does not proceed in a steady-state manner. The formation and decay of the current is shown to be related to the evolution of the electrostatic potential and the associated ion polarization currents. The size of the diffusion region is inferred from the detailed knowledge of the electrostatic potential, and is shown to scale with the drift orbit width of the electrons insensitive to the ion mass and plasma density [1]. This scaling is consistent with the drift kinetic approach in Ref. [2]. In addition to the prediction of the size of the VTF diffusion region, the drift kinetic approach [2] also appears to be relevant to the interpretation of resent satellite observations: The model predicts that effects due to trapped electron will cause the distribution of electrons to be anisotropic close to the X-line. The predicted anisotropy is in close agreement with observations by the Wind satellite in the Earth magnetotail [3]. The symmetry in the distribution function, imposed by the trapped electron motion, implies a high neoclassical resistivity consistent with the high rates of reconnection observed. [1] Egedal J, Fasoli A and Nazemi J, (2003) Phys. Rev. Lett. 90, 135003. [2] Egedal J, (2002) Phys. Plasmas, 9, 1095. [3] Øieroset M, Lin RP, Phan TD, Larson DE, and Bale SD, (2002) Phys. Rev. Lett. 89, 195001.

Egedal, Jan

2003-10-01

360

Laboratory Observation of Fast Collisionless Reconnection*  

Science.gov (United States)

Magnetic reconnection in the collisionless regime is studied on the Versatile Toroidal Facility (VTF). The detailed evolution of the profiles of plasma density, current density, and electrostatic potential at the onset of driven reconnection is reconstructed experimentally. Despite a constant, externally imposed reconnection drive, we show that the reconnection does not proceed in a steady-state manner. The formation and decay of the current is shown to be related to the evolution of the electrostatic potential and the associated ion polarization currents. The size of the diffusion region is inferred from the detailed knowledge of the electrostatic potential, and is shown to scale with the drift orbit width of the electrons insensitive to the ion mass and plasma density [1]. The accurate characterization of the steady state electric and magnetic field profiles provides an excellent basis for detailed kinetic simulations of the reconnection process. With the known electric and magnetic fields Liouville's equation is readily solved numerically providing the detailed phase space distribution function of the electrons. The current profiles, obtained from the first moment of the theoretical electron distribution function, are consistent with the measured current profile. Also consistent with VTF experiment results, the theoretical current densities are three orders of magnitude below the classical value, E/? s. The phase space distributions of the electrons reveal non-Maxwellian features, which are fundamental in accounting for the momentum balance of the electrons in the vicinity of the X-line. The strong non-Maxwellian features also represent a source of free energy which can excite electromagnetic instabilities and fluctuations. [1] Egedal J, Fasoli A and Nazemi J, (2003) Phys. Rev. Lett. 90, 135003. * This work is supported by DOE and NSF

Egedal, J.; Fox, W.; Porkolab, M.; Fasoli, A.

2003-12-01

 
 
 
 
361

Magnetopause reconnection under various space weather conditions  

Science.gov (United States)

In order to develop predictive capabilities for the Sun-Earth connection, the question of how various reconnection upstream conditions influence particle energization and the stability of the reconnection current layer needs to be answered. Using magnetopause reconnection events observed by the Cluster spacecraft, we address this question by comparing the observed plasma and field features in the vicinity of the magnetopause current layer for a wide range of geomagnetic conditions including nominal times and the most severe magnetic storms. Outstanding features include: 1. Plasmoid-like structures, when observed, tend to appear in series and more frequently on the magnetosheath side of the magnetopause current layer. These plasmoids contain accelerated electrons and ions up to ~100 keV, and can prevail in guide fields ranging from nearly zero to a strength approximately equal to the reconnecting field. Associated with each of these plasmoids are a bipolar DC component and intense fluctuations in the electric fields. 2. The fastest ion outflow jets occur in the magnetospheric side of the magnetopause. 3. The plasma density transition is in general removed from the magnetopause current layer to the magnetospheric side, in contrast to the predictions of a PIC simulation and THEMIS observations [1]. Feature 1 suggests that the current layer is unstable to plasmoid formation, and that the plasmoids are effective energization sites for plasmas. The above features are not sensitive functions of the degrees of upstream asymmetries. The observation results will be compared with PIC, global hybrid as well as global Hall MHD simulations to achieve fundamental understanding of asymmetric reconnection, separating two-fluid, ion kinetic and electron kinetic effects. [1] Mozer and Pritchett, JGR, 2008

Chen, L.; Argall, M. R.; Shuster, J. R.; Li, G.; Karimabadi, H.; Daughton, W. S.; Germaschewski, K.; Torbert, R. B.; Bhattacharjee, A.

2013-12-01

362

Magnetic reconnection process in accretion disk systems  

Science.gov (United States)

At the present study, we investigate the role of magnetic reconnection in three different astrophysical systems, namely young stellar objects (YSO's), microquasars, and active galactic nuclei (AGN's). In the case of microquasars and AGN's, violent reconnection episodes between the magnetic field lines of the inner disk region (which are established by a turbulent dynamo) and those anchored into the black hole are able to heat the coronal/disk gas and accelerate particles to relativistic velocities through a diffusive first-order Fermi-like process within the reconnection site that will produce relativistic blobs. The heating of the coronal/disk gas is able to produce a steep X-ray spectrum with a luminosity that is consistent with the observations and we argue that it is being produced mainly at the foot of the reconnection zone, while the Fermi-like acceleration process within the reconnection site results a power-law electron distribution with N(E) ? E-?, with ?=5/2, and a corresponding synchrotron radio power-law spectrum with a spectral index that is compatible with that observed during the radio flares in microquasars (S? ? ?-0.75). The scaling laws that we derive for AGN's indicate that the same mechanism may be occurring there. Finally, in the case of the YSO's, a similar magnetic configuration can be reached. The amount of magnetic energy that can be extracted from the inner disk region can heat the coronal gas to temperatures of the order of 10^8 K and could explain the observed X-ray flaring emission.

Piovezan, P.; de Gouveia Dal Pino, E. M.

2009-08-01

363

Three-dimensional magnetic reconnection through a moving magnetic null  

Directory of Open Access Journals (Sweden)

Full Text Available A computational study of three-dimensional magnetic reconnection between two flux ropes through a moving reconnection site is presented. The configuration is considered in the context of two interacting spheromaks constrained by a perfectly conducting cylindrical boundary and oriented to form a single magnetic field null at its center. The initial magnetic field configuration is embedded into a uniform thermal plasma and is unstable to tilting. As the spheromaks tilt, their magnetic fields begin to reconnect at the null, subsequently displacing both the null and the reconnection site. The motion of the reconnection region and the magnetic null are shown to be correlated, with stronger correlation and faster reconnection observed in plasmas with lower thermal to magnetic pressure ratio. It is also shown that ion inertial effects allow for yet faster reconnection, but do not qualitatively change the dynamics of the process. Implications of the coupling between moving magnetic nulls and reconnection sites, as well as of possible mechanisms for fast reconnection through a moving reconnection region, are discussed. The simulations are conducted using both single-fluid and Hall MHD plasma models within the HiFi multi-fluid modeling framework.

V. S. Lukin

2011-11-01

364

Experimental study of ion heating and acceleration during magnetic reconnection  

International Nuclear Information System (INIS)

This dissertation reports an experimental study of ion heating and acceleration during magnetic reconnection, which is the annihilation and topological rearrangement of magnetic flux in a conductive plasma. Reconnection is invoked often to explain particle heating and acceleration in both laboratory and naturally occurring plasmas. However, a simultaneous account of reconnection and its associated energy conversion has been elusive due to the extreme inaccessibility of reconnection events, e.g. in the solar corona, the Earth's magnetosphere, or in fusion research plasmas. Experiments for this work were conducted on MRX (Magnetic Reconnection Experiment), which creates a plasma environment allowing the reconnection process to be isolated, reproduced, and diagnosed in detail. Key findings of this work are the identification of local ion heating during magnetic reconnection and the determination that non-classical effects must provide the heating mechanism. Measured ion flows are sub-Alfvenic and can provide only slight viscous heating, and classical ion-electron interactions can be neglected due to the very long energy equipartition time. The plasma resistivity in the reconnection layer is seen to be enhanced over the classical value, and the ion heating is observed to scale with the enhancement factor, suggesting a relationship between the magnetic energy dissipation mechanism and the ion heating mechanism. The observation of non-classical ion heating during reconnection has significant implications for understanding the role played by non-classical dissipation mechanisms in generating fast reconnection. The findings are relevant for many areas of space and laboratory plasma research, a prime example being the currently unsolved problem of solar coronal heating. In the process of performing this work, local measurements of ion temperature and flows in a well-characterized reconnection layer were obtained for the first time in either laboratory or observational reconnection research. Furthermore, much progress was made in understanding the reconnection process itself

2000-01-01

365

Highly localized, fully 3-D disruptions of the reconnection layer in the Magnetic Reconnection Experiment  

Science.gov (United States)

Magnetic reconnection is a fundamental process in plasmas which converts magnetic energy to plasma kinetic and thermal energy through topological changes. One of the important goals in magnetic reconnection research is to explain the fast reconnection rate observed in real three-dimensional laboratory and astrophysical systems. In the Magnetic Reconnection Experiment (MRX), an enhancement of the reconnection electric field is often associated with a wholesale disruption of the reconnection current layer, an intrinsically 3-D phenomena observed in the presence of out-of-plane gradients of local quantities such as reconnection layer current and density. During a disruption, the out-of-plane current decreases as current carrying electrons are redirected in the outflow direction. Observed ``O-point'' signatures and density striations suggest that this redirection often occurs though the ejection of 3-D flux rope structures. Large fluctuations in the lower hybrid frequency range are also routinely seen, but the ratio of the phase speed to the diamagnetic drift speed does not match what is predicted by 3-D kinetic simulations without disruptions. A 2-D Hall MHD analysis of the out-of-plane gradients is consistent with the buildup of magnetic energy leading to the event [1], but variation in all three spacial dimensions is required in order to obtain results in agreement with the disruptive behavior observed. Analysis and comparison with 3-D simulations is ongoing to determine if the fluctuations and/or disruptive behavior are responsible for the corresponding discrepancies in the layer structure between the experiments and 2-D kinetic simulations [2,3,4]. Supported by DOE, NASA, and NSF. [4pt] [1] J.D. Huba and L.I. Rudakov, Phys. Plasmas 10, 3139 (2003).[0pt] [2] Y. Ren, et al., Phys. Plasmas 15, 082113 (2008).[0pt] [3] S. Dorfman, et al., Phys. Plasmas 15, 102107 (2008).[0pt] [4] V. Roytershteyn, et al., Phys. Plasmas 17, 055706 (2010).

Dorfman, Seth

2011-11-01

366

Theory of magnetic reconnection in solar and astrophysical plasmas  

CERN Multimedia

Magnetic reconnection is a fundamental process in a plasma that facilitates the release of energy stored in the magnetic field by permitting a change in the magnetic topology. In this article we present a review of the current state of understanding of magnetic reconnection. We discuss theoretical results regarding the formation of current sheets in complex 3D magnetic fields, and describe the fundamental differences between reconnection in two and three dimensions. We go on to outline recent developments in modelling of reconnection with kinetic theory, as well as in the MHD framework where a number of new 3D reconnection regimes have been identified. We discuss evidence from observations and simulations of solar system plasmas that support this theory, and summarise some prominent locations in which this new reconnection theory is relevant in astrophysical plasmas.

Pontin, D I

2012-01-01

367

Theory of magnetic reconnection in solar and astrophysical plasmas.  

Science.gov (United States)

Magnetic reconnection is a fundamental process in a plasma that facilitates the release of energy stored in the magnetic field by permitting a change in the magnetic topology. In this paper, we present a review of the current state of understanding of magnetic reconnection. We discuss theoretical results regarding the formation of current sheets in complex three-dimensional magnetic fields and describe the fundamental differences between reconnection in two and three dimensions. We go on to outline recent developments in modelling of reconnection with kinetic theory, as well as in the magnetohydrodynamic framework where a number of new three-dimensional reconnection regimes have been identified. We discuss evidence from observations and simulations of Solar System plasmas that support this theory and summarize some prominent locations in which this new reconnection theory is relevant in astrophysical plasmas. PMID:22665898

Pontin, David I

2012-07-13

368

Dispersive Waves and Magnetic Reconnection in the Solar Corona  

Science.gov (United States)

Fast collisionless magnetic reconnection is thought to be linked to the existence of dispersive wave dynamics, most familiarly in the connection between whistler waves and Hall reconnection. Previous fluid simulations of reconnection (Rogers et al., (2001), PRL, 87, 19) have shown that parameter regimes --- some of which reflect possible conditions in the solar corona --- without dispersive waves have a Sweet-Parker-like scaling with system size, while dispersive wave regimes exhibit reconnection rates that are independent of system size. Here we use particle-in-cell simulations to explore these different regimes and confirm the earlier findings: The introduction of dispersive wave dynamics into a system transitions it from Sweet-Parker-like reconnection to fast reconnection.

Flanagan, A. J.

2013-12-01

369

Statistics of magnetic reconnection in two-dimensional magnetohydrodynamic turbulence  

International Nuclear Information System (INIS)

The nonlinear dynamics of magnetic reconnection in turbulence is investigated through direct numerical simulations of decaying, incompressible, two-dimensional magnetohydrodynamics. Recently, it was shown by Servidio et al. [Phys. Rev. Lett. 102, 115003 (2009)] that in fully developed turbulence complex processes of reconnection occur locally. Here, the main statistical features of these multiscale reconnection events are further described, providing details on the methodology. It is found that is possible to describe the reconnection process in turbulence as a generalized local Sweet-Parker process in which the parameters are locally controlled by the turbulence cascade, thus providing a step toward reconciling classical turbulence analysis with reconnection theory. This general description of reconnection may be useful for laboratory and space plasmas, where the presence of turbulence plays a crucial role.

2010-03-01

370

Intermittent magnetic reconnection in TS-3 merging experiment  

International Nuclear Information System (INIS)

Ejection of current sheet with plasma mass causes impulsive and intermittent magnetic reconnection in the TS-3 spherical tokamak (ST) merging experiment. Under high guide toroidal field, the sheet resistivity is almost classical due to the sheet thickness much longer than the ion gyroradius. Large inflow flux and low current-sheet resistivity result in flux and plasma pileup followed by rapid growth of the current sheet. When the pileup exceeds a critical limit, the sheet is ejected mechanically from the squeezed X-point area. The reconnection (outflow) speed is slow during the flux/plasma pileup and is fast during the ejection, suggesting that intermittent reconnection similar to the solar flare increases the averaged reconnection speed. These transient effects enable the merging tokamaks to have the fast reconnection as well as the high-power reconnection heating, even when their current-sheet resistivity is low under high guide field.

2011-11-01

371

Magnetic Reconnection with Radiative Cooling. I. Optically-Thin Regime  

CERN Document Server

Magnetic reconnection, a fundamental plasma process associated with a rapid dissipation of magnetic energy, is believed to power many disruptive phenomena in laboratory plasma devices, the Earth magnetosphere, and the solar corona. Traditional reconnection research, geared towards these rather tenuous environments, has justifiably ignored the effects of radiation on the reconnection process. However, in many reconnecting systems in high-energy astrophysics (e.g., accretion-disk coronae, relativistic jets, magnetar flares) and, potentially, in powerful laser plasma and z-pinch experiments, the energy density is so high that radiation, in particular radiative cooling, may start to play an important role. This observation motivates the development of a theory of high-energy-density radiative magnetic reconnection. As a first step towards this goal, we present in this paper a simple Sweet--Parker-like theory of non-relativistic resistive-MHD reconnection with strong radiative cooling. First, we show how, in the a...

Uzdensky, Dmitri A

2010-01-01

372

Magnetic reconnection in space and laboratory plasmas; Proceedings of the Chapman Conference on Magnetic Reconnection, Los Alamos, NM, October 3-7, 1983  

International Nuclear Information System (INIS)

The physics of magnetic reconnection is discussed in reviews and reports of theoretical and experimental investigations. Topics examined include the theory of magnetic reconnection, reconnection in astronomical objects, reconnection in the earth magnetosphere and magnetotail, computer modeling, and laboratory plasmas. Diagrams, spectra, drawings, graphs, and photographs are provided

1983-10-03

373

Magnetic reconnection in space and laboratory plasmas; Proceedings of the Chapman Conference on Magnetic Reconnection, Los Alamos, NM, October 3-7, 1983  

Energy Technology Data Exchange (ETDEWEB)

The physics of magnetic reconnection is discussed in reviews and reports of theoretical and experimental investigations. Topics examined include the theory of magnetic reconnection, reconnection in astronomical objects, reconnection in the earth magnetosphere and magnetotail, computer modeling, and laboratory plasmas. Diagrams, spectra, drawings, graphs, and photographs are provided.

Hones, E.W. Jr.

1984-01-01

374

Study of magnetic reconnection in collisional and collionless plasmas in Magnetic Reconnection Experiment (MRX)  

Science.gov (United States)

Magnetic reconnection (Parker, 1957; Sweet, 1958; Petschek, 1964; Yamada et al., 2010; Biskamp, 2000; Tsuneta, 1996; Kivelson and Russell, 1995; Yamada, 2007; Birn et al., 2001; Drake et al., 2003) is considered important to many astrophysical phenomena including stellar flares, magnetospheric disruptions of magnetars, and dynamics of galactic lobes. Research on magnetic reconnection started with observations in solar coronae and in the Earths magnetosphere, and a classical theory was developed based on MHD. Recent progress has been made by understanding the two-fluid physics of reconnection, through space and astrophysical observations (Tsuneta, 1996; Kivelson and Russell, 1995), laboratory experiments (Yamada, 2007), and theory and numerical simulations (Birn et al., 2001; Daughton et al., 2006; Uzdensky and Kulsrud, 2006). Laboratory experiments dedicated to the study of the fundamental reconnection physics have tested the physics mechanisms and their required conditions, and have provided a much needed bridge between observations and theory. For example, the Magnetic Reconnection Experiment (MRX) experiment (http://mrx.pppl.gov) has rigorously cross-checked the leading theories though quantitative comparisons of the numerical simulations and space astrophysical observations (Mozer et al., 2002). Extensive data have been accumulated in a wide plasma parameter regime with Lundquist numbers of S = 100 - 3000, where S is a ratio of the magnetic diffusion time to the Alfven transit time.

Yamada, Masaaki; Ji, Hantao

2011-06-01

375

Magnetic Weibel field generation in thin collisionless current sheets in reconnection in space plasma  

CERN Document Server

In collisionless reconnection in space plasma like the magnetospheric tail or magnetopause current layer, magnetic fields can grow from thermal level by the action of the non-magnetic Weibel instability driven in thin ($\\Delta<$ few $\\lambda_i$) current layers by the counter-streaming electron inflow from the `ion diffusion' (ion inertial Hall) region into the inner current (electron inertial) region from where the ambient magnetic fields are excluded when released by the inflowing electrons which become non-magnetic on scales $<$ few $\\lambda_e$. It is shown that under magnetospheric tail conditions it takes $\\sim 40$ e-folding times ($\\sim 20$ s) for the Weibel field to reach observable amplitudes $|{\\bf b}_{\\rm W}|\\sim 1$ nT. In counter-streaming inflows these fields are predominantly of guide field type. In non-symmetric inflows the field may possess a component normal to the current which would be capable of initiating reconnection onset.

Treumann, R A

2009-01-01

376

Does the Rate of Collisionless Reconnection Depend on the Dissipation Mechanism?  

Science.gov (United States)

The importance of the electron dissipation effect on the reconnection rate is investigated in the general case of asymmetric collisionless magnetic reconnection. Contrary to the standard collisionless reconnection model, it is found that the reconnection rate, and them acroscopic evolution of the reconnecting system, crucially depend on the nature of the dissipation mechanism and that the Hall effect alone is not able to sustain fast reconnection.

Aunai, Nicolas; Hesse, Michael; Black, Carrie; Evans, Rebekah; Kuznetsova, maria

2012-01-01

377

Does the Rate of Collisionless Magnetic Reconnection Depend on the Dissipation Mechanism?  

Science.gov (United States)

The importance of the electron dissipation effect on the reconnection rate is investigated in the general case of asymmetric collisionless magnetic reconnection. Contrary to the standard collisionless reconnection model, it is found that the reconnection rate, and the macroscopic evolution of the reconnecting system, crucially depend on the nature of the dissipation mechanism and that the Hall effect alone is not able to sustain fast reconnection.

Aunai, Nicolas; Hesse, Michael; Black, Carrie; Evans, Rebekah; Kuznetsova, Maria

2012-01-01

378

The Role of Magnetic Reconnection in Solar Activity  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We argue that magnetic reconnection plays the determining role in many of the various manifestations of solar activity. In particular, it is the trigger mechanism for the most energetic of solar events, coronal mass ejections and eruptive flares. We propose that in order to obtain explosive eruptions, magnetic reconnection in the corona must have an ``on-off'' nature, and show that reconnection in a sheared multi-polar field configuration does have this property. Numerical s...

Antiochos, Spiro K.; Devore, C. Richard

1998-01-01

379

Theory of magnetic reconnection in solar and astrophysical plasmas  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Magnetic reconnection is a fundamental process in a plasma that facilitates the release of energy stored in the magnetic field by permitting a change in the magnetic topology. In this article we present a review of the current state of understanding of magnetic reconnection. We discuss theoretical results regarding the formation of current sheets in complex 3D magnetic fields, and describe the fundamental differences between reconnection in two and three dimensions. We go on...

Pontin, D. I.

2012-01-01

380

Magnetic reconnection in the near Venusian magnetotail.  

Science.gov (United States)

Observations with the Venus Express magnetometer and low-energy particle detector revealed magnetic field and plasma behavior in the near-Venus wake that is symptomatic of magnetic reconnection, a process that occurs in Earth's magnetotail but is not expected in the magnetotail of a nonmagnetized planet such as Venus. On 15 May 2006, the plasma flow in this region was toward the planet, and the magnetic field component transverse to the flow was reversed. Magnetic reconnection is a plasma process that changes the topology of the magnetic field and results in energy exchange between the magnetic field and the plasma. Thus, the energetics of the Venus magnetotail resembles that of the terrestrial tail, where energy is stored and later released from the magnetic field to the plasma. PMID:22491094

Zhang, T L; Lu, Q M; Baumjohann, W; Russell, C T; Fedorov, A; Barabash, S; Coates, A J; Du, A M; Cao, J B; Nakamura, R; Teh, W L; Wang, R S; Dou, X K; Wang, S; Glassmeier, K H; Auster, H U; Balikhin, M

2012-05-01

 
 
 
 
381

Nonlinear magnetic reconnection in low collisionality plasmas  

International Nuclear Information System (INIS)

The magnetic reconnection in collisionless regimes, where electron inertia is responsible for the decoupling of the plasma motion from that of the field lines, is discussed. Since the linear theory of m=1 modes breaks down for very small magnetic island widths, a non linear analysis is called for. Thus, the behaviour of a collisionless, 2-D fluid slab model in the limit ?/d -> 0, is analyzed. The main result is that, when the island size is larger than the linear layer but smaller than the equilibrium scale length, the reconnection rate exhibits a quasi-explosive time behaviour, during which a current density sub-layer narrower than the skin depth is formed. It is believed that the inclusion of the electron initial term in Ohm's law opens the possibility to understand the rapidity of relaxation process observed in low collisionality plasmas. 7 refs., 6 figs

1994-07-01

382

Introduction to Plasma Dynamo, Reconnection and Shocks  

Energy Technology Data Exchange (ETDEWEB)

In our plasma universe, most of what we can observe is composed of ionized gas, or plasma. This plasma is a conducting fluid, which advects magnetic fields when it flows. Magnetic structure occurs from the smallest planetary to the largest cosmic scales. We introduce at a basic level some interesting features of non linear magnetohydrodynamics (MHD). For example, in our plasma universe, dynamo creates magnetic fields from gravitationally driven flow energy in an electrically conducting medium, and conversely magnetic reconnection annihilates magnetic field and accelerates particles. Shocks occur when flows move faster than the local velocity (sonic or Alfven speed) for the propagation of information. Both reconnection and shocks can accelerate particles, perhaps to gigantic energies, for example as observed with 10{sup 20} eV cosmic rays.

Intrator, Thomas P. [Los Alamos National Laboratory

2012-08-30

383

On Tripolar Magnetic Reconnection and Coronal Heating  

CERN Document Server

Using recent data for the photosphere-chromosphere region of the solar atmosphere the magnetic reconnection in tripolar geometry has been investigated through the procedure of Sturrock (1999). Particular attention has been given to the width of the reconnecting region, wave number of the rapidly growing tearing mode, island length scales, frequency of MHD fluctuations, tearing mode growth rate, energy dissipation rate and minimum magnetic field strength required to heat chromospheric plasma to coronal temperatures. It is found that small length scales are formed in the upper chromosphere. The maximum growth rate of tearing mode instability coincides with the peak in the energy dissipation rate both of which occur in the upper chromosphere at the same height. It is realized that the distribution of magnetic field with height is essential for a better understanding of the coronal heating problem.

Pandey, K; Lohani, N K; Pandey, Kumud; Narain, Udit

2003-01-01

384

Particle acceleration by turbulent magnetohydro-dynamic reconnection  

Science.gov (United States)

Test particles in a two dimensional, turbulent MHD simulation are found to undergo significant acceleration. The magnetic field configuration is a periodic sheet pinch which undergoes reconnection. The test particles are trapped in the reconnection region for times of order an Alfven transit time in the large electric fields that characterize the turbulent reconnection process at the relatively large magnetic Reynolds number used in the simulation. The maximum speed attained by these particles is consistent with an analytic estimate which depends on the reconnection electric field, the Alfven speed, and the ratio of Larmor period to the Alfven transit time.

Matthaeus, W. H.; Ambrosiano, J. J.; Goldstein, M. L.

1984-01-01

385

The magnetotail reconnection region in a global MHD simulation  

Directory of Open Access Journals (Sweden)

Full Text Available This work investigates the nature and the role of magnetic reconnection in a global magnetohydrodynamic simulation of the magnetosphere. We use the Gumics-4 simulation to study reconnection that occurs in the near-Earth region of the current sheet in the magnetotail. We locate the current sheet surface and the magnetic x-line that appears when reconnection starts. We illustrate the difference between quiet and active states of the reconnection region: variations in such quantities as the current sheet thickness, plasma flow velocities, and Poynting vector divergence are strong. A characteristic feature is strong asymmetry caused by non-perpendicular inflows. We determine the reconnection efficiency by the net rate of Poynting flux into the reconnection region. The reconnection efficiency in the simulation is directly proportional to the energy flux into the magnetosphere through the magnetopause: about half of all energy flowing through the magnetosphere is converted from an electromagnetic into a mechanical form in the reconnection region. Thus, the tail reconnection that is central to the magnetospheric circulation is directly driven; the tail does not exhibit a cycle of storage and rapid release of magnetic energy. We find similar behaviour of the tail in both synthetic and real event runs.

T. V. Laitinen

2005-12-01

386

Electron self-reinforcing process of magnetic reconnection.  

Science.gov (United States)

The growth of collisionless magnetic reconnection is discovered to be a nonlinear electron self-reinforcing process. Accelerated by the reconnection electric field, the small portion of energetic electrons in the vicinity of the X point are found to be the cause of the fast reconnection rate. This new mechanism explains that recent simulation results of different reconnection evolutions (i.e., steady state, quasisteady state, or nonsteady state) are essentially determined by the availability of feeding plasma inflows. Simulations are carried out with open boundary conditions. PMID:18764118

Wan, Weigang; Lapenta, Giovanni

2008-07-01

387

Self-feeding turbulent magnetic reconnection on macroscopic scales.  

Science.gov (United States)

Within a MHD approach we find magnetic reconnection to progress in two entirely different ways. The first is well known: the laminar Sweet-Parker process. But a second, completely different and chaotic reconnection process is possible. This regime has properties of immediate practical relevance: (i) it is much faster, developing on scales of the order of the Alfvén time, and (ii) the areas of reconnection become distributed chaotically over a macroscopic region. The onset of the faster process is the formation of closed-circulation patterns where the jets going out of the reconnection regions turn around and force their way back in, carrying along copious amounts of magnetic flux. PMID:18643511

Lapenta, Giovanni

2008-06-13

388

Magnetic reconnection in two-dimensional magnetohydrodynamic turbulence.  

Science.gov (United States)

Systematic analysis of numerical simulations of two-dimensional magnetohydrodynamic turbulence reveals the presence of a large number of X-type neutral points where magnetic reconnection occurs. We examine the statistical properties of this ensemble of reconnection events that are spontaneously generated by turbulence. The associated reconnection rates are distributed over a wide range of values and scales with the geometry of the diffusion region. Locally, these events can be described through a variant of the Sweet-Parker model, in which the parameters are externally controlled by turbulence. This new perspective on reconnection is relevant in space and astrophysical contexts, where plasma is generally in a fully turbulent regime. PMID:19392208

Servidio, S; Matthaeus, W H; Shay, M A; Cassak, P A; Dmitruk, P

2009-03-20

389

Transient magnetic reconnection at the magnetopause boundary layer  

International Nuclear Information System (INIS)

The main purpose of this paper is to review the new progresses of transient magnetic reconnection at the magnetopause boundary layer. During the last four years, the explorations have been focused on the following problems: transient reconnection at the high latitude boundary layer for different interplanetary magnetic field conditions, shocks caused by the vortex induced reconnection (VIR) processes, VIR processes in multiple current sheet systems, and the magnetic reconnection caused by the rush and stop of transverse shear flow. Some new results are reviewed and discussed

1999-01-01

390

Relativistic Two-fluid Simulations of Guide Field Magnetic Reconnection  

CERN Multimedia

The nonlinear evolution of relativistic magnetic reconnection in sheared magnetic configuration (with a guide field) is investigated by using two-dimensional relativistic two-fluid simulations. Relativistic guide field reconnection features the charge separation and the guide field compression in and around the outflow channel. As the guide field increases, the composition of the outgoing energy changes from enthalpy-dominated to Poynting-dominated. The inertial effects of the two-fluid model play an important role to sustain magnetic reconnection. Implications for the single fluid magnetohydrodynamic approach and the physics models of relativistic reconnection are briefly addressed.

Zenitani, Seiji; Klimas, Alex

2009-01-01

391

Numerical examination of plasmoid-induced reconnection model for solar flares: the relation between plasmoid velocity and reconnection rate  

CERN Document Server

The plasmoid-induced-reconnection model explaining solar flares based on bursty reconnection produced by an ejecting plasmoid suggests a possible relation between the ejection velocity of a plasmoid and the rate of magnetic reconnection. In this study, we focus on the quantitative description of this relation. We performed magnetohydrodynamic (MHD) simulations of solar flares by changing the values of resistivity and the plasmoid velocity. The plasmoid velocity has been changed by applying an additional force to the plasmoid to see how the plasmoid velocity affects the reconnection rate. An important result is that the reconnection rate has a positive correlation with the plasmoid velocity, which is consistent with the plasmoid-induced-reconnection model for solar flares. We also discuss an observational result supporting this positive correlation.

Nishida, Keisuke; Shiota, Daikou; Takasaki, Hiroyuki; Magara, Tetsuya; Shibata, Kazunari

2008-01-01

392

Holography of D-Brane Reconnection  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Gukov, Martinec, Moore and Strominger found that the D1-D5-D5' system with the D5-D5' angle at 45 degrees admits a deformation "rho" preserving supersymmetry. Under this deformation, the D5-branes and D5'-branes reconnect along a single special Lagrangian manifold. We construct the near-horizon limit of this brane setup (for which no supergravity solution is currently known), imposing the requisite symmetries perturbatively in the deformation rho. Reducing to the three-dimen...

Berg, Marcus; Hohm, Olaf; Samtleben, Henning

2006-01-01

393

INTERCHANGE RECONNECTION AND CORONAL HOLE DYNAMICS  

International Nuclear Information System (INIS)

We investigate the effect of magnetic reconnection between open and closed fields, often referred to as 'interchange' reconnection, on the dynamics and topology of coronal hole boundaries. The most important and most prevalent three-dimensional topology of the interchange process is that of a small-scale bipolar magnetic field interacting with a large-scale background field. We determine the evolution of such a magnetic topology by numerical solution of the fully three-dimensional MHD equations in spherical coordinates. First, we calculate the evolution of a small-scale bipole that initially is completely inside an open field region and then is driven across a coronal hole boundary by photospheric motions. Next the reverse situation is calculated in which the bipole is initially inside the closed region and driven toward the coronal hole boundary. In both cases, we find that the stress imparted by the photospheric motions results in deformation of the separatrix surface between the closed field of the bipole and the background field, leading to rapid current sheet formation and to efficient reconnection. When the bipole is inside the open field region, the reconnection is of the interchange type in that it exchanges open and closed fields. We examine, in detail, the topology of the field as the bipole moves across the coronal hole boundary and find that the field remains well connected throughout this process. Our results, therefore, provide essential support for the quasi-steady models of the open field, because in these models the open and closed flux are assumed to remain topologically distinct as the photosphere evolves. Our results also support the uniqueness hypothesis for open field regions as postulated by Antiochos et al. On the other hand, the results argue against models in which open flux is assumed to diffusively penetrate deeply inside the closed field region under a helmet streamer. We discuss the implications of this work for coronal observations.

2010-05-01

394

An Electromagnetic Drift Instability in the Magnetic Reconnection Experiment (MRX) and its Importance for Magnetic Reconnection  

International Nuclear Information System (INIS)

The role which resistivity plays in breaking magnetic field lines, heating the plasma, and plasma field slippage during magnetic reconnection is discussed. Magnetic fluctuations are observed in the MRX (Magnetic Reconnection Experiment) that are believed to provide resistive friction or wave resistivity. A localized linear theory has been proposed for their origin as an obliquely propagating Lower Hybrid Drift Instability. In this paper, the linear theory of the instability is summarized, and the resulting heating and slippage are calculated from quasi-linear theory. Making use of measured amplitudes of the magnetic fluctuations in the MRX the amount of these effects is estimated. Within the experimental uncertainties they are shown to be quite important for the magnetic reconnection process

2005-01-01

395

An electromagnetic drift instability in the magnetic reconnection experiment and its importance for magnetic reconnection  

International Nuclear Information System (INIS)

The role which resistivity plays in breaking magnetic field lines, heating the plasma, and plasma-field slippage during magnetic reconnection is discussed. Magnetic fluctuations are observed in the MRX (magnetic reconnection experiment) [M. Yamada, H. Ji, S. Hsu, T. Carter, R. Kulsrud, N. Bertz, F. Jobes, Y. Ono, and F. Perkins, Phys. Plasmas 4, 1936 (1997)] that are believed to provide resistive friction or wave resistivity. A localized linear theory has been proposed for their origin as an obliquely propagating lower hybrid drift instability. In this paper, the linear theory of the instability is summarized, and the resulting heating and slippage are calculated from quasilinear theory. Making use of measured amplitudes of the magnetic fluctuations in the MRX, the amount of these effects is estimated. Within the experimental uncertainties they are shown to be quite important for the magnetic reconnection process

2005-08-01

396

Kelvin wave turbulence generated by vortex reconnections  

Science.gov (United States)

Reconnections of quantum vortex filaments create sharp bends, which degenerate into propagating Kelvin waves. These waves cascade their energy down-scale and their wave action up-scale via weakly nonlinear interactions, and this is the main mechanism of turbulence at scales less than the inter-vortex distance. In the case of an idealized forcing concentrated around a single scale k 0, the turbulence spectrum exponent has a pure direct cascade form -17/5 at scales k > k 0 [B. V. Svistunov, Phys. Rev. B 52, 3647 (1995)] and a pure inverse cascade form -3 at k k 0 (V. Lebedev, private communication). However, forcing produced by the reconnections contains a broad range of Fourier modes. What scaling should one expect in this case? An answer to this question has been obtained using the differential model for the Kelvin wave turbulence introduced in [S. Nazarenko, JETP Lett. 83, 198 (2005)]. The main result is that the direct cascade scaling dominates; i.e., the reconnection forcing is more or less equivalent to a low-frequency forcing.

Nazarenko, S.

2007-02-01

397

The Alfvén edge in asymmetric reconnection  

Directory of Open Access Journals (Sweden)

Full Text Available We show that in the case of magnetic reconnection where the Alfvén velocity is much higher in the plasma on one side of the current sheet than the other, an Alfvén edge is formed. This edge is located between the electron and ion edges on the high Alfvén velocity side of the current sheet. The Alfvén edge forms because the Alfvén wave generated near the X-line will propagate faster than the accelerated ions forming the ion edge. We discuss possible generation mechanism and the polarization of the Alfvén wave in the case when higher Alfvén speed is due to larger magnetic field and smaller plasma density, as in the case of magnetopause reconnection. The Alfvén wave can be generated due to Hall dynamics near the X-line. The Alfvén wave pulse has a unipolar electric field and the parallel current will be such that the outer current on the high magnetic field side is flowing away from the X-line. Understanding Alfvén edges is important for understanding the separatrix regions at the boundaries of reconnection jets. We present an example of Alfvén edge observed by the Cluster spacecraft at the magnetopause.

A. Vaivads

2010-06-01

398

Ion acceleration in high frequency magnetic reconnection  

Science.gov (United States)

Ion acceleration has been recently shown to occur [1] in Particle in Cell simulations of the coalescence instability of current filaments in relativistic plasmas. Here, with the help of 2D-3V Vlasov simulations (2D in physical space and 3D in velocity space) we investigate the nonlinear development of magnetic reconnection in the high frequency electron regime discussed in Ref. [2] in a plasma with an anisotropic electron population. This reconnection process occurs in strongly inhomogeneous plasmas and develops on the electron dynamical time scale. It is mostly driven by the anisotropy of the electron distribution and, as in the MHD frequency range, it leads to the formation of magnetic islands. In the present work we study the ion dynamics and its role on this high frequency reconnection process, and in particular we investigate the possibility of effective acceleration of ions and the mechanisms that are responsible for such acceleration. [1] J.I. Sakai, et al., Phys Plasmas 9, 2959 (2002) [2] F. Califano, et al., Phys. Rev. Letters, 86, 5293 (2001)

Lisseikina, T.; Bulanov, S. V.; Califano, F.; Pegoraro, F.

2002-11-01

399

Reconnection studies in field-reversed configurations  

International Nuclear Information System (INIS)

Internal magnetic field measurements are used to study the reconnection process near the ends of a low-compression field-reversed theta pinch. The measurements indicate that the addition of independently driven magnetic mirror coils at the ends are effective in inducing rapid reconnection and in minimizing plasma losses out the ends. Fast reconnection leading to the formation of a chain of magnetic islands along the length of the coil is observed on a time scale of a 100 nsec. These islands coalesce on a time scale of 1--2 ?sec. Measured values of the resistivity are two orders of magnitude greater than classical during the implosion phase. The resistivity during the equilibrium phase is four times the classical value. Axial contraction and the n = 2 rotational instability are not observed to occur in these experiments. Sudden termination of the configurations is thought to be caused by rapid loss of the internal field. This flux dissipation may be a consequence of electron cooling by the crossing of a radiation barrier. An oxygen impurity concentration of 2% is enough to account for the power dissipated during the collapse

1985-01-01

400

Two dimensional magnetic merging and reconnection  

International Nuclear Information System (INIS)

Magnetic energy release is mergin flows in investigated by numerical integration of unsteady resistive MHD equations in two dimensions. No explosive magnetic energy release is found in two topologically distinct merging flow geometries, in the absence of imposed strong plasma inflows. The first geometry is the merging of straight field lines without magnetic reconnection, and the second is merging with reconnection at an x-type neutral point. In each geometry the merging energy release is compared with the diffusive energy release in the absence of plasma motion. It is found in both geometries that the merging energy release is less than the diffusive energy release. Magnetic island formation occurs in the reconnection simulation. The magnetic energy release appears mainly as thermal rather than kinetic energy, but the heating is not localized. These results indicate that two dimensional merging without strong forcing is not promising as a mechanism for explosive magnetic energy release, but is more promising for gradual plasma heating and magnetic field dissipation. It is suggested that similar results would apply to any merging geometry which is stable in ideal MHD

1980-11-15

 
 
 
 
401

The relation between reconnected flux, the parallel electric field, and the reconnection rate in a three-dimensional kinetic simulation of magnetic reconnection  

Energy Technology Data Exchange (ETDEWEB)

We investigate the distribution of parallel electric fields and their relationship to the location and rate of magnetic reconnection in a large particle-in-cell simulation of 3D turbulent magnetic reconnection with open boundary conditions. The simulation's guide field geometry inhibits the formation of simple topological features such as null points. Therefore, we derive the location of potential changes in magnetic connectivity by finding the field lines that experience a large relative change between their endpoints, i.e., the quasi-separatrix layer. We find a good correspondence between the locus of changes in magnetic connectivity or the quasi-separatrix layer and the map of large gradients in the integrated parallel electric field (or quasi-potential). Furthermore, we investigate the distribution of the parallel electric field along the reconnecting field lines. We find the reconnection rate is controlled by only the low-amplitude, zeroth and first–order trends in the parallel electric field while the contribution from fluctuations of the parallel electric field, such as electron holes, is negligible. The results impact the determination of reconnection sites and reconnection rates in models and in situ spacecraft observations of 3D turbulent reconnection. It is difficult through direct observation to isolate the loci of the reconnection parallel electric field amidst the large amplitude fluctuations. However, we demonstrate that a positive slope of the running sum of the parallel electric field along the field line as a function of field line length indicates where reconnection is occurring along the field line.

Wendel, D. E.; Olson, D. K.; Hesse, M.; Kuznetsova, M.; Adrian, M. L. [NASA Goddard Space Flight Center, Greenbelt, Maryland 20771 (United States); Aunai, N. [Institute for Research in Astrophysics and Planetology, University Paul Sabatier, Toulouse (France); Karimabadi, H. [SciberQuest, Inc., Del Mar, California 92014 (United States); Department of Computer and Electrical Engineering, University of California, San Diego, La Jolla, California 92093 (United States); Daughton, W. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2013-12-15

402

RHESSI and EIS observations of an above-the-looptop reconnection region  

Science.gov (United States)

A variety of solar flare observations suggest particle acceleration in the corona, at or above the flare looptop. Hard X-ray (HXR) studies, for example, occasionally reveal accelerated electrons above flare looptops, in some cases suggesting the location of the acceleration region. However, since coronal HXR sources are faint and the structure of the flare as seen in extreme ultraviolet (EUV) images is complicated, it is difficult to say where these sources lie with respect to, for example, the reconnection region.HXR and EUV observations can provide complementary information for investigating this topic. EUV imaging spectroscopy reveals bulk flows and locations of line-broadened (potentially turbulent) sources. Such observations can, for example, identify outflows from the reconnection region. HXR imaging places the flare-accelerated electrons in the context of the overall flare geometry, allowing comparison of the locations of accelerated electrons, the reconnection region, and the flare loop.In this work, data from RHESSI and Hinode/EIS are used to investigate above-the-looptop sources in the 2013 May 15 X-class flare. Above-the-looptop EIS flows and loop-top line-broadening are compared with RHESSI HXR sources in the preimpulsive phase of the flare.

Glesener, Lindsay; Hara, Hirohisa; Krucker, Sam

2014-06-01

403

Global Two-Fluid Simulations of Magnetic Reconnection  

Science.gov (United States)

Two-fluid effects are known to influence the magnetic reconnection process through non-MHD communication between the reconnection layer and surrounding magnetic field topology^1. To examine the interrelationship between the local reconnection physics and the global magnetic field geometry, we perform two-fluid simulations of the Magnetic Reconnection Experiment (MRX) and the Swarthmore Spheromak Experiment (SSX) using the NIMROD extended MHD code. For MRX, we discuss the effects of toroidicity, the shape of the electron outflow region, and the effect of downstream pressure on the reconnection process. We find that much of the communication between local and global scales is due to the pressure gradients that result from the reconnection outflow. During counter-helicity push reconnection, we observe a radial shift in position of the current sheet and an asymmetric outflow, as seen in experiment^2. This asymmetric outflow is examined in terms of separate force-density contributions. For SSX, we present simulations of counter-helicity spheromak merging in both prolate and oblate flux conservers, and discuss the impact of geometry as well as two-fluid effects on the reconnection process.^1D. Biskamp et al., Phys. Plasmas 4, 1002, (1997).^2M. Inomoto et al., Phys. Rev. Lett. 97, 135002 (2006).

Murphy, Nicholas; Sovinec, Carl

2007-11-01

404

General magnetic reconnection, parallel electric fields, and helicity  

Energy Technology Data Exchange (ETDEWEB)

Analyzing the qualitative three-dimensional magnetic structure of a plasmoid, we were led to reconsider the concept of magnetic reconnection from a general point of view. The properties of relatively simple magnetic field models provide a strong preference for one of two definitions of magnetic reconnection that exist in the literature. Any concept of magnetic reconnection defined in terms of magnetic topology seems naturally restricted to cases where the magnetic field vanishes somewhere in the nonideal (diffusion) region. The main part of this paper is concerned with magnetic reconnection in nonvanishing magnetic fields (finite-B reconnection), which has attracted less attention in the past. We show that E/sub parallel/ (the electric field component parallel to the magnetic field) plays a crucial physical role in finite-B reconnection, and we present two theorems involving E/sub parallel/. The first states a necessary and sufficient condition on E/sub parallel/ for global reconnection to occur. Here the term ''global'' means the generic case where the breakdown of magnetic connection occurs for plasma elements that stay outside the nonideal region. The second theorem relates the change of magnetic helicity to E/sub parallel/ for cases where the electric field vanishes at large distances. That these results provide new insight into three-dimensional reconnection processes is illustrated in terms of the plasmoid configuration, which was our starting point. copyright American Geophysical Union 1988

Schindler, K.; Hesse, M.; Birn, J.

1988-06-01

405

Two-dimensional MHD model of the reconnection diffusion region  

Directory of Open Access Journals (Sweden)

Full Text Available Magnetic reconnection is an important process providing a fast conversion of magnetic energy into thermal and kinetic plasma energy. In this concern, a key problem is that of the resistive diffusion region where the reconnection process is initiated. In this paper, the diffusion region is associated with a nonuniform conductivity localized to a small region. The nonsteady resistive incompressible MHD equations are solved numerically for the case of symmetric reconnection of antiparallel magnetic fields. A Petschek type steady-state solution is obtained as a result of time relaxation of the reconnection layer structure from an arbitrary initial stage. The structure of the diffusion region is studied for various ratios of maximum and minimum values of the plasma resistivity. The effective length of the diffusion region and the reconnection rate are determined as functions of the length scale and the maximum of the resistivity. For sufficiently small length scale of the resistivity, the reconnection rate is shown to be consistent with Petschek's formula. By increasing the resistivity length scale and decreasing the resistivity maximum, the reconnection layer tends to be wider, and correspondingly, the reconnection rate tends to be more consistent with that of the Parker-Sweet regime.

N. V. Erkaev

2002-01-01

406

Viscous dissipation in 3D spine reconnection solutions  

Science.gov (United States)

Aims: We consider the influence of viscous dissipation on "spine" reconnection solutions in coronal plasmas. It is known from 2D and 3D "fan" reconnection studies that viscous losses can be important. We extend these arguments to 3D "spine" reconnection solutions. Methods: Steady 3D spine reconnection models were constructed by time relaxation of the governing visco-resistive MHD equations. Scaling laws were derived that compare the relative importance of viscous and resistive damping. Results: It is shown that viscous dissipation in spine reconnection models can dominate resistive damping by many orders of magnitude. A similar conclusion, but with less severe implications, applies to current sheet "fan" solutions. These findings are not sensitive to whether classical or Braginskii viscosity is employed.

Craig, I. J. D.; Lopez, N.

2013-12-01

407

Review of recent experiments on magnetic reconnection in laboratory plasmas  

Energy Technology Data Exchange (ETDEWEB)

The present paper reviews recent laboratory experiments on magnetic reconnection. Examples will be drawn from electron current sheet experiments, merging spheromaks, and from high temperature tokamak plasmas with the Lundquist numbers exceeding 10{sup 7}. These recent laboratory experiments create an environment which satisfies the criteria for MHD plasma and in which the global boundary conditions can be controlled externally. Experiments with fully three dimensional reconnection are now possible. In the most recent TFTR tokamak discharges, Motional Stark effect (MSE) data have verified the existence of a partial reconnection. In the experiment of spheromak merging, a new plasma acceleration parallel to the neutral line has been indicated. Together with the relationship of these observations to the analysis of magnetic reconnection in space and in solar flares, important physics issues such as global boundary conditions, local plasma parameters, merging angle of the field lines, and the 3-D aspects of the reconnection are discussed.

Yamada, M.

1995-02-01

408

A Generalized Flux Function for Three-dimensional Magnetic Reconnection  

CERN Document Server

The definition and measurement of magnetic reconnection in three-dimensional magnetic fields with multiple reconnection sites is a challenging problem, particularly in fields lacking null points. We propose a generalization of the familiar two-dimensional concept of a magnetic flux function to the case of a three-dimensional field connecting two planar boundaries. Using hyperbolic fixed points of the field line mapping, and their global stable and unstable manifolds, we define a unique flux partition of the magnetic field. This partition is more complicated than the corresponding (well-known) construction in a two-dimensional field, owing to the possibility of heteroclinic points and chaotic magnetic regions. Nevertheless, we show how the partition reconnection rate is readily measured with the generalized flux function. We relate our partition reconnection rate to the common definition of three-dimensional reconnection in terms of integrated parallel electric field. An analytical example demonstrates the the...

Yeates, A R

2011-01-01

409

Magnetic flux array for spontaneous magnetic reconnection experiments  

International Nuclear Information System (INIS)

Experimental investigation of reconnection in magnetized plasmas relies on accurate characterization of the evolving magnetic fields. In experimental configurations where the plasma dynamics are reproducible, magnetic data can be collected in multiple discharges and combined to provide spatially resolved profiles of the plasma dynamics. However, in experiments on spontaneous magnetic reconnection recently undertaken at the Versatile Toroidal Facility at MIT, the reconnection process is not reproducible and all information on the plasma must be collected in a single discharge. This paper describes a newly developed magnetic flux array which directly measures the toroidal component of the magnetic vector potential, A?. From the measured A?, the magnetic field geometry, current density, and reconnection rate are readily obtained, facilitating studies of the three-dimensional dynamics of spontaneous magnetic reconnection. The novel design of the probe array allows for accurate characterization of profiles of A? at multiple toroidal angles using a relatively small number of signal channels and with minimal disturbance of the plasma

2008-06-01