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Current Sheets
A current sheet is an electric current that is confined to a surface, rather than being spread through a volume of space. Current sheets feature in magnetohydrodynamics (MHD), a model of electrically conductive fluids: if there is an electric current through part of the volume of such a fluid, magnetic forces tend to expel it from the fluid, compressing the current into thin layers that pass through the volume. The largest occurring current sheet in the Solar System is the so-called heliospheric current sheet, which is about 10,000 km thick, and extends from the Sun and out beyond the orbit of Pluto. In astrophysical plasmas such as the solar corona, current sheets theoretically might have an aspect ratio (breadth divided by thickness) as high as 100,000:1. By contrast, the pages of most books have an aspect ratio close to 2000:1. Because current sheets are so thin in comparison to their size, they are often treated as if they have zero thickness; this is a result of the s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solar Corona
In astronomy, a corona (: coronas or coronae) is the outermost layer of a star's Stellar atmosphere, atmosphere. It is a hot but relatively luminosity, dim region of Plasma (physics), plasma populated by intermittent coronal structures such as solar prominence, prominences, coronal loops, and helmet streamers. The Sun's corona lies above the chromosphere and extends millions of kilometres into outer space. Coronal light is typically obscured by diffuse sky radiation and Glare (vision), glare from the solar disk, but can be easily seen by the naked eye during a total solar eclipse or with a specialized coronagraph. Spectroscopic measurements indicate strong ionization in the corona and a plasma temperature in excess of , much hotter than the surface of the Sun, known as the photosphere. is, in turn, derived . History In 1724, French-Italian astronomer Giacomo F. Maraldi recognized that the aura visible during a solar eclipse belongs to the Sun, not to the Moon. In 1809, Span ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnetic Confinement Fusion
Magnetic confinement fusion (MCF) is an approach to generate thermonuclear fusion power that uses magnetic fields to confine fusion fuel in the form of a plasma (physics), plasma. Magnetic confinement is one of two major branches of controlled fusion research, along with inertial confinement fusion. Deuterium–tritium fusion, Fusion reactions for reactors usually combine light Atomic nucleus, atomic nuclei of deuterium and tritium to form an alpha particle (helium-4 nucleus) and a neutron, where the energy is released in the form of the kinetic energy of the reaction products. In order to overcome the Coulomb barrier, electrostatic repulsion between the nuclei, the fuel must have a temperature of hundreds of millions of kelvin, at which the fuel is fully Ionization, ionized and becomes a Plasma (physics), plasma. In addition, the plasma must be at a sufficient density, and the energy must remain in the reacting region for a sufficient time, as specified by the Lawson criterion (tri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solar Flares
A solar flare is a relatively intense, localized emission of electromagnetic radiation in the Stellar atmosphere, Sun's atmosphere. Flares occur in active regions and are often, but not always, accompanied by coronal mass ejections, solar particle events, and other eruptive solar phenomena. The occurrence of solar flares varies with the 11-year solar cycle. Solar flares are thought to occur when stored magnetic energy in the Sun's atmosphere accelerates charged particles in the surrounding Plasma (physics), plasma. This results in the emission of electromagnetic radiation across the electromagnetic spectrum. The typical time profile of these emissions features three identifiable phases: a ''precursor phase'', an ''impulsive phase'' when particle acceleration dominates, and a ''gradual phase'' in which hot plasma injected into the Stellar corona, corona by the flare cools by a combination of radiation and conduction of energy back down to the lower atmosphere. The extreme ultravi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnetic Reconnection
Magnetic reconnection is a physical process occurring in electrically conducting Plasma (physics), plasmas, in which the magnetic topology is rearranged and magnetic energy is converted to kinetic energy, thermal energy, and particle acceleration. Magnetic reconnection involves plasma flows at a substantial fraction of the Alfvén wave speed, which is the fundamental speed for mechanical information flow in a magnetized plasma. The concept of magnetic reconnection was developed in parallel by researchers working in solar physics and in the interaction between the solar wind and magnetized planets. This reflects the bidirectional nature of reconnection, which can either disconnect formerly connected magnetic fields or connect formerly disconnected magnetic fields, depending on the circumstances. Ron Giovanelli is credited with the first publication invoking magnetic energy release as a potential mechanism for particle acceleration in Solar flare, solar flares. Giovanelli propose ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plasma Stability
In plasma physics, plasma stability concerns the stability properties of a plasma in equilibrium and its behavior under small perturbations. The stability of the system determines if the perturbations will grow, oscillate, or be damped out. It is an important consideration in topics such as nuclear fusion and astrophysical plasma. In many cases, a plasma can be treated as a fluid and analyzed with the theory of magnetohydrodynamics (MHD). MHD stability is necessary for stable operation of magnetic confinement fusion devices and places certain operational limits. The beta limit, for example, sets the maximum achievable plasma beta in tokamaks. On the other hand, small-scale plasma instabilities (typically described by kinetic theory), such as the drift wave instability, are believed to be the driving mechanism of turbulent transport in tokamaks, which leads to high rate of particle and energy transport across the confining magnetic fields. Plasma instabilities described by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnetic Field
A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to the magnetic field. A permanent magnet's magnetic field pulls on ferromagnetic materials such as iron, and attracts or repels other magnets. In addition, a nonuniform magnetic field exerts minuscule forces on "nonmagnetic" materials by three other magnetic effects: paramagnetism, diamagnetism, and antiferromagnetism, although these forces are usually so small they can only be detected by laboratory equipment. Magnetic fields surround magnetized materials, electric currents, and electric fields varying in time. Since both strength and direction of a magnetic field may vary with location, it is described mathematically by a function (mathematics), function assigning a Euclidean vector, vector to each point of space, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Charge Carriers
In solid state physics, a charge carrier is a particle or quasiparticle that is free to move, carrying an electric charge, especially the particles that carry electric charges in electrical conductors. Examples are electrons, ions and holes. In a conducting medium, an electric field can exert force on these free particles, causing a net motion of the particles through the medium; this is what constitutes an electric current. The electron and the proton are the elementary charge carriers, each carrying one elementary charge (''e''), of the same magnitude and opposite sign. In conductors In conducting mediums, particles serve to carry charge. In many metals, the charge carriers are electrons. One or two of the valence electrons from each atom are able to move about freely within the crystal structure of the metal. The free electrons are referred to as conduction electrons, and the cloud of free electrons is called a Fermi gas. Many metals have electron and hole bands. In som ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Books
A book is a structured presentation of recorded information, primarily verbal and graphical, through a medium. Originally physical, electronic books and audiobooks are now existent. Physical books are objects that contain printed material, mostly of writing and images. Modern books are typically composed of many pages Bookbinding, bound together and protected by a Book cover, cover, what is known as the ''codex'' format; older formats include the scroll and the Clay tablet, tablet. As a conceptual object, a ''book'' often refers to a written work of substantial length by one or more authors, which may also be distributed digitally as an electronic book (ebook). These kinds of works can be broadly Library classification, classified into fiction (containing invented content, often narratives) and non-fiction (containing content intended as factual truth). But a physical book may not contain a written work: for example, it may contain ''only'' drawings, engravings, photographs, s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aspect Ratio
The aspect ratio of a geometry, geometric shape is the ratio of its sizes in different dimensions. For example, the aspect ratio of a rectangle is the ratio of its longer side to its shorter side—the ratio of width to height, when the rectangle is oriented as a "landscape format, landscape". The aspect ratio is most often expressed as two integer numbers separated by a colon (x:y), less commonly as a simple or decimal Fraction (mathematics), fraction. The values x and y do not represent actual widths and heights but, rather, the proportion between width and height. As an example, 8:5, 16:10, 1.6:1, and 1.6 are all ways of representing the same aspect ratio. In objects of more than two dimensions, such as hyperrectangles, the aspect ratio can still be defined as the ratio of the longest side to the shortest side. Applications and uses The term is most commonly used with reference to: * Graphic / image ** Aspect ratio (image), Image aspect ratio ** Display aspect ratio ** Pape ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plasma (physics)
Plasma () is a state of matter characterized by the presence of a significant portion of charged particles in any combination of ions or electrons. It is the most abundant form of ordinary matter in the universe, mostly in stars (including the Sun), but also dominating the rarefied intracluster medium and Outer space#Intergalactic space, intergalactic medium. Plasma can be artificially generated, for example, by heating a neutral gas or subjecting it to a strong electromagnetic field. The presence of charged particles makes plasma electrically conductive, with the dynamics of individual particles and macroscopic plasma motion governed by collective electromagnetic fields and very sensitive to externally applied fields. The response of plasma to electromagnetic fields is used in many modern devices and technologies, such as plasma display, plasma televisions or plasma etching. Depending on temperature and density, a certain number of neutral particles may also be present, in wh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
