The Levitated Dipole Experiment ( LDX ) was an experiment investigating the generation of fusion power using the concept of a levitated dipole . The device was the first of its kind to test the levitated dipole concept and was funded by the US Department of Energy . The machine was also part of a collaboration between the MIT Plasma Science and Fusion Center and Columbia University , where another (non-levitated) dipole experiment, the Collisionless Terrella Experiment (CTX), was located.
41-464: LDX or ldx may refer to: Levitated Dipole Experiment , nuclear fusion energy generation experiment Lisdexamfetamine , stimulant prodrug Saint-Laurent-du-Maroni Airport , Saint-Laurent-du-Maroni, French Guiana (IATA: LDX ) Long distance xerography , an early form of facsimile transmission invented by the Xerox corporation Topics referred to by
82-572: A 40-minute suspension of the superconducting coil on February 9, 2007. Shortly after, the coil was damaged in a control test in February 2007 and replaced in May 2007. The replacement coil was inferior, a copper wound electromagnet , that was also water cooled. Scientific results, including the observation of an inward turbulent pinch, were reported in Nature Physics . This experiment needed
123-404: A change in its coupled magnetic flux, d Φ B d t {\displaystyle {\frac {d\Phi _{B}}{dt}}} . Therefore, an electromotive force is set up in the second loop called the induced emf or transformer emf. If the two ends of this loop are connected through an electrical load, current will flow. A current clamp is a type of transformer with
164-409: A circuit and a magnetic field is the phenomenon underlying electrical generators . When a permanent magnet is moved relative to a conductor, or vice versa, an electromotive force is created. If the wire is connected through an electrical load , current will flow, and thus electrical energy is generated, converting the mechanical energy of motion to electrical energy. For example, the drum generator
205-473: A concept he called lines of force . However, scientists at the time widely rejected his theoretical ideas, mainly because they were not formulated mathematically. An exception was James Clerk Maxwell , who used Faraday's ideas as the basis of his quantitative electromagnetic theory. In Maxwell's model, the time varying aspect of electromagnetic induction is expressed as a differential equation, which Oliver Heaviside referred to as Faraday's law even though it
246-592: A magnetic field for roughly an 8-hour period. Overall, the ring weighed 560 kilograms and levitated 1.6 meters above a superconducting ring. The ring produced a 5.7 T peak field. This superconductor was encased inside a liquid helium cryostat, which kept the electromagnet below 10 kelvins . This design is similar to the D20 dipole experiment at Berkeley and the RT-1 experiment at the University of Tokyo. The dipole
287-457: A result of the turbulent pinch phenomenon. There were two modes of operation observed: These had been proposed by Nicholas Krall in the 1960s. In the case of deuterium fusion (the cheapest and most straightforward fusion fuel) the geometry of the LDX has the unique advantage over other concepts. Deuterium fusion makes two products, that occur with near equal probability: In this machine,
328-420: A rotor approximately 20 mm in diameter from a DC motor used in a CD player. Note the laminations of the electromagnet pole pieces, used to limit parasitic inductive losses. In this illustration, a solid copper bar conductor on a rotating armature is just passing under the tip of the pole piece N of the field magnet. Note the uneven distribution of the lines of force across the copper bar. The magnetic field
369-473: A solid metallic mass is rotated in a magnetic field, because the outer portion of the metal cuts more magnetic lines of force than the inner portion; hence the induced electromotive force is not uniform; this tends to cause electric currents between the points of greatest and least potential. Eddy currents consume a considerable amount of energy and often cause a harmful rise in temperature. Only five laminations or plates are shown in this example, so as to show
410-426: A sort of wave would travel through the ring and cause some electrical effect on the opposite side. He plugged one wire into a galvanometer , and watched it as he connected the other wire to a battery. He saw a transient current, which he called a "wave of electricity", when he connected the wire to the battery and another when he disconnected it. This induction was due to the change in magnetic flux that occurred when
451-502: A special free-floating electromagnet, which created the unique "toilet-bowl" magnetic field. The magnetic field was originally made of three coils. Each coil contained a 19-strand niobium-tin Rutherford cable (common in low-temperature superconducting magnets). These looped around inside an inconel structure; creating a magnet that looked like an oversized donut. The donut was charged using induction . Once charged, it generated
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#1732775791130492-483: A split core which can be spread apart and clipped onto a wire or coil to either measure the current in it or, in reverse, to induce a voltage. Unlike conventional instruments the clamp does not make electrical contact with the conductor or require it to be disconnected during attachment of the clamp. Faraday's law is used for measuring the flow of electrically conductive liquids and slurries. Such instruments are called magnetic flow meters. The induced voltage ε generated in
533-811: Is an element of contour of the surface Σ, combining this with the definition of flux Φ B = ∫ Σ B ⋅ d A , {\displaystyle \Phi _{\mathrm {B} }=\int _{\Sigma }\mathbf {B} \cdot d\mathbf {A} \,,} we can write the integral form of the Maxwell–Faraday equation ∮ ∂ Σ E ⋅ d ℓ = − d d t ∫ Σ B ⋅ d A {\displaystyle \oint _{\partial \Sigma }\mathbf {E} \cdot d{\boldsymbol {\ell }}=-{\frac {d}{dt}}{\int _{\Sigma }\mathbf {B} \cdot d\mathbf {A} }} It
574-584: Is based upon the figure to the bottom-right. A different implementation of this idea is the Faraday's disc , shown in simplified form on the right. In the Faraday's disc example, the disc is rotated in a uniform magnetic field perpendicular to the disc, causing a current to flow in the radial arm due to the Lorentz force. Mechanical work is necessary to drive this current. When the generated current flows through
615-525: Is different from Wikidata All article disambiguation pages All disambiguation pages Levitated Dipole Experiment LDX ceased operations in November 2011 when its funding from the Department of Energy ended as resources were being diverted to tokamak research. The concept of the levitated dipole as a fusion reactor was first theorized by Akira Hasegawa in 1987. The concept
656-570: Is generally credited with the discovery of induction in 1831, and James Clerk Maxwell mathematically described it as Faraday's law of induction . Lenz's law describes the direction of the induced field. Faraday's law was later generalized to become the Maxwell–Faraday equation, one of the four Maxwell equations in his theory of electromagnetism . Electromagnetic induction has found many applications, including electrical components such as inductors and transformers , and devices such as electric motors and generators . Electromagnetic induction
697-444: Is more concentrated and thus stronger on the left edge of the copper bar (a,b) while the field is weaker on the right edge (c,d). Since the two edges of the bar move with the same velocity, this difference in field strength across the bar creates whorls or current eddies within the copper bar. High current power-frequency devices, such as electric motors, generators and transformers, use multiple small conductors in parallel to break up
738-528: Is one of the four Maxwell's equations , and therefore plays a fundamental role in the theory of classical electromagnetism . Faraday's law describes two different phenomena: the motional emf generated by a magnetic force on a moving wire (see Lorentz force ), and the transformer emf that is generated by an electric force due to a changing magnetic field (due to the differential form of the Maxwell–Faraday equation ). James Clerk Maxwell drew attention to
779-492: Is slightly different from Faraday's original formulation and does not describe motional emf. Heaviside's version (see Maxwell–Faraday equation below ) is the form recognized today in the group of equations known as Maxwell's equations . In 1834 Heinrich Lenz formulated the law named after him to describe the "flux through the circuit". Lenz's law gives the direction of the induced emf and current resulting from electromagnetic induction. Faraday's law of induction makes use of
820-447: Is the emf and Φ B is the magnetic flux . The direction of the electromotive force is given by Lenz's law which states that an induced current will flow in the direction that will oppose the change which produced it. This is due to the negative sign in the previous equation. To increase the generated emf, a common approach is to exploit flux linkage by creating a tightly wound coil of wire , composed of N identical turns, each with
861-409: The magnetic flux Φ B through a region of space enclosed by a wire loop. The magnetic flux is defined by a surface integral : Φ B = ∫ Σ B ⋅ d A , {\displaystyle \Phi _{\mathrm {B} }=\int _{\Sigma }\mathbf {B} \cdot d\mathbf {A} \,,} where d A is an element of the surface Σ enclosed by
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#1732775791130902-420: The applied B-field, tending to decrease the flux through that side of the circuit, opposing the increase in flux due to rotation. On the near side of the figure, the return current flows from the rotating arm through the near side of the rim to the bottom brush. The induced B-field increases the flux on this side of the circuit, opposing the decrease in flux due to r the rotation. The energy required to keep
943-433: The battery was connected and disconnected. Within two months, Faraday found several other manifestations of electromagnetic induction. For example, he saw transient currents when he quickly slid a bar magnet in and out of a coil of wires, and he generated a steady ( DC ) current by rotating a copper disk near the bar magnet with a sliding electrical lead (" Faraday's disk "). Faraday explained electromagnetic induction using
984-411: The chamber produced a magnetic field which attracted the floating dipole magnet. This external field would interact with the dipole field, suspending the dipole. The magnetic field produce by the floating dipole magnet is used to confine the plasma. The plasma forms around the dipole and inside the chamber. The plasma is formed by heating a low pressure gas using a radio frequency , essentially microwaving
1025-422: The conducting rim, a magnetic field is generated by this current through Ampère's circuital law (labelled "induced B" in the figure). The rim thus becomes an electromagnet that resists rotation of the disc (an example of Lenz's law ). On the far side of the figure, the return current flows from the rotating arm through the far side of the rim to the bottom brush. The B-field induced by this return current opposes
1066-481: The disc moving, despite this reactive force, is exactly equal to the electrical energy generated (plus energy wasted due to friction , Joule heating , and other inefficiencies). This behavior is common to all generators converting mechanical energy to electrical energy. When the electric current in a loop of wire changes, the changing current creates a changing magnetic field. A second wire in reach of this magnetic field will experience this change in magnetic field as
1107-401: The floating dipole magnet cannot have services (such as cooling) connected from the outside world, this makes thermal management of the floating magnet much harder in a D-T machine. Electromagnetic induction Electromagnetic or magnetic induction is the production of an electromotive force (emf) across an electrical conductor in a changing magnetic field . Michael Faraday
1148-393: The induced electromotive force in any closed circuit is equal to the rate of change of the magnetic flux enclosed by the circuit: E = − d Φ B d t , {\displaystyle {\mathcal {E}}=-{\frac {d\Phi _{\mathrm {B} }}{dt}}\,,} where E {\displaystyle {\mathcal {E}}}
1189-435: The magnetic field B due to a conductive liquid moving at velocity v is thus given by: where ℓ is the distance between electrodes in the magnetic flow meter. Electrical conductors moving through a steady magnetic field, or stationary conductors within a changing magnetic field, will have circular currents induced within them by induction, called eddy currents . Eddy currents flow in closed loops in planes perpendicular to
1230-422: The magnetic field. They have useful applications in eddy current brakes and induction heating systems. However eddy currents induced in the metal magnetic cores of transformers and AC motors and generators are undesirable since they dissipate energy (called core losses ) as heat in the resistance of the metal. Cores for these devices use a number of methods to reduce eddy currents: Eddy currents occur when
1271-416: The plasma in a ~15-kilowatt field. The machine was monitored using diagnostics fairly standard to all of fusion. These included: The plasma is confined by the dipole magnetic field. Single particles corkscrew along the field lines of the dipole magnet at the cyclotron resonance frequency while completing poloidal orbits. The electron population was shown to have a peaked pressure and density profile as
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1312-430: The relation between the emf E {\displaystyle {\mathcal {E}}} in a wire loop encircling a surface Σ, and the electric field E in the wire is given by E = ∮ ∂ Σ E ⋅ d ℓ {\displaystyle {\mathcal {E}}=\oint _{\partial \Sigma }\mathbf {E} \cdot d{\boldsymbol {\ell }}} where d ℓ
1353-436: The same magnetic flux going through them. The resulting emf is then N times that of one single wire. E = − N d Φ B d t {\displaystyle {\mathcal {E}}=-N{\frac {d\Phi _{\mathrm {B} }}{dt}}} Generating an emf through a variation of the magnetic flux through the surface of a wire loop can be achieved in several ways: In general,
1394-403: The same term [REDACTED] This disambiguation page lists articles associated with the title LDX . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=LDX&oldid=1228833036 " Category : Disambiguation pages Hidden categories: Short description
1435-609: The secondary tritium could be partially removed, a unique property of the dipole. Another fuel choice is tritium and deuterium. This reaction can be done at lower heats and pressures. But it has several drawbacks. First, tritium is far more expensive than deuterium. This is because tritium is rare. It has a short half-life making it hard to produce and store. It is also considered a hazardous material, increasing difficulties with storage and handling. Finally, tritium and deuterium produces fast neutrons which means any reactor burning it would require heavy radiation shielding for its magnets. As
1476-620: The separate physical phenomena in 1861. This is believed to be a unique example in physics of where such a fundamental law is invoked to explain two such different phenomena. Albert Einstein noticed that the two situations both corresponded to a relative movement between a conductor and a magnet, and the outcome was unaffected by which one was moving. This was one of the principal paths that led him to develop special relativity . The principles of electromagnetic induction are applied in many devices and systems, including: The emf generated by Faraday's law of induction due to relative movement of
1517-401: The subdivision of the eddy currents. In practical use, the number of laminations or punchings ranges from 40 to 66 per inch (16 to 26 per centimetre), and brings the eddy current loss down to about one percent. While the plates can be separated by insulation, the voltage is so low that the natural rust/oxide coating of the plates is enough to prevent current flow across the laminations. This is
1558-465: The wire loop, B is the magnetic field. The dot product B · d A corresponds to an infinitesimal amount of magnetic flux. In more visual terms, the magnetic flux through the wire loop is proportional to the number of magnetic field lines that pass through the loop. When the flux through the surface changes, Faraday's law of induction says that the wire loop acquires an electromotive force (emf). The most widespread version of this law states that
1599-425: Was discovered by Michael Faraday , published in 1831. It was discovered independently by Joseph Henry in 1832. In Faraday's first experimental demonstration (August 29, 1831), he wrapped two wires around opposite sides of an iron ring or " torus " (an arrangement similar to a modern toroidal transformer ). Based on his understanding of electromagnets, he expected that, when current started to flow in one wire,
1640-431: Was later proposed as an experiment by Jay Kesner of MIT and Michael Mauel of Columbia University in 1997. The pair assembled a team and raised money to build the machine. They achieved first plasma on Friday, August 13, 2004, at 12:53 PM. First plasma was done by (1) successfully levitating the dipole magnet and (2) RF heating the plasma. The LDX team has since successfully conducted several levitation tests, including
1681-399: Was suspended inside a "squashed-pumpkin"-shaped vacuum chamber, which was about 5.2 meters in diameter and ~3 meters high. At the base of the chamber was a charging coil. This coil is used to charge the dipole, using induction . Next, the dipole is raised into the center of the chamber using a launcher-rather system running through the bore of the dipole magnet. A copper magnet fixed on top of