Levitated Dipole
Encyclopedia
A Levitated Dipole is a proposed nuclear fusion
reactor technology using a solid superconducting torus
, magnetically
levitated in the reactor chamber. The superconductor forms an axisymmetric magnetic field
of a nature similar to Earth
's or Jupiter
's magnetosphere
s, and it is believed that such an apparatus could contain plasma
more efficiently than other fusion reactor designs.
On Friday, August 13, 2004 at 12:53 PM, the Levitated Dipole Experiment, a collaboration between Columbia University
and MIT
, successfully energized a superconducting torus with RF
and momentarily created plasma within the magnetic field of the dipole
. The LDX team has since successfully conducted its first levitation tests, including a 40-minute suspension of the superconducting coil on February 9, 2007. Scientific results, including the observation of an inward turbulent pinch, were reported in Nature Physics
.
The Levitated Dipole Experiment is funded by the United States Department of Energy
's Office of Fusion Energy.
Unlike other types of magnetically confined fusion
, the Levitated Dipole is designed to be robust to external fluctuations in electric/magnetic fields. In most laboratory plasmas, small fluctuations can cause significant energy loss; however in a dipolar magnetic field, fluctations tend to actually compress the plasma without energy loss. This compression effect was first noticed by Akira Hasegawa (of the Hasegawa-Mima equation
) after participating in the Voyager 2
encounter with Uranus.
A power source based on the LDX device would utilize an advanced fuel cycle known as the tritium suppressed DD reaction (deuterium-deuterium (D-D) reaction). In this fuel cycle the secondary tritium is removed from the plasma, a unique capability of a dipole. This has advantages relative to the more conventional deuterium-tritium (D-T) reaction of other confinement and compression devices such as the tokamak
or inertial confinement fusion
(ICF) devices that amplify and focus multiple high-energy beams of laser
s, electron
s or ion
s onto tiny pellets of D-T fuel.
Although heat and pressure requirements for D-D fusion are more difficult than D-T fusion, the payoff of the D-D reaction is the relative absence of "fast neutrons" produced by the D-T reaction that contaminate the containment vessel and require massive shielding. In addition, deuterium is readily available in sea water, unlike tritium, which must be bred in reactors before it can be used as fuel in the D-T reaction.
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
reactor technology using a solid superconducting torus
Torus
In geometry, a torus is a surface of revolution generated by revolving a circle in three dimensional space about an axis coplanar with the circle...
, magnetically
Magnetism
Magnetism is a property of materials that respond at an atomic or subatomic level to an applied magnetic field. Ferromagnetism is the strongest and most familiar type of magnetism. It is responsible for the behavior of permanent magnets, which produce their own persistent magnetic fields, as well...
levitated in the reactor chamber. The superconductor forms an axisymmetric magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
of a nature similar to Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
's or Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
's magnetosphere
Magnetosphere
A magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the intrinsic magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter,...
s, and it is believed that such an apparatus could contain plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
more efficiently than other fusion reactor designs.
On Friday, August 13, 2004 at 12:53 PM, the Levitated Dipole Experiment, a collaboration between Columbia University
Columbia University
Columbia University in the City of New York is a private, Ivy League university in Manhattan, New York City. Columbia is the oldest institution of higher learning in the state of New York, the fifth oldest in the United States, and one of the country's nine Colonial Colleges founded before the...
and MIT
Massachusetts Institute of Technology
The Massachusetts Institute of Technology is a private research university located in Cambridge, Massachusetts. MIT has five schools and one college, containing a total of 32 academic departments, with a strong emphasis on scientific and technological education and research.Founded in 1861 in...
, successfully energized a superconducting torus with RF
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
and momentarily created plasma within the magnetic field of the dipole
Dipole
In physics, there are several kinds of dipoles:*An electric dipole is a separation of positive and negative charges. The simplest example of this is a pair of electric charges of equal magnitude but opposite sign, separated by some distance. A permanent electric dipole is called an electret.*A...
. The LDX team has since successfully conducted its first levitation tests, including a 40-minute suspension of the superconducting coil on February 9, 2007. Scientific results, including the observation of an inward turbulent pinch, were reported in Nature Physics
Nature Physics
Nature Physics, is a monthly, peer reviewed, scientific journal published by the Nature Publishing Group. It was first published in October 2005 . The Chief Editor is Alison Wright, who is a full-time professional editor employed by this journal...
.
The Levitated Dipole Experiment is funded by the United States Department of Energy
United States Department of Energy
The United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...
's Office of Fusion Energy.
Unlike other types of magnetically confined fusion
Magnetic confinement fusion
Magnetic confinement fusion is an approach to generating fusion power that uses magnetic fields to confine the hot fusion fuel in the form of a plasma. Magnetic confinement is one of two major branches of fusion energy research, the other being inertial confinement fusion. The magnetic approach is...
, the Levitated Dipole is designed to be robust to external fluctuations in electric/magnetic fields. In most laboratory plasmas, small fluctuations can cause significant energy loss; however in a dipolar magnetic field, fluctations tend to actually compress the plasma without energy loss. This compression effect was first noticed by Akira Hasegawa (of the Hasegawa-Mima equation
Hasegawa-Mima equation
In plasma physics, the Hasegawa–Mima equation, named after Akira Hasegawa and Kunioki Mima, is an equation that describes a certain regime of plasma, where the time scales are very fast, and the distance scale in the direction of the magnetic field is long. In particular the equation is useful for...
) after participating in the Voyager 2
Voyager 2
The Voyager 2 spacecraft is a 722-kilogram space probe launched by NASA on August 20, 1977 to study the outer Solar System and eventually interstellar space...
encounter with Uranus.
A power source based on the LDX device would utilize an advanced fuel cycle known as the tritium suppressed DD reaction (deuterium-deuterium (D-D) reaction). In this fuel cycle the secondary tritium is removed from the plasma, a unique capability of a dipole. This has advantages relative to the more conventional deuterium-tritium (D-T) reaction of other confinement and compression devices such as the tokamak
Tokamak
A tokamak is a device using a magnetic field to confine a plasma in the shape of a torus . Achieving a stable plasma equilibrium requires magnetic field lines that move around the torus in a helical shape...
or inertial confinement fusion
Inertial confinement fusion
Inertial confinement fusion is a process where nuclear fusion reactions are initiated by heating and compressing a fuel target, typically in the form of a pellet that most often contains a mixture of deuterium and tritium....
(ICF) devices that amplify and focus multiple high-energy beams of laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
s, electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s or ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s onto tiny pellets of D-T fuel.
Although heat and pressure requirements for D-D fusion are more difficult than D-T fusion, the payoff of the D-D reaction is the relative absence of "fast neutrons" produced by the D-T reaction that contaminate the containment vessel and require massive shielding. In addition, deuterium is readily available in sea water, unlike tritium, which must be bred in reactors before it can be used as fuel in the D-T reaction.