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A magnetic mirror is a configuration of magnetic field lines in which a charged particle is reflected from a high density magnetic field to low density magnetic field. This mirror effect will only occur for particles within a limited range of velocity and angle of approach. Magnetic mirrors are made of specialized electromagnets designed to create a highly inhomogeneous field. Large magnetic mirrors have been used experimentally as a means of plasma confinement. One major application being researched is to confine the hot, electrically charged plasma inside a fusion reactor to generate fusion power (see magnetic confinement fusion). A category of experimental fusion reactors called mirror machines confine plasma within a magnetic field between two magnetic mirrors. The largest to be built was the Mirror Fusion Test Facility (MFTF) in 1986. A charged particle moving within a region of magnetic field experiences a Lorentz force that causes it to move in a helical (corkscrew) path along a magnetic field line. The radius of the circle that the particle describes is called the radius of gyration or gyroradius. If it enters a region of denser magnetic field lines, a field gradient, the combination of the radial component of the fields and the azimuthal motion of the particle results in a force pointed against the gradient, in the direction of lower magnetic field. It is this force that can reflect the particle, causing it to decelerate and reverse direction.〔Fitzpatrick, Richard. "Magnetic Mirrors." Home Page for Richard Fitzpatrick. The University of Texas at Austin, 31 Mar. 2011. Web. 19 July 2011. .〕 == History == The concept of magnetic-mirror plasma confinement was proposed in mid-1950s independently by Gersh Budker〔In Russian: Fizika Plazmy i Problema Upravlyaemykh Termoyadernykh Reaktsii, Vol. 3, p. 1 (Moscow: Izd. AN SSSR, 1958); in English: G. I. Budker, Plasma Physics and the Problem of Controlled Thermonuclear Reactions, Vol. 3, pp. 1-33 (Pergamon Press, 1959)〕 at the Kurchatov Institute, Russia and Richard F. Post〔R. F. Post, Proc. of Second U.N. Int. Conf. on Peaceful Uses of Atomic Energy, Vol. 32, p. 245 (Geneva, 1958)〕 at the Lawrence Livermore National Laboratory. The first small-scale open magnetic plasma trap machine ("probkotron") was built in 1959 at the Budker Institute of Nuclear Physics in Novosibirsk, Russia. By the late 1960s, magnetic mirror confinement was considered a viable technique for producing fusion energy. In the United States, еfforts were initially funded under the United States Atomic Energy Commissions' Project Sherwood. A machine design was first published in 1967.〔G. G. Kelley, Plasma Phys. 2, 503 (1967)〕 The concept was advocated by Richard F. Post, Kenneth Fowler, Fred Coensgen and many others at the Lawrence Livermore National Laboratory.〔"Mirror Systems: Fuel Cycles, loss reduction and energy recovery" by Richard F. Post, BNES Nuclear fusion reactor conferences at Culham laboratory, September 1969.〕 As a result of advocacy, the cold war, and the 1970s energy crisis a massive magnetic mirror program was funded by the U.S. federal government. This program resulted in a series of large magnetic mirror devices including: 2X,〔Principals of plasma physics, Nicholas Krall, 1973, Page 273〕 Baseball I, Baseball II, the Tandem Mirror Experiment, the Tandem mirror experiment upgrade, the Mirror Fusion Test Facility and the MFTF-B.〔"Summary of results from the tandem mirror experiment, TMX group, February 26, 1981〕〔"TMX Major Project proposal" Fred Coensgen, January 12, 1977〕 These machines were built and tested at Livermore from the late 60's to the mid 80's.〔Booth, William. "Fusion's $372-Million Mothball." Science (York City ) 9 Oct. 1987, Volume 238 ed.: 152-55. Print.〕 A number of institutions collaborated on these machines, conducting experiments. These included the Institute for Advanced Study and the University of Wisconsin–Madison.〔"ion losses from end-stoppered mirror trap" D P Chernnin, nuclear fusion 18 (1978)〕〔"Experiments in a tandem mirror sustained and heated solely by rf" R Breun, Physical Review Letters, December 21, 1981〕 The last machine, the Mirror Fusion Test Facility was 372 million dollars, at that time, the most expensive project in Livermore history. It opened on February 21, 1986 and was promptly shut down. The reason given was to balance the United States federal budget.〔 This program was supported from within the Carter and early Reagan administrations by Edwin E. Kintner, a U.S. Navy captain, under Alvin Trivelpiece. Kintner resigned in 1982 complaining that the federal government had not provided the resources needed for the research.〔KOPPEL, NIKO. "Edwin E. Kintner, Nuclear Power Pioneer, Dies at 90." The New York Times, Science Section. The New York Times, 20 May 2010. Web. 17 Apr. 2011. The concept had a number of technical challenges including maintaining the non-Maxwellian velocity distribution. This meant that instead of many high energy ions hitting one another, the ion energy spread out into a bell curve. The ions then thermalized, leaving most of the material too cold to fuse. Collisions also scattered the charged particles so much that they could not be contained. Lastly, velocity space instabilities contributed to the escape of the plasma. Magnetic mirrors play an important role in other types of magnetic fusion energy devices such as tokamaks, where the toroidal magnetic field is stronger on the inboard side than on the outboard side. The resulting effects are known as neoclassical. Magnetic mirrors also occur in nature. Electrons and ions in the magnetosphere, for example, will bounce back and forth between the stronger fields at the poles, leading to the Van Allen radiation belts. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Magnetic mirror」の詳細全文を読む スポンサード リンク
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