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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Non-neutral plasmas ： ウィキペディア英語版 Non-neutral plasmas A non-neutral plasma is a plasma for which the total charge is sufficiently different from zero, so that the electric field created by the un-neutralized charge plays an important or even dominant role in the plasma dynamics.〔R. C. Davidson, "Physics of Non-neutral Plasmas", (Addison-Wesley, Redwood City, CA, 1990)〕 The simplest non-neutral plasmas are plasmas consisting of a single charge species. Examples of single species non-neutral plasmas that have been created in laboratory experiments are (plasmas consisting entirely of electrons ),〔J. H. Malmberg and J. S. DeGrassie, Properties of a Non-neutral Plasma, Phys. Rev. Lett. 35, 577 (1975)〕 (pure ion plasmas ),〔J. J. Bollinger and D. J. Wineland, Strongly Coupled Non-neutral Ion Plasma, Phys. Rev. Lett. 53, 348 (1984)〕 (positron plasmas ),〔R. G. Greaves, M. D. Tinkle, and C. M. Surko, "Creation and uses of positron plasmas", Physics of Plasmas 1 (1994)〕 and antiproton plasmas.〔G. B. Andresen et al., "Evaporative Cooling of Trapped Antiprotons to Cryogenic Temperatures", Phys. Rev. Lett. 105, 013003 (2010).〕 Non-neutral plasmas are used for research into basic plasma phenomena such as cross-magnetic field transport,〔F. Anderegg, "Internal Transport in Non-Neutral Plasmas," presented at Winter School on Physics with Trapped Charged Particles; to appear, Imperial College Press (2013) http://nnp.ucsd.edu/pdf_files/Anderegg_transport_leshouches_2012.pdf〕 nonlinear vortex interactions,〔D. Durkin and J. Fajans, "Experiments on Two-Dimensional Vortex Patterns", Phys. Fluids, 12:289, 2000〕 and plasma waves and instabilities.〔F. Anderegg, C.F. Driscoll, D.H.E. Dubin, and T.M. O'Neil "Wave-Particle Interactions in Electron Acoustic Waves in Pure Ion Plasmas," Phys. Rev. Lett. 102, 095001 (2009)〕 They have also been used to create cold neutral antimatter, by carefully mixing and recombining cryogenic pure positron and pure antiproton plasmas. Positron plasmas are also used in (atomic physics experiments ) that study the interaction of antimatter with neutral atoms and molecules . Cryogenic pure ion plasmas have been used in studies of strongly coupled plasmas 〔 and (quantum entanglement ). More prosaically, pure electron plasmas are used to produce the microwaves in microwave ovens, via the magnetron instability. Neutral plasmas in contact with a solid surface (that is, most laboratory plasmas) are typically non-neutral in their edge regions. Due to unequal loss rates to the surface for electrons and ions, an electric field (the "ambipolar field" ) builds up, acting to hold back the more mobile species until the loss rates are the same. The electrostatic potential (as measured in electron-volts) required to produce this electric field depends on many variables but is often on the order of the electron temperature. Non-neutral plasmas for which all species have the same sign of charge have exceptional confinement properties compared to neutral plasmas. They can be confined in a thermal equilibrium state using only static electric and magnetic fields, in a Penning trap configuration (see Fig. 1).〔Daniel H. E. Dubin and T. M. O’Neil, “Trapped Non-neutral Plasmas, Liquids and Crystals (the thermal equilibrium states), Rev. Mod. Phys. 71, 87 (1999)〕 Confinement times of up to several hours have been achieved.〔J. H. Malmberg et al., "The Cryogenic Pure Electron Plasma", Proceedings of the 1984 Sendai Symposium on Plasma Nonlinear Phenomena" http://nnp.ucsd.edu/pdf_files/Proc_84_Sendai_1X.pdf〕 Using the "rotating wall" method,〔X.-P. Huang, F. Anderegg, E.M. Hollmann, C.F. Driscoll and T.M. O'Neil "Steady-State Confinement of Non-neutral Plasma by Rotating Electric Fields,"Phys. Rev. Lett. 78, 875 (1997)〕 the plasma confinement time can be increased arbitrarily. Such non-neutral plasmas can also access novel states of matter. For instance, they can be cooled to cryogenic temperatures without recombination (since there is no oppositely charged species with which to recombine). If the temperature is sufficiently low (typically on the order of 10 mK), the plasma can become a non-neutral liquid or a crystal.〔J. H. Malmberg and T. M. O’Neil, “The pure electron plasma, liquid and crystal, Phys. Rev. Lett. 39, 1333 (1977)〕 The body-centered-cubic structure of these plasma crystals has been observed by Bragg scattering in experiments on laser-cooled pure beryllium plasmas.〔J. N. Tan et al., "Observation of Long-Range Order in Trapped Ion Plasmas by Bragg Scattering", Phys. Rev. Lett. 75, 4198 (1995)〕 ==Equilibrium of a single species non-neutral plasma == Non-neutral plasmas with a single sign of charge can be confined for long periods of time using only static electric and magnetic fields. One such configuration is called a Penning trap, after the inventor F. M. Penning. The cylindrical version of the trap is also sometimes referred to as a Penning-Malmberg trap, after Prof. John Malmberg. The trap consists of several cylindrically symmetric electrodes and a uniform magnetic field applied along the axis of the trap (Fig 1). Plasmas are confined in the axial direction by biasing the end electrodes so as to create an axial potential well that will trap charges of a given sign (the sign is assumed to be positive in the figure). In the radial direction, confinement is provided by the Lorentz force due to rotation of the plasma about the trap axis. Plasma rotation causes an inward directed Lorentz force that just balances the outward directed forces caused by the unneutralized plasma as well as the centrifugal force. Mathematically, radial force balance implies a balance between electric, magnetic and centrifugal forces:〔 where particles are assumed to have mass ''m'' and charge ''q'', ''r'' is radial distance from the trap axis and ''Er'' is the radial component of the electric field. This quadratic equation can be solved for the rotational velocity $v\_\backslash theta$, leading to two solutions, a slow-rotation and a fast-rotation solution. The rate of rotation $\backslash omega\; =\; -v\_\backslash theta/r$ for these two solutions can be written as :$\backslash omega\; =\; \backslash frac\; \backslash pm\backslash sqrt$, where $\backslash Omega\_c\; =\; q\; B/m$ is the cyclotron frequency. Depending on the radial electric field, the solutions for the rotation rate fall in the range $0\; \backslash le\; \backslash omega/\backslash Omega\_c\; \backslash le\; 1$. The slow and fast rotation modes meet when the electric field is such that $q\; E\_r/\; =\; ^2/4$. This is called the Brillouin limit; it is an equation for the maximum possible radial electric field that allows plasma confinement. This radial electric field can be related to the plasma density ''n'' through the Poisson equation, :$\backslash frac\; \backslash frac(r\; E\_r)=\; qn/\backslash epsilon\_0\; ,$ and this equation can be used to obtain a relation between the density and the plasma rotation rate . If we assume that the rotation rate is uniform in radius (i.e. the plasma rotates as a rigid body), then Eq. (1) implies that the radial electric field is proportional to radius ''r''. Solving for ''Er'' from this equation in terms of $\backslash omega$ and substituting the result into Poisson's equation yields This equation implies that the maximum possible density occurs at the Brillouin limit, and has the value :$n\_B=\; \backslash frac=\backslash frac$ where $c=1/\backslash sqrt$ is the speed of light. Thus, the rest energy density of the plasma, n·m·c2, is less than or equal to the magnetic energy density $B^2/(2\backslash mu\_0)$ of the magnetic field. This is a fairly stringent requirement on the density. For a magnetic field of 10 tesla, the Brillouin density for electrons is only nB = . The density predicted by Eq.(2), scaled by the Brillouin density, is shown as a function of rotation rate in Fig. (2). Two rotation rates yield the same density, corresponding to the slow and fast rotation solutions. 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「Non-neutral plasmas」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. 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