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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 Coulomb collision ： ウィキペディア英語版 Coulomb collision A Coulomb collision is a binary elastic collision between two charged particles interacting through their own electric field. As with any inverse-square law, the resulting trajectories of the colliding particles is a hyperbolic Keplerian orbit. This type of collision is common in plasmas where the typical kinetic energy of the particles is too large to produce a significant deviation from the initial trajectories of the colliding particles, and the cumulative effect of many collisions is considered instead. == Mathematical Treatment for Plasmas == In a plasma a Coulomb collision rarely results in a large deflection. The cumulative effect of the many small angle collisions, however, is often larger than the effect of the few large angle collisions that occur, so it is instructive to consider the collision dynamics in the limit of small deflections. We can consider an electron of charge -''e'' and mass ''m''e passing a stationary ion of charge +''Ze'' and much larger mass at a distance ''b'' with a speed ''v''. The perpendicular force is (1/4πε0)''Ze''2/''b''2 at the closest approach and the duration of the encounter is about ''b''/''v''. The product of these expressions divided by the mass is the change in perpendicular velocity: :$\backslash Delta\; m\_e\; v\_\backslash perp\; \backslash approx\; \backslash frac\; \backslash ,\; \backslash frac$ Note that the deflection angle is proportional to $1/v^2$. Fast particles are "slippery" and thus dominate many transport processes. The efficiency of velocity-matched interactions is also the reason that fusion products tend to heat the electrons rather than (as would be desirable) the ions. If an electric field is present, the faster electrons feel less drag and become even faster in a "run-away" process. In passing through a field of ions with density ''n'', an electron will have many such encounters simultaneously, with various impact parameters (distance to the ion) and directions. The cumulative effect can be described as a diffusion of the perpendicular momentum. The corresponding diffusion constant is found by integrating the squares of the individual changes in momentum. The rate of collisions with impact parameter between ''b'' and (''b''+d''b'') is ''nv''(2π''b'' d''b''), so the diffusion constant is given by :$$ D_ = \int \left(\frac\right)^2 \, \frac \, nv (2\pi b\,b) = \left(\frac\right)^2 \, \frac \, \int \frac 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「Coulomb collision」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. All Rights Reserved.