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Keywords:

  • Plasma;
  • electric microfield;
  • microfield angular velocity;
  • distribution function;
  • angular velocity distribution;
  • quasi-static approximation;
  • Holtsmark approximation;
  • independent particles;
  • spectral line

Abstract

In theory of the spectral line shapes, the conventional scheme use two approximations for the local electric field (microfield) due to all charged particles of the plasma. The quasi-static approximations for the ions and the impact approximation for the electrons. The first approximation consists to say that the electric field is constant during the characteristic time. In this work we shall transpose the idea of the first approximation, to the angular velocity of the microfield whereas its strength is kept constant and equal to its mean value. We shall use the Holtsmark approach and the independent particles model (due to Margeneau and Lewis) to compute the static distribution function of the angular velocity of the microfield. In the first approach (Holtsmark), the distribution shows a Lorentzian behavior, whereas the second approach (Margenau and Lewis) shows a gaussian behavior. Subsequently, we have applied the obtained static distribution to show the effect on the broadening of Lyman-alpha line for a plasma composed of He+ ions. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)