Plasma Polarization Spectroscopy (PPS) is a new area of plasma spectroscopy by which we investigate anisotropic characteristics of the plasma. For example, from the observation of polarization of emission lines of atoms or ions in the plasma, we may obtain information about the anisotropic velocity distribution of electrons.
A helium plasma is produced by microwave resonance heating in a cusp-shaped magnetic field. Several neutral helium lines are found polarized in the direction perpendicular to the magnetic field; the maximum polarization degree exceeds 10 %.
In the kinetic model, the population-alignment collisional-radiative (PACR) model, we assign two quantities to each atomic level, the population and the alignment. The former gives the observed intensity of a line originating from this level and the latter gives the polarization. We construct a PACR model for neutral helium. In this model, we need various cross sections for electron impact: e.g., cross sections for ordinary excitation process, for alignment production from population, for alignment (coherence) transfer, for alignment destruction. In the case of neutral helium, we have several data calculated by the group of Dr. Csanak[1], and by Drs. Bray and Fursa[2]. By incorporating these cross sections into our model, we fit our calculated populations and alignments to the observation. We arrive at the conclusion that the velocity distribution is of a Saturn-type which consists of the central thermal component of 14 eV and the "ring" component displaced by 10 eV from the central component. The relative number of electrons in the ring part is 40 %.

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