In this and next chapters, we review laboratory PPS experiments performed so far. According to the classification in Chaps. 3 and 4, we classify the plasmas into ionizing plasma and recombining plasma. In the present chapter, we review experiments on plasmas belonging to the former class. Low-pressure gas discharge plasmas naturally fall into this class, since, in the stationary state, the ionization flux of atoms in the plasma is balanced with the recombination flux of ions due to the diffusion motion of the ions to the cell wall, not with the CR (collisional-radiative) or volume recombination flux. Another group would be z-pinch plasmas which are formed by strong plasma contraction leading to high temperature and density in a short time. Some laser-produced plasmas have been interpreted as ionizing plasma in the original papers so that they are introduced in this chapter. The magnetically confined plasmas belong to this class and are now becoming the subject of PPS experiments.
A correct estimation of plasma parameters in fusion experiments cannot be done unless the role of polarization of x-ray line emission is recognized.An x-ray polarimeter is presented, based on single hexagonal crystal. The polarimeter selects two polarized components simultaneously. Simple analytical formulae are suggested to determine Bragg angle for analysed x-rays and for the directions of reflected polarized components. The polarimeter is expected to be especially useful to study polarization of x-rays emitted from plasmas with thermonuclear parameters.
In high current pulse discharges of the plasma focus (PF) type, inside the collapsing pinch column, there are formed local micro-regions of high-density and high-temperature plasma, so-called hot spots. Individual hot spots are separated in space and time. Each hot spot is characterized by its specific electron concentration and temperature, as well as by the emission of x-ray lines with different polarization. When numerous hot spots are produced it is impossible to determine local plasma parameters and to interpret the polarization effects. To eliminate this problem this study was devoted to the realization of PF-type discharges with single hot spot only. It has been achieved by a choice of the electrode configuration, which facilitated the formation of a single hot spot emitting intense x-ray lines. At the chosen experimental conditions it was possible to determine local plasma parameters and to demonstrate evident differences in the polarization of the observed x-ray lines.
This paper presents recent space resolved experimental study of polarization of He-like argon spectra in plasma focus. Consideration is made on dominant anisotropy mechanisms responsible for preferential orientation of different excited states at the moment of de-excitation in dense hot plasmas. Essential attention is given to alignment along the resulting electromagnetic field created as by exciting electron and also by the local electromagnetic field existing inside the plasma. Such study would provide the tool to diagnose distribution of electromagnetic fields and to count for anisotropy effects when calculating plasma parameters.
The paper reports on recent studies of the X-ray emission from hot-spots formed within the Plasma-Focus (PF) pinch column. Differences in the polarization of selected X-ray lines, as well as those in local values of the electron concentration and temperature for various hot-spots, are estimated and discussed.
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