Research On Z-Pinch Of X-ray Polarization Spectroscopy Of High-Temperature Plasmas

In the experimental investigations of gas-puff Z-pinch implosion, the x-ray lines emitted from plasmas contain plentiful information, such as temperature, density and ionization of plasmas. Most of the spectroscopic diagnostics developed for plasmas have been based on properties of line intensity distributions and line profiles. X-ray line polarization spectroscopy is studied by changing the orientation of the crystal analyzer in separate measurements. The spectra were recorded simultaneously with two crystal crystal analyzers: one set up to record a polarization state parallel to the z-pinch column, and the other one set up to record a state of polarization perpendicular to the z-pinch axis, both crystal analyzers collected radiation emitted at 90°with respect to the z-pinch axis. Polarization x-ray lines from highly charged ions is especially useful, because such lines are typically less susceptible to the effects of magnetic and electric fields. Electron kinetic simulation and analysis of this regime indicate that the high-energy part of the electron velocity distribution exhibits noticeable deviation from a Maxwellian behavior and strong anisotropy. This paper was supported by National Natural Science Foundation of China (National Natural Science Associated Foundation) under contract No.10576041, the domestic first polarization crystal spectrograph has been successfully developed, and the experiments have been carried out at the Yang accelerator. X-ray lines emission has been used to diagnose the degree of polarization and electron temperature.X-ray line polarization spectroscopy can be interpreted with Zeeman effect. An electric dipole line transition with upper and lower states have the same value of the magnetic quantum number MJ, the emission is linearly polarized parallel to the direction of electron collision(z-axis). On the other hand, if the magnetic quantum number changes by one unit, the emission is polarized in a direction perpendicular to z-axis. The polarization degree is calculated with the multipole expansion of the radiation field and the photon density matrix in theory, and there is little different between the two approachs. The absolute value of polarization degree will decrease with the increase of collision-electron energy.The x-ray intensities of reflection and refraction from crystal are deduced in theory and the Brewster's angle is near 45°through calculation. The Bragg angle is 45°for the optimum ratio of the crystal reflectivities of x-rays polarized perpendicular and parallel to the plane of dispersion crystal. The capability of crystal is determined by lattice spacing, full wave at half maximum, peak of diffraction efficiency and integral reflective coefficient. The lattice spacing of crystal is in connection with the wavelength of x-ray line. Crystal with high lattice spacing could diffract x-ray with long and short wavelength, but the capability of angular dispersion is feeble in short wave band. The full wave at half maximum, peak of diffraction efficiency and integral reflective coefficient can be influenced by surface treatment.Several kinds of crystal spectrographs are investigated and the frameworks of polarization crystal spectrograph including crystal analyzer, flashboard, flange and black box of film are fabricated. The x-ray transmissivity of Al has relations with its density, thickness and x-ray wavelength. It is not strictly monotone with the increasing of x-ray wavelength.The experiments have been executed to diagnose plasma at Z-pinch Yang accelerator after the polarization spectrograph is developed. The experiments suggest that the x-ray spectra emitted from Ar plasma are photographed by using the polarization spectrograph and the wavelength resolution is above 1000. In the paper the polarization degree and electron temperature of plasma are investigated. Three methods for calculating the polarization degree with spectra intensity are analyzed. The experimental results have confirmed considerable differences in the relative intensities of the Ar resonance line(w) and intercombination line(y). The linear polarization of resonance line and inter-combination line are calculated according to the intensity of the spectra. The methods for calculating electron temperature with spectra intensity are analyzed, and the electron temperature(960～1060keV) of plasma is estimated on the basis of the line ratios between dielectronic recombination satellites and the w-resonance line.We discuss of the polarization degrees and compare them with the total energy of Z-pinch. The polarization degree is decreasing with the increasing of Z-pinch energy. A characteristic feature of the spectra appears to be a distinct difference in relative intensities of the spectra registered with the two crystal analyzers simultaneously in different directions. So the polarization degree could affect on the diagnosis of electron temperature and excluding it may lead to serious overestimates of plasmas temperature. Anisotropic plasmas have the characteristics and the intensity ratios of x-ray lines have to be taken into account in plasma diagnostics for estimating plasma electron density and electron temperature correspondingly. So the further work must be done to verify all the relevant influences properly.