Dynamics of plasma formation during quasicontinuous laser irradiation of metals in high-pressure nitrogen atmospheres

This is a study of target destruction and the dynamics of surface plasma formation during the interaction of quasicontinuous laser radiation (λ = 1.06 μm, q = 1–7 MW/cm², τ ∼ 1.5 msec) with D16T duraluminum and bismuth in nitrogen atmospheres at pressures p = 1–20 atm. High speed photography and spectroscopy of the erosion plasma flare are used to determine the onset time for vaporization of the target, as well as the times of appearance of erosion and nitrogen plasmas for different gas pressures and laser energy fluxes q. The emergence of the plasma front from the vapor zone into the surrounding nitrogen is detected experimentally and the properties of the nitrogen plasma are studied.     

Polycrystalline material diagnostics based on the peak of polarization bremsstrahlung radiation propagation against the velocity of emitting electrons

We discuss the possibility of using an anomalous peak of polarization bremsstrahlung radiation from relativistic electrons for the diagnostics of polycrystalline materials.     

X-ray topographic study of quartz cavities with a triple electrode

AT-cut quartz cavities with a triple electrode have been studied. Their main advantage over cavities with an orthogonally directed electric field is that the triple electrode hinders excitation of vibrations on the first mechanical harmonic. A comparison of the parameters of different cavities shows that, in the case of their excitation on the first harmonic, the equivalent resistance of triple-electrode cavities is higher by a factor of 24, their equivalent inductance is higher by a factor of 3, and their Q factor is lower by a factor of 12 compared to the corresponding parameters of conventional cavities. When working on the third harmonic, the parameters of triple-electrode cavity are comparable with those of cavities with an orthogonally directed electric field. An X-ray topographic study of the vibrations of piezoelectric cells in triple-electrode cavities showed a pronounced vibration antinode on the third harmonic, located at the plate center, whereas the corresponding first-harmonic antinode is distorted and diffuse. The values of the Q factor of element vibrations on these harmonics differ by a factor of almost 8. Thus, the use of a triple electrode provides optimal conditions for cavity operation on the third harmonic. There is no need to use any other tools (e.g., introduce an additional resistor) to suppress the first harmonic.     

Effect of anomalous photoabsorption on parametric X-ray radiation from relativistic electrons

Parametric x-ray radiation from relativistic electrons moving in a crystal is theoretically investigated in Bragg geometry. It is shown that the effect of anomalous photoabsorption can manifest itself within this geometry of the scattering of the pseudophoton field of a fast particle. In this case, the angular distribution of the radiation changes significantly, while the total radiation yield can increase by a factor of 3.     

Experimental Investigation of the Polarization Bremsstrahlung from Relativistic Electrons in Amorphous and Polycrystalline Media

The polarization bremsstrahlung (PBS) generated by relativistic charged particles in a dense medium represents a new and important problem in the radiation physics of charged particles. In the present paper, the results of experimental investigations of PBS conducted with the linear electron accelerator developed at the Scientific Research Institute for Nuclear Physics at Moscow State University (SRINP MSU) are presented; the specific features of spectral and angular PBS distribution in an amorphous and polycrystalline target and directions for their further study are discussed.     

Polarization bremsstrahlung from relativistic electrons moving in a small-grained medium

Polarization bremsstrahlung from relativistic electrons moving in a medium consisting of very small crystals oriented at random is studied theoretically. The results of this analysis predict a sharp dependence of the spectral and angular features of the radiation on the crystal dimensions and on the angle of observation. The possibility of developing, on the basis of the phenomena considered in the present study, a newmet hod for studying lowly ordered media is highlighted.