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The results of experimental research the dynamics and macrostructure of zone of interaction of hypersonic radiative high power density plasma flows generated by electromagnetic plasma accelerator of erosive type operated in MHD-compression regime with spatially restricted polymeric targets in gases are presented.
The effect of turbulent modification of optical properties (controllable essential variation of optical properties and structure of plasma – gas boundary layers due to shear flow instability and turbulization) has been discovered at the analysis of our experimental and theoretical research of high-current plasmodynamic discharges in gases. Using developed methods of laser interferometry and spectroscopy and new experimental technology of quantitative measurements of powerful radiation flows (> 10^6 W/cm^2) in VUV it is shown, that turbulent modification of optical properties is to take place at any radiating dense plasma flow propagation through a gas. If there is no turbulization at supersonic plasma flow movement in gas, a strong shock wave is generated, and the compressed gas between the plasma volume and the shock wave usually absorbs a considerable part of short wave plasma radiation. Due to Kelvin-Helmholtz instability the compressed gas blanket can be completely replaced with turbulent layer where plasma and gas are mixed. This layer is heated up to T~1–3 eV, which results in: a) an essential enhancement of its radiativity (10^2–10^3 times) in visible spectral region (due to ionization and inverse bremsstrahlung radiation); b) a considerable (10–100 times) reduction of the layer's optical thickness in VUV spectrum (due to thermal destruction of absorbing atoms and molecules) (formation of so-called windows of transparency in VUV spectrum). This yields: a) appearance of visible "skin" of the plasma jet (the skin's radiation being even more bright than radiation of the hottest Te~5–10 eV – inner regions of the radiating plasma flow); b) considerable enhancement of plasma's useful UV and VUV radiation flows that enter the unperturbed gas around the radiating plasma jet. The use of this effect in radiative-plasmodynamic technologies of surface modification and treatment by: powerful UV-VUV radiation and/or hypersonic plasma flows is discussed. |