Plasma Formation on the Surface of Condensed Matter under the Effect of Powerful X-Ray Pulse

In a number of experiments, the surfaces of condensed matter, for example, the electrodes of pulsed power facilities, are exposed to powerful pulsed X-ray radiation with an energy flux density of ~1 TW/cm². The source of this radiation can be, for example, Z-pinches formed by current compression of multi-wire liners. Under the effect of this radiation, evaporation and plasma formation processes can occur on the surface of the electrodes. This paper provides a theoretical examination of these processes. In the case where the plasma layer thickness is small compared to the characteristic dimensions of the electrodes, plasma formation can be described by one-dimensional equations of magnetohydrodynamics taking radiation transfer into account. One-dimensional calculations performed for the experimental conditions at the Angara-5-1 facility (energy flux density coming from the pinch, ~0.2 TW/cm², radiation exposure time ~15 ns, electrode material Fe), have shown that the characteristic plasma temperature in this case is ~40 eV, density ~3 mg/cm³, and its expansion speed is ~60 km/s. It is interesting that the magnetic fields in these experiments, which are relatively small (~0.8 MG) and are incapable to lead to plasma formation, restrain the expansion of the plasma with their pressure and affect its characteristic values and expansion speed. The speed obtained in the calculation is somewhat less than that measured experimentally using an X-ray electron-optical converter (~90 km/s), that may be due to not one dimensional turbulent plasma expansion or due to experimental errors.