"Point" X-ray source engendered by hot spots in a high-current discharge

The hot spots occurring in a high-Z plasma of high current vacuum discharges are the bright sources of EUV and soft X-rays. A thorough study of discharge dynamics and radiation performance of a vacuum spark was carried out. The experimental model of industrial EUV/X-ray source was designed and tested, and its application for X-ray lithography and X-ray microscopy was examined. The experiments show that the hot spot is a high-density, high-temperature plasma configuration caused by "neck" formation in the discharge plasma and subsequent compression of the neck pinch, apparently because of the radiative losses from the compressing plasma. Eventually, one or several high-density "micropinches" are formed in the neck, which emit a burst of soft X-rays generated by the highly ionized atoms mostly in the form of line radiation. The micropinch size displayed by the radiation near 1 keV is 40/spl times/150 /spl mu/m/sup 2/; usually it decays into several spots of 3/spl times/10 /spl mu/m/sup 2/ recorded in radiation above 4 keV. The X-ray output from a single micropinch is /spl sim/10/sup 15/ W/cm/sup 3/sr in a spectral band of 0.5-1.5 keV. The details of neck evolution are discussed and the limiting conditions of micropinch occurrence are outlined. The experimental data are compared with the computer simulation of high-Z plasma compression allowing for radiative losses.