Point-like Source of Extreme Ultraviolet Radiation Based on the Plasma of THz Gas Discharge in a Focused Beam

We have covered a study on an interaction of a high-power terahertz gyrotron radiation with a frequency of 0.67 THz, a power of 40 kW, and a pulse duration of 20 mu s with a flow of high mass gas - xenon for generating EUV (extreme ultraviolet) radiation by exited multicharged ions. The THz radiation was focused on the flow and a radius of the focusing beam was about 1.4 mm with a waist length of 2.7 cm. The flow was produced by injecting the gas to the vacuum chamber through a various nozzles with diameters from 20 mu m to 80 mu m with a background pressure about 10(-3) Torr and an injecting gas pressure of 0.3-3 bar. Such pressure range was chosen to cover a breakdown conditions in a small area that was calculated using the finite element method with boundary conditions same as inlet pressure and base pressure. Optimal diameter of a gas inlet is discussed, it defines by both radiation transmission of the gas and its ability to radiate that depends on the base pressure. In particular, size of a plasma discharge and the radiation output in vacuum ultraviolet (wavelength of 100-200 nm) and extreme ultraviolet (in a small range near 13.5 nm) spectral regions were measured. The discharge was localized in a small area less than 1 mm where the pressure level was high enough to fulfill the breakdown conditions, so it could be called "point-like". In the determined conditions the emission power in the wavelength range of 12-17 nm was measured as 100 Watt/cm(3) of the plasma discharge. According to the covered experiments increasing the degree of conversion from THz radiation to EUV emission in the same range can be achieved by increasing duration of the heating pulse.