Capillary discharge as a table-top soft xray source

Abstract

Summary form only given. Soft x-ray emission characteristics from a compact pulsed capillary ns discharge are described for a hollow cathode discharge operating in N/He gas mixtures. Different configurations with alumina and nitride capillaries of 21 and 36 mm in length and inner diameters of 1.6 and 3.2 mm were studied. Fast charging from an IGBT based pulsed power circuit stores ~0.5 J and allows operation from 17 to 600 Hz at peak current of ~5 kA for voltages of 10-35 kV. Time-evolution measurements of line emission in the visible range aid in the characterization of plasma dynamics. Time-integrated spectra from 20-200 Å show emission of He-like Nitrogen at 28.8 Å, representing a possible source for water window soft x-ray microscopy. Spectral contrast with 10-20 eV plasma spectra reveals the influence of axial electron beams, generated by hollow cathode dynamics, in plasma ionization and consequent x-ray emission. Time-of-flight measurements determine fast electrons of ~5 keV are produced in the hollow cathode and filtered diode emission measurements deliver energy output at 28.8 Å for the different configurations analyzed. Plasma source size was obtained by MCP images of a filtered slit-wire system, evidencing full wall detachment and good spatial stability. The optimal discharge conditions and system configuration for soft x-ray generation and its enhancement by e-beams production are discussed, as well as the feasibility of this plasma discharge as a table-top soft x-ray source for microscopy applications.