A compact ultrafast capillary plasma discharge as an intense XUV source

Abstract

A fast nanosecond capillary discharge for fast repetition rate operation has been designed and tested. Operated in Ar and Ar/He mixtures X-ray emission from ionization stages from Ar VIII to XII have been observed according to capillary dimensions and operating voltages. Intense electron beams are formed as a result of the transient hollow cathode effect. The emission characteristics are presented for capillaries of two lengths, 21 and 26 mm, and at three diameters, 0.8, 1.6 and 3.2 mm. In addition, time resolved observations allow comparison of theory and experiment of the emission in relation to the current and applied voltage. We find from the spectra a strong dependence on the capillary dimensions, capillary operating conditions such as voltage, gas mix and pressure, diameter and length with clear evidence of wall ablation under some conditions. This has important consequences on the long term reliability of the discharge. The energy output at 4.9 nm (Ar IX emission) and the in-band (13.5 nm 1%) is also presented.