Characteristics of plasma formation in a hollow cathode triggered fast capillary discharge

We reported previously, the combination of the features of a fast capillary discharge with the inherent features of a transient hollow cathode discharge (THCD) leading to a new type of hollow cathode triggered capillary discharge. Such discharges operate in a regime different from the standard capillary discharge known in literature. An electron beam being supported by the THCD creates an on-axis channel for discharge formation. The capillary wall acts only as limiter and wall material will not contaminate the discharge plasma until the later part of the discharge, providing that the initial rate of current rise is sufficiently high. A low inductance electrode configuration allows this condition to be satisfied. In this paper, we present a systematic study of several capillary discharge devices with different aspect ratio and filling gases, under different electrical drive parameters. Typical discharge current of several kA is delivered to the discharge with ns risetime, producing a sub-mm size plasma column radiating efficiently in the VUV to soft X-ray region. Extensive measurements have been carried out with VUV spectroscopy to characterize the plasma. The temporal development of the source diameter is measured by a slit-wire technique, demonstrating the on-axis initiation process. (5 pages)