The soft X-ray spectrum and plasma jet properties in a range of sub-joule capillary discharges operated in argon

Summary form only given. We present a series of observations of a small very low inductance sub-joule capillary discharge in a variety of different geometries and under a variety of operating conditions. The plasmas emit mainly in the corresponding filling gas and whose temperature attains about 20 eV for a few nanoseconds. However under certain modes of operation the strong axial electron beam associated with transient hollow cathode mechanism guides and interacts with the pinch plasma to give intense emission from higher ionization states. The spectra presented are for operation in Argon at stored driver energies from 60 to 500 mJ and additionally show a significant dependance on the repetition rate as well as the operating pressure and pressure gradient between the hollow cathode entrance aperture and the anode exit of the capillary. Inspite of the mm diameter of the capillary bore, emission from ablated alumina wall material is minimal for some geometrical configurations conforming to theoretical modelling of the discharge. In addition the electron beam and plasma jet emanating from the anode and propagating in the partially ionized argon may be observed from its optical emission and at the lowest discharge energies may be cuantified from time resolved double Langmuir probe observations.