Experimental observation in a high current capillary discharge

Experimental observations of the soft X-ray emission from a 5 mm diameter, 60 mm length capillary discharge in an initial vacuum show the effectiveness of transient hollow cathode mechanisms in establishing the initial plasma conditions for a 120 kA Z-pinch. Hollow cathode geometry is used. A laser spark behind the cathode orifice initiates an axial electron beam when an external bias provides a current-limited preionizing current in the capillary. These beams intensify during the first few ns of the main discharge. The Z-pinch dynamics are measured using time-resolved soft X-ray spectroscopy and filtered pinhole photography. These are found to vary according to the rate of rise of the current, 1.5 and 3.0 × 10¹² A/s, the polarity and level of the prionizing current. A stable pinch is formed with a preionizing current of ∼50A as an e-beam from the hollow cathode and with the higher value of di/dt. With higher values of preionizing current the e-beams show diode rather than hollow cathode origin and the stability of the following Z-pinch deteriorates notably. The pinched plasma is predominantly of wall material at ∼100 eV.