Experimental investigation of the pre-implosion stages of an annular puff-gas Z-pinch

The stages of an argon annular puff-gas z-pinch prior to implosion were experimentally investigated. A fast responding conical pressure probe was developed as an accurate supersonic gas flow diagnostic for evaluating the transient gas jet formed by the puff valve and nozzle. Neutral gas density profiles for two different nozzles show radial expansion of the annular gas jets. Radial and axial profiles at two different azimuthal positions of the azimuthal magnetic field at 20 ns into the main current pulse show that the current flows in the outer 1 cm of the shell, and is returned by posts supporting the wire mesh anode at initially low axial positions, which increase with time. Image converter and streak photographs show luminosity peaked azimuthally at the post positions, radially outside the positions of the neutral gas peaks, and axially near the cathode. The photography shows that the plasma is initially tapered but that it is swept into more of a right cylinder as the implosion begins, although strong axial and azimuthal dependencies are retained. Streak interferometry yields electron line density and average volume densities in particular regions of the plasma as functions of time. These results show that the early plasma is fully ionized only at high radial positions, and that it is strongly dependent on both axial and azimuthal position