The implosion of aluminum wire array $z$ pinches driven by a 1.4 MA, 240 ns current pulse is studied. Plasma evolution is measured in the $r-\theta$ plane for the first time by an end-on laser interferometer. Merging of coronal plasmas with density of ${10}^{17}{\mathrm{cm}}^{-3\mathrm{}}$ occurs in 90–65 ns for 16 mm diam arrays with 8–64 wires. Early uncorrelated instabilities (wavelength $\lambda \sim 0.5\mathrm{mm}$) are observed in individual wires with later development of a global $m=0\mathrm{}$ instability $\left(\lambda \sim 2\mathrm{mm}\right)$. The number of Rayleigh-Taylor instability $e$ foldings is 5.6–7 when the $m=0\mathrm{}$ instability reaches an observable level and increases with the number of wires.

• Received 30 June 1998

DOI:https://doi.org/10.1103/PhysRevLett.81.4152