Short-implosion-time 20-mm diameter, 300-wire tungsten arrays maintain high peak x-ray powers despite a reduction in peak current from 19 to 13 MA. The main radiation pulse on tests with a 1-mm on-axis rod may be explained by the observable $\overrightarrow{j}\times \overrightarrow{B}$ work done during the implosion, but bare-axis tests require sub-mm convergence of the magnetic field not seen except perhaps in $>1$ keV emission. The data include the first measurement of the imploding mass density profile of a wire-array $Z$ pinch that further constrains simulation models.

• Received 13 July 2007

DOI:https://doi.org/10.1103/PhysRevLett.100.145002