Current distribution and the azimuthal clumping instabilities in a Z-pinch wire array

Summary form only given. We have recently developed an analytic theory on the linear and nonlinear evolution of the most unstable azimuthal clumping mode (the pi mode, in which neighboring wires pair up) in a discrete wire array. This azimuthal instability is violent and dominates over the radial motion of the wire array, both in the linear and nonlinear regimes. Thus, the lack of wire-pairing provides a sensitive test on the maximum current that the discrete wires may carry. An experiment on this clumping instability was performed at Cornell, in which the pi mode was initially seeded in an 8-wire array in such a way that it was deeply in the nonlinear regime of the pi-mode. The analytic theory, the Sandia ALEGRA code (assuming no coronal plasmas), and the discrete wire circuit code (REIN), all indicate the wires carry at most a few percent of the total current to explain the lack of azimuthal clumping according to X-ray images. The remaining current necessarily resides with the plasma corona which has been neglected in the theory. A rudimentary model suggests that a radially spread-out current distribution is less susceptible to the azimuthal clumping instability.