Dynamic measurement of plasma density in wire array z-pinches by using continuum interferometry*

Measurement of the electron plasma density with regular laser interferometery encounters the zero-number fringe issue on the axis of the z-pinch. From the ablation stage on, the density of the inhomogeneous plasma increases quickly and produces a very complicated structure of fringes. We suggested a new continuous interferometry diagnostic that has been developed for the 1-MA Zebra generator. This diagnostic can record a continuous history of the interferograms and the individual evolution of the streaked fringes. It is based on a Nd:YAG laser with a long probing pulse of 300 ns at either the fundamental wavelength or the second harmonic, a Mach Zehnder interferometer, and an optical streak camera. By using this new diagnostic, the precursor z-pinch plasma density can be precisely measured during the ablation and the implosion phases in wire arrays.