Development of continuum interferometry for dynamic measurement of plasma density in wire array z-pinches

Summary form only given. Optical laser diagnostics are widely used for probing Z-pinch plasmas. Measurement of the electron plasma density with regular laser interferometry meets 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 very complicated structures of fringes. Even two-frame interferometry cannot derive the plasma density because it does not include non-perturbed reference fringes, and the plasma near the electrodes and the wires frame the axial area of the pinch. We suggest a new diagnostic to record a continuous history of the interferograms and the individual evolution of the fringes. In this case, the plasma density could be measured by deriving the shift of the fringes on the slit of a streak camera. This diagnostic is based on the Nd:YAG laser with a long probing pulse of 300 ns, at a fundamental wavelength of 1064, Mach Zehnder interferometer, and an optical streak camera. A CW laser at the wavelength of 1064 nm with a power 0.7 W, seeds two multi-pass amplifiers. A Pockels Cell cuts a 300-500 ns pulse from the CW radiation for amplification. A sevenpass amplification provides a total gain >10 s. Faraday rotators are used to prevent self-oscillation in the laser system. The laser pulse at the fundamental frequency will be converted to the second and fourth harmonics. This diagnostic has been developed in order to provide precision measurements of the plasma density during the ablation and the implosion phases in wire arrays.