Study of the 1-MA z-pinch with interferometry and shadowgraphy at the wavelengthes 266 and 532 NM

S D Altemara,V V Ivanov,D Papp,G S Sarkisov,A Haboub,A L Astanovitskiy,J M Kindel

doi:10.1109/plasma.2009.5227505

Abstract

Summary form only given. The UV laser probing at 266 nm is a promising diagnostics for the Z-pinch plasma. Laser diagnostics at the wavelength 532 nm are not applicable for Z-pinches with an electron plasma density n e >5-10 19 cm -3 because of the strong inverse bremsstrahlung absorption and refraction of the probing beam. UV laser probing has a significant advantage because the absorption increment for inverse bremsstrahlung in plasma is ~lambda 2 and the deflection angles on the density gradients are also ~lambda 2 for the linear gradient. Calculations show that the absorption in z-pinch plasma with the electron density of N e =2-10 20 cm -3 at 266 nm is a factor 4 less than at 532 nm. This factor increases to >200 in plasma with the electron density of N e =4-10 20 cm -3 . UV probing diagnostics has been in development at the Zebra generator since 2008. UV laser probing was tested with the Z-pinch plasmas at the ablation, implosion, and stagnation phases in the 1-MA Zebra generator. The UV interferograms and shadowgrams of the z-pinch plasma were compared with the regular interferograms and shadowgrams at 532 nm. The two lasers with wavelengths 532 nm and 266 nm and pulse durations of 0.15 ns were synchronized to plusmn2 ns for "two-color" probing of plasma. Experiments were carried out with star-like, cylindrical, and planar wire arrays. The UV laser shadowgraphy was shown to be a dramatic improvement in probing ability of the wire array plasma dynamics. Dense core in the corona plasma, the precursor in small-diameter wire arrays, plasma passed in the "gate" of two closely located wires, and details of the stagnated z-pinches were resolved with shadowgraphy at 266 nm. The UV interferometry allows for the measurement of the electron density of plasma of the stagnated z-pinch in the implosions of Al "light" wire arrays. Further development of the UV diagnostics includes: two-frame shadowgraphy, high-resolution probing of the Z-pinch, and Faraday rotation diagnostics. UV probing diagnostics can be applied to investigate the mass transport, hot spots, shock waves, and plasma turbulence in wire arrays implosions on the Zebra generator.

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