Experimental results of the characterization of a cavity hollow-cathode post-discharge sputtering source by optical emission spectroscopy are presented. The discharge parameters are similar to those currently used in sputter-deposited ferromagnetic (Ni, Fe) and nonferromagnetic targets (Cu, Ti): Ar pressures, 6×10-2–1×10-1 mbar and discharge currents, 5–60 mA. The spatial distribution of the relative electron density in front of the cathode nozzle was determined from the radial distribution of light intensity by applying the Abel transformation. Therefore, the optical data could be correlated with the electrical diagnostic results obtained under low-density plasma conditions. The radial and axial distributions of the emission spectra were also mapped in the 340 to 650 nm wavelength range for Ar and metal (Ni, Ti, Cu) species.
The control of chaos in nonlinear systems by different methods is still a high interest topic particularly when this is achieved by random noise as in this work. The change of chaotic dynamics into periodic dynamics induced by random noise in a system of two coupled perturbed van der Pol oscillators and comparison with the experimentally observed behavior of a double discharge plasma that it models is presented. Methods specific to nonlinear analysis such as phase portraits, Lyapunov exponents, and Fourier spectra are used to demonstrate the changeover from chaotic to regular dynamics induced by random noise. A phase diagram determines the range of noise parameters corresponding to the lowest orders of an observed bifurcation sequence of 3 x 2(n) type and particulars of the transitions are presented.
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