Browsing by Author "Favre, Mario"

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    Comparison between laser initiated hollow gas embedded z-pinches with different initial radius
    (2006) Veloso Espinosa, Felipe; Chuaqui, Herman; Aliaga-Rossel, Raul; Favre, Mario; Mitchell, Ian; Wyndham, Edmund; HerreraVelazquez, JJE
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    NITRIDING OF SUPER-FERRITIC STAINLESS STEEL BY PLASMA IMMERSION ION IMPLANTATION IN RADIO FREQUENCY AND ECR-MICROWAVE PLASMA SYSTEM
    (IEEE, 2015) Bhuyan, H.; Favre, Mario; Cisternas, M.; Henriquez, A.; Wyndham, E.; Mandl, S.; Manova, D.; Walczak, M.
    Stainless steel 470 Li-24 Cr and 460Li-21 Cr are two new generation super-ferritic nickel free grades, contains titanium (Ti), niobium (Nb) and very small percentage of carbon (C) and nitrogen (N). The Ti and Nb enhance the corrosion resistance while the low interstitial content of C and N leads to finer precipitates and greater ductility. These grades are economic alternative to 316L and 304 with corrosion resistance comparable or superior. However, as 316L and 304 can be nitrided efficiently to improve the mechanical surface properties like hardness and wear; it has to be asked whether these new generation super-ferritic grade stainless steels can be improved further by plasma nitriding too. Two sets of experiments have been carried out, one with capacitively coupled radio frequency Plasma at PUC Chile and the other is microwave plasma at IOM Leipzig, to investigate further improvements in the mechanical properties of 470 Li-24 Cr and 460Li-21 Cr steel. Nitrided and unnitrided substrates are further investigated using different surface characterization techniques including secondary ion mass spectroscopy, scanning electron microscopy, energy dispersive x-ray analysis, Vickers hardness, wear resistance, corrosion test etc. In most of the characterizations the nitrided 470 Li-24 Cr and 460Li-21 Cr shows similar results. Increase of surface roughness for higher treatment temperature is observed in both the experiments, independent of the steel types. The formation of chromium nitride compound takes place at treatment temperature around 400 o C-450 o C, and it increases with further increase in temperature. But at higher temperature corrosion property deteriorate. The characterization results show up to 25% of nitrogen, 4-5 times increased in hardness and diffusion of nitrogen layer up to 4-6 micron for different experimental conditions. The samples implanted with temperature higher than 400°C presented wear resistance values around two orders of magnitude higher than the others.
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    Refractive optical measurements on the Llampudken generator
    (AMER INST PHYSICS, 2006) Suzuki, Francisco; Veloso, Felipe; Molina, Francisco; Mitchell, Ian; Chuaqui, Hernan; Aliaga Rossel, Raul; Favre, Mario; Wyndham, Edmund; HerreraVelazquez, JJE
    Experiments with two different configurations of dense z-pinches have been carried out on the Llampudken generator with the objective of investigating the time evolution of the discharges. These configurations were studied with refractive optical measurements using the second harmonic of a Nd:YAG laser (10 ns FVVM lambda=532 run). The Llampudken generator delivered a pulse current of 450 kA with a 260 ns rise time. Refractive optical measurements with schlieren diagnostics were made using an optical system which provided two frames per discharge. The original beam was split into two separate beams with perpendicular polarizations using a polarizer beam splitter and an extra path length was introduced into one of the beams delaying it with respect to the other. The path through the discharge chamber was equal for both beams therefore providing identical views of the plasma at two different times. The images were recorded on 35mm cameras using suitably orientated polarizers to select the corresponding beam. As a complementary diagnostic technique, MCP cameras with exposure time of 2 ns were used to obtain VUV images of the loads. Preliminary results of these experiments will be presented and discussed.
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    The formation of ring shaped laser plasmas on a metal surface
    (AMER INST PHYSICS, 2006) Veloso, Felipe; Chuaqui, Hernan; Aliaga Rossel, Raul; Favre, Mario; Mitchell, Ian; Wyndham, Edmund; HerreraVelazquez, JJE
    A method to produce ring plasmas on a metal surface is presented. The ring plasma is produced by focusing a laser pulse into an annular shape. This is achieved by using a combination of a converging lens and an axicon. The axicon is a rotationally symmetric prism. The radius of the focused ring is determined by the base angle of the axicon, and the focal length of the converging lens. The experiments are performed on a titanium surface, using a 0.18 J, 10 ns, 1064 nm pulsed, from a Nd:YAG laser. The background gas is hydrogen, at pressures in the atmospheric range. The ring structure was measured using schlieren imaging and Mach Zehnder interferometry. The expansion velocities of the laser-produced plasma in the background gas were measured in two directions; parallel and perpendicular to the metallic surface. Characteristic values are 5-9(.)10(3) m/s, for the ring radius expansion, parallel to the surface, and 1.0-1.7(.)10(4) m/s, perpendicular to the surface. Characteristic electron densities of the order of 10(18) cm(-3) were measured, with hollow radial profiles. The temperature of the plasma was estimated to be between 0.1 and 0.4 eV. This ring plasma is used as precursor plasma to achieve a hollow gas embedded z-pinch.
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    X-ray emission from copper X-pinches driven at a current rate of similar to 1kA/ns
    (ELSEVIER, 2021) Vescovi, Milenko; Veloso, Felipe; Valenzuela, Julio; Favre, Mario
    A characterization of Cu X-pinches experiments driven at current rates similar to 1kA/ns is presented. The emission of two bursts of X-rays associated with hot-spot formation and electron beam-target mechanism are identified. The first burst, associated with the central hot-spot, appears consistently at currents in the range (154 +/- 20) kA, with time correlated noticiable dips in the current derivative signal, which indicate sudden changes in load impedance. This first burst emits photons pulses of similar to 1-2 ns width and with source sizes ranging between 50 and 150 mu m with emission in the 2-5 keV energy range combined with photons in the similar to 8-9 keV range. The second burst, associated with electron beam-target mechanism, emits longer pulses of tens of nanoseconds, with source sizes larger than similar to 0.75 mm and emission concentrated in energies >5 keV, reaching up to 9 keV or more. Spectroscopic data shows the presence of K-shell line emissions of Cu XXVII and Cu XXVIII, which combined with PrismSpect simulations indicate a electron temperature of similar to 850 eV with an ion density of 10(22) cm(-3). Further details and analysis of the X-pinch plasma and its possible applications are presented and discussed.