Browsing by Author "Aliaga Rossel, Raul"

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    Laser initiated hollow gas-embedded Z-pinch
    (IEEE, 2004) Chuaqui Kettlun, Hernán; Aliaga Rossel, Raul; Veloso Espinosa, Felipe; Pavez Morales, Cristian Arturo; Favre Domínguez, Mario; Mitchell, Ian H.; Wyndham Hodder, Edmund Sydenham
    Results of new optical method of generating a precursor plasma for a shell gas embedded Z-pinch are presented. Experiments were performed on a pulse power generator using a peak current up to 150 kA with a rise time of 70 ns, 120 ns pulse length. The optical precursor plasma was generated by using a Nd-Y AG laser, 200 ml, 8 ns at 1.06 μm. Two different optical schemes were used, one consists of a combination of lenses capable of producing a hollow beam; while the other uses an axicon to generate the hollow beam. In both cases the hollow beam was focused at the cathode surface where metallic ring plasma, of either 2 or 6 mm diameter, is created. The annular preionization is created immediately before or during the first 30 ns after the line voltage is applied. The discharge was carried out in a chamber filled with hydrogen gas at 1/3 atm. Flat electrodes were used with 10 mm separation. The anode has a 6 mm diameter central hole to allow the passage of the preionizing laser. Optical diagnostics (schlieren, shadowgraphy and interferometry) were performed using the second harmonics of the same laser used to preionize. Preionizing using an axicon results in better formed hollow discharges.
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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 X pinch experiments on the Llampudken Generator
    (IEEE, 2002) Mitchell, Ian H.; Aliaga Rossel, Raul; Gómez Luna, Jorge Antonio; Chuaqui Kettlun, Hernán; Favre Domínguez, Mario; Wyndham Hodder, Edmund Sydenham
    The results from the first plasma physics experiments on the Llampüdkeñ Generator (1MA, 250 ns) are presented. X Pinch experiments have been undertaken at current levels of 400 kA with a rise time of ∼250 ns. X pinches were produced mainly from aluminium wires of different diameters and with varying numbers of wires. Results from X-ray diagnostics characterising the emitted radiation are presented. The diagnostics include filtered PIN diodes and a pinhole and slit-wire camera. Radiation of energy greater then 2.5 keV was emitted from hot spots in timescales of a few nanoseconds. Using the results from the slit-wire camera, the diameter of the hot spots is shown to be less than 5 µm.
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    X-ray and plasma dynamics of an intermediate size capillary discharge
    (2002) Wyndham Hodder, Edmund Sydenham; Aliaga Rossel, Raul; Chuaqui Kettlun, Hernán; Favre Dominguez, Mario Benjamin; Mitchell, Ian H.; Choi, Peter
    A small pulsed power generator, 150 kA and 120 ns, is used to form a plasma in a 5-mm diameter alumina ceramic tube. A hollow cathode geometry is used and a preionized plasma is formed in an initial vacuum background by focussing a pulsed Nd:YAG laser onto a metallic target in the hollow cathode volume. The evolution of the preionizing plasma and its expansion into the main discharge volume may be assisted by applying a current of order Amps for a variable time before the main discharge current is applied. Strong electron beams are observed both during the preionizing stage and during the start of the main current. The plasma species and temporal evolution during the main discharge is observed using X-ray spectroscopy and X-ray pinhole imaging. On varying the rate of rise of the current in the pinching phase, the transient hollow cathode effect was found to be significant at early times in the discharge in the case of the lower value of dI/dt. Both the pinch temperature and diameter depend on varying the dI/dt from 1.5 to 3 /spl times/ 10/sup 12/ A/s. The implications of plasma injection for metal vapor capillary discharges are discussed.