Browsing by Author "Chuaqui, H."
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- ItemExperimental studies of ion beam anisotropy in a low energy plasma focus operating with methane(2006) Bhuyan, H.; Favre, M.; Valderrama, E.; Chuaqui, H.; Wyndham, E.We have investigated, with time and space resolution, the ion beam emission from a plasma focus (PF) device, operating in methane, at 20 kV, with 1.8 kJ stored energy. A detector array is used to measure simultaneously the ion beams at five different angular directions with respect to the PF axis (0 degrees, 10 degrees, 15 degrees, 20 degrees and 90 degrees), at a distance of 77 cm from the ion source. Ion beam energy correlations for operation in methane indicate that the dominant charge states on the detector are H+, C+4 and C+5, irrespective of the angular positions. The time integrated ion beam signal and the energy-dispersive x-ray analysis of a carbon films deposited on silicon surface shows the impurity emission from the PF electrode surface. Measured ion fluxes are maximum for the energy range of 15-40 keV, 50-100 keV and 100-300 keV, for H+, C+4, and C+5, respectively. Measurements of the angular distribution of hydrogen and carbon ions reveal a strong angular anisotropy. It is argued that the observed angular anisotropy of the ion beam emission can be explained in terms of ion Larmor radius effects during the z-pinch like plasma formation phase, which is characteristic of PF discharges.
- ItemFormation of hexagonal silicon carbide by high energy ion beam irradiation on Si(100) substrate(2007) Bhuyan, H.; Favre, M.; Valderrama, E.; Avaria, G.; Chuaqui, H.; Mitchell, I.; Wyndham, E.; Saavedra, R.; Paulraj, M.We report the investigation of high energy ion beam irradiation on Si (100) substrates at room temperature using a low energy plasma focus (PF) device operating in methane gas. The unexposed and ion exposed substrates were characterized by x-ray diffraction, scanning electron microscopy (SEM), photothermal beam deflection, energy-dispersive x-ray analysis and atomic force microscopy (AFM) and the results are reported. The interaction of the pulsed PF ion beams, with characteristic energy in the 60-450 keV range, with the Si surface, results in the formation of a surface layer of hexagonal silicon carbide. The SEM and AFM analyses indicate clear step bunching on the silicon carbide surface with an average step height of 50 nm and a terrace width of 800 nm.
- ItemLaser-produced annular plasmas(AMER INST PHYSICS, 2006) Veloso, F.; Chuaqui, H.; Aliaga Rossel, R.; Favre, M.; Mitchell, I. H.; Wyndham, E.A new technique is presented for the formation of annular plasmas on a metal surface with a high-power laser using a combination of axicon and converging lenses. The annular plasma formed on a titanium target in a chamber of hydrogen gas was investigated using schlieren imaging and Mach Zehnder interferometry. Expansion of the plasma was shown to be anisotropic with velocities of similar to 10(3)-10(4) m/s. Electron densities of 10(18) cm(-3) were measured with radial profiles that confirm the presence of a hollow structure. The interferometric observations also show the presence of an inward shock wave traveling to the center of the annular plasma, which compresses the background neutrals, reaching a density around 18 times initial gas density, at 95 ns after the initial annular plasma is produced.
- ItemObservations of Ablation Dynamics in Wire-Array Z-Pinch Experiments on the Llampudken Generator(2012) Veloso Espinosa, Felipe; Suzuki-Vidal, F.; Molina, F.; Mitchell, I. H.; Chuaqui, H.; Favre, M.; Wyndham, E.
- ItemObservations of the emission processes of a fast capillary discharge operated in nitrogen(2012) Valdivia, M. P.; Wyndham, E. S.; Favre, M.; Valenzuela, J. C.; Chuaqui, H.; Bhuyan, H.We present observations of the emission characteristics of the plasma processes of a low inductance, sub Joule, compact capillary discharge, when operated in nitrogen at up to 600 Hz. A quarter period of under 10 ns is achieved allowing currents of order 5 kA. Four geometries are explored: two lengths, 21 and 36 mm, and two internal diameters, 1.6 and 3.2 mm. Transient hollow cathode fast electrons are associated with enhanced soft x-ray emission at shorter wavelengths with measured output energies of N VI at 28.8 angstrom as compared with a Maxwellian plasma. Time-integrated spectroscopy together with filtered diode signals, and with spatial resolution, reveals a small axial emitting plasma close to the anode. Optical time-resolved spectroscopy gives larger scale plasma parameters both of the anode and the cathode plasmas. This volume plasma covers the range 2-8 eV, while the x-ray emitting plasma covers 10-20 eV, according to geometry. Nitrogen metastable emission is also observed in the hollow cathode volume prior to breakdown. Both internal wall diameter and capillary length affect both the spectrum and the x-ray emitting volume as does the axial pressure gradient. Electron beams from the transient hollow cathode are associated in model spectra with the observed N VI, O VI and Al VII-X ionization stages. Operating conditions that affect the spectral purity and discharge characteristics include the internal pressure gradient and nitrogen to helium mix ratio. We discuss the suitability of the capillary geometries as a soft x-ray source and in the context of available computer models.
- ItemRefractive optical measurements on the Llampüdkeñ generator(2006) Suzuki, F.; Veloso Espinosa, Felipe; Molina, F.; Mitchell, I.; Chuaqui, H.; Aliaga-Rossel, R.; Favre, M.; Wyndham, E.
- ItemSub-micron size carbon structures synthesized using plasma enhanced CVD without external heating and no catalyzer action(2010) Valderrama, Enrique; Favre Domínguez, Mario; Bhuyan, Heman; Ruiz, H. M.; Wyndham, Edmund; Valenzuela, J.; Chuaqui, H.