Browsing by Author "Wyndham, E. S."

Now showing 1 - 4 of 4
  • No Thumbnail Available
    Item
    Bayesian inference of plasma parameters from collective Thomson scattering technique on a gas-puff near stagnation
    (2023) Escalona, M.; Valenzuela, J. C.; Avaria, G.; Veloso, F.; Wyndham, E. S.
    The Collective Thomson scattering technique has been implemented to study the stagnation of a single liner gas-puff. The plasma parameters are determined by theoretically modelling the scattering form factor in combination with Bayesian inference to provide the set of the most probable parameters that describe the experimental data. Analysis of the data reveal that incoming flows are able to interpenetrate partially. Estimation of the mean free path shows a gradual transition from a weakly collisional to a collisional regime as the plasma gets to the axis. Furthermore, we find that the ion energy at r = 2.5 mm is 13.6(-0.9)(+1.0) keV and is mostly kinetic in nature and represents 98(+10) (-9) % of the total energy. This kinetic energy is far greater than the value on axis of 3.7(-0.5)(+0.4) keV which is 84(-14)(+15) % of the total energy. Energy transfer to the electrons and radiation losses are found to be negligible by this time. A possible explanation for this energy imbalance is the presence of an azimuthal magnetic field larger than similar to 4.7 T that deflect the ions vertically. The uncertainties quoted represent 68% credible intervals.
  • No Thumbnail Available
    Item
    Observations 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.
  • No Thumbnail Available
    Item
    Pulsed laser deposition of thin carbon films in a neutral gas background
    (2013) Guzman, F.; Favre, M.; Ruiz, H. M.; Hevia, S.; Caballero, L. S.; Wyndham, E. S.; Bhuyan, H.; Flores, M.; Maendl, S.
    We studied carbon film deposition using a laser-produced plasma, in argon and helium background gas, at pressures between 0.5 and 700 mTorr. A Nd : YAG, 370 mJ, 3.5 ns, at 1.06 mu m, operating at 10 Hz, with a fluence of 6.7 J cm(-2) was used. The laser plasma was characterized using space resolved OES and a fast response Faraday cup. The resulting carbon films were analysed using AFM, Raman spectroscopy, XPS and SIMS. The structural properties of the carbon films were found to be strongly correlated with the laser carbon plasma composition. Films with a relatively high content of sp(3), characteristic of DLC, were obtained at pressures below 200 mTorr. For these conditions the characteristic carbon ion energies in the expanding laser plasma were of the order of 100 eV. At higher pressures sp(2) bonds, associated with amorphous carbon, were dominant, which coincides with a high content of C-2 molecules in the laser plasma, and a characteristic carbon ion energy around 20 eV.
  • No Thumbnail Available
    Item
    STUDIES OF PLASMA DYNAMICS IN COLLIDING LASER PLASMA PLUMES
    (IEEE, 2015) Favre, M.; Merello, F.; Bhuyan, H.; Veloso, F.; Wyndham, E. S.; Ruiz, H. M.