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  • 1.
    Pettersson, Jonas
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Becerra Garcia, Marley
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Franke, Steffen
    Leibniz Inst Plasma Sci & Technol, D-17489 Greifswald, Germany..
    Gortschakow, Sergey
    Leibniz Inst Plasma Sci & Technol, D-17489 Greifswald, Germany..
    Spectroscopic and Photographic Evaluation of the Near-Surface Layer Produced by Arc-Induced Polymer Ablation2019In: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 47, no 4, p. 1851-1858Article in journal (Refereed)
    Abstract [en]

    High-intensity plasmas can release material from the surface of polymers by a process known as arc-induced ablation. As consequence, the formation of a near-surface layer of polymeric vapor is generally assumed. In order to investigate the near-surface layer formed by the ablation of polyoxymethylene, high-speed photography and space-resolved optical emission spectroscopy are used. Transient arc plasmas generated under a 1.9-kA, 50-Hz current semicycle are used as ablation source in air. It is found that the near-surface ablation layer strongly scatters radiation emitted by the arc core. This effect is caused by light scattering of micrometer-size fragments released by the ablating polymer. This finding shows that the near-surface layer is not only composed of vapor but also contains a significant density of large-sized polymer fragments. These fragments are formed a few milliseconds after the ignition of the arc plasma, and their density rapidly decreases with the distance to the surface.

  • 2.
    Becerra Garcia, Marley
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering. KTH Royal Inst Technol, Sch Elect Engn & Comp Sci, S-10044 Stockholm, Sweden.;ABB Corp Res, S-72226 Vasteras, Sweden..
    Pettersson, Jonas
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Franke, Steffen
    INP Leibniz Inst Plasma Sci & Technol, D-17489 Greifswald, Germany..
    Gortschakow, Sergey
    INP Leibniz Inst Plasma Sci & Technol, D-17489 Greifswald, Germany..
    Temperature and pressure profiles of an ablation-controlled arc plasma in air2019In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 52, no 43, article id 434003Article in journal (Refereed)
    Abstract [en]

    Experimental measurements of the spatial distribution of temperature and composition of ablation-controlled arc plasmas are a key to validate the predictions of metal evaporation and polymer ablation models. Thus, high-speed photography and space-resolved spectroscopic measurements have been performed to characterize a stable air arc plasma jet controlled by ablation of a polymer nozzle made of Polyoxymethylene copolymer (POM-C) or polyamide (PA6). The spectroscopic analysis is performed along a plane perpendicular to the arc jet axis for a current of 1.8 kA, corresponding to an estimated current density of similar to 65 A mm(-2). Temperature and partial pressure profiles of the plasma for copper, hydrogen and carbon in the gas mixture are estimated as an inverse optimization problem by using measured side-on radiance spectra and radiative transfer spectral simulations. It is shown that the generated ablation-controlled arc has a complicated, non-uniform gas composition. Thus, the generated arc jet has a thin metallic core with a lower almost constant hydrogen pressure, surrounded by a thicker hydrogen and carbon mantle at partial pressures slightly lower than atmospheric pressure. The separation of hydrogen and carbon in the core is a consequence of demixing of the polymer vapour in the plasma. It is found that the overall shape of the temperature and pressure profiles obtained for the arc plasmas with the POM-C and PA6 nozzles are similar although differ in peak values and width.

  • 3.
    Becerra Garcia, Marley
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Pettersson, Jonas
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Optical radiative properties of ablating polymers exposed to high-power arc plasmas2018In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, no 12, article id 125202Article in journal (Refereed)
    Abstract [en]

    The radiative properties of polymers exposed to high-intensity radiation are of importance for the numerical simulation of arc-induced ablation. The paper investigates the optical properties of polymethylmethacrylate PMMA and polyamide PA6 films exposed to high-power arc plasmas, which can cause ablation of the material. A four-flux radiative approximation is first used to estimate absorption and scattering coefficients of the tested materials in the ultraviolet (UV) and in the visible (VIS) ranges from spectrophotometric measurements. The temperature-induced variation of the collimated transmissivity of the polymers is also measured from room temperature to the glass temperature of PMMA and the melting temperature of PA6. Furthermore, band-averaged absorption and scattering coefficients of non-ablating and ablating polymers are estimated from the UV to the short-wavelength infrared (SWIR), covering the range of interest for the simulation of arc-induced ablation. These estimates are obtained from collimated transmissivities measured with an additional in situ photometric system that uses a high-power, transient arc plasma to both illuminate the samples and to induce ablation. It is shown that the increase in the bulk temperature of PA6 leads to a strong reversible increase in collimated transmissivity, significantly reducing the absorption and scattering coefficients of the material. A weaker but opposite effect of temperature on the optical properties is found in PMMA. As a consequence, it is suggested that the absorption coefficient of polymers used for arc-induced ablation estimates should not be taken directly from direct collimated transmissivity measurements at room temperature. The band-averaged radiation measurements also show that the layer of products released by ablation of PMMA produces scattering radiation losses mainly in the VIS-SWIR ranges, which are only a small fraction of the total incident arc radiation. In a similar manner, the ablation layer of PA6 leads to weak absorption radiation losses, although mainly in the UV range.

  • 4.
    Becerra, Marley
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Pettersson, Jonas
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bianchetti, Romeo
    ABB Corporate Research, Switzerland.
    On the Radiation Losses Introduced by the Vapour Layer Formed By Arc-Induced Ablation of Polymers in Air2016Conference paper (Refereed)
  • 5.
    Pettersson, Jonas
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Becerra Garcia, Marley
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Franke, Steffen
    INP, Germany.
    Gortschakow, Sergey
    INP, Germany.
    Bianchetti, Romeo
    ABB Corporate Research, Switzerland.
    Khakpour, Ali
    INP, Germany.
    Space-Resolved Spectroscopic And Photographic Studies of the Vapor Layer Produced By Arc-Induced Ablation of Polymers2016Conference paper (Refereed)
    Abstract [en]

    Utilization of polymers in switching devices is of increasing interest. Therefore, outgassing of polymeric walls (Polyamide PA6 –C6H11ON– and Polyoxymethylene POM –CH2O–) exposed to arc plasmas (fed by 1.9 kA peak AC currents) is investigated. Space-resolved optical emission spectro-scopy complemented with high speed photography is used to investigate the layer of vapour produced by arc-induced ablation of polymers in air. It is found that the vapour layer in front of an ablating polymer strongly scatters light from the arc core, hindering the evaluation of the layer temperature and composition. The measured light right in front of the polymer surface is significant. This signal has a similar optical signature as the arc core although considerably attenuated. It is found that the detected spectra contain a fraction of the arc radiation scattered by large ablated fragments released from the polymer surface. This paper focuses on categorizing the scattering from the vapour layer adjacent to the polymer surface and to estimate the ablated particle sizes.

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