FRVT - Artículos en Revistas Internacionales

Permanent URI for this collectionhttp://48.217.138.120/handle/20.500.12272/396

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End date: 2009Subject: search.filters.subject.Cutting arcs.

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    On the Use of Sweeping Langmuir Probes in Cutting-Arc Plasmas—Part II: Interpretation of the Results.
    (2008) Prevosto, Leandro; Kelly, Héctor; Minotti, Fernando
    A semiempirical Langmuir probe model is intro duced that is particularly adapted to high-energy-density cutting arcs, for which, as we have shown in Part I, the ion current collected by negatively biased probes shows no plateau in the ion branch of the current–voltage (I–V ) probe characteristic, and the signal amplitude is independent of the probe radius. According to the model, the ion drag due to the high-velocity plasma flow around the probe limits the effectively collecting area to a small fraction of the probe surface. If, according to the experimental evidence, this fraction is made independent of the probe radius, then its value results proportional to the probe bias, and so no plateau is found, at least as long as the collecting area is less than (half) the probe surface, which happens only at rather high probe bias. The model requires the determination of the function relating the electric field (in the region between the unperturbed plasma and the space-charge sheath close to the probe) to the parameters of the problem. Dimensional analysis together with empirical information allow to restrict the form of this function to leave only an auxiliary dimensionless function, which can be argued to be practically constant and whose value can be determined between rather tight bounds. As an example, radial profiles of plasma temperature and density are obtained by applying the proposed model to the experimental values of a I–V probe characteristic obtained in Part I. The derived temperature profile is in good agreement with a previous published numerical simulation for a similar cutting torch.
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    On the Use of Sweeping Langmuir Probes in Cutting Arc Plasmas—Part I: Experimental Results.
    (2008) Prevosto, Leandro; Kelly, Héctor; Mancinelli, Beatriz
    The first study of Langmuir probes applied to cut ting arcs using a sweeping-probe system is presented. It is found that, under a relatively broad range of experimental conditions (changes in the probe material, in the probe radii, or in the sweeping frequency of the probes), no probe damage is registered, notwithstanding the large value of the power flux present with these arcs. In practice, probes with radii down to 63 µm and with sweeping rotation frequencies down to 8.7 s−1 (probe transit time of ≈140 µs through the arc) were used without noticeable alterations. In the measurements of the ion current collected by negatively biased probes, the following two unexpected features are found: the lack of a current plateau in the ion branch of the I–V probe characteristic and the independence of the signal amplitude on the probe radius. According to the experimental evidence, as well as several estimations, we have neglected electron emission of the probe surface as a relevant mechanism in modi fying the ion branch of the characteristic. On the contrary, some arguments on which a collection model will be based are presented.