On the Use of Sweeping Langmuir Probes in Cutting Arc Plasmas-Part I: Experimental Results

PREVOSTO, LEANDRO; KELLY, HÉCTOR; MANCINELLI ,BEATRIZ

IEEE TRANSACTIONS ON PLASMA SCIENCE

IEEE

Año: 2007

0093-3813

The first study of Langmuir probes applied to cutting 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, or 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 mm and with sweeping rotation frequencies down to 8.7 s-1 (probe transit time of » 140 ms through the arc) were used without noticeable alterations.             In the measurements of the ion current collected by negatively biased probes, 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 modifying the ion branch of the characteristic. On the contrary, some arguments on which a collection-model will be based are presented.