On the dynamic behavior of the anode-arc-root at the nozzle surface in a non-transferred arc torch

PREVOSTO, LEANDRO; RISSO, M; INFANTE, D; CEJAS, E; KELLY, HÉCTOR; MANCINELLI ,BEATRIZ

Mar del Plata

Congreso; XIV Latin American Workshop on Plasma Physics; 2011

The dynamic behavior of the anode arc root at the nozzle surface of a plasma torchwas experimentally investigated in this work. A gas (N2) vortex stabilized non-transferred arctorch with a thoriated tungsten rod (2wt %) cathode (3.2 mm diameter) and a coaxial anode (5mm diameter, 30 mm length) was used in the experiment. By using a sweeping Langmuirprobe in floating condition, the voltage of the plasma jet outside the nozzle was inferred. Arcvoltage waveforms were also obtained. Data have been obtained for an arc current of 100 Aand a gas flow rate of 30 Nl min-1. A typical sawtooth shape (i.e., restrike mode) (with afluctuating level of º  25 %) and a dominant frequency of º 6.5 kHz was observed in the arcvoltage waveforms, which is attributed to anode?arc?root movements along the anode surfacefollowed by a restrike at a certain point close to the cathode. By performing a time correlationbetween the probe and arc voltage oscillograms together with simple estimations, theamplitude of the movement of the arc?root along the anode surface as well its velocity wereinferred.