Descripción: Langmuir probe measurements in an atmospheric pressure direct current (dc) plasma jet are reported. Sweeping probes were used. The experiment was carried out using a dc non-transferred arc torch with a rod-type cathode and an anode of 5 mm diameter. The torch was operated at a nominal power level of 15 kW with a nitrogen flow rate of 25 Nl min -1. A flat ion saturation region was found in the current-voltage curve of the probe. The ion saturation current to a cylindrical probe in a high-pressure non local thermal equilibrium (LTE) plasma was modeled. Thermal effects and ionization/recombination processes inside the probe perturbed region were taken into account. Averaged radial profiles of the electron and heavy particle temperatures as well as the electron density were obtained. An electron temperature around 11 000 K, a heavy particle temperature around 9500 K and an electron density of about 4 × 10 22 m -3, were found at the jet centre at 3.5 mm downstream from the torch exit. Large deviations from kinetic equilibrium were found throughout the plasma jet. The electron and heavy particle temperature profiles showed good agreement with those reported in the literature by using spectroscopic techniques. It was also found that the temperature radial profile based on LTE was very close to that of the electrons. The calculations have shown that this method is particularly useful for studying spraying-type plasma jets characterized by electron temperatures in the range 9000-14 000 K. © 2012 American Institute of Physics.

Descripción: Three-dimensional measurements of the ion flux along the filter of a magnetically filtered d-c vacuum arc are presented. The device includes a metallic plasma-generating chamber with cooper electrodes coupled to a substrate chamber through a quarter-torus magnetic filter. The filtering magnetic field was high enough to magnetize the electrons but not the ions. The ion current distribution was studied using a multi-element Cu probes, placed at three different positions along the filter. The ion saturation current of each probe was measured by biasing the probe at -70V with respect the grounded anode. Preliminary results of the three dimensional ion flux distribution and the floating potential of the plasma as functions of the bias filter voltage and magnetic field intensity are reported. © 2006 American Institute of Physics.

Descripción: In the present work, we studied the efficiency of a magnetic island filter for two vacuum arc designs, pulsed and continuous. The magnetic island filter consisted in a straight duct with an external solenoid and a magnet enclosed in a housing (magnetic island) located inside the duct on its axis, and both magnetic fields are in opposite direction. The housing of the magnetic island obstructs the line of sight between the cathode and the substrate. In this arrangement, the charged plasma components move along the curved magnetic field lines, around the magnetic island, but the macroparticles move in straight paths and deposit on the wall of the magnetic island housing. The performance of the filter was characterized for different external and internal field strengths. The plasma transport efficiency was analyzed by measuring the ion saturation current with Langmuir probes and the deposited mass rate. The ion transmission efficiency around the system axis achieved values around 25%. Observation of the coating surface morphology with optical microscopy determined that the macroparticles were effectively removed.

Descripción: An experimental study of the plasma jet generated in a pulsed copper vacuum arc with an annular anode and operated with a linear magnetic filter is presented. Two types of filters were employed, one consisting of an insulating duct and the other of a conducting duct, both of them surrounded by an external coil, which generates the axial magnetic field. To improve the ion flux at the filter entrance another auxiliary magnetic field in the cathode region was applied (focusing field). Also, the cathode shape was modified to confine the cathode spot onto the front cathode surface. Operating the arc under vacuum conditions, probe measurements of the ion saturation current and the plasma potential at different axial positions along the ducts and for different filtering magnetic field values are reported. A comparison between both kinds of filters is also presented. © 2006 American Institute of Physics.