Measurements with the emissive probe in the cylindrical magnetron

Abstract

This contribution describes the results of the measurements that were made with emissive probe in the argon dc discharge in the cylindrical magnetron. Main part of this emissive probe -the tungsten wire loop -was heated by the dc current to raise its temperature up to that allowing to reach the requested emission current. With such a probe we measured the dependence of floating potential on the heating current or voltage, I-V characteristics of the probe and radial distribution of potential between anode and cathode. Main goal of the measurements was the evaluation of plasma potential inside the magnetron and finding evidence, whether these methods bring us advantage for plasma potential estimation with respect to commonly used Langmuir probe method. For that purpose we compared several ways used for obtaining the plasma potential: (i) from the inflection point of the cold probe characteristic (ii) from the floating potential of sufficiently heated emissive probe (iii) from the abscissa of the crossing point of the cold and emissive probe characteristic (iv) from the ionization potential of the discharge gas (argon). : 52.25.-m PACS

The Use of Emissive Probes in Laboratory and Tokamak Plasmas

“…1a). This effect was described already by Klagge [17] (see also [18]), who also discusses its usefulness on the determination of the plasma potential and for gaining information on the ionization conditions and rates of the gas.…”

Emissive probes

“…Although not addressed in the original paper, it is clear from figure 28 that there are actually two inflection points: one indicated by the triangles and another much larger one that is more negative than the graph shows. The larger inflection point may be due to ionization caused by the probe, a phenomenon that has been observed elsewhere [38]. The authors of the original paper, however, do not address this at all.…”

“…The typical ordering is the separation point gives the highest measure of the plasma potential and the floating point method the lowest, with the inflection point method in between. Occasionally, papers include cursory comparisons to determine which technique to use, typically concluding that the floating point method is sufficiently accurate [38,39]. Bradley et al compared the various techniques in a plasma produced by a magnetron, though all the details were not included because that was not the focus of the paper [28].…”

Plasma potential mapping of high power impulse magnetron sputtering discharges

“…[26][27][28][29][30][31][32][33][34][35] As the name suggests, an emissive probe is sufficiently hot to emit electrons via the thermionic emission mechanism, where the current density is approximately described by the Richardson-Dushman equation (cf. e.g.…”