Estimating the electron temperature from fluctuations in a vacuum arc plasma: cathode spot operation on a contaminated surface

Abstract

High frequency fluctuations (up to 50 MHz) in the ion current arc voltage and plasma floating potential have been studied, together with the influence of the surface history on these fluctuations for arc currents ranging from 2 to 50 A. In the process of surface conditioning by repeated arcs, the amplitude of fluctuations increases. The fluctuations of a signal from the grounded probe situated at a distance of <or=0.1 mm from the cathode spot are accompanied by positive and negative bursts. The probe floating potential fluctuates between 0 and 10 V. The conclusion is drawn that these instabilities are caused by fluctuations in the plasma electron temperature Te./sub /Te is estimated to be about 4.6+or-0.5 and 5.8+or-0.5 eV, for Cu and W arcs respectively. The influence of surface contaminations on arc behaviour is discussed.

Time and material dependence of the voltage noise generated by cathodic vacuum arcs

“…So, as the arc burns and the cathode area surrounding the currently active spots is bombarded by ions, the arc creates conditions for type 2 spots, which are less numerous and thus the noise increases. This is consistent with previous observations of influence on surface contamination on the amplitude of arc voltage fluctuations [26].…”

Application of a vacuum arc model to the determination of cathodic microjet parameters

“…Therefore an assumption made is reasonable. have been obtained for the small but not exactly known distances r from the cathode surface [8][9][10][11][12][13][14][15][16]. However the variations of T e (r) and N e (r) are not too large in the distance range 10 −2 < r/d < 1 near the cathode [3][4][5].…”

Time-resolved investigations of the accelerated electron flow from the cathode region of a vacuum arc

“…The origin of the accelerated electrons cannot be associated with the thermal energy distribution of the electron gas since the characteristic electron energies (50 eV) are much greater than the estimated temperature of the electron gas in an arc (4-6 eV) [5], [6]. A possible reason for the acceleration of electrons in an arc might be a local increase in total arc voltage in a crisis.…”