Tsutomu Okutomi

Instability of vacuum arc in Ag-Cu contact alloys

To clarify the effect of contact material characteristics on the arc instability and chopping phenomena, the spectrum intensity of ionized and neutral vapor generated continuously during discharge is measured using contacts of Ag-Cu binary alloys. It is observed that arc instability and chopping are closely related to the behavior of the ionized vapor during discharge. The chopping current decreases with increased Ag content, while the instability-initiating current has a minimum value at 60 at.% Ag content. These effects are discussed from the viewpoint of the ion generation capability, including thermal properties, of contact materials. >

Measurement of Instability Initiation Current in Vacuum Arc

The arc current for initiating the appearance of noise on a current trace, the instability initiation current I0, and the arc voltage V0 corresponding to I0, have been measured using Cu-Ni alloy and Ag-Pd alloy electrode metals. The average values of I0 and V0 were plotted as a function of the thermal conductivity λ, showing a decrease with decreasing λ under a constant vapor pressure Ph.

Vaporization of carbon from Cu-WC contact during arc discharge in vacuum

To identify the components emitted from tungsten carbide (WC) base contact during arc discharge in vacuum, spectroscopic measurements were performed for vacuum arc discharges between Cu, W, C, WC, and Cu-WC contacts. As a result, spectra of C and W which have extremely low vapor pressures were observed as well as that of Cu. To obtain the conclusive evidence of the vaporization of C, W, and Cu, the deposits on the contact holders were also investigated by means of surface analysis methods such as Auger electron spectrometer and X-ray photo-electron spectrometer. The mechanism of simultaneous vaporization of those components with different vapor pressures was discussed by means of thermal analysis. It shows that the superheating of WC at the contact surface could cause the vaporization of carbon.