On the Heat Sources of the Arc Cathode Spot

Abstract

AbstractThe main heat sources of the are cathode root are ion impact and neutralization heating at the surface and Joule (resistance) heating in the volume of the cathode. The ratio IIji between these two components of cathode power supply is investigated, it depends only on J/a (spot current divided by spot radius). In the case of Cu cathodes both components are equal if J/a = 9.17A/μm, and their contributions to the increase of the spot temperature are equal if J/a = 10.25 A/μm. This holds approximately even if the electron emission cooling is taken into account (by inclusion in the surface power supply). In the real (non‐stationary) arc spot the influence of resistive heating is rather low (between 0.1 and 1 percent of the total power supply in the case of clean surfaces), with the exception of the explosive emission processes, where the Joule heat generation is comparable with or even superior to the surface heating processes by impact or possibly electron emission (Nottingham effect). The time average of the Joule component relative to the impact power input depends on the role of such essentially non‐stationary processes in the arc spot regime. An estimate of this ratio IIj,ie basing on theoretical investigations and experimental experiences results in 0.01 ≲ IIj,ie ≲ 1.