On the plasma density of metal vapour arcs

Abstract

The plasma density of metal vapour arcs in vacuum is discussed on the basis of ion currents measured at cylindrical walls around the electrodes. It is suggested the density varies inversely with the square of the distance to the cathode spot, reaching values up to 1026 m-3 within the spot. From the distribution of the plasma ions it is concluded that the ion current to the cathode area within the spot reaches several per cent of the arc current. Up to a pressure of at least 2 atm, the background pressure does not change the internal spot processes that lead to retrograde motion.

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].…”

Estimating cathodic plasma jet parameters from the vacuum arc charge state distribution

“…To estimate possible errors in I and d resulting from the inaccuracy in the electron temperature T, and density Ne. we shall use equations (8) and (9). Let us denote a relative error in S as 6s, where 6 = ASIS, S = Ne?…”

A comparison of electron-emission equations used in arc - cathode interaction calculations

“…In the case of metal vapour arcs, a cathode-spot plasma is formed by the strong vaporization of the cathode surface. The arc is locally burning in a metallic vapour atmosphere where the pressure is considerably higher than the ambient gas pressure [6,11,14]. Therefore, the ion density is calculated using the local metallic plasma pressure rather than the ambient gas pressure.…”

“…Results reported for a Cu cathode exposed to a macroscopic electric field strength E s = 10 9 V m −1 suggest that the enhancement of the T-F emission current (the Murphy and Good equation) sets in for cathode surface temperatures below 4000 K and ion densities above 10 24 m −3 [10]. These conditions of temperature and ion density are encountered within the cathode region of metal vapour arcs (vacuum arcs [5,11] and high-pressure arcs on non-refractory cathodes [6]) and also for high-pressure arcs on refractory cathodes ( 1 atm) [12,13].…”