Abstract:
Steady-state modelling and experimental results are given on the electric arc
attachment on cold carbon cathodes working at low pressure. The modelling
results are compared with the case of copper cathodes and with experimental
data on vacuum arc erosion characteristics for graphite materials. A region
of existence of a physically meaningful solution for self-sustained operation
of the steady-state cathode spot is given in the electron temperature?cathode
spot plasma pressure space. A solution domain comprised between
Te ? 1.2?1.5 eV and p ? 2?45 atm corresponding to carbon surface
temperatures in the range 4200?4900K is found. Values of the local heat
flux to the cathode surface are evaluated in the range 1?20 ? 10^10Wm^?2,
and ratios of the various contributions to this flux and current density are
given. Also given are the cathode spot radii and upper/lower limits for the
erosion rate through vapourization, these being compared with experimental
data. It is shown that the cathode spot pressure conditions can provide a
mechanism for the control of macroparticle emission on carbon. This effect
is used experimentally through cathode spot plasma confinement for the
reduction of the microdroplet emission in arc sources used for diamondlike
film deposition. Experimental data obtained on graphite materials are in
agreement with the model-based design guidelines.