Floating potential and plasma sheath in vacuum arc plasma

Variation of the electric field across the plasma sheath and floating-potential magnitude are calculated at vacuum arc plasma-plane floating surface contact. Due to the nonequilibrium conditions in the cathode-governed vacuum arc plasma, the floating-potential magnitude is smaller and the effective plasma sheath thickness is larger, compared to the values obtained from the expressions valid for the plasma in local thermodynamic equilibrium. The electric-field strength at floating surface is lower accordingly. It is suggested that the electric-field strength is insufficient to bring about the unipolar arc initiation by explosive field-emission mechanism at distances of the order of 1 cm away from the cathode spot(s).