"V" shape curves of physical parameters of field emitters versus applied voltage toward breakdown in vacuum

The objective of this paper is to determine the physical parameters evolution of field emitters with applied voltage increasing toward breakdown of a rod-plane gap in vacuum. Pulses of AC power frequency voltage are applied to vacuum gaps of 1.0, 0.8 and 0.5 mm to breakdown and the field emission current and applied voltage are measured. Through Fowler-Nordheim theory, the physical parameters of field emitters, including the electric field enhancement factor β, effective emission area A
_e
, microscopic electric field E, and field emission current density j
_FE
are obtained to represent the physical parameters evolution of the emitters up to breakdown. The results show that the electric field enhancement factor β, microscopic electric field E and field emission current density j
_FE
follow a "V" shape with increasing voltage. When the applied voltage is increased from starting voltage V
_S
to turning voltage V
_T
, the parameters β, E and j
_FE
decreased. When the applied voltage is further increased from the turning voltage V
_T
to the breakdown voltage V
_B
, the trend reverses, i.e. the parameters β, E and j
_FE
increases up to breakdown.