On the theory of ion current onset delay in liquid metal ion sources

The phenomenon of delayed onset of ion emission is studied in relation to the value of the applied voltage. On the basis of an analysis of the stability of a thin spherical layer of viscous conductive liquid covering the apex of a needle in a strong electric field, the character of the spatial structure reorganisation of spherical harmonics is described and the change of the volume of the liquid cone is calculated as a function of the value of the voltage. Taking this change and also liquid viscosity into account allows us to explain the main features of the observed dependences between the delay time before the ion current onset and the value of the voltage.