A schematic of the operation of a needle type liquid-metal ion source. A potential of 5-7kV is applied between the needle and an accelerating electrod. If this needle is well wetted by the liquified indium, the electrostatic stress of the applied field pulls the indium film towards the electrode. This stress is balanced by surface tension forces which leads to the establishment of a characteristic equilibrium configuration, the so called Taylor cone (see inset). Once the electric field at the apex of this cone gets to the order of volts per nanometer the most protruding surface atoms are field evaporated, ionized and accelerated towards the electrode. Via hydrodynamic flow the atoms leaving the tip area are contantly replenished and a stable regime can be maintained.
From LISA System and Technology Study Report (2000) (Fig 9.14)
ESA-SCI(2000)11