The beam divergence of an indium LMIS at a distance of 50 μm as determined by plasma diagnostic measurements

The current-dependent beam divergence at a distance of 50 μm from an indium-liquid metal ion source is derived from experimental data obtained by measuring the beam spread with a 3D Plasma diagnostic system at a distance of 10 cm from the needle tip. The observed relationship between emission current and beam divergence in vicinity of the emitting needle is used to design a focusing electrode for a field-emission electric propulsion thruster operating at currents up to 150 μA. Another application involves focused ion beam columns which may choose to forego a beam-limiting aperture, such as LMIS-based rapid machining tools with large beam currents. -- Research highlights: → Experimental data of the beam divergence of an indium LMIS. → Derived beam divergence close to needle tip from experimental data. → Provision of initial conditions for ion trajectory simulations. → Empiric formula for beam div. close to needle tip as function of emission current. → Result is of special interest for applications without beam-limiting aperture.