Charged particle beam transport

SIMS relies on the formation, collection, and transport of charged particle beams (most specifically ions, although electrons are also used in dealing with insulating samples), whether within the primary or secondary ion columns of the instrument. 

External forces can thus be used to control (focus, defocus, or deflect) a charged particle beam or some portion thereof. As a result, electrostatic or magnetic field gradients are often described as charged particle lenses or deflectors. 

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All of these ion sources emit beams of positive ions at relatively low velocities, the ions drift or are pulled out from the ionization region with relatively small electrostatic potentials (U 20 kV). These beams of charged particles can be focused and transported in vacuum to the main accelerating machines. 

An electrostatic mirror can be produced by an electrode at a potential energy that is greater than the kinetic energy divided by the charge of the particle. The bending and focusing power of electrostatic systems are limited by the maximum electric fields that can be applied across the electrodes. Extensive electrostatic systems have been constructed for the transport of low-energy beams, KE < 50 keV, for example, beams extracted from ion sources are usually transported with electrostatic elements. 

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