Einzel lens

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Implementation of an Einzel lens showing the ion path. Six plates are parallel to the ion flight path with the middle plate at a particular potential.

This shows the path of ions as they travel through a simulated Einzel lens. The ion mass is 200kDa accelerated to 40kV, the middle plate potential is at 200V and the plate size is 1m – these are very large settings used to show the focusing effect more easily and are not practical settings.

The Einzel lens is used in ion optics to focus ions in flight and is accomplished through manipulation of the electric field in the path of the ions. It consists of three or more sets of cylindrical or rectangular prisms in series along an axis. As the prisms consist of four sides, each pair of facing plates manipulate the electric field to deflect ions as they pass through.

The plates are symmetric so the ions will regain their initial speed on exiting the lens although the velocity of the outer particles will be altered such that they converge on to the axis. This causes the outer particles to arrive at the focus intersection slightly later than the ones that travel along a straight path as they have to travel an extra distance.