Wien Filter

The Wien Filter is a charged particle separator with a crossed electric and magnetic field configuration (ExB). It is characterized by a high dispersion at very small overall dimensions. The ion species of interest with a specific velocity due to its mass-to-charge ratio passes the Wien Filter straightforward by properly adjusted electric and magnetic fields. All other species are deflected and absorbed between the Wien filter apertures.

The setup is delivered with weak and strong permanent magnets (200 mT / 500 mT) which can easily be mounted and unmounted outside of the beamline vacuum. If necessary, the integral particle beam can pass the filter without deflection by simply removing the filter magnets.

The weak permanent magnets allow for analyzing a larger measurement range towards fast ions of low mass-to-charge ratios. For heavy ion beams the strong magnets are used as these beams are more stiff regarding deflection in the magnetic field and higher dispersion is necessary to separate individual mass-to-charge ratios.

Furthermore, different sizes of apertures (0.5 mm, 1.0 mm, 1.5 mm) are available. A smaller aperture at the entrance and exit of the filter results in a higher resolution. However, depending on the size of the ion beam, smaller diameters may lead to a reduction of the ion transport efficiency through the setup.

To give an example of the Wien filter resolution, a monoisotopic xenon spectrum was measured at a test setup with a DREEBIT electron beam ion source at an ion beam energy of 13.6 keV per charge state and a 1.0 mm filter aperture, see Figure 1. It shows that even the highest charge states Xe⁴⁵⁺ and Xe⁴⁶⁺ can still clearly be separated.