The Wien filter is a charged particle separator with a crossed electric and magnetic field configuration (ExB). It is characterized by high dispersion with very small overall dimensions. The ions of interest with a certain speed, which results from their mass-to-charge ratio, pass through the Vienna filter without detours with the help of correctly adjusted electric and magnetic fields. All other species are deflected and absorbed between the Vienna filter openings.
The setup comes with weak and strong permanent magnets (200 mT / 500 mT) that can be easily assembled and disassembled outside the beamline vacuum. If necessary, the integral particle beam can pass through the filter without deflection by simply removing the filter magnets.
The weak permanent magnets enable the analysis of a larger measuring range for fast ions with a low mass-to-charge ratio. For heavy ion beams, the strong magnets are used because these beams are stiffer in terms of deflection in the magnetic field and higher dispersion is required to separate individual mass-to-charge ratios.
In addition, different aperture sizes (0.5 mm, 1.0 mm, 1.5 mm) are available. A smaller aperture at the input and output of the filter results in higher resolution. However, depending on the size of the ion beam, smaller diameters may result in a reduction in the efficiency of ion transport through the structure.
Figure 1 – Vienna Filter Xenon Spectrum
To give an example of the resolution of the Wien filter, a monoisotopic xenon spectrum was measured on a test setup with a DREEBIT electron beam ion source at an ion beam energy of 13.6 keV per charge state and a filter opening of 1.0 mm, see Figure 1. It shows that even the highest charge states Xe45+ and Xe46+ can still be clearly separated.
