Beam Imaging 速度滤波器 Velocity Filters

The Colutron type velocity filter is an E x B type “Wien filter”, and consists of an electromagnet and a pair of electrostatic deflection plates. Using an electromagnet instead of the more traditional permanent magnet design enhances versatility and adjustability of the filter. The inherent focal property of the standard Wien filter has also been overcome by the velocity filter by properly biased guard ring electrodes. These electrodes guard the electric field from the magnet pole pieces, and also allow the electric field to be shaped for focussing and non-focussing configurations. The electric field plates are mounted between the magnet poles to produce an electric field E perpendicular to the magnetic field B (crossed E and B fields). The Model 300 (shown in diagram below) is 4.4″ long and 3.5″ wide. The Model 600 and 600-B are similar except that the overall length is 9.10″and width is 4.40″. In most cases, the velocity v = (2qV/m)1/2 of charged beams are obtained by accelerating the particles of mass m, and charge q across a constant electric potential V. Different masses in the beam will be dispersed by the filter since they have different velocities. The filter’s ability to disperse masses makes it a superior tool in mass spectroscopy, and some of its main features are: