Ray-tracing Analysis of the Wien Velocity Filter for Protons

Ray-tracing Analysis of the Wien Velocity Filter for Protons

A Wien velocity filter employs a combination of crossed magnetic and electrostatic fields in orderto select the desired velocity of ions. Several microscopes and spectrometers are used as filters toensure the introduction of a pure ion fraction into the lens, deflecting unnecessary particles whichhave slightly different energies. The Wien filter is also considered to be a useful device to transportmono-energy protons from a source to an injection system. In its simplest form, the Wien filter hastwo flat parallel electrodes that are arranged between two flat magnet poles, creating homogeneouselectric and magnetic fields which cross each other. However, this type of filter has no focusingeffect in the direction of the magnetic field and has an unmatched field distribution, which causesdeflections of protons at the entrance and the exit of the filter. At higher magnetic field strengs,for fast protons, the deflection of the trajectories becomes larger; thus, the transport efficiencyis reduced. A low-aberration velocity filter is needed for high transport efficiency. Recently, astigmatic focusing of the filter by using hyperbolic cylindrical magnet pole pieces, which producean inhomogeneous magnetic field inside the ExB filter, has been suggested. In this research, threetypes of Wien filters were designed in order to investigate the geometry of the electrodes and themagnet poles, thus minimizing aberrations. Ray-tracing analyses were carried out to estimate theperformance of the proposed Wien filters within a useful velocity selector.

A Wien velocity filter employs a combination of crossed magnetic and electrostatic fields in orderto select the desired velocity of ions. Several microscopes and spectrometers are used as filters toensure the introduction of a pure ion fraction into the lens, deflecting unnecessary particles whichhave slightly different energies. The Wien filter is also considered to be a useful device to transportmono-energy protons from a source to an injection system. In its simplest form, the Wien filter hastwo flat parallel electrodes that are arranged between two flat magnet poles, creating homogeneouselectric and magnetic fields which cross each other. However, this type of filter has no focusingeffect in the direction of the magnetic field and has an unmatched field distribution, which causesdeflections of protons at the entrance and the exit of the filter. At higher magnetic field strengs,for fast protons, the deflection of the trajectories becomes larger; thus, the transport efficiencyis reduced. A low-aberration velocity filter is needed for high transport efficiency. Recently, astigmatic focusing of the filter by using hyperbolic cylindrical magnet pole pieces, which producean inhomogeneous magnetic field inside the ExB filter, has been suggested. In this research, threetypes of Wien filters were designed in order to investigate the geometry of the electrodes and themagnet poles, thus minimizing aberrations. Ray-tracing analyses were carried out to estimate theperformance of the proposed Wien filters within a useful velocity selector.