High-homogeneity double-focusing stigmatic analyzer magnet for electromagnetic isotope separator

Abstract

An electromagnetic Isotope Separator (EMIS) is used for separating isotopes by magnetic dispersion method. A dipole-bending magnet performs the fundamental function of separation and is an essential building block of EMIS. Unlike mass spectrometers and ion implantation systems, the EMIS prefers ribbon beams for effective mass separation and collection. The bending magnet described in this paper has an inbuilt hexapole and a tunable quadrupole doublet. This magnet separates the charged particles based on the mass-to-charge ratio, performs chromatic correction, and focuses the beam in both axes. All sector magnets focus the beam in the radial direction, the introduction of edge angle results in the vertical focusing of the beam at the expense of radial focusing. The exit pole of the magnet is rotatable for adjusting the focal point. The entry pole is curved for ensuring stigmatism correction in the beam and works like a hexapole. High magnetic field homogeneity is a key requirement for this magnet. This enhances the mass resolution. As per beam simulations, magnetic field non-homogeneity shall not exceed 200 ppm in good field region (GFR) of 200 mm (radial) and 60 mm(vertical). The paper discusses the design, production, installation, testing, and commissioning of a double-focusing Stigmator dipole magnet. A method for achieving low non-homogeneity by using non-magnetic cavities and compensation coils is described and implemented. Very high homogeneity magnets can be designed using this technique. The paper also describes an efficient method for the Magnetic qualification of bending magnets. Based on the design, a double-focusing stigmatic dipole magnet is produced, characterized, and installed.