Compact and strong window core steering magnets with homogeneous dipole field
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Compact and strong window core steering magnets with homogeneous dipole field BHASKAR BISWAS Free Electron Laser and Utilization Section, Raja Ramanna Centre for Advanced Technology, Indore 452 013, India E-mail: [email protected] MS received 25 September 2019; revised 10 June 2020; accepted 24 July 2020 Abstract. A typical axially compact, square window core steering magnet has a very small 2D good field region (GFR) of 18% of the iron core aperture. It is weak with 85% of its dipole in the fringes. Increasing the current fed area (coil) to increase the dipole strength lowers the good field zone. Some novel and simple coil shapes can expand their 2D/3D GFR to 94/40% of the iron aperture. They are axially compact, i.e., stronger with 60–65% of the dipole in fringes. The reduction in error sextupole field is more profound. A novel 2D coil shape with vanished 2D sextupole proves the concept. For axially short cores, a gap between the coil and the iron aperture can increase the 3D sextupole, missing in 2D simulations. A new asymmetric one-axis steering magnet core and coil shape with high dipole field and homogeneity is also given. The new, practical coil shapes significantly improve the dipole field homogeneity and strength of these magnets. Keywords. Window core; coil; good field region; sextupole. PACS Nos 41.20.−q; 41.20.Gz; 03.50.De
1. Introduction Steering magnets with window iron core are basically dual, weak bending magnets meant for near normal beam entry and exit with a small bending angle. It is well known for iron core dipole magnets with a pole gap that the 2D field homogeneity is better than 3D field homogeneity. For uniform steering of the beam, the steering magnet requires a large 2D good field region (GFR) along with axial compactness in 3D. But, no literature is available which shows that, in window core steering magnets, the 2D dipole field inhomogeneity is higher (poorer) than 3D field inhomogeneity and their GFR is small compared to the aperture. First, we shall analyse the differences. First we consider the regular dipole magnets that bend, say in the horizontal plane. The iron core-based electromagnetic dipole magnets are commonly of C-, H-, window-, or cos θ -types [1]. We omit here the purepermanent, hybrid and cyclotron sector-type deflection magnets. The C-type dipole cores can be long (typically 0.5–4 m) and arced to match the radius of the bend in electron synchrotrons for easy one-sided access to 0123456789().: V,-vol
the light. The H- or C-type dipoles with moderate core length (< 1 m) and sector/parallel edge have most applications in beam transfer lines with large deviation. The 2D GFR is like a flattened ellipse [2] for wide poles with small gap and short pole taper, or, the GFR is squarish for long, tapered and shimmed poles [3]. The dipole field integral in horizontal plane is made uniform by profiled chamfer of the entry and exit pole edges [4]. The cos θ dipole in large circular colliders has very long iron core (e.g., 14 m in LHC, 2.8 km radius of
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