Compact low emittance light sources based on longitudinal gradient bending magnets

SLS-2 – the upgrade of the Swiss Light Source

“…I 5 is minimized by using longitudinal-gradient bends (LGBs; bending magnets for which the field varies along the beam path) and by suppressing the dispersion at the LGB center, where the field is strongest. An optimal function hðsÞ and optimal initial parameters o and xo at the magnet center can be calculated to obtain the minimal I 5 (or the minimal " x ), or a modified optimal function is obtained for given initial parameters (Streun & Wrulich, 2015). However, in a conventional periodic cell, quadrupoles are used to focus both x and , which leads to an insufficient focusing of the dispersion function (or an over-focusing of x ), since the dispersion production of the bending magnet acts like a defocusing term, and thus the optimal dispersion o is out of reach.…”

Numerical optimization of a low emittance lattice cell

“…where ψ n (ŝ) are Given the curvature functionĥ(ŝ) and focusing functionK(ŝ), the natural emittance ǫ n can be evaluated by Eqs. (7)(8)(9)(10)(11)(12). For the calculation of photon brightness B, the vertical emittance ǫ y due to the coupled motion from the horizontal plane should be considered.…”

“…The dipole field may be re-distributed to put stronger bending in the region with lower dispersion invariant and weaker bending elsewhere in order to achieve more evenly distributed quantum excitations throughout the magnet, which could in turn leads to smaller emittance. There have been many studies on the topic [7,8,9,10,11]. In a recent study, Ref.…”

“…In a recent study, Ref. [11], numeric optimization of the dipole field distribution for minimum emittance was conducted. Another important recent development in lattice design is the use of negative bends [12,13].…”

The HEPS project

“…For simplicity, in the following we refer to the modified H-7BA as MH-7BA. In the first place, the middle cell of an H-7BA was replaced by a novel cell very similar to that first proposed (Streun & Wrulich, 2015) for the SLS-2 project. In this novel cell, the dipole is a BLG instead of a BD, with the highest field in its central slice; neighboring the dipole, there are two dedicated defocusing quadrupoles (QDs) and two anti-bends combined with focusing gradients (i.e.…”