Abstract
The well-known relaxed theoretical minimum emittance (TME) cell is commonly used in the design of multi-bend achromat (MBA) lattices for the new generation of diffraction limited storage rings. But significantly lower emittance at moderate focusing properties can be achieved by combining longitudinal gradient bends (LGB) and reverse bends (RB) in a periodic lattice unit cell. LGBs alone, however, are of rather limited gain. We investigate the emittance achievable for different unit cell classes as a function of the cell phase advance in a most general framework, i.e. with a minimum of assumptions on the particular cell optics. Each case is illustrated with a practical example of a realistic lattice cell, eventually leading to the LGB/RB unit cell of the baseline lattice for the upgrade of the Swiss Light Source.
Highlights
The quantum nature of light is the origin of finite emittance in an electron storage ring: sudden loss of energy due to photon emission causes an electron to start a betatron oscillation around the closed orbit corresponding to its reduced energy
Separate-function lattice, this can be done in three ways: (1) Horizontal focusing of the beam into the bends, since dispersion occurs in the horizontal dimension in a planar lattice
For the new generation of diffraction limited storage rings, technological progress enabled miniaturization of vacuum chambers and magnets. This leads to a reduction of unit cell length, so that the double or triple bend achromats of third generation light sources could be replaced by multibend achromat (MBA) containing five or more lattice cells
Summary
The quantum nature of light is the origin of finite emittance in an electron storage ring: sudden loss of energy due to photon emission causes an electron to start a betatron oscillation around the closed orbit corresponding to its reduced energy. (2) Using many bends of small deflection angle to limit the dispersion growth inside the bend This is the concept of the multibend achromat (MBA) lattice in its classic form [1,2] and its modifications (hybrid MBA) [3]. For the new generation of diffraction limited storage rings, technological progress enabled miniaturization of vacuum chambers and magnets This leads to a reduction of unit cell length, so that the double or triple bend achromats of third generation light sources could be replaced by MBAs containing five or more lattice cells. In this work we generalize the TME cell and the class of homogeneous-bend cells towards two different bends per cell with arbitrary longitudinal gradient but no transverse gradient, still not making any assumptions on the detailed focusing in the cell This allows a general study of the alternative concept of the RB cell with and without LGB in a common framework.
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