  In this paper, a new lattice concept called the locally symmetric lattice is
proposed for storage ring light sources. In this new lattice, beta functions
are made locally symmetric about two mirror planes of the lattice cell, and the
phase advances between the two mirror planes satisfy the condition of nonlinear
dynamics cancellation. There are two kinds of locally symmetric lattices,
corresponding to two symmetric representations of lattice cell. In a locally
symmetric lattice, main nonlinear effects caused by sextupoles can be
effectively cancelled within one lattice cell, and generally there can also be
many knobs of sextupoles available for further optimizing the nonlinear
dynamics. Two kinds of locally symmetric lattices are designed for a 2.2 GeV
diffraction-limited storage ring to demonstrate the lattice concept.
