Low Emittance E/e Storage Ring Design Using Bending Magnets with Longitudinal Gradient

Low emittance is desired in most synchrotron light source and damping ring designs. The work presented in this paper demonstrates that by introducing dipoles with a longitudinal gradient, the minimum emittance can be lowered without increasing the number of dipoles. The minimum I5/I2 is limited by the ratio of maximum and average field in the dipole; by setting that ratio to 3, a factor of 4-5 in I5/I2 reduction can be achieved in TMEtype lattice. In practical lattice designs, the reduction factor still can be 2-4 depending on configurations and constraints.