Apochromatic Twiss Parameters of Drift-Quadrupole Systems with   Symmetries
  In this article we continue the study of the apochromatic Twiss parameters of straight drift-quadrupole systems with special attention given to the properties of these parameters for beamlines with symmetries. 
V.Balandin, R.Brinkmann, W.Decking, and N.Golubeva
physics.acc-ph