Second-Order Achromats with Arbitrary Linear Transfer Matrices
  In this article we consider a system where a bend magnet block arranged in an achromat-like fashion is followed by a straight drift-quadrupole cell which is not a pure drift space. We formulate the necessary and sufficient conditions for this system to be a second-order achromat and show that it can be achieved using six, four or even only two sextupole families. 
V.Balandin, R.Brinkmann, W.Decking, and N.Golubeva
physics.acc-ph