Adjustable Strength REC Ouadrupoles

We have derived the matrix elements for a five disk singlet and shown that the particular choice of disk lengths in (25) leads to the absence of x-y coupling terms with rotation angles of uniform magnitude, to a high degree of accuracy. Numerical computations, including fringing fields, confirm these results, and show that the rotations can be used to preserve the average focussing and defocussing strengths of the singlet over a wide range of variation of the beam particle momentum. A similar analysis for the four disk doublet leads to analagous results.