1 A DEFINITION OF THE EFFECTIVE ROTATION ANGLE FOR HELICAL

With the collaboration between Brookhaven National Lab. (BNL) and RIKEN, the helical dipole magnets is under construction for RHIC spin project.[1] It is required that the deflection of beam is negligible in the helical dipoles.[2] The relation between the rotation angle in the helical dipole and the cancellation of the integral of transverse field along the beam axis is investigated.[3-5] Then, with the derived optimization method, the optimal length of the full-length helical dipoles is obtained from the measured field of the half-length prototype