Beam-Based Confirmation of Skew-Quadrupole Field Correction in 10.8 m Long Undulator

The synchrotron radiation facility NewSUBARU is a 1.5 GeV storage ring which has two long straight sections. A permanent magnet, planar-type, out-of-vacuum 10.8 m Long Undulator is placed in one of the long straight sections. The longitudinal moments of the skew-quadrupole field errors in the undulator were determined from the response of the stored beam. The method used was to measure the change of the horizontal closed orbit distortion produced by two types of vertical local bump orbit in the undulator. This method is more reliable than the global modeling of a ring, which uses the response matrix of the whole ring, since the present method is not sensitive to skew-quadrupole field errors in sections other than the target section