Magnetic field correction of 11-m-long undulator of NewSUBARU

The NewSUBARU storage ring has an 11 m long, permanent magnet planar undulator. We adjusted its magnetic field distribution to minimize the imperfection fields mainly by an in-situ sorting method. The LU is separable into eight units and the imperfection fields were reduced for each of eight units to prevent them from exciting unnecessary betatron resonance in the ring.