Beam optics for the magnet recovery in 3-50BT beam transfer line

Coil layers of the bending magnet (B15D) in the transport line from Rapid cycle synchrotron (RCS) to Main Ring (MR) of J-PARC were partially shorted in the slow-extracted beam operation (RUN81). The magnetic field reduction rate by the partial layers shorting was estimated from the comparison between the measured BPM data and the calculation by SAD code. The shorted coil layers were bypassed to recover the beam operation temporarily. The effect on the beam by the skew field components generated by the bypass was investigated by the tracking simulation using SAD and POISSON code. A solution to correct the orbit shift generated after the 2nd layer shorting was derived, which used two steering magnets. (author)