Beam position control of SOR‐RING

Recently, a global feedback of beam position was switched on at SOR‐RING of Tokyo University. At a low beam current, the vertical orbit drift was suppressed almost within a few μm and the horizontal orbit drift within several μm. On the other hand, the suppression became worse at a high current because of a longitudinal instability, which deteriorated the accuracy of the beam position monitor system. It was also observed that at 21 Hz, the repetition rate of the electron synchrotron close to SOR‐RING, the horizontal orbit tends to vibrate uniformly around the ring, i.e., monopolelike expansion and contraction, while the vertical orbit has a dipolelike vibration; a result expected if a uniform magnetic field is impressed on the ring.