• I. Hwang, C. Kim, K.R. Kim, M. Kim, S.H. Nam, S.J. Park, S. Shin
  PAL, Pohang, Kyungbuk
• J. Hou, L.G. Liu
  SINAP, Shanghai

The measurement and the control of the coupling is essential to maximize synchrotron performance. Small coupling is required for small vertical size and high brightness. The Pohang Light Source has a 2.5 GeV storage ring and its coupling constant is measured as about 1%. In addition to errors at quadrupole or sextupole, the condition varying of the insertion device affects the coupling. The coupling for various condition is measured by the resonance and the response matrix and compared with the beam size and the lifetime. The correction and the control of the coupling is presented.