Control of reference orbit using wire position sensor for X-ray free electron laser

Abstract We present a method to control the reference orbit of the undulator line using the 2D wire position sensor (WPS) to maintain the FEL intensity circumventing the ground motion problem. The WPS data shows that FEL intensity variation during the user beamtime is closely related to the undulator hall ground motion. We successfully demonstrated that the correction method could recover the FEL intensity, not interrupting the user beamtime.