Status of the continuous mode scan for undulator beamlines at BESSY II

At the synchrotron light source BESSY II monochromator (MONO) and insertion device (ID) scans can be done synchronized in two different modes. In step mode MONO and ID move independently to intermediate target positions of an energy scan. In continuous mode (CM) MONO and ID cover the whole range of the scan nonstop in a coupled motion. Data acquisition is done continuously at the speed provided by the CM scan and is available in regular user operation. Currently CM is in operation at 11 undulator beamlines at BESSY II. 3 new beamlines requesting CM are under construction. During CM the MONO EPICS IOC acts as a controller forcing the MONO optics to follow the movement of the ID. A non-linear predictive control scheme is used to implement this dynamic coupling. The controller task utilizes polynomial regression to extrapolate the ID motion. Calculation of the trajectories for MONO grating and mirror is based on bijective gap to energy lookup tables and the grating equation. In this paper the technical implementation, limitations, recently developed diagnostic methods, and future plans for improvements are presented. (author)