Design and Development of a New Control Architecture for Elliptically Polarizing Undulators at the Taiwan Photon Source

During the phase-II beamline project at the Taiwan Photon Source (TPS), elliptically polarized undulators (EPU), called EPU66 and EPU168, will be installed in 2020. The new control system for the EPUs is based on the Experimental Physics and Industrial Control System (EPICS) and Ethernet Control Automation Technology (EtherCAT) framework. The EPU control elements include: motors with absolute optical encoders for gap and phase control, corrector magnets power supply control for trim coils, interlock safety systems to automatically stop motion based on encoder readings, limit switches, tilt sensors and emergency buttons. All control functionalities are coordinated by a fan-less embedded computer with three Ethernet ports. User interface for operators and beamline users are included to support the operation of the system, such as gap/phase control. Reliable operation of the EPU is important to users of beamlines. The most unpredictable fault is due to a soft error in the absolute optical encoders. There are several protection solutions to avoid faults, e.g., by increasing the distance of the encoder from the beam center, by a lead shield cover and finally by adopting an auxiliary position sensing device to cross check the position and perform the necessary procedure. Efforts to improve operational reliability of the EPU controls will be discussed. Features and benefits of the EPU66 and EPU168 control system will be summarized in this report.