DESIGN OF THE ACCELERATOR SAFETY INTERLOCK SYSTEM FOR XFEL IN SPring-8

The accelerator safety interlock system (ASIS) for the X-ray free electron laser (XFEL) at SPring-8 protects personnel from radiation hazards. We developed an ASIS consisting of three interlock systems: a central interlock system (CIS), an emergency interlock system (EIS), and a beam route interlock system (BIS). The CIS and EIS monitor the safety equipment status and emergency stop buttons, respectively. The BIS monitors the consistency between the predefined electron beam route to the downstream insertion devices and the actual transport route. If the state is unsafe, these systems do not permit accelerator operation and they stop the electron beam. The ASIS is required to stop the electron beam within 16.6 ms. Therefore, we developed an optical module to transmit high-speed stop signals. INTRODUCTION The X-ray free electron laser (XFEL) facility at SPring8 is currently under construction. Figure 1 shows the plan of the XFEL building and installation location of the equipment. The electron beam is injected from the 500 kV electron gun (GUN) and is boosted to 8 GeV by the linear accelerator. The boosted electron beam is switched to the beamline (BL) with a bending magnet. The maximum repetition frequency of the electron beam is designed to be 60 Hz, and the bending magnet switches the direction of the electron beam between BL1 and BL3. In the final plan, the electron beam is switched among five BLs, which are indicated by dashed lines in Fig. 1. The switched electron beam is injected into the undulator to generate XFEL radiation and is dumped at a beam dump. In addition, the XFEL-to-Storage ring beam transport line (XSBT), which connects from the XFEL linac to the existing 8 GeV storage ring at SPring-8, is now under construction. The accelerator safety interlock system (ASIS) has been established with the objective of protecting personnel from radiation hazards. It controls the permission signal for the accelerator and monitors the access to the machine tunnel. If the conditions are unsafe, the ASIS denies permission to the accelerators and stops the electron beam. BASIC CONCEPT OF ASIS The ASIS is based on the following concepts: • It must be fail-safe so that even in the case of a single fault, the system goes into a safe beaminhibiting state. • It requires double structure of the logic and signal translation. • It must monitor the equipment related to the machine tunnel, the emergency stop buttons, and the electron beam route. We have designed three independent systems that monitor the equipment. • If the electron beam route is unsafe, it must stop the electron beam within 16.6 ms (=1/60 Hz), since the next electron beam must be stopped. • It controls 73 radio frequencies (RFs) and the GUN by giving the permission signal.