Tracking Study for Top-off Safety Validation at SSRL

A tracking study was performed at SSRL to identify necessary controls and to prove the safety of top-off operation from radiation hazard under such conditions. The safety rationale, tracking setup and the results are presented. Top-off operational mode has become a trend for existing and planned third-generation storage ring light sources for the many benefits such as increased average brightness, improved thermal stability and elimination of the interruption to user experiments due to traditional injection [1, 2]. Unlike the traditional decay mode injection which happens a few times a day and during which the photon beamline shutters are closed, top-off mode injection requires photon beamline shutters to remain open during injection and occurs much more frequently, from once every 5 seconds to once every 30 minutes. Therefore injection may be transparent to user experiments and the stored current variation can be significantly reduced. For a facility equipped with a full-energy injector, the biggest challenge to the implementation of the top-off mode may be the control of radiation hazard. Studies at ALS and SSRL [2, 3] have shown that a single injected electron pulse that enters the photon beamline and exits the radiation shield wall would cause unacceptable radiation doses on the experimental floor. For the protection of users and experimental equipment, it is hence a prerequisite for top-off operation to establish controls that absolutely prevent such occurrences. Similar to other facilities such as ALS and APS [2, 4], tracking simulations were conducted at SSRL to identify the control measures, define the specifications and prove the radiation safety. However, a different approach toward the proof of safety is taken at SSRL. In this paper we first describe the SSRL accelerator complex with emphasis on the aspects related to top-off in section 2. The general considerations and requirements for top-off are presented in section 3. Section 4 and 5 give a detailed description of the tracking setup and results. Concluding remarks are given in section 6