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Description
The Linac Coherent Light Source II High-Energy (LCLS-II-HE) upgrade at SLAC extends the superconducting radiofrequency linac from a nominal beam energy of 4 GeV to 8 GeV, doubling available beam power to approximately 240 kW and enabling expanded free-electron laser capability. The higher beam energy produces harder and more forward-peaked electromagnetic showers, which can elevate dose rates at shielding boundaries, penetrations, and outside facility boundary, increase air-activation potential, cause damage to safety devices (beam dumps, stoppers, and collimators), and raise residual-radiation source terms. Meeting radiation-protection goals and operating the facility within the pre-defined safety envelope under these conditions requires an integrated approach that couples engineered access control and beam-limiting functions with updated shielding and instrumentation.
This work summarizes the implementation of the Radiation Safety System (RSS) for LCLS-II-HE, with emphasis on beam loss control and radiation protection for high-power operations. The RSS framework integrates engineered controls through shielding, the Access Control System (ACS), and the Beam Containment System (BCS). The ACS prevents personnel exposure during beam operations by enforcing controlled access states and interlocked entry protections. The BCS limits the radiological consequences of credible beam-loss scenarios through a combination of passive shielding, beam-loss monitoring with interlocked devices, and beam shutoff instrumentation. Major upgrades for LCLS-II-HE include the reevaluation of shielding for 8 GeV beam operation, expansion and reconfiguration of BCS components, and modifications to PPS boundaries and operational modes to support the enhanced accelerator capabilities.
A key component of safe high-power operation is power management using credited BCS devices limiting beam current and energy together with distributed long beam-loss monitoring, with conservative trip thresholds derived from systematic uncertainty tracking and protection-setting methodology. This integrated approach provides bounded operation across normal tuning and abnormal loss conditions, supporting reliable accelerator performance while maintaining protection of workers, users, the public, and the environment.
Keywords: LCLS-II-HE; radiation safety system; access control system; beam containment system; shielding; beam loss monitoring; power management
This work was supported by the United States Department of Energy Contract DE-AC02-76SF00515.
| Topics | T1. Source terms, new accelerator facilities and related topics |
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