The Free-Electron Laser in Hamburg (FLASH) and the future European X-Ray Free-Electron Laser (XFEL) are sources of brilliant extreme-ultraviolet and X-ray radiation pulses. Both facilities are based on superconducting linear accelerators (linacs) that can produce and transport electron beams of high average power. With up to 90 kW or up to 600 kW of power, respectively, these beams hold a serious potential to damage accelerator components. This thesis discusses several passive and active machine protection measures needed to ensure safe operation. At FLASH, dark current from the rf gun electron source has activated several accelerator components to unacceptable radiation levels. Its transport through the linac is investigated with detailed tracking simulations using a parallelized and enhanced version of the tracking code Astra; possible remedies are eval-uated. Beam losses can lead to the demagnetization of permanent magnet insertion devices. A number of beam loss scenarios typical for FLASH are investigated with shower simulations. A shielding setup is designed and its efficiency is evaluated. For the design parameters of FLASH, it is concluded that the average relative beam loss in the undulators must be controlled to a level of about 10−8. FLASH is equipped with an active machine protection system (MPS) comprising more than 80 hotomultiplier-based beam loss monitors and several subsystems. The maximum response time to beam losses is less than 4μs. Setup procedures and calibration algorithms for MPS subsystems and components are introduced and operational problems are addressed. Finally, an architecture for a fully programmable machine protection system for theXFEL is presented. Several options for the topology of this system are reviewed, with the result that an availability goal of at least 0.999 for the MPS is achievable with moderate hardware requirements
