Machine protection for high average current linacs

A fully integrated Machine Protection System (MPS) is critical to efficient commissioning and safe operation of all high current accelerators. The Jefferson Lab PEL has multiple electron beam paths and many different types of diagnostic insertion devices. The MPS needs to monitor both the status of these devices and the magnet settings which define the beam path. The matrix of these devices and beam paths are programmed into gate arrays, the output of the matrix is an allowable maximum average power limit. This power limit is enforced by the drive laser for the photocathode gun. The Beam Loss Monitors (BLMs), RF status, and laser safety system status are also inputs to the control matrix. There are 8 Machine Modes (electron path) and 8 Beam Modes (average power limits) that define the safe operating limits for the FEL. Combinations outside of this matrix are unsafe and the beam is inhibited. The power limits range from no beam to 2 megawatts of electron beam power. The timing requirements for the BLMs and RF is ∼1 microsecond and for the insertion devices (viewers) is ∼1 millisecond. The entire system is VME based and EPICS compatible. This paper describes the system as it is installed on the JLab 10 kW FEL.