Self-organzied critical control for the European XFEL using black box parameter identification for the quench detection system

The European Free Electron Laser (XFEL) consists of a large and complex plant, with many cost intensive and technological high-end components. It is therefore important that the XFEL can be operated reliably and safely using exception handling and fault detection systems. A crucial part of the system are the superconducting cavities for which especially quenches, i.e. the break down of the superconductivity have to be avoided. The paper shows the interaction of the fault detection system with the Low Level RF (LLRF) control system to maximize the field gradients. This is an example for process supervision, which can neither be classified as fault-tolerant, nor is it a reconfiguration system, but uses the result of the fault detection to operate the system at its fault critical limit. This scheme simulates a system which behaves like a self-organized critical system, and drives the process at its critical performance limit. It is therefore called Self-organized Critical Control (SOCC). The paper shows the basic set-up and quench detection methods of the European XFEL and gives an example for an application of SOCC.