Development of a finite state machine for the automated operation of the LLRF control at FLASH

Alexander Brandt
The entry of digital signal processors in modern control systems not only allows for extended diagnostics compared to analog systems but also for sophisticated and tricky extensions of the control algorithms. With modern DSP-and FPGA-technology * , the processing speed of digital systems is no longer inferior to analog systems in many applications. A higher degree of digitalization leads to an increased complexity of the systems and hence to higher requirements on their operators. The focus of
more » ... tors. The focus of research and development in the field of high frequency control has changed in the last few years and moved towards the direction of software development and complexity management. In the presented thesis, a frame for an automation concept of modern high frequency control systems is developed. The developed automation is based on the concept of finite state machines (FSM), which is established in industry for years. A flexible framework was developed, in which procedures communicate using standardized interfaces and can be exchanged easily. With that, the developer of high frequency control components as well as the operator on shift shall be empowered to improve and adapt the automation to changed conditions without special programming skills required. Along the automation concept a number of algorithms addressing various problems were developed which satisfy the needs of modern high frequency control systems. Among the developed and successfully tested algorithms are the calibration of incident and reflected wave of resonators without antennas, the fast adaptive compensation of repetitive errors, the robust estimation of the phase advance in the control loop and the latency adjustment for the rejection of instabilities caused by passband modes. During the development of the resonator theory, high value was set on the usability of the equation in algorithms for high frequency control. The usage of the common nomenclature of control theory emphasizes the underlying mathematical structures of the equations. Several physical limitations and requirements, for example the limits of the vector sum calibration, were newly and adequately calculated based on the developed theory. The linear accelerator of the Free-Electron Laser in Hamburg (FLASH) served as the main platform for testing of the algorithms and concepts. The developed automation, in particular the flexible and transparent framework and methods for the reduction of the complexity of the various communication channels (quantization) is not only suited for high fequency control but also for other aspects of an accelerator and beyond. * DSP=Digital Signal Processor, FPGA=Field Programmable Gate Array i Conclusions 109 Appendices 113 A. Slopes of Amplitude and Phase of the Step Response 115 B. Derivation of the Extended Naive Adaptive Feedforward 117 Light at the end of the tunnel. Linac Based Free-Electron Laser Linear Accelerator for Free-Electron Lasers When building a free-electron laser based on a linear accelerator (linac), the largest effort in terms of manpower and finance goes into the linac itself. Its purpose is to deliver a bright, highenergy electron beam. A linear accelerator, compared to a circular one, does not suffer from energy-loss due to synchrotron-radiation and the longitudinal emittance is thus not limited by the synchrotron-radiation process. While in a synchrotron or storage ring particles reach their maximum energy after several revolutions, a linac transfers the energy with a single pass. The main components of a linear accelerator shall briefly be introduced at the example of FLASH (figure 2.1). Linear Accelerator for Free-Electron Lasers
doi:10.3204/desy-thesis-2007-024 fatcat:4ssc4yy2d5a2dhnsjc7274ctdm