Abstract
The output power of a free electron laser (FEL) has extremely high variance even when all FEL parameter set points are held constant because of the stochastic nature of the self-amplified spontaneous emission (SASE) FEL process, drift of thousands of coupled parameters, such as thermal drifts, and uncertainty and time variation of the electron distribution coming off of the photo cathode and entering the accelerator. In this work, we demonstrate the application of automatic, model-independent feedback for the maximization of average pulse energy of the light produced by free electron lasers. We present experimental results from both the European x-ray free electron laser at DESY and from the Linac Coherent Light Source at SLAC. We demonstrate application of the technique on rf systems for automatically adjusting the longitudinal phase space of the beam, for adjusting the phase shifter gaps between the undulators, and for adjusting steering magnets between undulator sections to maximize the FEL output power. We show that we can tune up to 105 components simultaneously based only on noisy average bunch energy measurements.
Highlights
Free electron lasers (FEL) are incredibly powerful scientific tools for studying physics at previously inaccessible length and time [femtoseconds] scales for high energy physics, biology, chemistry, material science, and accelerator physics experiments [1,2,3]
In this work we demonstrate a general adaptive feedback algorithm for automatic accelerator tuning with in-hardware demonstrations on both the Linac Coherent Light Source (LCLS) free electron laser (FEL) and the European XFEL for laser pulse energy maximization [23,24,25,26,27]
At the European X-Ray FEL (EuXFEL), we demonstrated our technique on various combinations of accelerator components in order to develop tools that can aid the operators in achieving spontaneous emission (SASE) setup
Summary
Free electron lasers (FEL) are incredibly powerful scientific tools for studying physics at previously inaccessible length (nanometers) and time [femtoseconds (fs)] scales for high energy physics, biology, chemistry, material science, and accelerator physics experiments [1,2,3]. Traditional model-based approaches are severely limited by such uncertainties and time variation of both the accelerated beam’s phase space distribution and the accelerator’s components as well as misalignments, thermal cycling, and collective effects such as space charge forces, wakefields, and coherent synchrotron radiation emitted by extremely short high current bunches. One example of such difficulties is the process of reconfiguring the LCLS to a low charge mode to provide 3 fs bunches, a process which may require many hours of expert hands on tuning. We show that we can tune up to 105 components simultaneously
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