Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Regulating the arrival time of electron bunches is a crucial step to improve the temporal resolution
of accelerator-based pump-probe experiments. In this regard, an electron beam regulation method,
called beam-based feedback, has been shown to work well for stabilizing longitudinal beam properties
on pulsed accelerator machines. Essentially, the method resembles a typical design of a proportional
regulator, where the plant is represented by an electron beam response matrix, and where the
inversion of such matrix produces the regulator. In recent years, however, linear accelerators (linacs)
that operate in a continuous-wave (CW) mode have received increasing attention. One of the key
features of such machines is the improved statistics of measured data, which enables a high-resolution
spectral analysis of the noise acting on the electron beam. This new insight allows to reinterpret the
electron beam regulation as a disturbance rejection goal, where the disturbance is based on measured
frequency data. In this work, we show that the proportional beam-based feedback method has a
principal performance limitation that becomes apparent by analyzing CW data. To improve this
situation, we propose a regulator design that incorporates a dynamical disturbance model formulated
in the context of the so-called H2 mixed-sensitivity problem. The designed regulator demonstrated
excellent agreement between the model and measurements carried out at the CW linac ELBE and
showed a potential to improve the proportional regulator approach.