Abstract
Feedback control of the longitudinal and transverse electron beam profiles are considered to be critical for beam control in accelerators. In the feedback scheme, the longitudinal or transverse beam profile is measured and compared to a desired profile to give an error estimate. The error is then used to act on the appropriate actuators to correct the profile. The role of the transverse feedback is to steer the beam in a particular trajectory, known as the ``orbit.'' The common approach for orbit correction is based on approximately inverting the response matrix, and in the best case, involves regulating or filtering the singular values. In the current contribution, a more systematic and structured way of handling orbit correction is introduced giving robustness against uncertainties in the response matrix. Moreover, the input bounds are treated to avoid violating the limits of the corrector currents. The concept of the robust orbit correction has been successfully tested at the SwissFEL injector test facility. In the SwissFEL machine, a photo-injector laser system extracts electrons from a cathode and a similar robust control method is developed for the longitudinal feedback control of the current profile of the electron bunch. The method manipulates the angles of the crystals in the laser system to produce a desired charge distribution over the electron bunch length. This approach paves the way towards automation of laser pulse stacking.
Highlights
Many orbit correction algorithms have been devised for synchrotron light sources
The task of orbit correction is to determine a suitable set of currents in the corrector magnets in order to keep the beam on a specified trajectory
A static response matrix maps the changes in corrector currents to the changes in the equilibrium position of the beam at each beam position monitors” (BPMs)
Summary
Many orbit correction algorithms have been devised for synchrotron light sources. The task of orbit correction is to determine a suitable set of currents in the corrector magnets in order to keep the beam on a specified trajectory. Orbit correction attempts to invert the response matrix to translate the beam positions into the actuation on each of the corrector magnets This procedure is usually based on the singular value decomposition (SVD) method which is already in use at many accelerator laboratories over the world [1,2,3,4,5,6,7,8]. This approach has been successfully tested at the SwissFEL [13] injector test facility on 10 sets of BPM and corrector magnets This method may be applied to different systems and in this paper, we develop an automated procedure for the laser pulse stacking system, using the same mathematical approach, to achieve a desired charge distribution over the bunch length.
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