arXiv subjects

S. Tomin

Publications and source records attributed to S. Tomin.

3 recordsLinked to original sources

arXiv2026

Design criteria for a beam-driven resonant passive transverse deflector for longitudinal beam diagnostics

Conventional radio-frequency (rf) transverse deflecting structures provide high-resolution longitudinal beam diagnostics, but require externally generated high-power rf, waveguide distribution, synchronization and input coupling at the operating frequency. We propose design criteria for a beam-driven resonant passive transverse deflector that does not require an external rf source. A leading drive bunch excites long-range wakefields in an off-axis periodic copper structure and a delayed witness bunch experiences the transverse wake near a zero crossing. The concept is based on the large temporal slope available from high-frequency wake components. A structure designed for installation after the second bunch compressor in the three-bunch-compressor layout of the European XFEL is optimized to place the zero crossing of the drive-bunch-induced transverse wake potential approximately one rf-bucket spacing of the 1.3 GHz linac, behind the drive bunch. The selected geometry produces a multi-mode transverse kick dominated by TM-like modes. We use time-domain wake simulations, frequency-domain decomposition, cell-number scaling, mechanical-tolerance scans, orbit-offset studies and uniform thermal scaling to determine the operating point and its sensitivity. For this geometry, the zero crossing occurs at s0 = 230.6 mm, with a per-cell temporal slope of Scell = 1.186 mV/(pC fs cell). For a compact 1 m structure operated with a 250 pC drive bunch and a 700 MeV witness beam, the estimated temporal resolution is about 33 fs.

physics.acc-ph↗

arXiv2026

Beam-Driven Transverse Deflecting Structure for Femtosecond Electron-Beam Diagnostics

High-resolution longitudinal phase-space (LPS) diagnostics are essential for X-ray free-electron lasers and advanced accelerators. Conventional radio-frequency transverse deflecting structures (TDSs) provide direct femtosecond-scale LPS measurements, but their substantial RF-power and infrastructure requirements strongly limit their deployment at multi-GeV beam energies. Here, we propose a beam-driven transverse deflecting structure in which a leading driver bunch, separated by one RF bucket from a trailing witness bunch under study, excites long-lived wakefields in a resonant cavity array. By placing the witness bunch near a zero crossing of the wakefield, the bunch experiences an approximately linear time-dependent transverse kick. Electromagnetic simulations of the resonant structure, combined with start-to-end beam-dynamics simulations based on European XFEL parameters at a final beam energy of 14 GeV, demonstrate a temporal resolution of $\sim 1.6$ fs for a 500 pC driver bunch, with a clear scaling toward the sub-femtosecond regime at higher charge.

physics.acc-ph↗

arXiv2017

Automatic tuning of Free Electron Lasers

Existing FEL facilities often suffer from stability issues: so electron orbit, transverse electron optics, electron bunch compression and other parameters have to be readjusted often to account for drifts in performance of various components. The tuning procedures typically employed in operation are often manual and lengthy. We have been developing a combination of model-free and model-based automatic tuning methods to meet the needs of present and upcoming XFEL facilities. Our approach has been implemented at FLASH \cite{flash} to achieve automatic SASE tuning using empirical control of orbit, electron optics and bunch compression. In this paper we describe our approach to empirical tuning, the software which implements it, and the results of using it at FLASH. We also discuss the potential of using machine learning and model-based techniques in tuning methods.

physics.acc-ph↗