arXiv subjects

I. Zagorodnov

Publications and source records attributed to I. Zagorodnov.

13 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↗

arXiv2024

Two-bunch seeding of soft X-ray free electron lasers

Seeded Free Electron Lasers (FELs) demonstrate a good performance and are successfully used in different user experiments in extreme ultraviolet and soft X-ray regimes. In this paper a simple modification of the seeding scenario is proposed relying on generation of two closely spaced bunches with very different properties: a low-current seeding bunch, and a high-current bunch that amplifies coherent radiation, produced by the seeding bunch. This approach eliminates different limitations and mitigates some harmful effects in the standard scenario. In particular, one can generate very high harmonic numbers with a moderate laser power in a simple high-gain harmonic generation (HGHG) scheme. Alternatively, in case of moderate harmonic numbers, one can strongly reduce the required laser power thus simplifying design of high repetition rate seeded FELs. An influence of beam dynamics effects (like nonlinearities of the longitudinal phase space of electron beams, coherent synchrotron radiation, longitudinal space charge, geometrical wakefields, microbunching instabilities etc.) on properties of output radiation (spectrum broadening, pedestals, stability) can be to a large extent reduced in the proposed scheme. In this paper we illustrate the operation of the two-bunch seeding scheme in HGHG configuration with realistic start-to-end simulations for the soft X-ray user facility FLASH. We show that nearly Fourier-limited multi-gigawatt pulses can be generated at 4 nm using the present compact design of the undulator system. With several thousand pulses per second this can be a unique source for photon science.

physics.acc-ph↗

arXiv2021

Observation of harmonic lasing in the Angstrom regime at European XFEL

Harmonic lasing provides an opportunity to extend the photon energy range of existing and planned X-ray FEL user facilities. Contrary to nonlinear harmonic generation, harmonic lasing can generate a much more intense, stable, and narrow-band FEL beam. Another interesting application is Harmonic Lasing Self-Seeding (HLSS) that allows to improve the longitudinal coherence and spectral power of a Self-Amplified Spontaneous Emission (SASE) FEL. This concept was tested at FLASH in the range of 4.5 - 15 nm and at PAL XFEL at 1 nm. In this paper we present recent results from the European XFEL where we successfully demonstrated harmonic lasing at 5.9 Angstrom and 2.8 Angstrom. In the latter case we obtained both 3rd and 5th harmonic lasing and, for the first time, operated a harmonic lasing cascade (5th-3rd-1st harmonics of the undulator). These results pave the way for reaching very high photon energies, up to 100 keV.

physics.acc-ph↗

arXiv2018

Beam Dynamics and Tolerance Studies of the THz-driven Electron Linac for the AXSIS Experiment

A dielectric-loaded linac powered by THz-pulses is one of the key parts of the "Attosecond X-ray Science: Imaging and Spectroscopy" (AXSIS) project at DESY, Hamburg. As in conventional accelerators, the AXSIS linac is designed to have phase velocity equal to the speed of light which, in this case, is realized by tuning the thickness of the dielectric layer and the radius of the vacuum channel. Therefore, structure fabrication errors will lead to a change in the beam dynamics and beam quality. Additionally, errors in the bunch injection will also affect the acceleration process and can cause beam loss on the linac wall. This paper numerically investigates the process of electron beam acceleration in the AXSIS linac, taking into account the aforementioned errors. Particle tracking simulations were done using the code ECHO, which uses a low-dispersive algorithm for the field calculation and was specially adapted for the dielectric-loaded accelerating structures.

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↗

arXiv2016

Corrugated structure insertion for extending the SASE bandwidth up to 3% at the European XFEL

The usage of x-ray free electron laser (XFEL) in femtosecond nanocrystallography involves sequential illumination of many small crystals of arbitrary orientation. Hence a wide radiation bandwidth will be useful in order to obtain and to index a larger number of Bragg peaks used for determination of the crystal orientation. Considering the baseline configuration of the European XFEL in Hamburg, and based on beam dynamics simulations, we demonstrate here that the usage of corrugated structures allows for a considerable increase in radiation bandwidth. Data collection with a 3% bandwidth, a few microjoule radiation pulse energy, a few femtosecond pulse duration, and a photon energy of 5.4 keV is possible. For this study we have developed an analytical modal representation of the short-range wake function of the flat corrugated structures for arbitrary offsets of the source and the witness particles.

physics.acc-ph↗

arXiv2016

Analytical Formulas for Short Bunch Wakes in a Flat Dechirper

We develop analytical models of the longitudinal and transverse wakes, on and off axis for realistic structures, and then compare them with numerical calculations, and generally find good agreement. These analytical "first order" formulas approximate the droop at the origin of the longitudinal wake and of the slope of the transverse wakes; they represent an improvement in accuracy over earlier, "zeroth order" formulas. In example calculations for the RadiaBeam/LCLS dechirper using typical parameters, we find a 16\% droop in the energy chirp at the bunch tail compared to simpler calculations. With the beam moved to 200~$μ$m from one jaw in one dechiper section, one can achieve a 3~MV transverse kick differential over a 30~$μ$m length.

physics.acc-ph↗

arXiv2015

Calculation of wakefields in 2D rectangular structures

We consider the calculation of electromagnetic fields generated by an electron bunch passing through a vacuum chamber structure that, in general, consists of an entry pipe, followed by some kind of transition or cavity, and ending in an exit pipe. We limit our study to structures having rectangular cross-section, where the height can vary as function of longitudinal coordinate but the width and side walls remain fixed. For such structures, we derive a Fourier representation of the wake potentials through one-dimensional functions. A new numerical approach for calculating the wakes in such structures is proposed and implemented in the computer code ECHO(2D). The computation resource requirements for this approach are moderate and comparable to those for finding the wakes in 2D rotationally symmetric structures. Numerical examples obtained with the new numerical code are presented.

physics.acc-ph↗

arXiv2009

Explicit TE/TM Scheme for Particle Beam Simulations

In this paper we propose an explicit two-level conservative scheme based on a TE/TM like splitting of the field components in time. Its dispersion properties are adjusted to accelerator problems. It is simpler and faster than the implicit version [1]. It does not have dispersion in the longitudinal direction and the dispersion properties in the transversal plane are improved. The explicit character of the new scheme allows a uniformly stable conformal method without iterations and the scheme can be parallelized easily. It assures energy and charge conservation. A version of this explicit scheme for rotationally symmetric structures is free from the progressive time step reducing for higher order azimuthal modes as it takes place for Yee's explicit method used in the most popular electrodynamics codes.

physics.comp-ph↗

arXiv2007

Impedance Calculations of Non-Axisymmetric Transitions Using the Optical Approximation

In a companion report, we have derived a method for finding the impedance at high frequencies of vacuum chamber transitions that are short compared to the catch-up distance, in a frequency regime that (in analogy to geometric optics for light) we call the optical regime. In this report we apply the method to various non-axisymmetric geometries such as irises/short collimators in a beam pipe, step-in transitions, step-out transitions, and more complicated transitions of practical importance. Most of our results are analytical, with a few given in terms of a simple one dimensional integral. Our results are compared to wakefield simulations with the time-domain, finite-difference program ECHO, and excellent agreement is found.

physics.acc-ph↗

arXiv2007

Optical approximation in the theory of geometric impedance

In this paper we introduce an optical approximation into the theory of impedance calculation, one valid in the limit of high frequencies. This approximation neglects diffraction effects in the radiation process, and is conceptually equivalent to the approximation of geometric optics in electromagnetic theory. Using this approximation, we derive equations for the longitudinal impedance for arbitrary offsets, with respect to a reference orbit, of source and test particles. With the help of the Panofsky-Wenzel theorem we also obtain expressions for the transverse impedance (also for arbitrary offsets). We further simplify these expressions for the case of the small offsets that are typical for practical applications. Our final expressions for the impedance, in the general case, involve two dimensional integrals over various cross-sections of the transition. We further demonstrate, for several known axisymmetric examples, how our method is applied to the calculation of impedances. Finally, we discuss the accuracy of the optical approximation and its relation to the diffraction regime in the theory of impedance.

physics.acc-ph↗

arXiv2005

A Test Facility for the International Linear Collider at SLAC End Station A, for Prototypes of Beam Delivery and IR Components

The SLAC Linac can deliver damped bunches with ILC parameters for bunch charge and bunch length to End Station A. A 10Hz beam at 28.5 GeV energy can be delivered there, parasitic with PEP-II operation. We plan to use this facility to test prototype components of the Beam Delivery System and Interaction Region. We discuss our plans for this ILC Test Facility and preparations for carrying out experiments related to collimator wakefields and energy spectrometers. We also plan an interaction region mockup to investigate effects from backgrounds and beam-induced electromagnetic interference.

physics.ins-det↗