arXiv subjects

Najmeh Mirian

Publications and source records attributed to Najmeh Mirian.

9 recordsLinked to original sources

arXiv2026

Integration of Retrieval-Augmented Generation for Knowledge Access in the ELBE Accelerator Control System

The efficient operation of accelerator facilities increas- ingly relies on rapid access to heterogeneous operational knowledge, including logbooks, interlock reports, machine parameters, and historical archive data. At ELBE, we pro- posed a Retrieval-Augmented Generation (RAG) frame- work that integrates facility documentation and operational records into a unified AI-assisted support tool for operators. The system is expected to index electronic logbooks, ma- chine archive time-series data, and subsystem manuals using domain-adapted embeddings stored in a vector database. User queries will be expected to be processed through a large language model that retrieves the most relevant oper- ational context and generates structured, operator-oriented responses with traceable source references. This contribu- tion presents the system architecture, data integration strat- egy, and challenges toward real-time AI-assisted accelerator operation

physics.acc-ph↗

arXiv2026

Attosecond soft X-ray pulses generated by chirp-dispersed manipulation in an XFEL reveal nonlinear core-electron dynamics in neon

Free-electron lasers have demonstrated their capability of generating intense attosecond X-ray pulses, which are the key to studying electron dynamics at their natural time scale and in specifically targeted electronic states, but come at the expanse of complicated generation schemes and stochastic pulse shapes. Here, we demonstrate a novel and simple operation concept based on the manipulation of the electron-bunch chirp-dispersion and working with the full 4.5 MHz repetition rate at the European XFEL in Germany. With a high-fidelity single-shot temporal characterisation, we detect X-ray pulses with durations of down to 200 attoseconds and peak powers reaching into the terawatt regime at ~1 keV photon energy. As a direct application, we present simultaneous measurements of nonlinear X-ray-matter interaction via time-resolved electron spectroscopy. Using the derived temporal pulse information and restricting the durations to a regime where individual X-ray pulses are shorter than the single-core-hole life time in neon atoms, we reveal an otherwise hidden peak-intensity dependence in the nonlinear dynamics of double-core-hole formation. Our results open the field of attosecond science to the investigation of electronic processes not only in the ground state but also in systems driven far off their equilibrium. They shed light on highly transient intermediate steps in complex electronic dynamics and thus promise to help build the conceptual bridge between fundamental physical processes and chemical photo-reactions.

physics.optics↗

arXiv2026

Short-Pulse High-Power THz Generation Using Optical Klystron FELs: Simulation Results

The generation of high-power radiation in the terahertz (THz) regime using free-electron lasers (FELs) is challenging due to strong diffraction and pronounced slippage effects. These constraints often limit the achievable pulse duration and peak power in conventional single-pass THz FEL configurations. In this work, we investigate an unseeded optical klystron (OK) FEL concept tailored for the THz regime. Using time-dependent three-dimensional simulations for resonant wavelengths of 10, 30, and 100 μm, we demonstrate that this approach enables the generation of coherent ultrashort THz pulses with durations of a sub picoseconds (FWHM) and peak powers in the multi-hundred- megawatt range at wavelengths 10 and 30 μm. To address the slippage challenge, we propose and numerically demonstrate a novel chicane-embedded optical delay scheme, which restores phase alignment between the radiation and microbunched electrons. Simulations confirm that careful tuning of the dispersive strengths allows staged amplification, preserving beam quality and reaching multi-megawatt output power. These results highlight the potential of THz-tailored optical klystrons to generate compact, short, and high-intensity THz pulses, and lay the groundwork for future experimental studies and facility implementation

physics.acc-ph↗

arXiv2026

Conceptual Design of a Transverse Deflecting Structure for Longitudinal Diagnostics at DALI

A conceptual design study of a Transverse Deflecting Structure (TDS) for longitudinal beam diagnostics at the DALI accelerator facility is presented. The TDS provides a time-dependent transverse kick to the electron bunch, enabling direct measurement of the longitudinal bunch profile and reconstruction of the longitudinal phase space when combined with a dispersive spectrometer section. The report reviews the physical principles of RF deflecting cavities, including the transverse kick mechanism, temporal-to-spatial mapping, and the relationship between beam optics and achievable temporal resolution. Engineering considerations such as RF frequency choice, cavity design, wakefield effects, timing synchronization, and mechanical stability are also discussed.

physics.acc-ph↗

arXiv2026

Spectrum Phase and Constraints on THz-Optical klystron

Optical klystrons provide an efficient mechanism for enhancing coherent radiation through laser-induced microbunching and dispersive amplification. In the terahertz (THz) regime and at low beam energy, however, the radiation wavelength becomes comparable to the characteristic wavelengths of longitudinal space-charge (LSC) and coherent synchrotron radiation (CSR) driven microbunching. In this work, we analyze the impact of electron-beam microbunching on the spectral amplitude and phase of a seeded optical klystron operating in the THz regime. Using a phase-space formalism, incoherent energy modulations generated by collective effects are shown to enter the bunching spectrum as a stochastic longitudinal phase, producing local wavenumber jitter and spectral broadening. An explicit connection between the microbunching-induced energy modulation and LSC/CSR gain is established for low-energy beams, demonstrating that the overlap between collective-effect wavelengths and the optical-klystron radiation wavelength leads to strong spectral phase distortion. These effects impose fundamental constraints on the achievable harmonic bunching and spectral purity and stability of THz optical klystrons and must be considered in the design and optimization of next-generation low-energy THz FEL facilities.

physics.optics↗

arXiv2024

Virtual Pulse Reconstruction Diagnostic for Single-Shot Measurement of Free Electron Laser Radiation Power

Accurate characterization of radiation pulse profiles is crucial for optimizing beam quality and enhancing experimental outcomes in Free Electron Laser (FEL) research. In this paper, we present a novel approach that employs machine learning techniques for real-time virtual diagnostics of FEL radiation pulses. Our advanced artificial intelligence (AI)-based diagnostic tool utilizes longitudinal phase space data obtained from the X-band transverse deflecting structure to reconstruct the temporal profile of FEL pulses in real time. Unlike traditional single-shot methods, this AI-driven solution provides a non-invasive, highly efficient alternative for pulse characterization. By leveraging state-of-the-art machine learning models, our method facilitates precise single-shot measurements of FEL pulse power, offering significant advantages for FEL science research. This work outlines the conceptual framework, methodology, and validation results of our virtual diagnostic tool, demonstrating its potential to significantly impact FEL research.

physics.acc-ph↗

arXiv2024

Harnessing Machine Learning for Single-Shot Measurement of Free Electron Laser Pulse Power

Electron beam accelerators are essential in many scientific and technological fields. Their operation relies heavily on the stability and precision of the electron beam. Traditional diagnostic techniques encounter difficulties in addressing the complex and dynamic nature of electron beams. Particularly in the context of free-electron lasers (FELs), it is fundamentally impossible to measure the lasing-on and lasingoff electron power profiles for a single electron bunch. This is a crucial hurdle in the exact reconstruction of the photon pulse profile. To overcome this hurdle, we developed a machine learning model that predicts the temporal power profile of the electron bunch in the lasing-off regime using machine parameters that can be obtained when lasing is on. The model was statistically validated and showed superior predictions compared to the state-of-the-art batch calibrations. The work we present here is a critical element for a virtual pulse reconstruction diagnostic (VPRD) tool designed to reconstruct the power profile of individual photon pulses without requiring repeated measurements in the lasing-off regime. This promises to significantly enhance the diagnostic capabilities in FELs at large.

cs.LG↗

arXiv2023

Generation and Measurement of Ultrashort Free Electron Laser Pulses in Ultraviolet and Soft-X-ray Spectral Regions

Over the last few years, tremendous progress has been gained in the generation and application of ultrashort radiation pulses. Recently, free-electron lasers generating ultrashort pulses with high peak power from the extreme ultraviolet (EUV) to the soft-X-ray region are opening a wide range of new scientific opportunities. Taking advantage of this short timescale permits probing ultrafast, out-of-equilibrium dynamics, and the high intensities are key for nonlinear optics. The core structure of the extremely important light elements carbon, nitrogen, and oxygen can be accessed by soft-X-ray wavelengths by providing chemical sensitivity. Externally seeded free electron lasers generate coherent pulses with the ability to be synchronized with femtosecond accuracy. In this contribution, we present new achievements in the generation of coherent ultrashort pulses in the range of EUV to the soft X-ray in externally seeded FELs. In particular, we present the recently successful robust experiment at FERMI in Trieste, where few-femtosecond extreme-ultraviolet pulses were generated and characterized in terms of energy, and duration via autocorrelation.

physics.acc-ph↗

arXiv2020

A new method for measuring angle-resolved phases in photoemission

Quantum mechanically, photoionization can be fully described by the complex photoionization amplitudes that describe the transition between the ground state and the continuum state. Knowledge of the value of the phase of these amplitudes has been a central interest in photoionization studies and newly developing attosecond science, since the phase can reveal important information about phenomena such as electron correlation. We present a new attosecond-precision interferometric method of angle-resolved measurement for the phase of the photoionization amplitudes, using two phase-locked Extreme Ultraviolet pulses of frequency $ω$ and $2ω$, from a Free-Electron Laser. Phase differences $Δ\tilde η$ between one- and two-photon ionization channels, averaged over multiple wave packets, are extracted for neon $2p$ electrons as a function of emission angle at photoelectron energies 7.9, 10.2, and 16.6 eV. $Δ\tilde η$ is nearly constant for emission parallel to the electric vector but increases at 10.2 eV for emission perpendicular to the electric vector. We model our observations with both perturbation and \textit{ab initio} theory, and find excellent agreement. In the existing method for attosecond measurement, Reconstruction of Attosecond Beating By Interference of Two-photon Transitions (RABBITT), a phase difference between two-photon pathways involving absorption and emission of an infrared photon is extracted. Our method can be used for extraction of a phase difference between single-photon and two-photon pathways and provides a new tool for attosecond science, which is complementary to RABBITT.

physics.atom-ph↗