Policy gradient methods for free-electron laser and terahertz source optimization and stabilization at the FERMI free-electron laser at Elettra

In this article we report on the application of a model-free reinforcement learning method to the optimization of accelerator systems. We simplify a policy gradient algorithm to accelerator control from sophisticated algorithms that have recently been demonstrated to solve complex dynamic problems. After outlining a theoretical basis for the functioning of the algorithm, we explore the small hyperparameter space to develop intuition about said parameters using a simple number-guess environment. Finally, we demonstrate the algorithm optimizing both a free-electron laser and an accelerator-based terahertz source in-situ. The algorithm is applied to different accelerator control systems and optimizes the desired signals in a few hundred steps without any domain knowledge using up to five control parameters. In addition, the algorithm shows modest tolerance to accelerator fault conditions without any special preparation for such conditions

AESIS: a support tool for the evaluation of sustainability of agroecosystems. Example of applications to organic and integrated farming systems in Tuscany, Italy

Agricultural researchers widely recognise the importance of sustainable agricultural production systems and the need to develop appropriate methods to measure sustainability on the farm level. Policy makers need accounting and evaluation tools to be able to assess the potential of sustainable production practices and to provide appropriate agro-environmental policy measures. Farmers are in search of sustainable management tools to cope with regulations and enhance efficiency. This paper presents the outcomes of applications to organic and integrated farming of an indicator-based framework to evaluate sustainability of farming systems (Agro-Environmental Sustainability Information System, AESIS). The AESIS was described together with a review of applications dating from 1991 in a previous paper. The objective of the present paper is to present the AESIS application to organic and integrated farming systems in Val d’Elsa (Tuscany) and discuss how it is adapted for application to ordinary farms. The AESIS is organised into a number of environmental and production systems. For each system, environmental critical points are identified with corresponding agro-environmental indicators and processing methods. Possible solutions to sustainability issues, and critical points of relevance to the agricultural sector of the local economic and agro-ecological zone, are formulated by including an experimental layout, identifying indicator thresholds and by defining management systems with corresponding policy measures. Alternative solutions are evaluated by calculating and measuring the relevant indicators. The outcomes of the AESIS applications are discussed with specific relevance to the operational adoptability of AESIS to ordinary, agri-touristic farms managed with the organic and the integrated production method, respectively. The AESIS framework proved to be sufficiently flexible to meet the requirements for ordinary farm applications while keeping a holistic perspective and considering pedo-climatic and production factors on different spatial scales

Assessment of management of a golf course by means of sustainability indicators

Golf courses are supposed to produce remarkable negative effects on the environment, due to some techniques involved in their management. To provide data useful for the proper assessment of the agro-environmental sustainability of a golf course, the framework agro-environmental sustainability information system (AESIS) was used, utilizing a set of indicators suitable to evaluate different dimensions of sustainability (physical, ecological, productive and social). The management of areal golf course located in Tuscany (central Italy) was compared to an alternative land use of the same area represented by an ordinary farm based on a sunflower-wheat rotation. Assessment indicators were selected by applying a conceptual model based on ecology theory and were calculated considering site-specific production and pedo-climatic features of the area. Different weighting scenarios were hypothesized in order to have different management options assessed and to carry out a targeted sensitivity analysis. Main results confirmed the significant impact of golf management on some ecological characteristics but the holistic assessment of AESIS approach permitted an overall evaluation that comprised a wide range of different issues. AESIS demonstrated to be a practical and adaptive tool able to perform an efficient comparison of possible land destinations

How the optical timing system, the longitudinal diagnostics and the associated feedback systems provide femtosecond stable operation at the FERMI free electron laser

FERMI, the seeded free electron laser (FEL) in operation in Italy, is providing the User Community with unique fully coherent radiation, in the wavelength range 100–4 nm. FERMI is the first FEL fully synchronized by means of optical fibers. The optical timing system ensures an ultra-stable phase reference to its distributed clients. Several femtosecond longitudinal diagnostics verify the achieved performance; the bunch length monitor (BLM) and the bunch arrival monitor (BAM) will be presented in this paper. Feedback systems play a crucial role to guarantee the needed long-term electron beam stability. A real-time infrastructure allows shot-to-shot communication between front-end computers and the servers. Orbit feedbacks are useful in machine tuning, whereas longitudinal feedbacks control electron energy, compression and arrival time. A flexible software framework allows a rapid implementation of heterogeneous multi-input–multi-output (MIMO) longitudinal loops simply by selecting the appropriate sensors and actuators

Free-electron laser spectrum evaluation and automatic optimization

The radiation generated by a seeded free-electron laser (FEL) is characterized by a high temporal coherence, which is close to the Fourier limit in the ideal case. The setup and optimization of a FEL is a non-trivial and challenging operation. This is due to the plethora of highly sensitive machine parameters and to the complex correlations between them. The fine tuning of the FEL process is normally supervised by physicists and is carried out by scanning various parameters with the aim of optimizing the spectrum of the emitted pulses in terms of intensity and line-width. In this article we introduce a novel quantitative method for the evaluation of the FEL spectrum via a quality index. Moreover, we investigate the possibility of optimization of the FEL parameters using this index as the objective function of an automatic procedure. We also present the results of the preliminary tests performed in the FERMI FEL focused on the effectiveness and ability of the automatic procedure to assist in the task of machine tuning and optimization

AC/DC: The FERMI FEL Split and Delay Optical Device for Ultrafast X-ray Science

Free-electron lasers (FELs) are the most advanced class of light-sources, by virtue of their unique capability to lase high-brightness pulses characterized by wavelengths spanning the extreme-ultraviolet, the soft and hard X-ray spectral domains, as well as by temporal lengths lying in the femtosecond (fs) timescale. The next step to push the current standards in ultrafast X-ray science is strongly linked to the possibility of engineering and exploiting time-resolved experiments exclusively for FELs pulses, ideally having different colors tunable at specific electronic resonance of the chemical elements. At the seeded FERMI FEL (Trieste, Italy) this goal is committed to the optical device known as AC/DC, which stands for the auto correlator/delay creator. AC/DC is designed to double the incoming FEL pulse splitting the photon beam by inserting a grazing incidence flat mirror, thus preserving the spectral and temporal properties, and further delaying one of these two pulses in time. It can independently tune the FEL pulses fluence on the two optical paths by means of solid-state filters, too. Here, we present a detailed description about this optical device. Strong emphasis is dedicated to the AC/DC opto-mechanical design and to the laser-based feedback systems implemented to compensate for any mismatch affecting the FEL optical trajectory, ascribable to both mechanical imperfections and paraxial errors rising during a temporal delay scan

Two-bunch operation with ns temporal separation at the FERMI FEL facility

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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 $\omega$ and $2\omega$, from a Free-Electron Laser. Phase differences $\Delta \tilde \eta$ 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. $\Delta \tilde \eta$ 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

A detailed investigation of single-photon laser enabled Auger decay in neon

Single-photon laser enabled Auger decay (spLEAD) is an electronic de-excitation process which was recently predicted and observed in Ne. We have investigated it using bichromatic phase-locked free electron laser radiation and extensive angle-resolved photoelectron measurements, supported by a detailed theoretical model. We first used separately the fundamental wavelength resonant with the Ne+ 2s?2p transition, 46.17 nm, and its second harmonic, 23.08 nm, then their phase-locked bichromatic combination. In the latter case the phase difference between the two wavelengths was scanned, and interference effects were observed, confirming that the spLEAD process was occurring. The detailed theoretical model we developed qualitatively predicts all observations: branching ratios between the final Auger states, their amplitudes of oscillation as a function of phase, the phase lag between the oscillations of different final states, and partial cancellation of the oscillations under certain conditions