X-Ray Simulations Boosted by New Model for Light Beam Design and Control

Researchers have developed a new model to accurately simulate x-ray reflection from solid surfaces within the FLUKA Monte Carlo software package. Giuseppe Mazzola, Sunil Chitra, and Arnaud Devienne, from the European Organization for Nuclear Research, alongside Alessandro Frasca, María José García Fusté, and Dominique Heinis from ALBA Synchrotron et al., implemented a reflectivity model accounting for photon energy, incidence angle, polarisation, and surface roughness. This advancement significantly enhances FLUKA’s capabilities, transforming it into a comprehensive tool for simulating the entire synchrotron radiation process, from emission to interaction and now, reflection. The model’s validation against established optical device characterisation data, and its subsequent application to scenarios such as the ALBA synchrotron’s MINERVA beamline and the CERN Future Circular Collider, demonstrates its potential to streamline complex simulations and improve the design of future light sources.

This advancement addresses a long-standing need for streamlined simulations in fields like synchrotron radiation and high-energy physics. The model accurately predicts reflectivity variations based on photon energy, incidence angle, and polarisation, while also accounting for the effects of surface roughness.

Validated against established codes for optical device characterisation, FLUKA now provides consistent results for both homogeneous solids and multilayer mirrors. This new capability transforms FLUKA into a comprehensive tool for synchrotron radiation simulations. The research team demonstrated the model’s utility through two application scenarios. The model relies on atomic scattering factors from evaluated databases, constructing the refractive index of materials to determine x-ray behaviour.

By adopting an angle-independent atomic-scattering-factor approximation, valid for energies below absorption edges, the model efficiently calculates reflectivity across a broad energy range, from 100 eV to 10 MeV. The implementation leverages data from the Henke et al. database, ensuring consistency with established standards and providing a robust foundation for accurate simulations. This integrated approach promises to accelerate research and development in diverse areas reliant on precise modelling of x-ray interactions.

Implementation and validation of x-ray reflectivity modelling within the FLUKA simulation package

A new model for x-ray reflectivity on solids has been developed for FLUKA v4-6.0, relying on atomic scattering factors from evaluated databases. This model accurately simulates the variation of reflectivity as a function of photon energy, incidence angle, and linear polarisation, also incorporating the effects of surface roughness.

The implementation utilises data from sources such as the Evaluated Photon Data Library (EPDL97) and the Centre for X-Ray Optics to define atomic scattering factors, ensuring precision in the calculations. FLUKA reflectivities were validated against state-of-the-art characterisation data for both homogeneous solids and multilayer mirrors, demonstrating strong agreement with experimental results.

This capability significantly expands FLUKA’s functionality, enabling comprehensive synchrotron radiation simulations encompassing emission, transport, interaction, shower development, and now, x-ray reflection, all within a single software package. First, simulations accurately modelled the deflection of x-rays by a multilayer mirror at the MINERVA beamline of the ALBA synchrotron, directing radiation from an optical hutch to the experimental hall. These simulations demonstrate the model’s ability to predict radiation transport in complex experimental environments.

Validation of x-ray reflectivity modelling within FLUKA for synchrotron radiation simulations

Researchers have integrated a new x-ray reflectivity model into FLUKA v4-6.0, enabling comprehensive synchrotron radiation simulations within a single software package. This model accurately accounts for reflectivity variations based on photon energy, incidence angle, and linear polarisation, while also incorporating roughness effects.

Agreement between FLUKA-calculated reflectivities and those obtained from established characterisation tools, such as XOP, XOPPY, and IMD, has been demonstrated for both homogeneous solids and multilayer mirrors. The implementation of this model was showcased through two application scenarios. A simulation of the MINERVA beamline at the ALBA synchrotron, utilising a 3 GeV electron beam, demonstrated the model’s ability to accurately represent photon transport and reflection.

Specifically, a multilayer mirror consisting of 30 Si-W bilayers, each 4.1nm and 1.2nm thick respectively, at a 7-degree grazing angle, was modelled. Prior to the new model, simulations with FLUKA v4-5.1 showed absorption of photons impinging upon the mirror. Simulations of the final 720m of the electron beam line, including dipoles, quadrupoles, and a solenoid field, were performed using a 45.6 GeV electron beam. The logarithmic spectrum of produced synchrotron radiation photons revealed a dominant contribution from dipoles, exhibiting a critical energy of 19.47 keV, alongside a higher-energy contribution from the solenoid field. Scoring of photon fluence along the beamline, with and without activated x-ray reflection, will allow assessment of radiation background around the interaction point.

X-ray Reflectivity Modelling Extends FLUKA Capabilities for Synchrotron Radiation Simulation

Scientists have developed a new model within the FLUKA simulation package to accurately represent x-ray reflectivity from solid surfaces. This model accounts for variations in reflectivity based on photon energy, incidence angle, and polarisation, while also incorporating the effects of surface roughness.

The implementation utilises atomic scattering factors from established databases, enabling realistic simulation of x-ray behaviour at material interfaces. The model’s accuracy has been validated against data from state-of-the-art optical device characterisation, for both homogeneous solids and multilayer mirrors. They also note the importance of careful selection and consistent use of atomic scattering factor data from evaluated databases.

Future work may focus on extending the model to incorporate coherent effects like x-ray diffraction, currently disregarded due to the assumption of material homogeneity and isotropy within FLUKA. This new reflectivity model represents a substantial step towards streamlined and accurate modelling of x-ray interactions in complex experimental facilities.