The Athena X-ray Integral Field Unit: a consolidated design for the system requirement review of the preliminary definition phase

The Athena X-ray Integral Unit (X-IFU) is the high resolution X-ray spectrometer studied since 2015 for flying in the mid-30s on the Athena space X-ray Observatory. Athena is a versatile observatory designed to address the Hot and Energetic Universe science theme, as selected in November 2013 by the Survey Science Committee. Based on a large format array of Transition Edge Sensors (TES), X-IFU aims to provide spatially resolved X-ray spectroscopy, with a spectral resolution of 2.5 eV (up to 7 keV) over a hexagonal field of view of 5 arc minutes (equivalent diameter). The X-IFU entered its System Requirement Review (SRR) in June 2022, at about the same time when ESA called for an overall X-IFU redesign (including the X-IFU cryostat and the cooling chain), due to an unanticipated cost overrun of Athena. In this paper, after illustrating the breakthrough capabilities of the X-IFU, we describe the instrument as presented at its SRR (i.e. in the course of its preliminary definition phase, so-called B1), browsing through all the subsystems and associated requirements. We then show the instrument budgets, with a particular emphasis on the anticipated budgets of some of its key performance parameters, such as the instrument efficiency, spectral resolution, energy scale knowledge, count rate capability, non X-ray background and target of opportunity efficiency. Finally, we briefly discuss the ongoing key technology demonstration activities, the calibration and the activities foreseen in the X-IFU Instrument Science Center, touch on communication and outreach activities, the consortium organisation and the life cycle assessment of X-IFU aiming at minimising the environmental footprint, associated with the development of the instrument. Thanks to the studies conducted so far on X-IFU, it is expected that along the design-to-cost exercise requested by ESA, the X-IFU will maintain flagship capabilities in spatially resolved high resolution X-ray spectroscopy, enabling most of the original X-IFU related scientific objectives of the Athena mission to be retained. The X-IFU will be provided by an international consortium led by France, The Netherlands and Italy, with ESA member state contributions from Belgium, Czech Republic, Finland, Germany, Poland, Spain, Switzerland, with additional contributions from the United States and Japan.The French contribution to X-IFU is funded by CNES, CNRS and CEA. This work has been also supported by ASI (Italian Space Agency) through the Contract 2019-27-HH.0, and by the ESA (European Space Agency) Core Technology Program (CTP) Contract No. 4000114932/15/NL/BW and the AREMBES - ESA CTP No.4000116655/16/NL/BW. This publication is part of grant RTI2018-096686-B-C21 funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe”. This publication is part of grant RTI2018-096686-B-C21 and PID2020-115325GB-C31 funded by MCIN/AEI/10.13039/501100011033

The Athena X-ray Integral Field Unit: a consolidated design for the system requirement review of the preliminary definition phase

The Athena X-ray Integral Unit (X-IFU) is the high resolution X-ray spectrometer, studied since 2015 for flying in the mid-30s on the Athena space X-ray Observatory, a versatile observatory designed to address the Hot and Energetic Universe science theme, selected in November 2013 by the Survey Science Committee. Based on a large format array of Transition Edge Sensors (TES), it aims to provide spatially resolved X-ray spectroscopy, with a spectral resolution of 2.5 eV (up to 7 keV) over an hexagonal field of view of 5 arc minutes (equivalent diameter). The X-IFU entered its System Requirement Review (SRR) in June 2022, at about the same time when ESA called for an overall X-IFU redesign (including the X-IFU cryostat and the cooling chain), due to an unanticipated cost overrun of Athena. In this paper, after illustrating the breakthrough capabilities of the X-IFU, we describe the instrument as presented at its SRR, browsing through all the subsystems and associated requirements. We then show the instrument budgets, with a particular emphasis on the anticipated budgets of some of its key performance parameters. Finally we briefly discuss on the ongoing key technology demonstration activities, the calibration and the activities foreseen in the X-IFU Instrument Science Center, and touch on communication and outreach activities, the consortium organisation, and finally on the life cycle assessment of X-IFU aiming at minimising the environmental footprint, associated with the development of the instrument. Thanks to the studies conducted so far on X-IFU, it is expected that along the design-to-cost exercise requested by ESA, the X-IFU will maintain flagship capabilities in spatially resolved high resolution X-ray spectroscopy, enabling most of the original X-IFU related scientific objectives of the Athena mission to be retained. (abridged).Comment: 48 pages, 29 figures, Accepted for publication in Experimental Astronomy with minor editin

Numerical modeling of impulsive loads using the Smoothed Particle Hydrodynamics method

The present thesis aims to enhance the applicability of Smoothed Particle Hydrodynamics (SPH) method to simulate impulsive loads. This type of pressure load appears in problems related to wave impacts, which are relevant to the offshore industry and, particularly, in the context of floating platforms for wind energy generation. To that aim, special emphasis is set on deepening into the mathematical grounds of the method. This research conducted during the completion of this thesis has been structured around three blocks: a theoretical study of the convergence of the SPH method; an experimental campaign involving a case where impulsive loads play a relevant role, i.e the dam break experiment; validation of the computation of impulsive loads with SPH by comparing the simulations with the experimental results. The convergence of the SPH method is still an open problem. While some interesting research has been carried out, the results are still partial and a global understanding of conditions required for convergence in the general case is still an open issue. Herein, the convergence of the SPH hydrostatic problem in 1D, considering a free surface, is studied at both the integral and discrete levels of approximation. The consistency of this problem is also addressed. Moreover, the convergence of the integral SPH solution to diffusion problems, including the heat and the advection-diffusion equations, is established using Fourier analysis. The convergence of their discrete versions is also studied numerically. Boundary conditions and their influence on both consistency and convergence are also open problems within SPH. Several aspects regarding the treatment of boundary conditions are considered herein. In particular, the treatment of the free surfaces is studied in the case of the hydrostatic problem. The semi-analytical formulation of the Boundary integrals methodology is revisited and applied to the computational experiments. The role of the time integration scheme in energy conservation and the numerical stability of the method is addressed. To that aim, the error produced at the discrete level due to the time integration scheme is studied. An explicit formula to compute that error is provided. Numerically, several algorithms are compared. A stable simulation is presented using an implicit time integration scheme. This allows for avoidance of the use of artificial viscous terms, so common in the context of SPH to ensure stability. An experimental campaign using the dam break problem with an obstacle has been carried out. The presence of an obstacle induces three-dimensional effects in the flow. The results have been statistically characterized by performing enough repetitions of each case until the statistical parameters (mean and standard deviation) converged. Regarding validation, the dam break problem has been numerically simulated using SPH. More precisely, the open-source code AQUAgpusph has been used. This allowed us to validate the computation of impulsive loads in the context of three-dimensional flows. The numerical simulations show, in general, good agreement with the experimental results. The role of the approximation parameters and the influence of the choice of the kernel have been addressed. RESUMEN Esta tesis tiene como objetivo mejorar la aplicabilidad del método “Smoothed Particle Hydrodynamics” (SPH) a la simulación de cargas impulsivas. Este tipo de cargas de presión aparece en problemas relacionados con impactos de olas, que son relevantes para la industria offshore y, en particular, en el contexto de las plataformas flotantes para la generación de energía eólica marina. Para ello, se pone el acento en profundizar en los fundamentos matemáticos del método. La investigación desarrollada durante la realización de esta tesis se ha estructurado en torno a tres bloques: un estudio teórico de la convergencia del método SPH; una campaña experimental que involucra un caso en el que las cargas impulsivas juegan un papel fundamental (el experimento llamado “dam break”); validación del cálculo de cargas impulsivas con SPH comparando las simulaciones con los resultados experimentales. La convergencia del método SPH sigue siendo un problema abierto. Si bien se han publicado trabajos interesantes al respecto, los resultados son aún parciales y deben darse pasos para esclarecer las condiciones necesarial para la convergencia en el caso general. En esta tesis, se estudia la convergencia del problema hidrostático SPH en 1D, considerando la superficie libre, tanto a nivel de la aproximación integrtal como discreta. La consistencia de este problema se aborda también. Además, la convergencia de la solución integral SPH en problemas de difusión, incluidas las ecuaciones de calor y convección-difusión, se demuestra usando análisis de Fourier. También se estudia numéricamente la convergencia de sus versiones discretas. Las condiciones de contorno y su influencia tanto en la consistencia como en la convergencia también son problemas abiertos en el contexto de SPH. En esta tesis se consideran varios aspectos relacionados con el tratamiento de las condiciones de contorno. En particular, se estudia el tratamiento de las superficies libres en el caso del problema hidrostático. Además, se revisa la formulación semianalítica en el contexto de la metodología “boundary integrals” y se aplican los resultados en los casos computacionales. Se considera también el papel del esquema de integración temporal en la conservación de la energía y la estabilidad numérica del método. Para ello, se estudia el error causado por el esquema de integración temporal a nivel de la aproximación discreta, obteniendo una fórmula explícita para calcular ese error. Se comparan varios algoritmos realizando simulaciones numéricas. Se presenta además una simulación estable utilizando un esquema de integración de tiempo implícito, en la que no es necesario el uso de términos viscosos artificiales, tan comunes en el contexto de SPH para garantizar la estabilidad. Se ha realizado una campaña experimental centrada en el problema de la rotura de presa (“dam break”, en inglés) con un obstáculo. La presencia de un obstáculo induce efectos tridimensionales en el flujo. Los resultados se han caracterizado estadísticamente realizando suficientes repeticiones de cada caso hasta que los parámetros estadísticos (media y desviación estándar) convergieran. En cuanto a la validación, el problema de la rotura de presa se ha simulado numéricamente utilizando SPH. En concreto, se ha empleado el código AQUAgpusph. Esto ha permitido validar el cálculo de cargas impulsivas en el contexto de flujos tridimensionales. Los resultados numéricos, en general, reproducen adecuadamente los resultados experimentales. Se ha estudiado el papel de los parámetros de aproximación y la influencia de la elección del kernel en los resultados

The Athena X-ray Integral Field Unit: a consolidated design for the system requirement review of the preliminary definition phase

48 pages, 29 figures, submitted for publication in Experimental AstronomyThe Athena X-ray Integral Unit (X-IFU) is the high resolution X-ray spectrometer, studied since 2015 for flying in the mid-30s on the Athena space X-ray Observatory, a versatile observatory designed to address the Hot and Energetic Universe science theme, selected in November 2013 by the Survey Science Committee. Based on a large format array of Transition Edge Sensors (TES), it aims to provide spatially resolved X-ray spectroscopy, with a spectral resolution of 2.5 eV (up to 7 keV) over an hexagonal field of view of 5 arc minutes (equivalent diameter). The X-IFU entered its System Requirement Review (SRR) in June 2022, at about the same time when ESA called for an overall X-IFU redesign (including the X-IFU cryostat and the cooling chain), due to an unanticipated cost overrun of Athena. In this paper, after illustrating the breakthrough capabilities of the X-IFU, we describe the instrument as presented at its SRR, browsing through all the subsystems and associated requirements. We then show the instrument budgets, with a particular emphasis on the anticipated budgets of some of its key performance parameters. Finally we briefly discuss on the ongoing key technology demonstration activities, the calibration and the activities foreseen in the X-IFU Instrument Science Center, and touch on communication and outreach activities, the consortium organisation, and finally on the life cycle assessment of X-IFU aiming at minimising the environmental footprint, associated with the development of the instrument. It is expected that thanks to the studies conducted so far on X-IFU, along the design-to-cost exercise requested by ESA, the X-IFU will maintain flagship capabilities in spatially resolved high resolution X-ray spectroscopy, enabling most of the original X-IFU related scientific objectives of the Athena mission to be retained (abridged)

The Athena X-ray Integral Field Unit: a consolidated design for the system requirement review of the preliminary definition phase

48 pages, 29 figures, submitted for publication in Experimental AstronomyThe Athena X-ray Integral Unit (X-IFU) is the high resolution X-ray spectrometer, studied since 2015 for flying in the mid-30s on the Athena space X-ray Observatory, a versatile observatory designed to address the Hot and Energetic Universe science theme, selected in November 2013 by the Survey Science Committee. Based on a large format array of Transition Edge Sensors (TES), it aims to provide spatially resolved X-ray spectroscopy, with a spectral resolution of 2.5 eV (up to 7 keV) over an hexagonal field of view of 5 arc minutes (equivalent diameter). The X-IFU entered its System Requirement Review (SRR) in June 2022, at about the same time when ESA called for an overall X-IFU redesign (including the X-IFU cryostat and the cooling chain), due to an unanticipated cost overrun of Athena. In this paper, after illustrating the breakthrough capabilities of the X-IFU, we describe the instrument as presented at its SRR, browsing through all the subsystems and associated requirements. We then show the instrument budgets, with a particular emphasis on the anticipated budgets of some of its key performance parameters. Finally we briefly discuss on the ongoing key technology demonstration activities, the calibration and the activities foreseen in the X-IFU Instrument Science Center, and touch on communication and outreach activities, the consortium organisation, and finally on the life cycle assessment of X-IFU aiming at minimising the environmental footprint, associated with the development of the instrument. It is expected that thanks to the studies conducted so far on X-IFU, along the design-to-cost exercise requested by ESA, the X-IFU will maintain flagship capabilities in spatially resolved high resolution X-ray spectroscopy, enabling most of the original X-IFU related scientific objectives of the Athena mission to be retained (abridged)