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The report presents, as the main result of the CompactLight project, the conceptual design of the CompactLight hard X-ray FEL. It is devided in the following chapters: 1. Executive Summary 2. Introduction 3. Science Goals and Photon Output Requirements 4. Systems Design and Performance 5. Accelerator 6. Light Production 7. Civil Engineering 8. Strategy and Implementation 9. Examples of CompactLight Facilities 10. Alternative Technology Solutions A. Appendices, On behalf of the CompactLight Partnership - see list of all authors in the document.

CompactLight Deliverable D2.1: Science Requirements and Performance Specification for the CompactLight X-Ray Free-Electron Laser, On behalf of the CompactLight Collaboration

The aim of WP7 is to promote the use of the CompactLight technologies through activities that address and inform potential users and by generating instruments and documents that support them in developing and implementing their projects for the construction or upgrading of CompactLight-based facilities. D7.1 is the first version of the corresponding documentation, containing the state of the work and the results achieved by the end of 2019. It presents in particular the insights obtained so far from the dialogue with the scientific user community, preliminary results for the landscape analysis, an explanation of the methodologies and strategies used for market, SWOT and risk analyses, a description of the Project Breakdown Structure and the methodology for the cost analyses, as well as user-relevant information on the project’s data management and ’Open Data’., On behalf of The CompactLight Collaboration.

This report describes the salient conceptual features of the CompactLight photon source, describing the machine layout and its modus operandi. The main parameters of the facility, grouped into facility sub-systems, are summarized in tables, which identify the baseline facility configuration, the proposed upgrade phases, and the technological recommendations provided by the individual work packages for its implementation. As a result, this document anticipates the CompactLight design study, and paves the way to the production of a more detailed conceptual design report., On behalf of the CompactLight Collaboration

European physical journal special topics 229(24), 3675 - 4284 (2020). doi:10.1140/epjst/e2020-000127-8, This report presents the conceptual design of a new European research infrastructure EuPRAXIA. The concept has been established over the last four years in a unique collaboration of 41 laboratories within a Horizon 2020 design study funded by the European Union. EuPRAXIA is the first European project that develops a dedicated particle accelerator research infrastructure based on novel plasma acceleration concepts and laser technology. It focuses on the development of electron accelerators and underlying technologies, their user communities, and the exploitation of existing accelerator infrastructures in Europe. EuPRAXIA has involved, amongst others, the international laser community and industry to build links and bridges with accelerator science — through realising synergies, identifying disruptive ideas, innovating, and fostering knowledge exchange. The Eu-PRAXIA project aims at the construction of an innovative electron accelerator using laser- and electron-beam-driven plasma wakefield acceleration that offers a significant reduction in size and possible savings in cost over current state-of-the-art radiofrequency-based accelerators. The foreseen electron energy range of one to five gigaelectronvolts (GeV) and its performance goals will enable versatile applications in various domains, e.g. as a compact free-electron laser (FEL), compact sources for medical imaging and positron generation, table-top test beams for particle detectors, as well as deeply penetrating X-ray and gamma-ray sources for material testing. EuPRAXIA is designed to be the required stepping stone to possible future plasma-based facilities, such as linear colliders at the high-energy physics (HEP) energy frontier. Consistent with a high-confidence approach, the project includes measures to retire risk by establishing scaled technology demonstrators. This report includes preliminary models for project implementation, cost and schedule that would allow operation of the full Eu-PRAXIA facility within 8—10 years., Published by Springer, Heidelberg

Plasma wakefield acceleration represents one of the most promising techniques able to overcome the limits of conventional rf technology and make possible the development of compact accelerators. With respect to laser-driven schemes, the particle beam-driven scenario is not limited by diffraction and dephasing issues; thus, it allows one to achieve larger acceleration lengths. Nevertheless, one of the most prominent drawbacks occurs at the end of the acceleration process and consists in the removal of the depleted high-charge driver while preserving the main features (emittance and peak current) of the accelerated witness bunch. Here we present a theoretical study demonstrating the possibility to reach these goals by using an innovative system consisting of an array of beam collimators and discharge capillaries operating as active-plasma lenses. Such a system allows one to extract and transport the accelerated and highly divergent witness bunch and, at the same time, provides for the removal of the driver. The study is completed with a set of numerical simulations conducted for different beam configurations. The physics of the interaction of particles with collimator is also investigated.

CompactLight (XLS) is an International Collaboration of 24 partners and 5 third parties, funded by the European Union through the Horizon 2020 Research and Innovation Programme. The main goal of the project, which started in January 2018 with a duration of 36 months, is the design of an hard X-ray FEL facility beyond today’s state of the art, using the latest concepts for bright electron photo-injectors, high-gradient accelerating structures, and innovative shortperiod undulators. The specifications of the facility and the parameters of the future FEL are driven by the demands of potential users and the associated science cases. In this paper we will give an overview on the ongoing activities and the major results achieved until now.

In this deliverable we report an overview of the available tools to perform start to end simulations for the CompacLight facility, covering the beam transport from the cathode to the undulator exit, including space charge effects, coherent synchrotron radiation in magnetic compressors, wakefield effects in the X-band linac and FEL performance. The main objective of WP6 is to provide the key parameters and performance estimates of a facility which meets the user requirements. We need to develop consistent tools for modelling the machine, as the basis for the final integrated performance studies. To this end the tasks of WP6 can be split into three simulation sections, in parallel to facility sections Low energy injector (including gun, prelinac and first bunch compressor) High energy linac (including high energy BCs for both soft and hard X-Ray layout) FEL production (both soft and hard X-Ray FELs) Different simulation tools have been used by the collaborating institutions suitable for the problems mentioned above. All programs used by the team will be utilized during the course of CompactLight design in order to benefit the experience of partners. However, to perform an integrated simulation one of the existing tool for each section is going to be used. Many of the those tools have been evaluated properly on specific problem for each tool and capabilities has been summarized in this report. In addition, the requirement for the translator tool between each code has been discussed., On behalf of the CompactLight Collaboration.

A central element in designing CompactLight is a global optimization that takes into account the performances and costs of the different parts of the facility; injector, linac and photon production. Each of these different areas is individually highly complex, and there are many interconnections. This deliverable report describes the array key computer-based tools which have been assembled and developed for use in the optimization of the CompactLight linac This report describes the array of key computer tools which have been put into place in order to carry out the design, simulation and optimization of the CompactLight linac as well as some preliminary results., On behalf of the CompactLight Collaboration

This document describes with analytical and numerical methods, i.e., approximated mathematical expressions and particle tracking runs, the process of bunch length compression of relativistic electron beams in linear accelerators. In particular, it reviews state-of-the-art compression options, based on magnetic insertions and radio-frequency (RF) accelerators, for the increase of peak current and preservation of the six-dimensional beam brightness as requested by x-ray freeelectron lasers (FELs). After a theoretical introduction to the topic, guidelines for the determination of the compression scheme for the CompactLight FEL are provided, by considering for example RF compression in combination with four dipoles chicanes. The study considers single particle dynamics, tolerance budget and collective effects involved in the compression process. On the basis of FEL specifications, the main parameters of the electron beam and of the compressors in the CompactLight accelerator are illustrated. Finally, a preliminary RF design of X-band and Ka-band accelerating cavities to support magnetic compression is presented. As a result, this review of most advanced electron beam compression schemes provides a solid basis for the definition of the beam manipulation aimed to meet the requirements of CompactLight FEL., On behalf of the CompactLight Collaboration.

News article in Accelerating News (Issue 29, CERN, Geneva, 12 July 2019) on the project's secondMidterm Review Meeting in Helsinki 2019.

The CompactLight project is currently developing the design of a next generation hard X-ray FEL facility, based on high-gradient X-band (12 GHz) structures, bright electron photo-injectors, and compact short period undulators. However, to improve the brightness limitations due to the non- linear energy spread of the electron bunches, a Kaband (36 GHz) linearizer is being considered to provide a harmonic compensation during the bunch compression. In this paper, we analyze the feasibility of such linearizer. &nbsp

The CompactLight project supported by European H₂020 is to design a hard X-ray FEL facility beyond today’s state of the art. The project integrates photo injector, X-band acceleration and innovative compact short-period undulators together to make the machine more compact. RF undulator has an extraordinary advantage of working at very short undulator period. A conceptual design for a RF undulator at 36 GHz using a corrugated cylindrical waveguide operating in the HE11 mode is presented in this paper. Based on beam dynamics simulation and photon beam radiation simulations, the possibility of RF undulator to be used in CompactLight project is evaluated., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The H2020 CompactLight Project aims at designing the next generation of compactX-rays Free-Electron Lasers, relying on very high gradient accelerating structures (X-band, 12 GHz), the most advanced concepts for high brightness electron photo injectors, and innovative compact short-period undulators. Compared to existing facilities, the proposed facility will benefit from a lower electron beam energy, due to the enhanced undulators performance, and will be significantly more compact, with a smaller footprint, as a consequence of the lower energy and the high-gradient X-band structures. In addition, the whole infrastructure will also have a lower electrical power demand as well as lower construction and running costs.

In this paper we report the start-to-end simulation results of one of the options under consideration for the Compact- Light Project (XLS). The XLS is a hard X-ray Free Electron Laser under design, using the latest concepts for bright electron photo injectors, very high-gradient X-band structures, and innovative short-period undulators. Presently there exist various tracking codes to conduct the design process. Therefore identifying the most convenient code is of notable importance. This paper compares the tracking codes, Placet and General Particle Tracer, using the XLS lattice based on a S and X-band Injector. The calculation results in terms of beam quality and tracking performance of a full 6-D simulation are presented.

The Compact Linear Collider (CLIC) is a TeV-scale high-luminosity linear e+e- collider under development by international collaborations hosted by CERN. This document provides an overview of the design, technology, and implementation aspects of the CLIC accelerator. For an optimal exploitation of its physics potential, CLIC is foreseen to be built and operated in stages, at centre-of-mass energies of 380 GeV, 1.5 TeV and 3 TeV, for a site length ranging between 11 km and 50 km. CLIC uses a Two-Beam acceleration scheme, in which normal-conducting high- gradient 12 GHz accelerating structures are powered via a high-current Drive Beam. For the first stage, an alternative with X-band klystron powering is also considered. CLIC accelerator optimisation, technical developments, and system tests have resulted in significant progress in recent years. Moreover, this has led to an increased energy efficiency and reduced power consumption of around 170 MW for the 380 GeV stage, together with a reduced cost estimate of approximately 6 billion CHF. The construction of the first CLIC energy stage could start as early as 2026 and first beams would be available by 2035, marking the beginning of a physics programme spanning 25–30 years and providing excellent sensitivity to Beyond Standard Model physics, through direct searches and via a broad set of precision measurements of Standard Model processes, particularly in the Higgs and top-quark sectors.

The development of compact accelerator facilities providing high-brightness beams is one of the most challenging tasks in the field of next-generation compact and cost affordable particle accelerators, to be used in many fields for industrial, medical, and research applications. The ability to shape the beam longitudinal phase space, in particular, plays a key role in achieving high-peak brightness. Here we present a new approach that allows us to tune the longitudinal phase space of a high-brightness beam by means of plasma wakefields. The electron beam passing through the plasma drives large wakefields that are used to manipulate the time-energy correlation of particles along the beam itself. We experimentally demonstrate that such a solution is highly tunable by simply adjusting the density of the plasma and can be used to imprint or remove any correlation onto the beam. This is a fundamental requirement when dealing with largely time-energy correlated beams coming from future plasma accelerators.

High gradient rf photo-injectors have been a key development to enable several applications of high quality electron beams. They allow the generation of beams with very high peak current and low transverse emittance, satisfying the tight demands for free-electron lasers, energy recovery linacs, Compton/Thomson sources and high-energy linear colliders. In the paper we present the design of a new full C-band RF photo-injector recently developed in the framework of the XLS-Compact Light design study and of the EuPRAXIA@SPARC_LAB proposal. It allows to reach extremely good beam performances in terms of beam emittance (at the level of few hundreds nm), energy spread and peak current. The photo-injector is based on a very high gradient (>200 MV/m) ultra-fast (RF pulses 200 ns) C-band RF gun, followed by two C band TW structures. Different types of couplers for the 1.6 cell RF gun have been considered and also a new compact low pulsed heating coupler working on the TM020 mode on the full cell has been proposed. In the paper we report the design criteria of the gun, the powering system, and the results of the beam dynamics simulations. We also discuss the case of 1 kHz repetition rate., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

Following the promising results obtained at the SPARC_LAB test-facility in Frascati (Italy), we have recently submitted a proposal to develop a new facility driven by a plasma accelerator module for extended and user-oriented applications. The new multi-disciplinary user-facility will be equipped with a soft X-ray Free Electron Laser (FEL) operating with energies larger than 1 GeV. This design study is performed to be fully compatible with the EuPRAXIA design study. Here, the latest layout and beam parameters are presented.

This report summarises progress and results of the CLIC studies at the time of submitting input to the update of the European Strategy for Particle Physics, in December 2018. The report describes recent achievements in accelerator design, technology development, system tests and beam tests.

Plasma-based acceleration experiments require capillaries with a radius of a few hundred microns to confine plasma up to a centimeter scale capillary length. A long and controlled plasma channel allows to sustain high fields which may be used for manipulation of the electron beams or to accelerate electrons. The production of these capillaries is relatively complicated and expensive since they are usually made with hard materials whose manufacturing requires highly specialized industries. Fine variations of the capillary shape may significantly increase the cost and time needed to produce them. In this article, we demonstrate the possibility of using 3D printed polymeric capillaries to drive a hydrogen-filled plasma discharge up to 1 Hz of repetition rate in an RF based electron linac. The plasma density distribution has been measured after several shot intervals, showing the effect of the surface ablation on the plasma density distribution. This effect is almost invisible in the earlier stages of the discharge. After more than 55000 shots (corresponding to more than 16 h of working time), the effects of the ablation on the plasma density distribution are not evident and the capillary can still be used. The use of these capillaries will significantly reduce the cost and time for prototyping, allowing us to easily manipulate their geometry, laying another building block for future cheap and compact particle accelerators.

Plasma-based technology promises a tremendous reduction in size of accelerators used for research, medical, and industrial applications, making it possible to develop tabletop machines accessible for a broader scientific community. By overcoming current limits of conventional accelerators and pushing particles to larger and larger energies, the availability of strong and tunable focusing optics is mandatory also because plasma-accelerated beams usually have large angular divergences. In this regard, active-plasma lenses represent a compact and affordable tool to generate radially symmetric magnetic fields several orders of magnitude larger than conventional quadrupoles and solenoids. However, it has been recently proved that the focusing can be highly nonlinear and induce a dramatic emittance growth. Here, we present experimental results showing how these nonlinearities can be minimized and lensing improved. These achievements represent a major breakthrough toward the miniaturization of next-generation focusing devices.

Presentation of the CompactLight project at the FLS2018 Conference, which took place on 05-09 March 2018 in Shanghai (China), held by Andrea Latina (CERN) on behalf of the CompactLight Collaboration.

Plasma confinement inside capillaries has been developed in the past years for plasma-based acceleration to ensure a stable and repeatable plasma density distribution during the interaction with either particles or laser beams. In particular, gas-filled capillaries allow a stable and almost predictable plasma distribution along the interaction with the particles. However, the plasma ejected through the ends of the capillary interacts with the beam before the inner plasma, affecting the quality of the beam. In this article we report the measurements on the evolution of the plasma flow at the two ends of a 1 cm long, 1 mm diameter capillary filled with hydrogen. In particular, we measured the longitudinal density distribution and the expansion velocity of the plasma outside the capillary. This study will allow a better understanding of the beam-plasma interaction for future plasma-based experiments., Comment: 5 pages, 6 figures, EAAC 2017

H2020 CompactLight Project aims at designing the next generation of compact hard X-Rays Free-Electron Lasers, relying on very high accelerating gradients and on novel undulator concepts. CompactLight intends to design a compact Hard X-ray FEL facility based on very high-gradient acceleration in the X band of frequencies, on a very bright photo injector, and on short-period/superconductive undulators to enable smaller electron beam energy. If compared to existing facilities, the proposed facility will benefit from a lower electron beam energy, due to the enhanced undulators performance, be significantly more compact, as a consequence both of the lower energy and of the high-gradient X-band structures, have lower electrical power demand and a smaller footprint. CompactLight is a consortium of 24 institutes (21 European + 3 extra Europeans), gathering the world-leading experts both in the domains of X-band acceleration and undulator design., Proceedings of the 60th ICFA Advanced Beam Dynamics Workshop on Future Light Sources, FLS2018, Shanghai, China

Physical review accelerators and beams 20(4), 042801(2017). doi:10.1103/PhysRevAccelBeams.20.042801, Generation of a well-aligned bunch train is of vital importance for preserving the beam quality in a Plasma Wake Field Accelerator (PWFA). The simultaneous measurements of the relative misalignments in both planes, of the individual femtosecond electron bunches with THz repetition rate in a train, are reported and analyzed with simulations. The new method proposed in this paper demonstrates that the measurements can be done quickly by applying a single quadrupole scan together with a radio-frequency deflector (RFD),while the RFD strength and the RFD phase for each bunch do not need to be known., Published by American Physical Society, College Park, MD

The Horizon 2020 Project EuPRAXIA ("European Plasma Research Accelerator with eXcellence In Applications") is preparing a conceptual design report of a highly compact and cost-effective European facility with multi-GeV electron beams using plasma as the acceleration medium. The accelerator facility will be based on a laser and/or a beam driven plasma acceleration approach and will be used for photon science, high-energy physics (HEP) detector tests, and other applications such as compact X-ray sources for medical imaging or material processing. EuPRAXIA started in November 2015 and will deliver the design report in October 2019. EuPRAXIA aims to be included on the ESFRI roadmap in 2020. © Published under licence by IOP Publishing Ltd.

In this deliverable we report an overview of the possible injector options suitable to match the CompactLight X-band high brightness linac able to drive short wavelength FELs user facilities. Different schemes have been investigated including RF gun injectors at different operating frequency (S, C and X band) and a DC gun based design. The electromagnetic and RF designs for all cases are reported and discussed, including a preliminary evaluation of the laser/cathode system requirements. Matchings with the downstream linac are also investigated with beam dynamics simulations. State of the art S-band injectors look appropriate to achieve the required parameters at low repetition rate ( 100 Hz). On the other end a compact C-band (or X-band) RF gun design is expected to have even better performances at low repetition rates and moreover, due to the lower thermal load, could allow higher repetition rates operation, up to 1 kHz, with acceptable performances degradation. DC guns are also very promising solutions for kHz range operation.

CompactLight is a consortium funded by the European Union through the Horizon 2020 Research and Innovation Programme under Grant Agreement No. 777431. The 24 partner institutes are working collaboratively towards the conceptual design of a next-generation x-ray free-electron laser (FEL). CompactLight intends to design an x-ray FEL facility beyond today’s state of the art, using the latest concepts for bright electron photo-injectors, high-gradient X-band structures at 12 GHz, and innovative short-period undulators. All of these enhancements will make our design more affordable to build and operate when compared against the existing facilities. The CompactLight prime objective is to generate a compact and affordable FEL facility design. The specifications of this future FEL are driven by the demands of potential users and the associated science case. This report summarizes the findings of our interactions with potential users since the start of the design study through a number of different avenues, culminating in a dedicated CompactLight User Meeting that was held from the 27th to the 28th of November 2018 at CERN., On behalf of the CompactLight Collaboration.

The Horizon 2020-funded project, CompactLight, will soon begin to design the first hard X-ray Free Electron Laser based on 12 GHz X-band technology. A consortium of 21 leading European institutions, including industries, together with the Shanghai Institute Of Applied Physics, the Australian Synchrotron, and the University of Melbourne, are partnering up to achieve this goal within the 36-month duration of the recently-awarded grant. The ambition of the CompactLight collaboration goes even beyond compact acceleration, as the consortium aims at simultaneously investigating and developing the next generation of undulators.

The Horizon 2020-funded project, CompactLight, will soon begin to design the first hard X-ray Free Electron Laser based on 12 GHz X-band technology. A consortium of 21 leading European institutions, including industries, together with the Shanghai Institute Of Applied Physics, the Australian Synchrotron, and the University of Melbourne, are partnering up to achieve this goal within the 36-month duration of the recently-awarded grant. The ambition of the CompactLight collaboration goes even beyond compact acceleration, as the consortium aims at simultaneously investigating and developing the next generation of undulators., On behalf of the CompactLight Collaboration

CompactLight is a consortium funded by the European Union through the Horizon 2020 Research and Innovation Programme under Grant Agreement No. 777431. The 24 partner institutes are working collaboratively towards the conceptual design of a next-generation x-ray free-electron laser (FEL). CompactLight intends to design an x-ray FEL facility beyond today’s state of the art, using the latest concepts for bright electron photo-injectors, high-gradient X-band structures at 12 GHz, and innovative short-period undulators.All of these enhancements will make our design more affordable to build and operate when compared against the existing facilities. The CompactLight prime objective is to generate a compact and affordable FEL facility design.The specifications of this future FEL are driven by the demands of potential users and the associated science case. This report summarizes the findings of our interactions with potential users since the start of the design study through a number of different avenues, culminating in a dedicated CompactLight User Meeting that was held from the 27th to the 28th of November 2018 at CERN.

In this deliverable we report an overview of the possible injector options suitable to match the CompactLight X-band high brightness linac able to drive short wavelength FELs user facilities. Different schemes have been investigated including RF gun injectors at different operating frequency (S, C and X band) and a DC gun based design. The electromagnetic and RF designs for all cases are reported and discussed, including a preliminary evaluation of the laser/cathode system requirements. Matchings with the downstream linac are also investigated with beam dynamics simulations. State of the art S-band injectors look appropriate to achieve the required parameters at low repetition rate ( 100 Hz). On the other end a compact C-band (or X-band) RF gun design is expected to have even better performances at low repetition rates and moreover, due to the lower thermal load, could allow higher repetition rates operation, up to 1 kHz, with acceptable performances degradation. DC guns are also very promising solutions for kHz range operation., On behalf of the CompactLight Collaboration

The light sources currently existing or under development in Europe address needs in the Central and Northwestern regions, whereas in the Southeastern European region there is no facility of this kind. The CompactLight collaboration, an H2020 funded project, is going to deliver a Conceptual Design Report (CDR) of a novel generation X-ray Free Electron Laser (XFEL) facility which is compact, innovative, relatively cheap and to be implemented for industrial and medical applications. The CDR will facilitate technological updates of the many European region institutions and enable them to construct a novel light source. Cost and risk analysis, as well as technology transfer and market survey of the project results are also discussed.