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In early 2019, the UK initiated a project to develop the science case for a UK XFEL, featuring a diverse team of UK scientists and international advisors. Accelerator scientists were engaged to highlight potential future accelerator developments and to develop concept outlines for a facility design meeting the requirements for world-leading capabilities. The UK XFEL Science Case, featuring the concept outlines, was published in late 2020. Subsequent exercises further demonstrated the support of the UK community and the project is anticipated to enter a more detailed design phase. The concept outlines are reviewed and potential next steps are outlined.

CLARA is an electron beam test facility being developed in phases at STFC Daresbury Laboratory. The first phase, with up to 35 MeV electron beam energy, has been operated since 2018 for a wide range of accelerator applications. The second phase, presently being installed, will expand the range of applications by taking the beam to 250 MeV energy and via a dog-leg to an experimental station that will feature a new high-power laser. A third phase utilising the 250 MeV beam in the straight-ahead line is also envisaged. Machine learning will play an important role in the future development of the facility, with aims to rapidly deliver bespoke beam properties, to detect and diagnose anomalies, and to provide virtual diagnostics. This paper summarises machine learning developments to date, in the areas of RF breakdown detection, photo-injector laser pulse shaping, and longitudinal phase space shaping. Studies to date have largely been offline or using simulated data but steps towards deployment are also reported.

The CompactLight collaboration designed a compact and cost-effective hard X-ray FEL facility, complemented by a soft X-ray option, based on X-band acceleration, capable of operating at 1 kHz pulse repetition rate. In this paper, we present a new simple start-to-end optimisation strategy that is developed for the CompactLight accelerator beamline, focusing on the hard X-ray mode. The optimisation is divided into two steps. The first step improves the electron beam quality that finally leads to a better FEL performance by optimising the major parameters of the beamline. The second step provides matched twiss parameters for the FEL undulator by tuning the matching quadrupoles at the end of the accelerator beamline. A single objective optimisation method, with different objective functions, is used to optimise the performance. The sensitivity of the results to jitters is also minimised by including their effects in the final objective function., Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK

CLARA (Compact Linear Accelerator for Research and Applications) is a test facility for Free Electron Laser (FEL) research and other applications at STFC’s Daresbury Laboratory. The Front End of CLARA has been used for user exploitation programme from 2018. The second exploitation period in 2021-22 provided a range of beam parameters to 8 user experiments. We report on the status, further machine development, and future plans for CLARA including Full Energy Beam Exploitation (FEBE) beamline which will provide 250 MeV/c high brightness beam for novel experiments., Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK

Maximising the accelerating gradient of RF structures is fundamental to improving accelerator facility performance and cost-effectiveness. Structures must be subjected to a conditioning process before operational use, in which the gradient is gradually increased up to the operating value. A limiting effect during this process is breakdown or vacuum arcing, which can cause damage that limits the ultimate operating gradient. Techniques to efficiently condition the cavities while minimising the number of breakdowns are therefore important. In this paper, machine learning techniques are applied to detect breakdown events in RF pulse traces by approaching the problem as anomaly detection, using a variational autoencoder. This process detects deviations from normal operation and classifies them with near perfect accuracy. Offline data from various sources has been used to develop the techniques, which we aim to test at the CLARA facility at Daresbury Laboratory. Deployment of the machine learning system on the high repetition rate gun upgrade at CLARA has begun., Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK

Accurate prediction of longitudinal phase space and other properties of the electron beam are computationally expensive. In addition, some diagnostics are destructive in nature and/or cannot be readily accessed. Machine learning based virtual diagnostics can allow for the real-time generation of longitudinal phase space and other graphs, allowing for rapid parameter searches, and enabling operators to predict otherwise unavailable beam properties. We present a machine learning model for predicting a range of diagnostic screens along the accelerator beamline of a free-electron laser facility, conditional on linac and other parameters. Our model is a combination of a conditional variational autoencoder and a generative adversarial network, which generates high fidelity images that accurately match simulation data. Work to date is based on start-to-end simulation data, as a prototype for experimental applications., Proceedings of the 18th International Conference on Accelerator and Large Experimental Physics Control Systems, ICALEPCS2021, Shanghai, China

The temporal profile of the electron bunch is of critical importance in accelerator areas such as free-electron lasers and novel acceleration. In FELs, it strongly influences factors including efficiency and the profile of the photon pulse generated for user experiments, while in novel acceleration techniques it contributes to enhanced interaction of the witness beam with the driving electric field. Work is in progress at the CLARA facility at Daresbury Laboratory on temporal shaping of the ultraviolet photoinjector laser, using a fused-silica acousto-optic modulator. Generating a user-defined (programmable) time-domain target profile requires finding the corresponding spectral phase configuration of the shaper; this is a non-trivial problem for complex pulse shapes. Physically informed machine learning models have shown great promise in learning complex relationships in physical systems, and so we apply machine learning techniques here to learn the relationships between the spectral phase and the target temporal intensity profiles. Our machine learning model extends the range of available photoinjector laser pulse shapes by allowing users to achieve physically realisable configurations for arbitrary temporal pulse shapes., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

Successful user experiments at particle beam facilities are dependent upon the awareness of beam characteristics at the interaction point. Often, properties are measured beforehand for fixed operation modes; users then rely on the long-term stability of the beam. Otherwise, diagnostics must be integrated into a user experiment, costing resources and limiting space in the user area. This contribution proposes the application of machine learning to develop a suite of virtual diagnostic systems. Virtual diagnostics take data at easy to access locations, and infer beam properties at locations where a measurement has not been taken, and often cannot be taken. Here the focus is the user area at the planned Full Energy Beam Exploitation (FEBE) upgrade to the CLARA facility (UK). Presented is a simulation-based proof-of-concept for a variety of virtual diagnostics. Transverse and longitudinal properties are measured upstream of the user area, coupled with the beam optics parameters leading to the user area, and input into a neural network, to predict the same parameters within the user area. Potential instrumentation for FEBE CLARA virtual diagnostics will also be discussed., Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK

Machine learning algorithms were used for image and parameter recognition and generation with the aim to optimise the CLARA facility at Daresbury, using start-to-end simulation data. Convolutional and fully connected neural networks were trained using TensorFlow-Keras for different instances, with examples including predicting Longitudinal Phase Space (LPS) images with machine parameters as input and FEL parameter prediction (e.g. pulse energy) from LPS images. The K-means clustering algorithm was used to cluster the LPS images to highlight patterns within the data. Machine learning techniques can enhance the way large amounts of data are processed and analysed and so have great potential for application in accelerator science R, Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

The H₂020 CompactLight Project aims for the design of innovative, cost-effective, compact FEL facilities to generate higher peak brilliance radiation in the soft and hard X-ray. In this paper we assess via simulation studies the performance of a variably polarising APPLE-X afterburner positioned downstream of a helical Super Conducting Undulator (SCU). We discuss the optimum balance between the active SCU length and the afterburner length, considering the peak brilliance and pulse energy of the output. Our studies are complemented with analysis of the optical beam quality of the afterburner output to determine the design constraints of the photon beamline that delivers the FEL output to the experimental areas., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

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 short-period 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., Proceedings of the 39th Free Electron Laser Conference, FEL2019, Hamburg, Germany

STFC Daresbury Laboratory are developing a compact electron beam energy dechirper system, based on dielectric wakefield structure, for the on-site electron accelerator CLARA (Compact Linear Accelerator for Research and Applications). CLARA will be an experimental free electron laser (FEL) facility operating at 250MeV and will be a test bed for a variety of novel FEL schemes. The dechirper dielectric quartz plates will induce wakefields within the structure which can remove the beam chirp that is initially introduced to compress the electron bunch longitudinally. Removing or adjusting the amount of chirp enables researchers to reduce or adjust the bunch energy/momentum spread, expanding the FEL capabilities. The attachment and alignment of the quartz plates present numerous mechanical design challenges that require high precision manufacturing and quartz plate positioning via fiducialisation. This paper will review the dechirper specifications, the chosen design solutions, measured mechanical performance, and the expected effect of the dechirper on CLARA FEL operation., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

XARA (X-band Accelerator for Research and Applications) is a proposal for a compact ~1 GeV/c accelerator to produce attosecond light pulses in the EUV to soft X-ray region. It is under consideration as a potential future upgrade to the CLARA facility at Daresbury Laboratory, utilising high-performance X-band RF technology to increase the electron beam momentum from 250 MeV/c. Emerging techniques for generating single-cycle undulator light [1] would give access to attosecond timescales, enabling studies of ultra-fast dynamics, while also being very compact. XARA would also enhance the existing capabilities for accelerator science R by incorporating X-band development and increasing the electron beam momentum for novel acceleration studies., Proceedings of the 39th Free Electron Laser Conference, FEL2019, Hamburg, Germany

The H₂020 CompactLight Project (www. CompactLight.eu) aims at designing the next generation of compact X-rays Free-Electron Lasers, relying on very high gradient accelerating structures (X-band, 12 GHz), the most advanced concepts for bright 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.

CLARA (Compact Linear Accelerator for Research and Applications) is a test facility for Free Electron Laser (FEL) research and other applications at STFC’s Daresbury Laboratory. The first exploitation period using CLARA Front End (FE) provided a range of beam parameters to 12 user experiments. Beam line to Beam Area 1 (BA1) was commissioned and optimised for these experiments, some involving TW laser integration. In addition to the user exploitation programme, significant advances were made to progress on machine development. This paper summarises these developments and presents the near future plan for CLARA., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

We studied the degree of polarisation of the FEL radiation from the diverted-beam scheme [1,2] using the layout of the CompactLight facility, which is in the process of being designed. To satisfy the polarisation requirements defined by the users [3] without compromising the aim of the facility to be compact, we studied a configuration comprising a helical Super Conductive Undulator (SCU) followed by a Delta afterburner (configured to generate linearly polarised light). The trade-offs between the SCU length, afterburner length, degree of polarisation and output power are presented and discussed.

Simulation studies were carried out to optimise the performance of various FEL designs, with examples including longitudinal current profile shaping for a seeded FEL, and selection of the chicane delays for the High-Brightness SASE technique. In these examples multi-objective genetic algorithms were applied to a single section of the overall facility simulation, i.e. the undulator, as is the common approach. Further studies are also reported in which a full start-to-end simulation chain was optimised, with the aim of delivering a more holistic facility design optimisation., Proceedings of the 39th Free Electron Laser Conference, FEL2019, Hamburg, Germany

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 short-period 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.

CLARA is a new FEL test facility being developed at STFC Daresbury Laboratory in the UK, aiming to deliver advanced FEL capabilities including few-cycle pulse generation and Fourier transform limited output. Commissioning is underway on the front-end (photo-injector and first linac) while the later stages are being procured and assembled. Start-to-end (S2E) simulations of the full facility are presented, including optimisation of the accelerator setup to deliver the required properties of one of the electron beam modes specified for FEL operation. FEL simulations are performed using the Genesis 1.3 and Puffin codes and the results are compared., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

CLARA (Compact Linear Accelerator for Research and Applications) is a Free Electron Laser (FEL) test facility being developed at STFC Daresbury Laboratory. The principal aim of CLARA is to test advanced FEL schemes which can later be implemented on existing and future short wavelength FELs. The installation of the Front End (FE) section of CLARA, a S-bend merging with existing VELA (Versatile Electron Linear Accelerator) beam line and installation of a high repetition rate RF gun on VELA was completed in 2017. First beam commissioning results and high level software developments are presented in this paper., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

CLARA is a new FEL test facility being developed at STFC Daresbury Laboratory in the UK. Commissioning has started on the front-end (photo-injector and linac) while the design of the later stages is still being finalised. We present the latest design work, focusing on the layout and specification of components in and around the undulator sections. We give an overview of the design and modelling of the FEL schemes planned to be tested., Proceedings of the 38th Int. Free Electron Laser Conf., FEL2017, Santa Fe, NM, USA

A Virtual Accelerator (VA) has been developed to mimic the accelerators Versatile Electron Linear Accelerator (VELA) and Compact Linear Accelerator for Research and Applications (CLARA). Its purpose is to test control room applications, run start-to-end simulations with multiple simulation codes, accurately reproduce measured beam properties, conduct 'virtual experiments'and gain insight into ‘hidden beam parameters'. This paper gives an overview into the current progress in constructing this VA, detailing the areas of: developing a 'Virtual EPICS' control system, using multiple simulation codes (both particle tracking and analytic), the development of a ‘Master Lattice' and the construction of a Python interface in which to run the VA., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

CLARA (Compact Linear Accelerator for Research and Applications) is a Free Electron Laser (FEL) test facility under development at Daresbury Laboratory. The principal aim of CLARA is to test advanced FEL schemes which can later be implemented on existing and future short wavelength FELs. We report on the commissioning of the CLARA front end, consisting of a photoinjector and the first linac section, and merger into the existing VELA (Versatile Electron Linear Accelerator) beamline., Proceedings of the 29\textsuperscript{th} Linear Accelerator Conf., LINAC2018, Beijing, China

Methods to generate ultra-short radiation pulses from X-ray FELs commonly slice a relatively long electron bunch to feature one (or more) short regions of higher beam quality which then lase preferentially. The slotted foil approach spoils the emittance of all but a short region, while laser-based alternatives modulate the electron beam energy, improving potential synchronisation to external sources. The CLARA FEL test facility under development in the UK will operate at 100-400 nm, aiming to demonstrate FEL schemes applicable at X-ray wavelengths. We present new laser-based slicing schemes which may better suit the wavelength range of CLARA and provide options for X-ray facilities., Proceedings of the 38th Int. Free Electron Laser Conf., FEL2017, Santa Fe, NM, USA

X-ray free-electron lasers are promising candidates to deliver high-brightness radiation pulses with duration significantly shorter than the present leading technique, high harmonic generation (HHG). This would extend attosecond science to probe ultrafast dynamics with even finer resolution. To do so requires breaking below a characteristic FEL timescale of typically a few hundred optical cycles, dictated by the relative slippage of the radiation and electrons during amplification. The concept of mode-locking enables this, with the mode-locked afterburner configuration predicted to deliver few-cycle pulses (~ 1 attosecond at hard X-ray). However such techniques would produce a train of closely separated pulses, while an isolated pulse would be preferable for some types of experiment. Building on previous techniques, a new concept has been developed for isolated few-cycle pulse generation and it is presented alongside simulation studies., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

We studied and characterised the FEL optical radiation in simulations of the CLARA FEL test facility under development at Daresbury Laboratory in the UK. In particular, we determined the optical beam quality coefficient, waist position and other source properties corresponding to different potential FEL operating modes via wavefront propagation in free space using OPC (Optical Propagation Code) and Second Moment Analysis. We were able to find the operation mode and undulator design for which the optical beam has the optimum quality at highest brightness. Furthermore, we studied the way that different properties of the electron bunches (emittance, peak current, bunch length) affect the optical beam. We are now able to understand how the optical beam will propagate from the end of the undulator and through the photon transport system to the experimental stations. This knowledge is necessary for the correct design of the photon transport and diagnostic systems., Proceedings of the 38th Int. Free Electron Laser Conf., FEL2017, Santa Fe, NM, USA

Dielectric lined waveguides have drawn interest due to their application as high gradient accelerating structures, in both externally driven and wakefield schemes. We present simulation studies of sub-picosecond electron bunches interacting with dielectric structures in the self-wake regime. The parameter space for a tunable, sub-millimeter aperture, terahertz frequency structure is investigated. The potential application as a longitudinal phase space dechirper is demonstrated, with specific application to CLARA at Daresbury Laboratory. The impact of transverse effects is considered and minimised. The resulting FEL output is simulated., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

We present recent developments in the accelerator design of CLARA (Compact Linear Accelerator for Research and Applications), the proposed UK FEL test facility at Daresbury Laboratory. The requirement to co-propagate the beam with laser seeds of very different wavelengths has led to a redesign of the section preceding the undulators, with a dogleg being replaced by a chicane. Additional refinements of the facility design include the inter-undulator sections. With this finalised design we show start to FEL simulations for all beam modes envisaged., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

Ultrashort pulse operation in FELs is a highly desirable capability for imaging matter on ultrafast timescales. This paper presents a design study for a proof-­of-­principle demonstration of the mode-locked afterburner (ML-AB) scheme on the FEL test facility CLARA. A start-to-end simulation has been constructed using the time-­dependent three-­dimensional FEL code GENESIS 1.3 to evaluate the performance of the scheme. The ability to produce pulses of several femtoseconds in duration with peak powers of the order of 100 MW at 100 nm wavelength is predicted.­ Such pulses have duration of 2 fs (6 optical cycles), a factor of ~5 shorter than the FEL cooperation length. Potential routes for further optimisation and alternative operating modes are explored., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

Free electron lasers (FELs) are currently enabling cutting edge research in chemistry, biology and physics. We use simulations to assess a new FEL capability that would add to the impressive repertoire of experiments made possible by the technology: a two-colour independent polarization mode, which allows for light pulses with variable temporal separation, individually tuneable polarisation, and widely separated wavelength. Simulations are carried out using the broad bandwidth FEL code Puffin, the results of which are used to discuss the radiation properties of the output. This scheme is applicable to existing and proposed facilities which feature undulators with variable ellipticity and gap., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

A new HPC simulation suite, intended to aid in both the investigation of novel FEL physics and the design of new FEL facilities, is described. The integrated start-to-end suite, currently under development, incorporates both plasma (VSim) and linac (ELEGANT, ASTRA) accelerator codes, and will include the 3D unaveraged FEL code Puffin to probe novel FEL effects., Proceedings of the 37th International Free Electron Laser Conference, FEL2015, Daejeon, Republic of Korea

Undulator tapering is a well-known method for enhancing the performance of free-electron lasers [1]. It works by keeping the resonant wavelength constant, despite variation in the electron beam energy. Both the energy-extraction efficiency and the spectral brightness of the FEL can be improved using this technique. In this paper we present recent studies of undulator tapering for the CLARA FEL in both SASE and seeded modes. The methods used to optimise the taper profile are described, and the properties of the final FEL pulses are compared., Proceedings of the 37th International Free Electron Laser Conference, FEL2015, Daejeon, Republic of Korea

The ALICE (Accelerators and Lasers In Combined Experiments) accelerator at STFC Daresbury Laboratory in the UK was conceived in 2003 and constructed as a short-term Energy Recovery Linac demonstrator to develop the underpinning technology and expertise required for a proposed 600MeV ERL-based FEL facility. In this paper we present an update on the performance and status of ALICE which now operates as a funded IR-FEL user facility. We discuss the challenges of evolving a short-term demonstrator into a stable, reliable user facility and present a summary of the current scientific programme., Proceedings of the 37th International Free Electron Laser Conference, FEL2015, Daejeon, Republic of Korea

CLARA is a new FEL test facility being developed at STFC Daresbury Laboratory in the UK. The main motivation for CLARA is to test new FEL schemes that can later be implemented on existing and future short wavelength FELs. Particular focus will be on ultra-short pulse generation, pulse stability, and synchronisation with external sources. The project is now underway and the Front End section (photoinjector and first linac) installation will begin later this year. This paper will discuss the progress with the Front End assembly and also highlighting other topics which are currently receiving significant attention., Proceedings of the 37th International Free Electron Laser Conference, FEL2015, Daejeon, Republic of Korea

We present progress in the design of the recirculating linac option for the UK New Light Source. Improvements in all accelerator sections have been made such that the output meets the required specifications to drive the seeded NLS FELs. Full start-to-end simulations and tolerance studies are presented together with a comparison to the baseline, single pass linac design., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

The crossed-planar undulator is a promising scheme for full polarization control in an x-ray FEL*. For SASE FELs, it has been shown a maximum degree of circular polarization of about 80% is achievable**. In this paper, we study the effectiveness of a cross undulator for a seeded x-ray FEL. The degree of circular polarization for both the fundamental and the harmonic radiation are considered., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

We present the progress with the design of the 2.25 GeV superconducting linac for the NLS project. We discuss the performance achieved, the optimisation strategies, the relevance of microbunching instability and the analysis of the effect of various jitter sources, Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

A scheme for the generation of attosecond pulse trains in FEL amplifiers was recently proposed*. The method uses repeated equal temporal delays between the electron bunch and co-propagating radiation to generate a modal structure in the radiation field. The modes may be phase-locked via an energy modulation in the electron beam. As a consequence of the radiation /electron delays, the relative radiation /electron slippage during the interaction is increased and leads to a longer cooperation length with the effect of improving the temporal coherence. In this paper we present simulations demonstrating this effect. In particular, we show that the average spacing between the temporal spikes in a SASE FEL is increased in proportion to the increase in the cooperation length. It may therefore be possible to operate a SASE FEL in single-spike mode with longer, higher charge, electron bunches than previously thought possible., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

The New Light Source project aims to construct a suite of seeded free-electron lasers driven by a 2.25GeV cw super conducting linac. As part of the upgrade path, a number of options are being considered for generating ultra short (1fs) soft x-ray pulses, with low-charge ’single-spike’ operation and bunch slicing like approaches of particular interest, including as a possible extension to echo-enhanced harmonic generation. In this paper we present the status of this work, including recent results from fully start to end simulations., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

Optimisation studies of an HHG-seeded harmonic cascade FEL design for the UK¿s proposed New Light Source (NLS) facility are presented. Three separate FELs are planned to meet the requirements for continuous coverage of the photon energy range 50-1000 eV with variable polarisation, 20 fs pulse widths and good temporal coherence. The design uses an HHG seed source tuneable from 50-100 eV to provide direct FEL seeding in this range, and one or two stage harmonic cascades to reach the higher photon energies. Studies have been carried out to optimise a harmonic cascade FEL operating at 1 keV; topics investigated include modulator configuration, seed power level and effects of the HHG seed structure. FEL simulations using realistic electron beam distributions are presented and tolerance to increased emittance has been considered., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

Progress made in ALICE (Accelerators and Lasers In Combined Experiments) commissioning and a summary of the latest experimental results are presented in this paper. After an extensive work on beam loading effects in SC RF linac (booster) and linac cavities conditioning, ALICE can now operate in full energy recovery mode at the bunch charge of 40pC, the beam energy of 30MeV and train lengths of up to 100us. This improved operation of the machine resulted in generation of coherently enhanced broadband THz radiation with the energy of several tens of uJ per pulse and in successful demonstration of the Compton Backscattering x-ray source experiment. The next steps in the ALICE scientific programme are commissioning of the IR FEL and start of the research on the first non-scaling FFAG accelerator EMMA. Results from both projects will be also reported., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

We studied the degree of polarisation of the FEL radiation from the diverted-beam scheme [1,2] using the layout of the CompactLight facility, which is in the process of being designed. To satisfy the polarisation requirements defined by the users [3] without compromising the aim of the facility to be compact, we studied a configuration comprising a helical Super Conductive Undulator (SCU) followed by a Delta afterburner (configured to generate linearly polarised light). The trade-offs between the SCU length, afterburner length, degree of polarisation and output power are presented and discussed., Proceedings of the 39th Free Electron Laser Conference, FEL2019, Hamburg, Germany

We present recent developments in the accelerator design of CLARA (Compact Linear Accelerator for Research and Applications), the proposed UK FEL test facility at Daresbury Laboratory. Updates on the electron beam simulations and code comparisons including wakefields are described. Simulations of the effects of geometric wakefields in the small-aperture FEL undulator are shown, as well as further simulations on potential FEL experiments using chirped beams. We also present the results of simulations on post-FEL diagnostics., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany