A study on the feasibility of a plasma wakefield acceleration based FEL at the FLASHForward facility, DESY - Eine Durchführbarkeitsstudie eines auf Plasma-Wakefield Beschleunigung basierten FELs an der FLASHForward Anlage, DESY

In this thesis, the feasibility of a plasma wakefield acceleration based free-electronlaser at the FLASHForward facility, DESY is examined. For this purpose, beamparameters which are expected for wakefield-induced ionization injection serve as reference.Even though the electron bunch provides a high current, the large slice energyspread is challenging.It is analyzed under which conditions the former Tesla-Test-Facility undulators aresuitable to demonstrate a sufficiently large gain in power. Requirements on the beamlineand in particular the undulator of the FEL are investigated by means of the MingXie formalism. The average beta function, the undulator parameter as well as theundulator period length are optimized with respect to a short gain length. The optimizationis based on a planar undulator with a F0D0 lattice. Aspects of the technicalimplementation, like spaces for beam alignment devices between the undulator segments,are already taken into account in the 3D approach.For a verification of the obtained results, the three-dimensional FEL simulation codeGENESIS 1.3 is used, taking also slippage effects into consideration.ZusammenfassungIn der vorliegenden Bachelorarbeit wird die Realisierbarkeit eines Freien-ElektronenLasers auf der Basis von Plasma-Wakefield Beschleunigung an der FLASHForwardAnlage, DESY untersucht. Strahlparameter, die für wakefield-induced ionization injectionerwartet werden, dienen als Referenz. Auch wenn der Elektronenbunch einenhohen Strom bietet, stellt der große slice energy spread eine Herausforderung dar.Es wird untersucht, unter welchen Bedingungen die früheren Tesla-Test-Facility Undulatorenzur Demonstration einer ausreichend hohen Leistungsverstärkung geeignetsind. Es werden Anforderungen an die Strahlführung und insbesondere an den Undulatordes FELs mit Hilfe des Ming Xie Formalismus ermittelt. Die durchschnittlicheBetafunktion, der Undulatorparameter sowie die Länge der Undulatorperiode werdenin Hinblick auf eine möglichst kurze Verstärkungslänge optimiert. Die Optimierungbasiert auf einem planaren Undulator mit einer F0D0 Struktur. Aspekte der technischenUmsetzbarkeit, wie Platz für Strahlführungselemente zwischen den Undulatorsegmenten,werden dabei schon in der 3D-Näherung beachtet.Zur Überprüfung der Ergebnisse wird der dreidimensionale FEL SimulationscodeGENESIS 1.3 verwendet, wobei auch Slippage Effekte Beachtung finden

Advanced Scheme to Generate MHz, Fully Coherent FEL Pulses at nm Wavelength

Current FEL development efforts aim at improving the control of coherence at high repetition-rate while keeping the wavelength tunability. Seeding schemes, like HGHG and EEHG, allow for the generation of fully coherent FEL pulses, but the powerful external seed laser required limits the repetition-rate that can be achieved. In turns, this impacts the average brightness, and the amount of statistics that experiments can do. In order to solve this issue, here we we take a unique approach and discuss the use of one or more optical cavities to seed the electron bunches accelerated in a superconducting linac to modulate their energy. Like standard seeding schemes, the cavity is followed by a dispersive section, which manipulates the longitudinal phase space of the electron bunches, inducing longitudinal density modulations with high harmonic content that undergo the FEL process in an amplifier placed downstream. We will discuss technical requirements for implementing these setups and their operation range based on numerical simulations

Mitigation of Beam Instabilities in the Echo-Enabled Harmonic Generation Beamline for FLASH2020+

With the FLASH2020+ upgrade, one of the beamlines of the free-electron laser FLASH at DESY will be based on the Echo-Enabled Harmonic Generation (EEHG) seeding scheme and provide high-repetition-rate, coherent radiation down to 4 nm. To reach this wavelength, it is necessary to imprint intricate structures on the longitudinal phase space of the electron bunch at a very high harmonic of the seed laser wavelength, making the scheme potentially vulnerable to beam instabilities. Part of the beamline is a strong chicane, which is necessary to create the dispersion required by EEHG. Resulting effects such as Coherent Synchrotron Radiation (CSR) can be very detrimental for the bunching process and have to be taken into account already in the design of the beamline to ensure optimum FEL performance. We investigate and propose possible mitigation solutions to such instabilities in the FLASH2020+ parameter range

Sensitivity of EEHG Simulations to Dynamic Beam Parameters

Currently, the Free electron laser user facility FLASH at DESY is undergoing a significant upgrade involving the complete transformation of one of its beamlines to allow external seeding. With the Echo-Enabled Harmonic Generation (EEHG) seeding method, we aim for the generation of fully coherent XUV and soft X-ray pulses at wavelengths down to 4 nm. The generated FEL radiation is sensitive to various electron beam properties, e.g., its energy profile imprinted either deliberately or by collective effects such as Coherent Synchrotron Radiation (CSR). In dedicated particle tracking simulations, one usually makes certain assumptions concerning the beam properties and the collective effects to simplify implementation and analysis. Here, we estimate the influence of some of the common assumptions made in EEHG simulations on the properties of the output FEL radiation, using the example of FLASH and its proposed seeding beamline. We conclude that the inherent properties of the FLASH1 beam, namely the negatively chirped energy profile, has dominant effect on the spectral intensity profile of the radiators output compare to that of the CSR induced chirp

Improving the Realistic Modeling of the EEHG Seed Section in Start to End Simulations

A tunable and multicolor light source with near Fourier-limited pulses, controlled delay, and fully coherent beam with precisely adjustable phase profiles enables state-of-the-art measurements and studies of femtosecond dynamic processes with high elemental sensitivity and contrast. The start-to-end simulations efforts aim to take advantage of the available global pool of software and past and present extensive efforts to provide realistic simulations, particularly for cases where precise and fine manipulation of the beam phase space is concerned. Since, for such cases, tracking of beams with billions of particles through magnetic structures and handover between multiple codes are required, extensive realistic studies for such cases are limited. Here we will describe a workflow that reduces the needed computational resources and share studies of the EEHG seed section for the FLASH2020+ [1] project

Status of the Seeding Upgrade for FLASH2020+ Project

In the framework of the FLASH2020+ project, the FLASH1 beamline will be upgraded to deliver seeded FEL pulses for users. This upgrade will be achieved by combining high gain harmonic generation and echo-enabled harmonic generation with a wide-range wavelength-tunable seed laser, to efficiently cover the 60-4 nm wavelength range. The undulator chain will also be refurbished entirely using new radiators based on the APPLE-III design, allowing for polarization control of the generated light beams. With the superconducting linac of FLASH delivering electron beams at MHz repetition rate in burst mode, laser systems are being developed to seed at full repetition rates. In the contribution, we will report about the progress of the project

Flexible and Coherent Soft X-ray Pulses at High Repetition Rate

The successful realization of high gain free-electron lasers has opened new possibilities to X-ray scientists for investigating matter in different states. The availability of unprecedented photon properties stimulated the development of new experimental techniques capable of taking full advantage of these options and has started a virtuous collaboration between machine experts and photon users to improve further and optimize the generated X-ray pulses. Over the recent years, this has led to the development of several advanced free-electron laser (FEL) schemes to tailor the photon properties to specific experimental needs. Nowadays, tunable wavelength X-ray pulses with extremely high brilliance and short pulse characteristics are a few of the many options available at FELs. Few facilities can offer options such as narrowband or extremely short pulses below one~fs duration and simultaneous pulses of multiple colors enabling resonant X-ray pump - X-ray probe experiments with sub fs resolution. Fully coherent X-ray radiation (both spatial and temporal) can also be provided and has stimulated the application of coherent control techniques to the X-ray world, allowing for experiments with few attoseconds resolution. FELs often operate at a relatively low repetition rate, typically on the order of tens of Hz. At FLASH and the European XFEL, however, the superconducting accelerators allow generating thousands of pulses per second.With the implementation of a new seeded FEL line and with an upgrade at FLASH linac, all the new features will become available in the soft-X-ray spectral range down to the oxygen K edge with unprecedented average photon flux due to the high repetition rate of pulses

Flexible and Coherent Soft X-ray Pulses at High Repetition Rate: Current Research and Perspectives

The successful realization of high gain free-electron lasers has opened new possibilities to X-ray scientists for investigating matter in different states. The availability of unprecedented photon properties stimulated the development of new experimental techniques capable of taking full advantage of these options and has started a virtuous collaboration between machine experts and photon users to improve further and optimize the generated X-ray pulses. Over the recent years, this has led to the development of several advanced free-electron laser (FEL) schemes to tailor the photon properties to specific experimental demands. Presently, tunable wavelength X-ray pulses with extremely high brilliance and short pulse characteristics are a few of the many options available at FELs. Few facilities can offer options such as narrowband or extremely short pulses below one fs duration and simultaneous pulses of multiple colors enabling resonant X-ray pump—X-ray probe experiments with sub fs resolution. Fully coherent X-ray radiation (both spatial and temporal) can also be provided. This new option has stimulated the application of coherent control techniques to the X-ray world, allowing for experiments with few attoseconds resolution. FELs often operate at a relatively low repetition rate, typically on the order of tens of Hz. At FLASH and the European XFEL, however, the superconducting accelerators allow generating thousands of pulses per second. With the implementation of a new seeded FEL line and with an upgrade at FLASH linac, all the new features will become available in the soft X-ray spectral range down to the oxygen K edge with unprecedented average photon flux due to the high repetition rate of pulses

Future-oriented wakefield-accelerator research and development at FLASH

FLASHForward is a beam-driven plasma wakefield acceleration facility,currently under construction at DESY (Hamburg, Germany),aiming at the stable generation of electron beams of several \si{\GeV} with small energy spread and emittance.High-quality 1 GeV-class electron beams from the free-electron laser FLASH will act as the wake driver.The setup will allow studies on external injection as well as on various internal injection techniques, such as density-downramp or ionisation injection.With a triangular-shaped drive beam electron energies of up to 5 GeV from a few centimeters of plasma can be anticipated.Particle-In-Cell simulations are used to assess the feasibility of each technique and to predict properties of the accelerated electron bunches.In this contribution the physics case and the current status of FLASHForward will be reviewed.Concepts of the main components - the extraction beamline from the FLASH linac, the target area, the plasma cell and the post-plasma beam transport and diagnostics - will be described