Controlled density-downramp injection in a beam-driven plasma wakefield accelerator

This paper describes the utilization of beam-driven plasma wakefield acceleration to implement a high-quality plasma cathode via density-downramp injection in a short injector stage at the FLASHForward facility at DESY. Electron beams with charge of up to 105 pC and energy spread of a few percent were accelerated by a tunable effective accelerating field of up to 2.7 GV/m. The plasma cathode was operated drift-free with very high injection efficiency. Sources of jitter, the emittance and divergence of the resulting beam were investigated and modeled, as were strategies for performance improvements that would further increase the wide-ranging applications for a plasma cathode with the demonstrated operational stabilityComment: 11 pages, 9 figure

Resource-aware Research on Universe and Matter: Call-to-Action in Digital Transformation

Given the urgency to reduce fossil fuel energy production to make climate tipping points less likely, we call for resource-aware knowledge gain in the research areas on Universe and Matter with emphasis on the digital transformation. A portfolio of measures is described in detail and then summarized according to the timescales required for their implementation. The measures will both contribute to sustainable research and accelerate scientific progress through increased awareness of resource usage. This work is based on a three-days workshop on sustainability in digital transformation held in May 2023.Comment: 20 pages, 2 figures, publication following workshop 'Sustainability in the Digital Transformation of Basic Research on Universe & Matter', 30 May to 2 June 2023, Meinerzhagen, Germany, https://indico.desy.de/event/3748

Electrodynamics of Relativistic Electron Beam X-Ray Sources

Ph.D. University of Hawaii at Manoa 2016.Includes bibliographical references.Probing matter at atomic scales provides invaluable information about its structure; as a result interest in sources of x-rays and γ-rays with high spectral resolution, low angular divergence and small source size has been on the rise. Explorations in this domain require x-ray or γ-ray sources with high brightness. In the past decade, relativistic electron sources such as synchrotron rings and free electron lasers have proven to be the best technology available for the production of such beams. We1 start with an introduction to the physics of radiation and provide a summary of the theoretical grounds this work is based on. This dissertation is dedicated to different aspects of both fundamental processes of radiation in relativistic electron sources, and critical control and diagnostics that are required for the operation of these sources. Therefore this work is broken into two main parts. In the first part, the electron source that is currently set up at University of Hawai‘i at Manoa will be introduced in detail. This source has unique capabilities as it is an inverse- Compton scattering (ICS) source that uses a free electron laser (FEL) with pulses of pi-cosecond duration at ~ 3 GHz rate for production of a coherent/semi-coherent x-ray beam by means of an optical cavity. After introducing the essential elements of the system and what was achieved prior to this work, we will focus on the requirements for achieving an optimum electron beam matched for the operation of the system which is the main focus of part I of this dissertation. The transport beam line of our system is unique and complex. For this reason, a simulation module has been developed for the study and delivery of an optimal beam. We will discuss the capabilities of this system and its compatibility with other elements that were already installed on the beam line. Finally, we will present results and experimental data as well as guidelines for future operation of the system when the microwave gun has been enhanced and/or the optical cavity (the final step of this proof-of-principle experiment) has been commissioned. Due to the complexity of this integrated system, one of the goals of this work is to serve the future members and staff of the UH FEL laboratory in configuring and operating this complex system. The final goal of the UH ICS project is to establish the principles on which producing a successful turn-key commercial inverse-Compton x-ray source will depend on. In the second part of this work we start with the discussion of coherent radiation at its most fundamental level, with emphasis on conservation of energy. We show that for coherently radiating particles the failure of conventional classical electrodynamics (CED) is far more serious than the well-known failure of CED at small scales. We will present a covariant picture of radiation in terms of the theory of action-at-a-distance and introduce a time-symmetric approach to electrodynamics. We demonstrate that this time symmetric ap- proach provides a perfect match to the energy radiated by two coherently oscillating charged particles. This work is novel, as this was an unsolved problem in classical electrodynamics up until now. We also discuss how the conceptual implication of this work is demanding. For this purpose, we will propose two different experiments that can further our understanding of the presented problem. The first experiment involves a small (λ/10) antenna, and the goal is to measure the advanced field of the absorber at distances of 5λ or less. Calculation and precise measurement of the antenna field/potential at distances of order λ is challenging, causing this experiment to be a difficult yet possible task. In the second experiment, we discuss in some detail the experimental setup that would verify and/or further our understanding of the underlying physics of Self Amplified Spontaneous Emission (SASE) FELs. We provide an analytical verification as a first step toward better understanding the process, and provide a list of required parameters for the SASE test. These parameters are at the edge of current technol- ogy of current light sources, making this experiment also a demanding and challenging task. We conclude that further detailed studies by means of simulation or analytical approaches can reduce the strain of SASE test

Calculation of the CSR Effect on EEHG Performance

Externally seeded FELs can produce fully coherent short-wavelength pulses with the advantage of higher shot-to-shot stability and spectral intensity than SASE radiation. For the FLASH2020+ project, the Echo-Enabled Harmonic Generation (EEHG) seeding technique achieves seeded FEL radiation in the XUV and soft X-ray range down to wavelengths of 4 nm. The implementation of the EEHG requires precise phase space manipulations in the seeding section of the beamline, which would make the performance of the EEHG sensitive to the collective effects, such as Coherent Synchrotron Radiation (CSR) in some working range. Therefore, it is essential to consider the CSR in EEHG simulations and to understand its impact on the electron beam properties. In this work, we compare different methods for calculating CSR and investigate the mechanism of its effect on the EEHG performance

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

FLASHforward Findings for the EuPRAXIA Design Study and the Next-Generation of Compact Accelerator Facilities

FLASHForward, the exploratory FLASH beamline for Future-ORiented Wakefield Accelerator Research and Development, is a European pilot test bed facility for accelerating electron beams to GeV-levels in a few centimeters of ionized gas. The main focus is on the advancement of plasma-based particle acceleration technology through investigation of injection schemes, novel concepts and diagnostics, as well as benchmarking theoretical studies and simulations. Since the plasma wakefield will be driven by the optimal high-current-density electron beams extracted from the FLASH L-band Superconducting RF accelerator, FLASHForward has been in a unique position for studying and providing insight for the design study of next-generation light source and high energy physics facilities such as EuPRAXIA*. Summary of these findings and their broader impact is discussed here

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

High-resolution sampling of beam-driven plasma wakefields

Plasma-wakefield accelerators driven by intense particle beams promise to significantly reduce the size of future high-energy facilities. Such applications require particle beams with a well-controlled energy spectrum, which necessitates detailed tailoring of the plasma wakefield. Precise measurements of the effective wakefield structure are therefore essential for optimising the acceleration process. Here we propose and demonstrate such a measurement technique that enables femtosecond-level (15 fs) sampling of longitudinal electric fields of order gigavolts-per-meter (0.8 GV m⁻¹). This method—based on energy collimation of the incoming bunch—made it possible to investigate the effect of beam and plasma parameters on the beam-loaded longitudinally integrated plasma wakefield, showing good agreement with particle-in-cell simulations. These results open the door to high-quality operation of future plasma accelerators through precise control of the acceleration process

FLASHForward X-1: High-brightness electron beams from a plasma cathode

The beam-driven FLASHForward experiment 1 (X-1) aims at the generation of high-brightness electron bunches for photon science applications in several centimeters of plasma, with the plasma acting both as a cathode and accelerator.The 1 GeV electron-bunch with a peak current of 2.5 kA and a synchronized TW-laser system makes FLASHForward a unique facility[1] to study controlled electron-injection into plasma wakes.With density downramp injection, witness bunches of ~1 kA peak current at emittances well below 1 µm are achievable[2]. The sharp plasma density gradients are produced by means of controlled gas flow[3] or by localized laser ionization transverse to the electron-beam orbit[4]. Precise laser-to-electron-beam synchronization enables controlled injection as e.g. the Trojan Horse scheme[5], which is predicted to support sub-0.1-µm-emittance witness bunches.experimental installation status, planning, and prospects of the FLASHForward X-1 experiments are presented