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Modern high-gain free-electron lasers make use of high-brightness ultra-relativistic electron beams. The uncorrelated energy spread of these beams is upon creation of the beam in the sub-permille range and below the resolution of state-of-the-art diagnostics. One method to determine the slice energy spread is to use an external seed laser to imprint a coherent microbunching structure that gives rise to coherent radiation processes, different radiation sources such as transition radiation, synchrotron radiation, or undulator radiation and others. Here, we present a method and show measurements to determine the slice energy spread using an external seed laser with 266 nm wavelength to produce coherent undulator radiation at higher harmonics. The distribution of these harmonics allows retrieval of the electron beam slice energy spread with high precision., Proceedings of the 38th Int. Free Electron Laser Conf., FEL2017, Santa Fe, NM, USA

The experimental seeding setup at FLASH has operated now for two years in high-gain harmonic generation mode. Using a transverse deflecting structure downstream of the seeding section allows a temporal characterization of seeded electron bunches. In addition, temporal characterization of the seeded FEL beam can be performed in a dedicated diagnostic hutch. In this contribution, we give an overview of the latest achievements and present an outlook of the planned studies., Proceedings of the 38th Int. Free Electron Laser Conf., FEL2017, Santa Fe, NM, USA

8th International Particle Accelerator Conference, IPAC17, Copenhagen, Denmark, 15 May 2017 - 19 May 2017; Geneva : JACoW, 4 pp. (2017). doi:10.18429/JACoW-IPAC2017-MOPAB046, An X-band TDS is a well-known device for the characterization of the longitudinal properties of an electron bunch in a linear accelerator. It is planned that a novel X-band TDS with variable polarization* will be installed within the next few years at SINBAD, an upcoming accelerator R&D facility at DESY**. There are several measurements that can be performed with the TDS, each with specific optics requirements to reach the highest possible resolution and keep induced energy spread to a tolerable level. Quadrupoles will be installed between the TDS and the screen to help satisfy these conditions. In this paper, the requirements for the bunch length measurements, a novel 3D charge density reconstruction technique and slice energy measurements are discussed and some simulation results for the slice energy measurement using example lattices are presented., Published by JACoW, Geneva

8th International Particle Accelerator Conference, IPAC 2017, Copenhagen, Denmark, 14 May 2017 - 19 May 2017 ; 2520-2525(2017). doi:10.18429/JACoW-IPAC2017-WEYB1, Dielectric laser acceleration of electrons has recently been demonstrated with significantly higher accelerating gradients than other structure-based linear accelerators. Towards the development of an integrated 1 MeV electron accelerator based on dielectric laser accelerator technologies, development in several relevant technologies is needed. In this work, recent developments on electron sources, bunching, accelerating, focussing, deflecting and laser coupling structures are reported. With an eye to the near future, components required for a 1 MeV kinetic energy tabletop accelerator producing sub-femtosecond electron bunches are outlined., Published by JACoW, Geneva, Switzerland

8th International Particle Accelerator Conference, IPAC2017, Copenhagen, Denmark, 14 May 2017 - 19 May 2017; JACoW, Geneva, Switzerland 1707 - 1710 (2017). doi:10.18429/JACoW-IPAC2017-TUPIK013, External injection into laser wakefield accelerators is one of the possible routes towards high energy, high quality electron beams through plasma acceleration. Among other reasons this is due to the increased control over the electron beam parameters and overall experimental setup when compared to other plasma schemes, such as controlled self-injection. At the future SINBAD (Short INnovative Bunches and Accelerators at DESY) facility at DESY this technique is planned to be tested experimentally through injection and acceleration of a sub-femtosecond electron beam, produced from a conventional RF-injector, with a charge of around 0.7 pC and initial mean energy of 100 MeV at the plasma entrance. A summary of optimisation steps for the potential experimental setup is presented in this paper, including considerations regarding effects of electron beam self-fields and matching of the beam into the plasma stage. The discussion is complemented by first start-to-end simulations of the plasma accelerator setup based on these findings., Published by JACoW, Geneva, Switzerland

8th International Accelerator Conference, IPAC17, Copenhagen, Denmark, 15 May 2017 - 19 May 2017 ; Geneva : JACoW, 3260-3263(2017). doi:10.18429/JACoW-IPAC2017-WEPVA006, The concept of dielectric laser accelerators (DLA) has gained increasing attention in accelerator research, because of the high achievable acceleration gradients (GeV/m). This is due to the high damage threshold of dielectrics at optical frequencies. In the context of the Accelerator on a Chip International Program (ACHIP) we plan to inject electron bunches into a laser-illuminated dielectric grating structure. At a laser wavelength of 2 micro-meter the accelerating bucket is, Published by JACoW, Geneva

8th International Particle Accelerator Conference, IPAC17, Copenhagen, Denmark, 15 May 2017 - 19 May 2017; Geneva : JACoW, 2592-2595 (2017). doi:10.18429/JACoW-IPAC2017-WEPAB015, The free-electron laser facility FLASH has a dedicated experimental setup for external FEL seeding applications for the XUV and soft x-ray spectral range. Recently the setup is operated as high-gain harmonic generation FEL. Furthermore, it also allows the operation of echo-enabled harmonic generation (EEHG). A versatile laser injection system allows operation with seed wavelength in the infra-red, visible, and ultra-violet. Here, we present the parameter optimization for operating the seeding setup with EEHG. First experimental tests are planned in the first half of 2017., Published by JACoW, Geneva

8th International Particle Accelerator Conference, IPAC17, Copenhagen, Denmark, 15 May 2017 - 19 May 2017 ; Geneva : JACoW, 215-218(2017). doi:10.18429/JACoW-IPAC2017-MOPAB052, Longitudinal bunch measurements are typically done with rf-powered transverse deflection structures with operating frequencies 1-12 GHz. We explore the use of mm-scale,THz-driven, dielectric-lined cylindrical waveguides as transverse deflectors by driving the fundamental deflecting mode of the structure, the HEM$_{11}$. We give a brief overview ofthe physics, history, and provide an example with a 5 MeV beam using$\tiny{ASTRA}$ andCST-MWS., Published by JACoW, Geneva

This paper summarizes the session on design concepts at the ICFA workshop on future circular electron-positron factories "eeFACT2016"., Proceedings of the 58th ICFA Advanced Beam Dynamics Workshop on High Luminosity Circular e^+e^- Colliders, eeFACT2016, Daresbury, UK

The SINBAD facility (Short and INnovative Bunches and Accelerators at Desy) is foreseen to host various experiments in the field of production of ultra-short electron bunches and novel high gradient acceleration technique. The SINBAD linac, also called ARES (Accelerator Research experiment at SINBAD), will be a conventional S-band linear RF accelerator allowing the production of low charge (0.5 pC - few pC) ultra-short electron bunches (FWHM, length, Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

In order to monitor long-term stability of beam optics, simple and at the same time minimally invasive procedures are desirable. Using selectively kicked bunches, betatron phase advance, as well as potential growth of the betatron oscillation amplitude and the Twiss parameters alpha and beta can be extracted from BPM data. If done periodically, this data can be compiled into a long-term history that is accessible via the control system. This way it is possible to identify potential sources of beam optics errors. At FLASH the procedure could be implemented as a server/client tool. Since the whole procedure takes less than five seconds, operation is not disturbed significantly. In this work the possible implementation of the procedure is presented. It is also shown how the history data can be evaluated in order to infer possible beam optics error sources., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

The free-electron laser facility FLASH at DESY operates in SASE mode with MHz bunch trains of high-intensity extreme ultraviolet and soft X-ray FEL pulses. A seeded beamline which is designed to be operated parasitically to the main SASE beamline has been used to test different external FEL seeding methods. First lasing at the 7th harmonic of a 266 nm seed laser using high-gain harmonic generation has been demonstrated. Studies of the influence of the microbunching instability are being pursued., Proceedings of the 37th International Free Electron Laser Conference, FEL2015, Daejeon, Republic of Korea

A new compact versatile linear accelerator named FLUTE (Ferninfrarot Linac Und Test Experiment) is currently under construction at the Karlsruhe Institute of Technology (KIT). It will serve as an accelerator test facility and allow conducting a variety of accelerator physics studies. In addition, it will be used to generate intense, ultra-short THz pulses for photon science experiments. FLUTE consists of a ~7 MeV photo-injector gun, a ~41 MeV S-band linac and a D-shaped chicane to compress bunches to a few femtoseconds. This contribution presents an overview of the project status and the accompanying simulation studies., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

Enormous progress in compact plasma accelerators has been demonstrated over the recent years in various experiments. These experiments rely on high power, pulsed lasers or short electron bunches to excite ultra-strong wakefields in plasmas. Accelerating gradients have reached several 10 GV/m up to 100 GV/m and the absolute energy gain of electron beams is in the regime of several GeV to 30 GeV. The principle and potential of plasma accelerators has been proven impressively and performance parameters are steadily improving. It is noted that particle accelerators are powerful tools that are ultimately justified by their applications in science, medicine or industry. The demonstration of useable beam quality and a realistic use case remains to be achieved for plasma accelerators. The accelerator physics challenges to arrive at this goal are analyzed and discussed., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

The Horizon 2020 Project EuPRAXIA ('European Plasma Research Accelerator with eXcellence In Applications') aims at producing a 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., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark