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Summary of ARIES WP6 APEC & iFAST WP5.2 PAF joint Brainstorming & Strategy Workshop (BSW22) R. Assmann (DESY), C. Carli (CERN), A. Faus-Golfe (IJCLab), E. Fol (CERN), G. Franchetti (GSI & GU Frankfurt), R. Jacobsson (CERN), V. Kain (CERN), F. Kling (DESY), M.W. Krasny (LPNHE), R. Ischebeck (PSI), A. Scheinker (LANL), V. Shiltsev (FNAL), R. Tomas Garcia (CERN), F. Zimmermann (CERN) edited by the BSW2022 workshop organisers A. Faus-Golfe (IJCLab), G. Franchetti (GSI & GU Frankfurt), F. Zimmermann (CERN) The ARIES WP6 APEC & iFAST WP5.2 PAF joint Brainstorming & Strategy Workshop (BSW22) from 30 March to 1 April 2022 addressed (1) present and future AI accelerator applications, and (2) beam requirements and accelerators for the dark sector. For both themes a number of conclusions were formulated. For example, dielectric acceleration appears to be an interesting approach for dark sector searches, calling for a suitable DLA accelerator design and experimental demonstration, while Machine Learning will become a community standard, and should be used for the design optimization of future machines. An intriguing proposal was the use of the LHC based Gamma Factory for driving a subcritical reactor with integrated waste transmutation., This project has received funding from the European Union's Horizon 2020 Research and Innovation programme under Grant Agreements No. 730871 (ARIES) and 101004730 (iFAST).

Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK 31st International Linear Accelerator Conference, LINAC2022, Liverpool, United Kingdom, 28 Aug 2022 - 2 Sep 2022; [Geneva] : JACoW Publishing, Geneva, Switzerland 4 pp. (2022). doi:10.18429/JACoW-LINAC2022-THPOJO02, We present the first commissioning results of the movable bunch compressor (BC) designed for the ARES linac at DESY. The development and simulated performance has been reported earlier and predicts sub-fs electron bunches with high charge densities. Commissioning results of the injector part of the ARES linac delivered promising beam quality results to achieve these numbers. The bunch compressor system is foreseen to be used to bench mark numerical models for coherent synchrotron radiation (CSR) and space charge (SC) for ultra-short electron bunches. Here we will present first measurements of the dispersion as well as calculations for the longitudinal dispersion. In the future the PolariX transverse deflecting structure (TDS) will be commissioned to fully characterize the ARES electron beam., Published by JACoW Publishing, Geneva, Switzerland, [Geneva]

Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand 13th International Particle Accelerator Conference, IPAC'22, Bangkok, Thailand, 12 Jun 2022 - 17 Jun 2022; [Geneva] : JACoW Publishing, Geneva, Switzerland 1526-1529 (2022). doi:10.18429/JACoW-IPAC2022-TUPOMS044, Emerging high power THz sources pave the road for THz-driven acceleration of ultra-short bunches, and enable theirmanipulation for diagnostic purposes. Due to the smallfeature sizes of THz-guiding devices new methods are nec-essary for their electromagnetic characterization. A newtechnique has recently been developed which characterizesTHz waveguides with respect to their dispersion relationsand attenuation. Here, the method is applied to circularwaveguides, partially filled with polymer capillaries of dif-ferent thicknesses, to find a suitable size for THz drivenstreaking at 287 GHz. Further, rough 3d-printed metallicwaveguides are measured to study the effect of roughnesson attenuation and phase constant. In general, additive man-ufacturing techniques show promise for advanced integrateddesigns of THz driven structures., Published by JACoW Publishing, Geneva, Switzerland, [Geneva]

Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK, 28 Aug 2022 - 2 Sep 2022; [Geneva] : JACoW Publishing, Geneva, Switzerland 247-251 (2022). doi:10.18429/JACoW-LINAC2022-MOPORI10, A new beam diagnostics method to reconstruct the full 5-dimensional phase space (x, x’, y, y’, t) of bunches has recently been proposed. This method combines a quadrupole-based transverse phase-space tomography with the variable streaking angle of a polarizable X-band transverse deflecting structure (PolariX TDS). Two of these novel structures have recently been installed at the ARES beamline at DESY, which is a linear accelerator dedicated to accelerator research and development, including advanced diagnostics methods and novel accelerating techniques. In this paper, realistic simulation studies in preparation for planned experimental measurements are presented using the beamline setup at ARES. The reconstruction quality of the method for three beam distributions is studied and discussed, and it is shown how this method will allow the visualization of detailed features in the phase-space distribution., Published by JACoW Publishing, Geneva, Switzerland, [Geneva]

Physical review letters 129(9), 094801 (2022). doi:10.1103/PhysRevLett.129.094801, Laser-plasma accelerators outperform current radio frequency technology in acceleration strength by orders of magnitude. Yet, enabling them to deliver competitive beam quality for demanding applications, particularly in terms of energy spread and stability, remains a major challenge. In this Letter, we propose to combine bunch decompression and active plasma dechirping for drastically improving the energy profile and stability of beams from laser-plasma accelerators. Realistic start-to-end simulations demonstrate the potential of these postacceleration phase-space manipulations for simultaneously reducing an initial energy spread and energy jitter of ∼1–2% to ≲0.1%, closing the beam-quality gap to conventional acceleration schemes., Published by APS, College Park, Md.

The generation and acceleration of ultra-short, high quality electron beams has attracted more and more interest in accelerator science. Electron bunches with these properties are necessary to operate and test novel diagnostics and advanced high gradient accelerating schemes. Furthermore, several medical and industrial applications require high-brightness electron beams. The dedicated R linac ARES at DESY (Deutsches Elektronen-Synchrotron) is now fully operational and able to produce these electron beams at the nominal energy of 155 MeV and deliver it to users. This paper gives an overview of the ARES linac and summarizes the beam parameter measurements. The possibilities for user operation will be described in detail., Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK

Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand 13th International Particle Accelerator Conference, IPAC`22, Bangkok, Thailand, Thailand, 12 Jun 2022 - 17 Jun 2022; [Geneva] : JACoW Publishing, Geneva, Switzerland 279-283 (2022). doi:doi:10.18429/JACoW-IPAC2022-MOPOPT021, The ARES linear accelerator at DESY aims to deliver stable and well-characterized electron bunches with durations down to the sub-fs level. Such bunches are highly sought after to study the injection into novel high-gradient accelerating structures, test diagnostics devices, or perform autonomous accelerator studies. For such applications, it is advantageous to have a complete and detailed knowledge of the beam properties. Tomographic methods have shown to be a key tool to reconstruct the phase space of beams. Based on these techniques, a novel diagnostics method is being developed to resolve the full 5-dimensional phase space (x,x’,y,y’,z) of bunches including their transverse and longitudinal distributions and correlations. In simulation studies, this method shows an excellent agreement between the reconstructed and the original distribution for all five planes. Here, the 5-dimensional phase space tomography method is presented using a showcase simulation study at ARES., Published by JACoW Publishing, Geneva, Switzerland, [Geneva]

Various physical and technology-dependent limits are en-countered for key performance parameters of accelerators such as high-gradient acceleration, high-field bending, beam size, beam brightness, beam intensity and luminosity. This paper will review these limits and the associated challenges. Possible figures-of-merit and pathways to ultimate colliders will also be explored.

Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil 12th International Particle Accelerator Conference, IPAC 2021, Campinas, Brazil, 24 Nov 2021 - 28 Nov 2021; JACoW Publishing, Geneva, Switzerland 2983-2985 (2021). doi:doi:10.18429/JACoW-IPAC2021-WEPAB158, Novel accelerator concepts such as all-optical THz based compact accelerators promise to enable new science due to unique features such as reduced timing-jitter and improved space-charge broadening of the generated electron bunches. However, multi-keV electron photo-guns based on short single-cycle THz pulses for acceleration have not been demonstrated experimentally so far. Here, we present a modular THz-driven electron gun with both tunable interaction length and output orifice allowing optimization of the sub-mm interaction volume. First extraction of multi-keV electrons is demonstrated and the parameter space as well as resulting performance of the THz-driven gun by varying the timing of the two single-cycle THz pulses and the UV photo-excitation pulse are explored. Such compact gun prototypes are not only promising as injectors for compact THz-based LINACs but also as source for ultrafast electron diffraction experiments., Published by JACoW Publishing, Geneva, Switzerland

Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil 12th International Particle Accelerator Conference, IPAC���21, Campinas, Brazil, 24 May 2021 - 28 May 2021; Geneva : JACoW 4 pp. (2021). doi:10.18429/JACOW-IPAC2021-MOPAB284, AXSIS (Attosecond X-ray Science: Imaging and Spectroscopy) is a compact, accelerator-driven X-ray source currently under construction at DESY Hamburg. It comprises a THz-powered electron gun and THz-driven linac for all-optical electron extraction and acceleration to several MeV with the goal of providing X-rays generated by inverse Compton scattering for photon science experiments. For the commissioning and characterisation of the THz gun and linac the facility includes a dedicated accelerator testing area, for which an electron diagnostic beamline has been designed and is currently under construction. The challenges imposed by the AXSIS project on the development of the diagnostics beamline are the wide ranges of bunch charge (15 fC to 3 pC) and energy (5 MeV to 20 MeV) expected from the THz-driven accelerator as well as the limited available space of only ca. 2.5 metres length. In this contribution we present an overview of the design and the current commissioning status of the electron diagnostic beamline as well as plans for future steps., Published by JACoW, Geneva

Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil 12th International Particle Accelerator Conference, IPAC���21, Campinas, Brazil, 24 May 2021 - 28 May 2021; Geneva : JACoW Publishing 4 pp. (2021). doi:10.18429/JACoW-IPAC2021-MOPAB302, The ARES linear accelerator at the SINBAD facility (DESY) is dedicated to perform accelerator R studies with sub-fs short electron bunches to test novel acceleration techniques and diagnostics devices. Currently, the commissioning of the linac is ongoing and first experiments are being performed. For this, the knowledge of the full phase space of the particle beams is of high interest to, for example, optimize the accelerator performance and identify possible errors in the beam line. Tomographic methods can be used to gain insight into the full 4D transverse phase space and its correlations. Here, simulation results and first experimental preparations of a 4D transverse phase-space tomography of electron bunches at ARES are presented and discussed., Published by JACoW Publishing, Geneva

Various physical and technology-dependent limits are encountered for key performance parameters of accelerators such as high-gradient acceleration, high-field bending, beam size, beam brightness, beam intensity and luminosity. This paper will review these limits and the associated challenges. Possible figures-of-merit and pathways to ultimate colliders will also be explored., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

Scientific reports 9(1), 19912 (2019). doi:10.1038/s41598-019-56433-8, Transverse deflection structures are useful devices for characterizing the longitudinal properties of bunches in electron accelerators. With efforts to produce ever-shorter bunches for applications such as external injection into novel accelerator structures, e.g. plasma cells or dielectric structures, the applicability of deflection structures to measuring ultrashort bunches has been considered. In this paper, charge-density and bunch-length measurements of femtosecond and subfemtosecond bunches at the ARES linac at the SINBAD facility at DESY are studied with simulations and the limitations discussed in detail. The novel polarizable X-band transverse deflection structure (PolariX-TDS) will allow the streaking of bunches at all transverse angles, making a 3D charge-density reconstruction of bunches possible, in addition to the standard 1D charge-density reconstruction and bunch-length measurements. These various measurements of the charge-density distributions of bunches have been simulated, and it is shown that useful information about ultrashort bunches down to subfemtosecond lengths may be obtained using the setup planned for the ARES linac., Published by Macmillan Publishers Limited, part of Springer Nature, [London]

This document provides detailed information on the status of Advanced and Novel Accelerators techniques and describes the steps that need to be envisaged for their implementation in future accelerators, in particular for high energy physics applications. It complements the overview prepared for the update of the European Strategy for particle physics, and provides a detailed description of the field. The scientific priorities of the community are described for each technique of acceleration able to achieve accelerating gradient in the GeV~range or above. ALEGRO working group leaders have coordinated the preparation of their working group contribution and contributed to editing the documents. The preparation of this document was coordinated by the Advanced LinEar collider study GROup, ALEGRO. The content was defined through discussions at the ALEGRO workshop in Oxford UK, March 2018, and an advanced draft was discussed during a one day meeting prior to the AAC workshop in Breckenridge, CO, USA, August 2018. This document was submitted as an addendum to the ALEGRO submission to the European Strategy for Particle Physics., 83 pages

39th International Free-Electron Laser Conference, FEL19, Hamburg, Germany, 26 Aug 2019 - 30 Aug 2019; 0-3 (2019).

10th International Particle Accelerator Conference, IPAC'19, Melbourne, Australia, 19 May 2019 - 24 May 2019; JACoW Publishing, Geneva, Switzerland 143-146 (2019). doi:10.18429/JACOW-IPAC2019-MOPGW027, SINBAD (Short and INnovative Bunches and Accelerators at DESY) facility aims to produce ultrashort bunches (sub-fs) at ~100 MeV, suitable for injection into novel accelerators e.g. dielectric Laser acceleration (DLA) and Laser Driven Wakefield acceleration (LWFA). The LWFA experiment demands β functions to be of the order of 1 mm to reduce energy spreads and emittance growth from nonlinearities. Matching such a space charge dominated beam to such constraints with conventional electromagnets is challenging. A Permanent Magnetic Quadrupole (PMQ) triplet is one promising focusing strategy. In this paper, we investigate the performance of a PMQ triplet to fit the requirements of the electron beam properties in a plasma cell and discuss the realizable phase spaces for the LWFA experiment planned at SINBAD., Published by JACoW Publishing, Geneva, Switzerland

10th International Particle Accelerator Conference (IPAC 2019), Melbourne, Australia, 24 May 2019 - 29 May 2019; JACoW Publishing, Geneva, Switzerland 1 pp. (2019). doi:10.18429/JACOW-IPAC2019-TUPRB008, The proposed experiment aims to measure QED in the presence of strong fields and above the Schwinger critical field. An experiment is being considered at the European XFEL, which should be able to measure non-perturbative QED and its transition from the perturbative regime. This paper presents the current status of the LUXE (Laser und XFEL Experiment) design study. First layout considerations; accelerator beam line design, electron and laser beam parameters, radioprotection issues and first results of the start to end simulations will be presented and discussed in detail. An outlook concerning the implementation into the XFEL schedule and timeline of this experiment will be given., Published by JACoW Publishing, Geneva, Switzerland

10th International Particle Accelerator Conference, IPAC'19, Melbourne, AUSTRALIA, 19 May 2019 - 24 May 2019; JACoW Publishing, Geneva, Switzerland 3624-3627 (2019). doi:10.18429/JACOW-IPAC2019-THPGW022, Laser plasma accelerators with external injection of an RF-generated electron beam, providing high accelerating field gradients and increased control over the electron beam injection process, are promising candidates for production electron beams matching the requirements of modern user-applications. The experiments are planned at the SINBAD (Short INnovative Bunches and Accelerators at DESY) facility to test this acceleration technique in the context of the ATHENAe (Accelerator Technology HElmholtz iNfrAstructure) project. In this paper we present numerical studies on the effect of the transverse electron beam jitter on the final quality of a sub-femtosecond, 0.75 pC, 100 MeV electron beam accelerated to 1 GeV energy in the plasma wakefield driven by a 196 TW, 5 J laser pulse., Published by JACoW Publishing, Geneva, Switzerland

10th International Particle Accelerator Conference, IPAC'19, Melbourne, Australia, 19 May 2019 - 24 May 2019; JACoW Publishing, Geneva, Switzerland 3605-3608 (2019). doi:10.18429/JACOW-IPAC2019-THPGW014, Laser-driven hollow core photonic bandgap (PBG) fibers were proposed by Lin in 2001 as high-gradient accelerators. The central defect in the transversely periodic lattice supports an accelerating mode for synchronous acceleration in the ultra-relativistic regime. The optical frequencies in such dielectric laser accelerators motivate a sensitivity and tolerance study to overcome manufacturing imperfections. Finally we discuss the propagation characteristics of Lin-fibers and find that small-bandwidth (~ns) pulses would be needed for efficient acceleration over longer distances., Published by JACoW Publishing, Geneva, Switzerland

39th International Free-Electron Laser Conference, FEL19, Hamburg, Germany, 26 Aug 2019 - 30 Aug 2019; JACoW Publishing, Geneva, Switzerland 396-399 (2019). doi:10.18429/JACOW-FEL2019-WEP036, A collaboration between DESY, PSI and CERN has been established to develop and build an advanced modular X- band transverse deflection structure (TDS) system with the new feature of providing variable polarization of the deflecting force. The prototype of the novel X-band TDS, the Polarizable X-band (PolariX) TDS, was fabricated at PSI following the high-precision tuning-free production process developed for the C-band Linac of the SwissFEL project. Bead-pull RF measurements were also performed at PSI to verify, in particular, that the polarization of the dipole fields does not have any rotation along the structure. The high-power test was performed at CERN and now the TDS is at DESY and has been installed in FLASHForward, where the first streaking experience with beam will be accomplished. We summarize in this paper the status of the project, the results of the bead-pull measurements and the high power test., Published by JACoW Publishing, Geneva, Switzerland

10th International Particle Accelerator Conference, IPAC'19, Melbourne, Australia, 19 May 2019 - 24 May 2019; JACoW Publishing, Geneva, Switzerland 3609-3611 (2019). doi:10.18429/JACOW-IPAC2019-THPGW015, While Laser Plasma Accelerators produce beams with the high output energy required for FELs, up to now the relatively high energy spread has prohibited FEL lasing. Therefore it was proposed to replace the normal FEL undulators by Transverse Gradient Undulators (TGUs). For a first, small scale test of the TGU concept, a 40 period prototype high gradient superconductive TGU was built at KIT and will be tested with beam at the ARES-linac in the new accelerator test facility SINBAD (Short Innovative Bunches and Accelerators at Desy) at DESY. The proposed tests are summarized in this paper., Published by JACoW Publishing, Geneva, Switzerland

The SINBAD facility (Short and INnovative Bunches and Accelerators at DESY) is foreseen to host multiple experiments relating to the production of ultra-short electron bunches and novel high gradient acceleration techniques. The SINBAD-ARES linac will be a conventional S-band linear RF accelerator allowing the production of low charge (0.5 pC - tens pC) ultra-short electron bunches (FWHM length =< 1 fs - few fs) with 100 MeV energy. The installation of the linac will proceed in stages. In this paper we report on the status of the characterization of the ARES RF gun and the installations of the related infrastructure., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

8th EPS-QEOD EUROPHOTON CONFERENCE, Barcelona, Spain, 2 Sep 2018 - 7 Sep 2018, We use 267nm femtosecond laser pulses to modulate electrons of a XUV free electron laser. By changing the chirp of this laser pulses we can influence the chirp of the generated XUV FEL pulses, which are characterized by THz streaking. The emeasured effect is in agreement with simulations.

9th International Particle Accelerator Conference, IPAC'18, Vancouver, Canada, 29 Apr 2018 - 4 May 2018; Geneva, Switzerland : JACoW Publishing 3808-3811 (2018). doi:10.18429/JACOW-IPAC2018-THPAL068, A collaboration between DESY, PSI and CERN has been established to develop and build an advanced modular X-band transverse deflection structure (TDS) system with the new feature of providing variable polarization of the deflecting force. This innovative CERN design requires very high manufacturing precision to guarantee highest azimuthal symmetry of the structure to avoid the deterioration of the polarization of the streaking field. Therefore, the high-precision tuning-free production process developed at PSI for the C-band and X-band accelerating structures will be used for the manufacturing. We summarize in this paper the status of the production of the prototype and the waveguide networks foreseen in the different facilities., Published by JACoW Publishing, Geneva, Switzerland

9th International Particle Accelerator Conference (IPAC'18), IPAC'18, Vancouver, Canada, 29 Apr 2018 - 4 May 2018, Seeded free-electron lasers (FELs) produce intense, ultrashort and fully coherent X-ray pulses. These seeded FEL pulses depend on the initial seed properties. Therefore, controlling the seed laser allows tailoring the FEL radiation for phase-sensitive experiments. In this contribution, we present detailed simulation studies to characterize the FELprocess and to predict the operation performance of seeded pulses. In addition, we show experimental data on the temporal characterization of the seeded FEL pulses performed at the sFLASH experiment in Hamburg.

9th International Particle Accelerator Conference, IPAC'18, Vancouver, Canada, 29 Apr 2018 - 4 May 2018; 6 pp. (2018)., Symmetrically driven dual-grating type DLA (Dielectric Laser Accelerator) linac structures allow for in-channel electric field gradients on the order of GV/m at optical wavelengths. In this work we study the sensitivity of important final beam parameters like mean energy, energy spread and transverse emittance on DLA drive laser as well as input beam parameters. To this end a fast specialized particle tracking code (DLATracker) is used to compute the so called first order sensitivity indices based on a large number of Monte Carlo simulation runs of an exemplary external injection based DLA experiment. The results of this work point out important stability constraints on the drive laser setup and the externally injected electron beam.

9th International Particle Accelerator Conference, IPAC'18, Vancouver, Canada, 29 Apr 2018 - 4 May 2018; Jacow 5 pp. (2018)., Plasma-based accelerators are a promising novel technology that could signiĄcantly reduce the size and cost of future accelerator facilities. However, the typical quality and stabil-ity of the produced beams is still inferior to the requirements of Free Electron Lasers (FELs) and other applications. We present here our recent work in understanding the limita-tions of this type of accelerators, particularly on the energy spread and bunch length, and possible mitigating measures for future applications, like the plasma-based FEL in theEuPRAXIA design study., Published by Jacow