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At the KIT electron storage ring KARA (Karlsruhe Research Accellerator) an electro-optical (EO) near-field monitor is in operation performing single-shot, turn-by-turn measurements of the longitudinal bunch profile using electro-optical spectral decoding (EOSD). In context of the Future Circular Collider Innovation Study (FCCIS), a similar setup is investigated with the aim to monitor the longitudinal bunch profile of each bunch for dedicated top-up injection at the future electron-positron collider FCC-ee. This contribution presents the status of a monitor design adapted to cope with the high-current and high-energy lepton beams foreseen at FCC-ee.

Two parallel, corrugated plates will be installed at the KIT storage ring KARA (KArlsruhe Research Accelerator). This impedance manipulation structure can be used to study and eventually control the electron beam dynamics and the emitted coherent synchrotron radiation (CSR) at KARA. In this contribution, we present the design of the impedance manipulation structure with corrugated plates, simulation results showing the influence of different corrugation parameters on its impedance, and the impact of this additional impedance source on the temporal changes in the emitted CSR in the presence of the microbunching instability., Proceedings of the 11th International Beam Instrumentation Conference, IBIC2022, Kraków, Poland

For measuring the temporal profile of the coherent synchrotron radiation (CSR) at the KIT storage ring KARA (Karlsruhe Research Accelerator) an experimental setup based on electro-optical spectral decoding (EOSD) is currently being implemented. The EOSD technique allows single-shot, phase-sensitive measurements of the far-field radiation on a turn-by-turn basis at rates in the MHz range. Therefore, the resulting THz radiation from the dynamics of the bunch evolution, e.g. the microbunching, can be observed with high temporal resolution. This far-field setup is part of the distributed sensor network at KARA. Additionally to the information acquired from the near-field EOSD spectral decoding and the horizontal bunch profile monitor, it enables to monitor the longitudinal phase-space of the bunch. In this contribution, the characterization of the far-field setup is summarized and its implementation is discussed., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

FLUTE (Ferninfrarot Linac- Und Test-Experiment) is a compact linac-based test facility for accelerator and diagnostics R An example for a new accelerator diagnostics tool currently studied at FLUTE is the split-ring-resonator (SRR) experiment, which aims to measure the longitudinal bunch profile of fs-scale electron bunches. Laser-generated THz radiation is used to excite a high frequency oscillating electromagnetic field in the SRR. Particles passing through the SRR gap are time-dependently deflected in the vertical plane, which allows a vertical streaking of an electron bunch. This principle allows a diagnosis of the longitudinal bunch profile in the femtosecond time domain and will be tested at FLUTE. This contribution presents an overview of the SRR experiment and the results of various tracking simulations for different scenarios as a function of laser pulse length and bunch charge. Based on these results possible working points for the experiments at FLUTE will be proposed., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

A compact, longitudinal diagnostics for fs-scale electron bunches using a THz electric-field transient in a split-ring resonator (SRR) for streaking will be tested at the Ferninfrarot Linac- Und Test- Experiment (FLUTE). For this new streaking technique, intensive THz pulses are required, which will be generated by laser-based optical rectification. We present a setup for generating THz pulses using tilted-pulse-front pumping in lithium niobate at room temperature. Excited by an 800 nm Ti:Sa pump laser with 35 fs bandwidth-limited pulse length, conversion efficiencies up to 0.027% were achieved. Furthermore, the status of the SRR experiment is shown., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

FLUTE (Ferninfrarot Linac- und Test-Experiment) at KIT is a compact linac-based test facility for novel accelerator technology and a source of intense THz radiation. FLUTE is designed to provide a wide range of electron bunch charges from the pC- to nC-range, high electric fields up to 1.2 GV/m, and ultra-short THz pulses down to the fs-timescale. The electrons are generated at the RF photoinjector, where the electron gun is driven by a commercial titanium sapphire laser. In this kind of setup the electron beam properties are determined by the photoinjector, but more importantly by the characteristics of the laser pulses. Spatial light modulators can be used to transversely and longitudinally shape the laser pulse, offering a flexible way to shape the laser beam and subsequently the electron beam, influencing the produced THz pulses. However, nonlinear effects inherent to the laser manipulation (transportation, compression, third harmonic generation) can distort the original pulse. In this paper we propose to use machine learning methods to manipulate the laser and electron bunch, aiming to generate tailor-made THz pulses. The method is demonstrated experimentally in a test setup., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

Laser-plasma acceleration is an outstanding candidate to drive the next-generation compact light sources and FELs. To compensate large chromatic effects using novel compact beam optic elements in the beam transport line is required. We aim at designing miniature, high strength, normal conducting and superconducting transport line magnets and optics for capturing and matching LPA-generated electron bunches to given applications. Our primary application case is a demonstration experiment for transverse gradient undulator (TGU) FELs, to be performed at the JETI laser facility, Jena, Germany. In this contribution, we present the current design of the beam transport line magnets and the beam optics calculations., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

Computer studies of longitudinal motion have been performed with the objective to estimate the possibility of detection of alpha-buckets at the KIT storage ring KARA (Karlsruhe Research Accelerator). The longitudinal equations of motion and the Hamiltonian were expanded to high order terms of the energy deviation of particles in a beam. Roots of third order equation for three leading terms of momentum compaction factor and free energy independent term were derived in a form suitable for analytical estimations. Averaged quadratic terms of closed orbit distortions caused by misalignment of magnetic elements in a ring lead to orbit lengthening independent of particle energy deviation. Particle transverse excursions were estimated and are taken into account. Simulations have been bench-marked on existing experiments at Metrology Light Source (MLS) in Berlin (Germany) and SOLEIL (France). Parameters of three simultaneous beams and alpha buckets at MLS and SOLEIL have been reproduced with high accuracy. A computer model of KARA was used to predict behavior and the dynamics of possible simultaneous beams in the ring., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

To produce small-scale high-field undulators for table-top free electron lasers (FELs), compact designs have been proposed using high temperature superconducting (HTS) tapes, which show both large critical current densities and high critical magnetic fields with a total tape thickness of about 50 μm and a width of up to 12 mm. Instead of winding coils, a meander structure can be laser-scribed directly into the superconductor layer, guiding the current path on a quasi-sinusoidal trajectory. Stacking pairs of such scribed tapes allows the generation of the desired sinusoidal magnetic fields above the tape plane, along the tape axis. Two practically feasible designs are presented, which are currently under construction at KIT: A coil concept wound from a single structured tape with a length of 15 m, which is a progression of a design that has been presented already in the past, as well as a novel stacked and soldered design, made from 25 cm long structured tapes, soldered in a zig-zag-pattern. In this contribution the designs are briefly recapped and the experimental progress is presented., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

A very large acceptance compact storage ring (VLA-cSR) is under design at the Institute for Beam Physics and Technology (IBPT) of the Karlsruhe Institute of Technology (KIT, Germany). The combination of a compact storage ring and a laser wakefield accelerator (LWFA) might be the basis for future compact light sources and advancing user facilities. Meanwhile, the post-LWFA beam should be adapted for storage and accumulation in a dedicated storage ring. Modified geometry and lattice of a VLA-cSR operating at 50 MeV energy range have been studied in detailed simulations. The main features of a new model are described here. The new design, based on 45° bending magnets, is suitable to store the post-LWFA beam with a wide momentum spread (1% to 2%) as well as ultra-short electron bunches in the fs range from the Ferninfrarot Linac- Und Test- Experiment (FLUTE). The DBA-FDF lattice with relaxed settings, split elements, and higher-order optics of tolerable strength allows improving the dynamic aperture to an acceptable level. This contribution discusses the lattice features in detail and different possible operation schemes of a VLA-cSR., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

The Ferninfrarot Linac- Und Test-Experiment (FLUTE) is a KIT-operated linac-based test facility for accelerator research and development as well as a compact, ultra-broadband and short-pulse terahertz (THz) source. As a key component of FLUTE, the bunch compressor (chicane) consisting of four specially designed dipoles will be used to compress the 40-50 MeV electron bunches after the linac down to single fs bunch length. The maximum vertical magnetic field of the dipoles reach 0.22 T, with an effective length of 200 mm. The good field region is ±40 mm and ±10.5 mm in the horizontal and vertical direction, respectively. The latest measurement results of the dipoles in terms of field homogeneity, excitation and field reproducibility within the good field regions will be reported, which meet the predefined specifications. The measured 3D magnetic field distributions have been used to perform beam dynamics simulations of the bunch compressor. Effects of the real field properties on the beam dynamics, which are different from that of the ASTRA built-in dipole field, will be discussed., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

In its short-bunch operation mode, the KIT storage ring KARA provides picosecond-long electron bunches, which emit coherent synchrotron radiation (CSR) up to the terahertz frequency range. Due to the high spatial compression under these conditions, the self-interaction of the bunch with its own emitted CSR induces a wake-field, which significantly influences the longitudinal charge distribution. Above a given threshold current, this leads to the formation of dynamically evolving micro-structures within the bunch and is thus called micro-bunching instability. As CSR is emitted at wavelengths corresponding to the spatial dimension of the emitter, these small structures lead to an increased emission of CSR at higher frequencies. The instability is therefore deliberately induced at KARA to provide intense THz radiation to dedicated experiments. To further increase the emitted power in the desired frequency range, we consider the potential of RF amplitude modulations to intentionally excite this form of micro-bunching in short electron bunches. This work is supported by the BMBF project 05K19VKC TiMo (Federal Ministry of Education and Research)., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

A 40-period superconducting transverse gradient undulator (TGU) has been designed and fabricated at Karlsruhe Institute of Technology (KIT). Combining a TGU with a Laser Wakefield Accelerator (LWFA) is a potential key for realizing an extremely compact Free Electron Laser (FEL) radiation source. The TGU scheme is a viable option to compensate the challenging properties of the LWFA electron beam in terms of beam divergence and energy spread. In this contribution, we report on the operational experience of this TGU inside its own cryostat and show the current status of the TGU and the further plan for experiments. This work is supported by the BMBF project 05K19VKA PlasmaFEL (Federal Ministry of Education and Research)., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

During the operation of an electron synchrotron with short electron bunches, the beam dynamics are influenced by the occurrence of the micro-bunching instability. This collective instability is caused by the self-interaction of a short electron bunch with its own emitted coherent synchrotron radiation (CSR). Above a certain threshold bunch current dynamic micro-structures start to occur on the longitudinal phase space density. The resulting dynamics depend on various parameters and were previously investigated in relation to, amongst others, the momentum compaction factor and the acceleration voltage. In this contribution, the influence of the energy of the electrons on the dynamics of the micro-bunching instability is studied based on measurements at the KIT storage ring KARA (Karlsruhe Research Accelerator)., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

Synchrotron light sources operate with bunch repetition rates in the MHz regime. The longitudinal and transverse beam dynamics of these electron bunches can be investigated and characterized by experiments employing linear array detectors. To improve the performance of modern beam diagnostics and overcome the limitations of commercially available detectors, we have at KIT developed KALYPSO, a detector system operating with an unprecedented frame rate of up to 12 MHz. To facilitate the integration in different experiments, a modular architecture has been utilized. Different semiconductor microstrip sensors based on Si, InGaAs, PbS, and PbSe can be connected to the custom-designed low noise front-end ASIC to optimize the quantum efficiency at different photon energies, ranging from near-UV, visible, and up to near-IR. The front-end electronics are integrated within a heterogeneous DAQ consisting of FPGAs and GPUs, which allows the implementation of real-time data processing. This detector is currently installed at KARA, European XFEL, FLASH, Soleil, DELTA. In this contribution, we present the detector architecture, the performance results, and the ongoing technical developments., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

The KIT storage ring KARA operates in a wide energy range from 0.5 to 2.5 GeV. Different operation modes have been implemented at KARA, so far, the double-bend achromat (DBA) lattice with non-dispersive straight sections, the theoretical minimum emittance (TME) lattice with distributed dispersion, different versions of low-compaction factor optics with highly stretched dispersion function. Short bunches of a few ps pulse width are available at KARA. Low-alpha optics has been simulated, tested and implemented in a wide operational range of the storage ring and is now routinely used at 1.3 GeV for studies of beam bursting effects caused by coherent synchrotron radiation in the THz frequency range. Different non-linear effects, in particular residual high-order components of the magnetic field, generated in high-field superconducting wigglers have been studied and cured. Based on good agreement between computer simulations and experiments, a new operation mode at high vertical tune was implemented. The beam performance during user operation as well as at low-alpha regimes has been improved. A specific optic with negative compaction factor was simulated, tested and is in operation., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

With the deployment of a storage spaces direct hyper-converged cluster in 2018, the whole control system server and network infrastructure of the Karlsruhe Research Accelerator have been virtualized to improve the control system availability. The cluster with 6 Dell PowerEdge R740Xd servers with 1.152 GB RAM, 72 cores and 40 TByte hyperconverged storage operates in total 120 virtual machines. We will report on our experiences running EPICS IOCs and the industrial control system WinCC OA in this virtual environment., Proceedings of the 17th International Conference on Accelerator and Large Experimental Physics Control Systems, ICALEPCS2019, New York, NY, USA

The German Helmholtz Innovation Pool project will explore and provide novel cutting edge Machine Learning techniques to address some of the most urgent challenges in the era of large data harvests in accelerator physics. Progress in virtually all areas of accelerator based physics research relies on recording and analyzing enormous amounts of data. This data is produced by progressively sophisticated fast detectors alongside increasingly precise accelerator diagnostic systems. As KIT contribution to AMALEA it is planned to investigate a design of a fast and adaptive feedback system that reacts to small changes in the charge distribution of the electron bunch and establishes extensive control over the longitudinal beam dynamics. As a promising and well-motivated approach, reinforcement learning methods are considered. In a second step the algorithm will be implemented as a pilot experiment to a novel PCIe FPGA readout electronics card based on Zynq UltraScale⁺ MultiProcessor System on-Chip (MPSoC)., Proceedings of the 17th International Conference on Accelerator and Large Experimental Physics Control Systems, ICALEPCS2019, New York, NY, USA

Scientific reports 13(1), 4618 (2023). doi:10.1038/s41598-023-31196-5, The description of physical processes with many-particle systems is a key approach to the modeling of numerous physical systems. For example in storage rings, where ultrarelativistic particles are agglomerated in dense bunches, the modeling and measurement of their phase-space distribution is of paramount importance: at any time the phase-space distribution not only determines the complete space-time evolution but also provides fundamental performance characteristics for storage ring operation. Here, we demonstrate a non-destructive tomographic imaging technique for the 2D longitudinal phase-space distribution of ultrarelativistic electron bunches. For this purpose, we utilize a unique setup, which streams turn-by-turn near-field measurements of bunch profiles at MHz repetition rates. To demonstrate the feasibility of our method, we induce a non-equilibrium state and show that the phase-space distribution microstructuring as well as the phase-space distribution dynamics can be observed in great detail. Our approach offers a pathway to control ultrashort bunches and supports, as one example, the development of compact accelerators with low energy footprints., Published by Macmillan Publishers Limited, part of Springer Nature, [London]

In recent and future synchrotron radiation facilities, relativistic electron bunches with increasingly high charge density are needed for producing brilliant light at various wavelengths, from X-rays to terahertz. In such conditions, interaction of electrons bunches with their own emitted electromagnetic fields leads to instabilities and spontaneous formation of complex spatial structures. Understanding these instabilities is therefore key in most electron accelerators. However, investigations suffer from the lack of non-destructive recording tools for electron bunch shapes. In storage rings, most studies thus focus on the resulting emitted radiation. Here, we present measurements of the electric field in the immediate vicinity of the electron bunch in a storage ring, over many turns. For recording the ultrafast electric field, we designed a photonic time-stretch analog-to-digital converter with terasamples/second acquisition rate. We could thus observe the predicted link between spontaneous pattern formation and giant bursts of coherent synchrotron radiation in a storage ring., 9 pages, 5 figures

For future synchrotron light source development novel operation modes are under investigation. At the Karlsruhe Research Accelerator (KARA) an optics with negative momentum compaction has been proposed, which is currently under commissioning. In this context, the collective effects expected in this regime are studied with an initial focus on the head-tail instability and the micro-bunching instability resulting from CSR self-interaction. In this contribution, we will present the proposed optics and the status of implementation for operation in the negative momentum compaction regime as well as a preliminary discussion of expected collective effects., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The KAPTURE system (KArlsruhe Pulse Taking and Ultrafast Readout Electronics), developed at the Karlsruhe Institute of Technology (KIT), was designed to digitize detector pulses during multi-bunch operation at the KIT storage ring KARA (Karlsruhe Research Accelerator). KAPTURE provides digitization for pulses at rates of 500 MHz using up to 4 sampling points per pulse to record each bunch and each turn for potentially unlimited time. The new KAPTURE-2 system now provides eight sampling points per pulse, including baseline sampling between pulses, which allows improved reconstruction of the pulse shape. The advanced reconstruction of the pulse shape is realized with a highly parallelised implementation on GPU. The system will be used for the investigation on longitudinal beam dynamics e.g. by measuring instability induced CSR fluctuations or arrival time oscillations. This contribution will report on first results of the KAPTURE-2 system at KARA., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The first electron beams were generated in the 7 MeV section of the short-pulse linear accelerator test facility FLUTE (Ferninfrarot Linac- Und Test-Experiment) at the Karlsruhe Institute of Technology (KIT). In this contribution we show images of the electron beam on a YAG-screen (yttrium aluminum garnet) as well as signals from an integrating current transformer (ICT) and a Faraday cup. Furthermore, the progress of tuning the FLUTE electron bunches for experiments is presented., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The storage ring Karlsruhe Research Accelerator (KARA) at KIT operates in a wide energy range from 0.5 to 2.5 GeV. Initially, the ring was designed to serve as a Light Source for synchrotron radiation facility ANKA. Since then different operation modes have been implemented at KARA: in particular, the double bend achromat (DBA) lattice with non-dispersive straight sections, the theoretical minimum emittance (TME) lattice with distributed dispersion, and different versions of low compaction factor optics with highly stretched dispersion function. Short bunches of a few ps pulse width are available at KARA. Low alpha optics have been tested and implemented in a wide operational range of the ring and are now routinely used at 1.3 GeV for studies of CSR-induced beam dynamics and THz bursting in the micro-bunching instability. Different non-linear effects, in particular, residual high order components of magnetic fields generated in insertion devices have been studied and cured. A new operation mode at high vertical tune implemented at KARA essentially improves beam performance during user operation as well as at low alpha regimes., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

FLUTE (Ferninfrarot Linac- Und Test-Experiment) is a compact versatile linear accelerator at the Karlsruhe Institute of Technology (KIT). It serves as a platform for a variety of accelerator studies as well as a source of strong ultra-short THz pulses for photon science. In the commissioning phase of the 7 MeV low energy section the electron bunches are used to test the different diagnostics systems installed in this section. An example is the split-ring-resonator-experiment. In this contribution we report on the commissioning status of the beam diagnostics and present first beam measurements at FLUTE., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The energy spread is an important beam dynamics parameter. It can be derived from measurements of the horizontal bunch size. At the KIT storage ring KARA a fast-gated camera is routinely used for horizontal bunch size measurements with a single-turn resolution for a limited time span. To overcome the limits of the current camera setup in respect to resolution and time span, a high-speed line array with up to 10 Mfps, the KALYPSO system, is foreseen as a successor. The KALYPSO versions range from 256-pixel to 1024-pixel and allow unlimited turn-by-turn imaging of a single bunch at KARA. We successfully tested such a system at our visible light diagnostics port and present first results in this contribution., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The microbunching instability is a longitudinal collective instability which occurs for short electron bunches in a storage ring above a certain threshold current. The instability leads to a charge modulation in the longitudinal phase space. The resulting substructures on the longitudinal bunch profile vary over time and lead to fluctuations in the emitted power of coherent synchrotron radiation (CSR). To study the underlying longitudinal dynamics on a turn-by-turn basis, the KIT storage ring KARA (Karlsruhe Research Accelerator) provides a wide variety of diagnostic systems. By synchronizing the single-shot electro-optical spectral decoding setup (longitudinal profile), the bunch-by-bunch THz detection systems (THz power) and the horizontal bunch size measurement setup (energy spread), three important properties of the bunch during this instability can be measured at every turn for long time scales. This allows a deep insight into the dynamics of the bunch under the influence of the microbunching instability. This contribution will discuss effects like the connection between the emitted CSR power and the deformations in the longitudinal bunch profile on the time scale of the instability., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The compact storage ring for accelerator research and technology (cSTART) is being designed and will be realized at the Institute for Beam Physics and Technology (IBPT) of the Karlsruhe Institute of Technology (KIT). One important goal of the project is to demonstrate injection and storage of a laser wakefield accelerator (LWFA) beam in a storage ring. As a first stage the compact linear accelerator FLUTE will serve as an injector of 50 MeV bunches to test the ring’s performance. A highly non-linear lattice of DBA-FDF type was studied extensively. The specific features of ring optics are reported. A special transfer line from FLUTE to cSTART including bunch compressor and non-linear elements is presented that maintains the ultra-short bunch length of FLUTE., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

At the storage ring KARA (Karlsruhe Research Accelerator) of the Karlsruhe Institute of Technology (KIT) we have installed a function for the RF phase modulation to the low-level RF system. By choosing proper conditions of the modulation, the electron distribution on the longitudinal phase space can be changed in a large range. There are several applications of this longitudinal manipulation to the accelerator operation: an improvement of the beam lifetime and suppression of collective instabilities. We have performed tracking simulations for the longitudinal beam manipulation by the RF phase modulation. The results have implied that the longitudinal phase space distribution strongly depends on the modulation frequency. We have also performed experiments, which aimed at improving the beam lifetime in 2.5 GeV KARA multi-bunch operations. In this contribution, the low-level RF system at KARA, the simulation and experimental results under the RF phase modulation will be presented. As one of the options of the modulation, we consider manipulation of the internal fine structure in the longitudinal phase space by the modulation., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

Short electron bunches in a storage ring are subject to complex longitudinal dynamics due to self-interaction with their own CSR. Above a particular threshold current, this leads to the formation of dynamically changing micro-structures within the bunch, generally known as the micro-bunching instability. The longitudinal dynamics of this phenomenon can be simulated by solving the Vlasov-Fokker-Planck equation, where the CSR self-interaction can be added as a perturbation to the Hamiltonian. This contribution particularly focuses on the comprehension of synchrotron motion in the micro-bunching instability and how it relates to the formation of the occurring micro-structures. Therefore, we adopt the perspective of a single particle and comment on its implications for collective motion. We explicitly show how the shape of the parallel plates CSR wake potential breaks homogeneity in longitudinal phase space and propose a quadrupole-like mode as potential seeding mechanism of the micro-bunching instability. The gained insights are verified using the passive particle tracking method of the Vlasov-Fokker-Planck solver Inovesa., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The operation of ring-based synchrotron light sources with short electron bunches increases the emission of coherent synchrotron radiation (CSR) in the THz frequency range. However, the micro-bunching instability resulting from self-interaction of the bunch with its own radiation field limits stable operation with constant intensity of CSR emission to a particular threshold current. Above this threshold, the longitudinal charge distribution and thus the emitted radiation vary rapidly and continuously. Therefore, a fast and adaptive feedback system is the appropriate approach to stabilize the dynamics and to overcome the limitations given by the instability. In this contribution, we discuss first efforts towards a longitudinal feedback design that acts on the RF system of the KIT storage ring KARA (Karlsruhe Research Accelerator) and aims for stabilization of the emitted THz radiation. Our approach is based on methods of adaptive control that were developed in the field of reinforcement learning and have seen great success in other fields of research over the past decade. We motivate this particular approach and comment on different aspects of its implementation., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

Photon science research at accelerators is influenced radically by the developments of sensor and readout technologies for imaging. These technologies enable a wide range of applications in beam diagnostics, tomography and spectroscopy. The repetition rate of commercially available linear array detectors is a limiting factor for the emerging synchrotron applications. To overcome these limitations, KALYPSO(Karlsruhe Linear arraY detector for MHz rePetition rateSpectrOscopy), an ultra-fast and wide-field of view linear array detector operating at several mega-frames per second(Mfps), has been developed. A silicon micro-strip sensor is connected to custom cutting-edge front end ASICs to achieve unprecedented frame rate in continuous readout mode. In this contribution, the third generation of KALYPSO will be presented., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

THz streaking with split ring resonators (SRR) promise ultra-high (sub-femtosecond) temporal resolution even for relativistic electron bunches. A proof-of-principle experiment in collaboration between the University of Bern, the Paul Scherrer Institute (PSI) and the Karlsruhe Institute of Technology (KIT) is currently prepared at the FLUTE facility (Ferninfrarot Linac und Test Experiment) at KIT. Most of the critical components have been designed, tested and set-up in the 7 MeV diagnostics part of FLUTE. In this contribution we will present an update on the experimental set-up and report on SRR configurations which have been optimized for highest THz deflection, while simultaneously accounting for the restrictions of the manufacturing process. Test measurements characterizing the SRR samples and the THz source, which has been matched to the FLUTE gun laser, will also be presented., Proceedings of the 6th Int. Beam Instrumentation Conf., IBIC2017, Grand Rapids, MI, USA

The first phase of FLUTE, a new linac based test facility and THz source is currently being commissioned at the Karlsruhe Institute of Technology (KIT). It consist of an RF photo gun and a traveling wave linac accelerating electrons to beam energies of 40 to 50 MeV. The control system is based on a virtualized infrastructure running Ubuntu Linux and Linux KVM. As base for the SCADA system we use EPICS 3.15 with Control System Studio (CSS) for the GUI. The long term data storage is provided by a Cassandra NoSQL database. This contribution will present the architecture and the current status of the FLUTE control system., Proceedings of the 12th Int. Workshop on Emerging Technologies and Scientific Facilities Controls, PCaPAC2018, Hsinchu, Taiwan

Recently, a new setup for measuring the beam energy spread has been commissioned at the ANKA storage ring at the Karlsruhe Institute of Technology. This setup is based on a fast-gated intensified camera and detects the horizontal profiles of individual bunches in a multi-bunch environment on a single-turn base. As the radiation source point is located in a dispersive section of the storage ring, this allows time-resolved studies of the energy spread. These studies are of particular interest in the framework of short-bunch beam dynamics and the characterization of instabilities. The system is fully synchronized to other beam diagnostics devices allocated in various places along the storage ring, such as the single-shot electro-optical spectral decoding setup or the turn-by-turn terahertz detection systems. Here we discuss the results of the synchronous measurements with the various systems with special emphasis on the energy spread studies., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

The Karlsruhe Institute of technology operates the 2.5 GeV electron storage ring ANKA as an accelerator test facility and synchrotron radiation source. A superconducting wiggler is installed in a short straight section of the ring where vertical beta-function is large (13 m). The life time of the electron beam was reduced from 15 to 12 hours at a high field level of the wiggler (2.5 T) even though the coherent shift of vertical tune was compensated locally. Computer simulations show the non-linear nature of the effect. The ANKA storage ring operates with strong sextupoles at a positive chromaticity of +2/+6. Even residual octupole components of the wiggler field, set at the tolerance limit of fabrication conditions, could reduce the dynamic aperture for off-momentum particles providing the betatron tune is located in the vicinity of a weak octupole resonance and the chromaticity is high. Also the vertical betatron tune is close to the sextupole resonance Qy=8/3. Large resonance stop-band and proximity of sextupole resonance affect the life time as well. Betatron tunes of ANKA have been shifted away of suspected high-order resonances and beam life time was essentially improved., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

Combining a circular storage ring and a laser wakefield accelerator (LWFA) might be the basis for future compact light sources and advancing user facilities to different commercial applications. Meanwhile the post-LWFA beam is not directly suitable for storage and accumulation in conventional storage rings. New generation rings with adapted features are required. Different geometries and ring lattices of very large-acceptance compact storage ring operating between 50 to 500 MeV energy range were studied. The main objective was to create a model suitable to store the post-LWFA beam with a wide momentum spread (2% to3%) and ultra-short electron bunches of fs range. The DBA-FDF lattice with relaxed settings, split elements and optimized parameters allows to open the dynamic aperture up to 20 mm while dispersion is limited and sextupole strength is high. The proposed machine model could be a basis for further, more detailed design studies., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

A linear beam transport system, experimentally tested at the Laser Wakefield Accelerator in Jena, Germany, has been carefully analyzed in order to gain a deeper understanding of the experimental results and to develop experimental strategies for the future. This analysis encompassed a detailed characterization of the focusing magnets and an investigation of the effects of source parameters as well as magnet and alignment errors on the observables accessible in the experiment. A dedicated tracking tool was developed for these investigations. In this contribution we review the main results of these studies., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

At the ANKA synchrotron radiation facility measurements in the microwave range (~10 to 12 GHz) employing a LNB (Low Noise Block), which is the receiving part of a Satellite-TV system, have been carried out. Experiments showed that the observed signal depends on the length of the electron bunches. Furthermore the temporal shape of the microwave signal depends on the detector's position along the accelerator. Due the LNB antenna's sensitivity to polarisation it was also possible to measure the polarisation along the several ns long signal, revealing polarised and non-polarised regions. This paper describes the experimental setup and summarises the observations of the systematic studies performed with the LNB system., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

Time-resolved electron diagnostics with ultra-high temporal resolution is increasingly required by the state-of-the-art accelerators. Strong terahertz (THz) fields, excited in a split ring resonator (SRR), have been recently proposed to streak electron bunches for their temporal characterisation. Thanks to the high amplitude and frequency of the THz field, temporal resolution down to the sub-femtosecond range can be expected. We are planning a proof-of-principle experiment of the SRR time-resolved diagnostics at the accelerator test-facility FLUTE (Ferninfrarot Linac und Test Experiment) at the Karlsruhe Institute of Technology. The design of the experimental chamber has been finished and integrated into the design layout of the FLUTE accelerator. Beam dynamics simulations have been conducted to investigate and optimise the performance of the SRR diagnostics. In this paper, we present the design layout of the experimental setup and discuss the simulation results for the optimised parameters of the accelerator and the SRR structure., Proceedings of the 5th Int. Beam Instrumentation Conf., IBIC2016, Barcelona, Spain

The test facility and synchrotron light source ANKA at the Karlsruhe Institute of Technology (KIT) operates in the energy range from 0.5 to 2.5 GeV and can generate brilliant coherent synchrotron radiation (CSR) in the THz range employing a dedicated bunch length-reducing optic at 1.3 GeV beam energy. The high degree of spatial compression leads to complex longitudinal dynamics and to time evolving sub-structures in the longitudinal phase space of the electron bunches. The results of the micro-bunching instability are time-dependent fluctuations and strong bursts in the radiated THz power. To study these fluctuations in the emitted THz radiation simultaneously for each individual bunch in a multi-bunch environment, fast THz detectors are combined with KAPTURE, the dedicated KArlsruhe Pulse Taking and Ultrafast Readout Electronics system, developed at KIT. In this contribution we present measurements conducted to study possible multi-bunch effects on the characteristic bursting behavior of the micro-bunch instability., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

Kurzperiodische Undulatoren mit hohen Magnetfeldamplituden sind wesentliche Komponenten für die Erzeugung von brillantem kohärentem Licht mit Wellenlängen bis in den Röntgenbereich in kompakten Lichtquellen, wie beispielsweise in Synchrotrons oder Freie-Elektronen-Lasern (FELs). Die Kompaktheit sollte mit einer kleinen Stellfläche und damit relativ niedrigen Betriebsenergien einhergehen; beides hat geringere Investitions- und Betriebskosten zur Konsequenz. Auf der anderen Seite des Energiespektrums benötigen künftige Leptonen-Collider wie CLIC oder FCC-ee Dämpfungswiggler mit hohen Magnetfeldamplituden für die Erzeugung von Strahlen mit geringer Emittanz, um die Kollisionsluminosität zu erhöhen. Der Bedarf an hohen Magnetfeldern für solche Insertion Devices (IDs) hat bereits die Weiterentwicklung von Wigglern und Undulatoren basierend auf Permanentmagneten zu supraleitenden IDs angeregt. Hier stößt der Stand der Technik Nb-Ti schon an seine Leistungsgrenzen und wird üblicherweise bei 4.2 K oder darunter betrieben, was Betrieb und Kühlung komplex und teuer macht. Daher könnten die oben beschriebenen Beschleuniger von der Verwendung von Hochtemperatursupraleitern (HTS) wie $\textit{Re}$BCO (Seltene Erden mit Barium-Kupferoxid) profitieren: Einerseits ermöglichen HTS Magnetfeldamplituden im Bereich von 2 T oder höher für kurze Undulatorperioden von 15 mm oder kleiner mit Magnetspalten von 6 mm bei 4.2 K oder niedriger; dies kann auch auf längere Wigglerperioden, wie z.B. 50 mm, skaliert werden. Andererseits wird durch größere Temperaturspannen der Betrieb bei höheren Temperaturen wie 20 K oder höher möglich, was die kryogenen Anforderungen lockern und somit die Kosten senken kann. Im Rahmen dieser Dissertation wurde die Anwendung von $\textit{Re}$BCO in Form von beschichteten bandförmigen Supraleitern für den Bau von supraleitenden Undulatoren für kompakte FELs für die drei gängigsten Spulengeometrien (vertikale und horizontale Renn-bahnen, sowie ein helischer Undulator) untersucht. Der Parameterraum wurde in Bezug auf die Undulatorperiodenlänge $\lambda_\text{u}$, die Amplitude der magnetischen Flussdichte und den Undulatorspalt mittels elektromagnetischen Berechnungen untersucht. Dabei ergab sich ein Betriebsbereich von $\lambda_\text{u} \leq $ 20 mm, in welchem die Anwendung von $\textit{Re}$BCO der derzeitigen Nb-Ti-Technologie signifikant überlegen sein kann. Infolgedessen wurden modulare Spulenmodelle für alle drei Geometrien mit einem $\lambda_\text{u}$ von 13 mm entworfen und ihre elektromagnetische Leistung sowie mechanische Strapazierfähigkeit untersucht. Um die hohen technischen Stromdichten von 2 kA/mm$^2$ oder mehr zu handhaben, wurde der Ansatz einer nicht isolierten (NI) Wicklung gewählt. In der Folge wird in dieser Dissertation das technische Design einer vertikalen Rennbahn-(VR-)spule und das nach Wissensstand des Autors allererste Design eines mit HTS Band gewickelten helischen Undulators präsentiert. Wichtige Eigenschaften von beschichteten $\textit{Re}$BCO-Supraleiterbänder für die Spulenherstellung wurden durch Biege- und Heizexperimente sowie Messungen von kritischen Strömen in Eigenfeldern und externen Feldern bei 77 K analysiert. Darüber hinaus wurden Wickel- und Verbindungstechniken für die Spulenherstellung entwickelt. Drei VR-Prototypspulen wurden gefertigt und erfolgreich bei 77 K in Flüssigstickstoff bestromt, wobei die Machbarkeit und Stabilität des NI-Spulendesigns durch den Betrieb mit bis zu 300% des kritischen Stroms nachgewiesen wurde. Bestromungstests von zwei VR-Spulen bei 4.2 K zeigten einen sicheren Betrieb bei hohen technischen Stromdichten von 2.3 kA/mm$^2$ und erzeugten Magnetfelder von bis zu 1.5 T in 3.5 mm Distanz zu den magnetischen Eisenpolen. Die Stabilität der getesteten VR-Spulen wurde nochmals durch den Betrieb bei und jenseits von 3.6 kA/mm$^2$ mit erzeugten Magnetfeldern im Bereich von 2 T aufgezeigt. Darüber hinaus wurde der allererste helische HTS Undulator-Demonstrator basierend auf Wicklungen mit beschichteten $\textit{Re}$BCO-Supraleiterbändern in Form eines Kurzmodells mit fünf Perioden gefertigt. Die ersten Bestromungstests bei 77 K haben das Prinzip und die Machbarkeit dieses extrem kompakten und hochfeldfähigen Undulators erfolgreich bewiesen. Zusammenfassend wurde das Potential von HTS für supraleitende Undulatoren erfolgreich demonstriert, ebenso wie die Machbarkeit, solche Designs mit modularen Spulen zu bauen und zu betreiben.

Die Erzeugung kohärenter Strahlung in einem herkömmlichen planaren Undulator mit einem transversal homogenen und longitudinal periodischen Magnetfeld erfordert Elektronenstrahlen mit geringer Energieverteilungsbreite. Im Allgemeinen werden solche Elektronenstrahlen in Großanlagen wie Linearbeschleunigern und Speicherringen generiert. Ein Laser-Plasma-Elektronenbeschleuniger, der auf dem Mechanismus der Laser-Wake\-field-Beschleunigung (LWFA) basiert, kann Elektronenstrahlen auf eine Energie von mehreren hundert MeV in einem sehr kurzen Beschleunigungsmedium von einigen Millimetern bis Zentimetern Länge beschleunigen. Allerdings sind die Elektronenstrahleigenschaften aufgrund der Plasmainstabilität im Medium deutlich schlechter als bei konventionellen Elektronenbeschleunigern. Insbesondere die erhöhte Energieeverteilungsbreite, Strahldivergenz und Richtungsinstabilität führen zu inkohärenter Strahlung in einem planaren Undulator. Der Transversalgradient-Undulator (TGU) mit transversal abnehmender Magnetfeldamplitude ist eine Alternative, um den Nachteil der LWFA-Elektronenstrahlen mit der großen Energieverteilungsbreite zu überwinden. Ein TGU, der auf modernen supraleitenden Technologien für extrem starke Magnetfelder basiert, wurde am am Karlsruher Institut für Technologie (KIT) entwickelt, um experimentell zu zeigen, dass das TGU-Schema ein gangbarer Weg ist, mit LWFA-erzeugten Elektronenpaketen auch Freie-Elektronen-Laser (FEL) -Verstärkung zu erreichen. Die vorliegende Arbeit beschreibt die magnetische Charakterisierung des supraleitenden TGU, dessen Design für einen kompakten LWFA-getriebenen FEL entwickelt wurde. Magnetische Leistungstests und Quenchstudien mit dem TGU wurden bei einer Temperatur von \SI{4,3}{\kelvin} bis \SI{4,4}{K} in dessen eigenem Kryostaten durchgeführt. Die TGU-Spulen erreichten den supraleitenden Zustand und wurden erfolgreich mit bis zu \SI{850}{A} betrieben. Die senkrechte Komponente des Magnetfelds in der Mittelebene des TGU wurden mit einem System sieben äquidistanter Hall-Sensoren bei Temperaturen von \SI{5}{K} bis \SI{6}{K} und daher bei relativ kleinen Stromstärken von \SI{10}{A} bis \SI{50}{A} erfasst. Die Magnetfelder unter nominalen Betriebsbedingungen (\SI{750}{A}) konnten jedoch aufgrund ihrer proportionalen Abhängigkeit vom Strom ermittelt werden. Darüber hinaus wurden die gemessenen Magnetfeldkarten verwendet, um die erwarteten Strahlungseigenschaften durch Simulationen mit dem Code WAVE zu bewerten. Die schmale Bandbreite der Undulatorstrahlung wurde bestätigt und die spektrale Dispersion des Elektronenstrahls, die zur Anpassung an den transversalen Feldgradienten des TGU erforderlich ist, wurde bestimmt. Die Ergebnisse der WAVE-Simulationen und die Auswirkungen der bei den Messungen beobachteten Feldfehler auf die Strahlung werden in dieser Arbeit diskutiert.

Several novel diagnostic systems based on the detection of coherent THz radiation are presented. The investigation of the photon beam properties allow for bunch-by-bunch and turn-by-turn diagnostics of the emitting electron bunches in the accelerator. It is used for time-resolved studies of the micro-bunching instability. Accompanying simulations with Inovesa show a good agreement with the measurement which enhances the knowledge of the physics behind the micro-bunching instability.