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The self-interaction of short electron bunches with their own radiation field can have a significant impact on the longitudinal beam dynamics in a storage ring. While higher bunch currents increase the power of the emitted CSR which can be provided to dedicated experiments, it simultaneously amplifies the strength of the self-interaction. Eventually, this leads to the formation of dynamically changing micro-structures within the bunch and thus fluctuating CSR emission, a phenomenon that is generally known as micro-bunching or micro-wave instability. The underlying longitudinal dynamics can be simulated by solving the VFP equation, where the CSR self-interaction can be added as a perturbation to the Hamiltonian. In this contribution, we focus on the perturbation of the synchrotron motion that is caused by introducing this additional wake field. Therefore, we adopt the perspective of a single particle and eventually comment on its implications for collective motion. We explicitly show how the shape of the parallel plates CSR wake potential breaks homogeneity in the longitudinal phase space and propose a quadrupole-like mode as potential seeding mechanism of the micro-bunching instability. Moreover, we consider synchrotron motion above the instability threshold and thereby motivate an approach to control of the occurring micro-bunching dynamics. Using dynamically adjusted RF amplitude modulations we can directly address the continuous CSR-induced perturbation at the timescale of its occurrence, which allows for substantial control over the longitudinal charge distribution. While the approach is not limited to this particular application, we demonstrate how this can significantly mitigate the micro-bunching dynamics directly above the instability threshold. The gained insights are supported and verified using the VFP solver Inovesa and put into context with measurements at KARA.

In electron storage rings, it is possible to increase the electron bunch length by applying a phase modulation on the radio frequency accelerating field by choosing appropriate parameters for the modulation. Such a bunch lengthening effect improves beam parameters such as the beam lifetime, which can help us to get better beam stability. The dependence of the bunch lengthening on the modulation frequency, the so-called detuning property, tends to have a peak with asymmetric slopes around it. The modulation amplitude and the beam current also affect the properties of the detuning condition of such bunch lengthening. We have investigated the detuning property with systematic measurements at the electron storage ring KARA. The experimental results agree with the theoretical model and the simulation results., Comment: To be submitted to Physical Review Accelerators and Beams

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 development of fast detection methods for comprehensive monitoring of electron bunches is a prerequisite to gain comprehensive control over the synchrontron emission in storage rings with their MHz repetition rate. Here, we present a proof-of-principle experiment with at detailed description of our implementation to detect the longitudinal electron bunch profiles via single-shot, near-field electro-optical sampling at the Karlsruhe Research Accelerator (KARA). Our experiment is equipped with an ultra-fast line array camera providing a high-throughput MHz data stream. We characterize statistical properties of the obtained data set and give a detailed description for the data processing as well as for the calculation of the charge density profiles, which where measured in the short-bunch operation mode of KARA. Finally, we discuss properties of the bunch profile dynamics on a coarse-grained level on the example of the well-known synchrotron oscillation., Comment: 8 pages, 5 figures

At the KIT storage ring KARA (KArlsruhe Research Accelerator), the momentum compaction factor can be reduced leading to natural bunch lengths in the ps range. Due to the high degree of longitudinal compression the micro-bunching instability arises. During this longitudinal instability the bunches emit bursts of intense coherent synchrotron radiation in the THz frequency range caused by the complex longitudinal dynamics. The temporal pattern of the emitted bursts depends on given machine parameters, like momentum compaction factor, acceleration voltage, and damping time. In this paper the influence of the damping time is studied by utilizing the CLIC damping wiggler prototype installed in KARA as well as by simulations using the Vlasov-Fokker-Planck solver Inovesa., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

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 ANKA storage ring of the Karlsruhe Institute of Technology (KIT) operates in the energy range from 0.5 to 2.5 GeV and generates brilliant coherent synchrotron radiation in the THz range with a dedicated bunch length reducing optic. The producing of radiation in the so-called THz-gap is challenging, but this intense THz radiation is very attractive for certain user experiments. The high degree of compression in this so-called low-alpha optics leads to a complex longitudinal dynamics of the electron bunches. The resulting micro-bunching instability leads to time dependent fluctuations and strong bursts in the radiated THz power. The study of these fluctuations in the emitted THz radiation provides insight into the longitudinal beam dynamics. Fast THz detectors combined with KAPTURE, the dedicated KArlsruhe Pulstaking and Ultrafast Readout Electronics system developed at KIT, allow the simultaneous measurement of the radiated THz intensity for each bunch individually in a multi-bunch environment. This contribution gives an overview of the first experience gained using this setup as an online diagnostics tool., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

Coherent ultrashort THz pulses induced by a laser-electron interaction are routinely produced and observed at DELTA, a 1.5-GeV synchrotron light source operated by the TU Dortmund University. The turn-by-turn evolution of the radiation spectrum is known to shift to the sub-THz regime after the initial laser-electron interaction. Recently, an ultrafast YBCO-based THz detector has been permanently installed and a Schottky diode has been tested at the THz beamline. Measurements with these detectors showing the temporal evolution of the coherent signals after several revolutions are presented. Furthermore, the concept of a recently designed Fourier-transform spectrometer optimized for the sub-THz region is shown., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

Interferometry is the quasi-standard for spectral measurements in the THz- and IR-range. The frequency resolution, however, is limited by the travel range of the interferometer mirrors. Therefore, a resolution in the low megahertz range would require interferometer arms of about 100 m. As an alternative, heterodyne measurements provide a resolution in the Hertz range, an improvement of 6 orders of magnitude. Here we present measurements done at ANKA with a VDI WR3.4SAX, a mixer that can be tuned to frequencies from 220 GHz to 330 GHz and we show how the bunch filling pattern influences the amplitude of specific frequencies., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

ANKA is the first storage ring worldwide with a near-field single-shot electro-optical bunch profile monitor. Previously, the method of electro-optical spectral decoding (EOSD) was employed to record single-shot longitudinal bunch profiles. The readout rate of the required spectrometer detector system limited the acquisition rate to a few Hz and thus did not allow us to study the evolution of the longitudinal bunch shape on a turn-by-turn basis. The setup at ANKA was combined with the novel method of photonic time-stretch* for which the modulated laser pulse is not detected in the spectral domain, but stretched to a few nanoseconds by a long fiber and, subsequently, detected in the time domain. This method allows the sampling of the longitudinal bunch profile on a turn-by-turn basis for several milliseconds, uninterrupted. Here, we present first results obtained with the photonic time-stretch method in the near-field at the ANKA storage ring., Proceedings of the 4th International Beam Instrumentation Conference, IBIC2015, Melbourne, Australia

Micro-bunching instabilities occur at synchrotron light sources when the particle density rises due to compression of the electron bunches. They lead to powerful bursts of coherent synchrotron radiation (CSR) in the THz range at the cost of very unstable intensity and spectral properties, highly fluctuating on a millisecond time scale. For interferometry this changing source demands a long averaging time to achieve a reasonably high signal-to-noise ratio or balancing by the use of an additional reference detector. In this study we present measurements taken by a Martin-Puplett-interferometer in the bursting regime with ultra-fast THz-detectors., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

High-Tc thin-film YBa2Cu3O7-x (YBCO) detectors were deployed for the real-time observation of Coherent Synchrotron Radiation (CSR). Due to enhanced fabrication techniques enabling the patterning of sub-μm sized detector areas responsivity values as high as 1V/pJ for pulsed THz excitations have been achieved at the ANKA synchrotron facility at the Karlsruhe Institute of Technology (KIT). Response of the detectors is linear over the whole dynamic range of the IR1 beamline. Combining the picosecond scaled response mechanism of the high-temperature superconductor YBa2Cu3O7-x (YBCO) to THz excitations with broad-band readout a temporal resolution of 15 ps full width at half maximum (FWHM) was reached. Real-time resolution of CSR single shots was observed at ANKA and UVSOR-III, the synchrotron facility of the Institute of Molecular Science in Okazaki, Japan., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

Terahertz diagnostics* for investigating the properties of electron and photon beams**, especially the investigation of electron bunch instabilities, accompanied by terahertz photon bursts is increasingly employed to monitor and investigate electron bunch dynamics***. Recent advances in information and communications technology promise compact sensors based on telecom and thus industry standards. We present potential applications of such technology concepts for accelerators, including a miniature probe for electro-optical sampling, which could be employed for electron bunch electrical near-field studies, and laser sources with widely tunable pulse repetition rates adaptable for pulsed diagnostics***., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

ANKA, the synchrotron light source of the Karlsruhe Institute of Technology (KIT), is the first storage ring with a near-field single-shot electro-optical (EO) bunch profile monitor inside its vacuum chamber. Using the method of electro-optical spectral decoding (EOSD), the current setup made it possible to study longitudinal beam dynamics (e.g. microbunching) occurring during ANKA's low-alpha-operation with sub-ps resolution (granularity). However, the setup induces strong wake-fields spanning the distance between consecutive bunches which cause heat load to the in-vacuum setup for high beam currents. This heat load in turn leads to a laser misalignment thus preventing measurements during multi-bunch operation. Fortunately, the EOSD setup also allows us to directly study these wake-fields so simulation results can be compared to measurement data. This paper reviews possible changes of the setup's geometry with respect to a reduction of the wakefield effects., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

We present the effects of the filling pattern structure in multi-bunch mode on the beam spectrum. This effects can be seen by all detectors whose resolution is better than the RF frequency, ranging from stripline and Schottky measurements to high resolution synchrotron radiation measurements. Our heterodyne measurements of the emitted coherent synchrotron radiation at 270 GHz reveal discrete frequency harmonics around the 100 000th revolution harmonic of ANKA, the synchrotron radiation facility in Karlsruhe, Germany. Significant effects of bunch spacing, gaps between bunch trains and variations in individual bunch currents on the emitted CSR spectrum are described by theory and supported by observations., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

The test facility and synchrotron radiation source ANKA at the Karlsruhe Institute of Technology (KIT) in Karlsruhe, Germany, can be operated in a short-bunch mode. Above a threshold current, the high charge density leads to microwave instabilities and the formation of sub-structures. These time-varying sub-structures on bunches of picosecond duration lead to the observation of bursting coherent synchrotron radiation (CSR) in the terahertz (THz) frequency range. The spectral information in this range contains valuable information about the bunch length, shape and sub-structures. We present recent measurements of a spectrometer setup that consists of 4 ultra-fast THz detectors, sensitive in different frequency bands, combined with the KAPTURE readout system developed at KIT for studies requiring high data throughput. This setup allows to record continuously the spectral information on a bunch-by-bunch and turn-by-turn basis. This contribution describes the potential of time-resolved spectral measurements of the short-bunch beam dynamics., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

For electron accelerators, electro-optical methods in the near-field have been shown to be a powerful tool to detect longitudinal bunch profiles. In 2013, we demonstrated for the first time, electro-optical bunch profile measurements in a storage ring at the accelerator test facility and synchrotron light source ANKA at the Karlsruhe Institute of Technology (KIT). To study possible bunch-bunch interactions and its effects on the longitudinal dynamics, these measurements need to be performed in a multi-bunch environment. Up to now, due to long-ranging wake-fields the electro-optical monitoring was limited to single-bunch operation. Here, we present our new in-vacuum setup to overcome this limitation. First measurements show reduced wake-fields in particular around 2 ns, where the subsequent bunch can occur in a multi-bunch environment at ANKA., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

ANKA is the first storage ring in the world with a near-field single-shot electro-optical (EO) bunch profile monitor. The method of electro-optical spectral decoding (EOSD) uses the Pockels effect to modulate the longitudinal electron bunch profile onto a long, chirped laser pulse passing through an EO crystal. The laser pulse is then analyzed with a single-shot spectrometer and from the spectral modulation, the temporal modulation can be extracted. The setup has a sub-ps resolution (granularity) and can measure down to bunch lengths of 1.5 ps RMS for bunch charges as low as 30 pC. With this setup it is possible to study longitudinal beam dynamics (e. g. microbunching) occurring during ANKA's low-alpha-operation, an operation mode with compressed bunches to generate coherent synchrotron radiation in the THz range. In addition to measuring the longitudinal bunch profile, long-ranging wake-fields trailing the electron bunch can also be studied, revealing bunch-bunch interactions., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

At ANKA, the Karlsruhe synchrotron radiation source, the so called short bunch-length operation mode allows the reduction of the bunch length down to a few picoseconds. The micro-bunching instability resulting from the high degree of longitudinal compression leads to fluctuations in the emitted intensity in the THz regime, referred to as bursting. For extremely compressed bunches at ANKA bursting also occurs, in a certain current range, below the main bursting threshold. This contribution shows measurements of this short bunch-length bursting and makes first comparisons with theory., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

A dedicated optics with a low momentum compaction factor is used at the ANKA storage ring to reduce the bunch length to generate coherent synchrotron radiation (CSR). A double sweep streak camera is employed to determine the bunch length and shape for different optics and as a function of the beam current. Measurements of the longitudinal bunch profile have been performed for many different momentum compaction factors and various bunch currents. This paper describes the set up of the streak camera experiments and compares the measured bunch lengths to theoretical expectations., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

The commissioning of a new real-time and high-accuracy data acquisition system suitable for recording individual ultra-short coherent pulses detected by fast terahertz detectors will be presented. The system is able to monitor turn-by-turn all buckets in streaming mode. The main board consists of a direct sampling board operating with a minimum sampling time of 3 psec and a time jitter less than 1.7 psec. The very low noise layout design combined with a wide dynamic range and bandwidth of the analog front-end allows to sample pulse signals generated by various GHz/THz detectors, like NbN and YBCO superconductor film detectors or zero biased Schottky Diode detectors. The digitized data is transmitted to the DAQ system by an FPGA readout board with a data transfer rate of 4 GByte/s. The setup is accomplished by a real-time data processing unit based on high-end graphics processors (GPUs) for on-line analysis of the frequency behaviour of the coherent synchrotron emissions. The system has been successfully used to study the beam properties of the ANKA synchrotron radiation source located at the Karlsruhe Institute of Technology and operating in the energy range between 0.5-2.5 GeV, Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

For the transport and matching of electrons generated by a Laser Wakefield Accelerator (LWFA) a beam transport system with strong focusing magnets and a compact design is required. For the realization of such a beam transport system at the LWFA in Jena, Germany, two small series of inexpensive, modular quadrupoles were designed and built. The quadrupoles are iron-dominated electromagnets in order to keep the transport system adaptable to different energies and target parameters. To achieve the required field strength it was necessary to choose a small magnetic aperture. Therefore the magnets were designed for in-vacuum use with water-cooled coils. In this contribution the design, the realization and first field measurements of these quadrupoles are presented., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

Synchrotron radiation in the visible light range is a versatile diagnostics tool for accelerator studies. At the ANKA storage ring of the Karlsruhe Institute of Technology (KIT), we have a dedicated visible light diagnostics beamline and two additional beam ports close to the radiation's source point. The visible light diagnostics beamline hosts a time-correlated single-photon-counting unit to measure the bunch filling pattern and a streak camera for longitudinal diagnostics. Recently, the beamline has been extended with a fast-gated intensified camera to study transverse instabilities. The synchrotron light monitor ports were previously used for direct source imaging. Due to the diffraction limit the vertical beam size could not be resolved. One of the two ports has recently been equipped with a double-slit to allow for interferometric measurements of the vertical beam size. In this paper we give an overview of the different setup modifications and present first results., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

The ANKA storage ring can generate brilliant coherent synchrotron radiation (CSR) in the THz range due to a dedi- cated low-αc -optics with reduced bunch lengths. At higher electron currents the radiation is not stable, but occurs in powerful bursts caused by micro-bunching instabilities. This intense THz radiation is very attractive for users. However, the reproducibility of the experimental conditions is very low due to those power fluctuations. Systematic studies of bursting CSR in multi-bunch operation were performed with fast THz detectors at ANKA using a dedicated, ultra-fast DAQ-FPGA board. The technique and preliminary results of these studies are presented in this paper., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

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

A new, dedicated accelerator research facility SINBAD (Short INnovative Bunches and Accelerators at DESY) is proposed. This facility is aimed at promoting two major goals: (1) Short electron bunches for ultra-fast science. (2) Construction of a plasma accelerator module with useable beam quality. Research and development on these topics is presently ongoing at various places at DESY, as add-on experiments at operational facilities. The two research goals are intimately connected: short bunches and precise femtosecond timing are requirements for developing a plasma accelerator module. The scientific case of a dedicated facility for accelerator research at DESY is discussed. Further options are mentioned, like the use of a 1 GeV beam from Linac2 for FEL studies and the setup of an attosecond radiation source with advanced technology. The presently planned conversion of the DORIS storage ring and its central halls into the SINBAD facility is described. The available space will allow setting up several independent experiments with a cost-effective use of the same infrastructure. National and international contributions and proposals can be envisaged., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany