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In the scope of the HERO ERC project, we are implementing a laser-based seeding scheme at the SwissFEL soft X-ray Athos beamline to generate fully coherent X-ray FEL pulses. With this perspective, we designed and built a new laser facility. It consists of a terawatt-class, femtosecond laser system based on Titanium Sapphire technology with wavelength tuning capability, an optical transfer line as well as a launching optical setup and diagnostics to spatially and temporally overlap the laser and the electron bunch inside the modulator, where the seeding process occurs. We present an overview of the facility with details of the laser performance as well as first commissioning results with the electron beam.

In order to improve the brightness and coherence of the soft x-ray FEL line of SwissFEL (Athos), components for an Echo Enabled Harmonic Generation (EEHG) scheme are currently in preparation. The first components have been installed to allow first ESASE operation test in Spring 2022. This first stage consists in a 10 mJ class seed laser, a U200 modulator with individual control of each half period and a four electromagnets dipole chicane (R56 < 800 um). The large magnetic chicane and the second modulator are still in preparation for an installation by end 2022. This paper will give a technical description of the different systems as well as preliminary results of the commissioning with beam.

The Hard X-ray FEL machine SwissFEL at the Paul Scherrer Institut in Switzerland is commissioned and transiting to user operation smoothly. FEL operation requires stringent requirements for the beam stability at the linac output, such as the electron bunch arrival time, peak current and beam energy. Among other things, a highly stable RF system is required to guarantee the beam stability. RF performance often dominates the overall performance and availability of FELs, and for this reason the SwissFEL RF system has been designed based on the state-of-the-art technologies that have enabled excellent RF stability, resulting in an arrival time jitter of ~10 fs rms and relative beam energy stability of 10⁻⁴ rms. This paper aims to provide an understanding of the peak performance of the RF systems and to highlight possible limitation currently faced, focusing on the S-, C- and X-Band systems., Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK

SwissFEL is a linear electron accelerator based, X-ray Free Electron Laser at the Paul Scherrer Institute, Switzerland. It is a user oriented facility capable of producing short, high brightness X-ray pulses covering the spectral range from 1 to 50 Å. SwissFEL is designed to run in two electron bunch mode in order to serve simultaneously two experimental beamline stations (hard and soft X-ray one) at its full repetition rate. Two closely spaced (28 ns) electron bunches are accelerated in one RF macro pulse up to 3 GeV. A high stability resonant kicker system and a Lambertson septum magnet are used to separate the bunches and to send them to their respective beamlines. With the advancement of the construction of the second beamline (Athos) the bunch-separation system was successfully commissioned. In order to confirm that the beam separation process is fully transparent a stability study of the electron beam and the free electron laser in the main beamline (Aramis) was done., Proceedings of the 39th Free Electron Laser Conference, FEL2019, Hamburg, Germany

The SwissFEL Aramis beamline provides hard X-ray FEL radiation down to 1 Angström with 5.8 GeV and short period, 15 mm, in-vacuum undulators (U15). To reach the maximum designed K-value of 1.8 the U15s have to be operated with vacuum gaps down to 3.0 mm. The thirteen-undulator modules are 4 m long and each of them is equipped with a pair of permanent magnet quadrupoles at the two ends, aligned magnetically to the undulator axis. Optical systems and dedicated photon diagnostics are used to check the alignment and improve the K-value calibration. In this talk the main steps of the undulator commissioning will be recalled and a systematic comparison between the magnetic results and the electron and photon based measurements will be reported to highlight achievements and open issues., Proceedings of the 39th Free Electron Laser Conference, FEL2019, Hamburg, Germany

Dielectric Laser Acceleration (DLA) achieves the high- est gradients among structure-based electron accelerators. The use of dielectrics increases the breakdown field limit, and thus the achievable gradient, by a factor of at least 10 in comparison to metals. Experimental demonstrations of DLA in 2013 led to the Accelerator on a Chip International Program (ACHIP), funded by the Gordon and Betty Moore Foundation. In ACHIP, our main goal is to build an acceler- ator on a silicon chip, which can accelerate electrons from below 100keV to above 1MeV with a gradient of at least 100MeV/m. For stable acceleration on the chip, magnet- only focusing techniques are insufficient to compensate the strong acceleration defocusing. Thus spatial harmonic and Alternating Phase Focusing (APF) laser-based focusing tech- niques have been developed. We have also developed the simplified symplectic tracking code DLAtrack6D, which makes use of the periodicity and applies only one kick per DLA cell, which is calculated by the Fourier coefficient of the synchronous spatial harmonic. Due to coupling, the Fourier coefficients of neighboring cells are not entirely independent and a field flatness optimization (similarly as in multi-cell cavities) needs to be performed. The simu- lation of the entire accelerator on a chip by a Particle In Cell (PIC) code is possible, but impractical for optimization purposes. Finally, we have also outlined the treatment of wake field effects in attosecond bunches in the grating within DLAtrack6D, where the wake function is computed by an external solver., Proceedings of the 13th Int. Computational Accelerator Physics Conf., ICAP2018, Key West, FL, USA

Parameter tuning is a notoriously time-consuming task in accelerator facilities. As tool for global optimization with noisy evaluations, Bayesian optimization was recently shown to outperform alternative methods. By learning a model of the underlying function using all available data, the next evaluation can be chosen carefully to find the optimum with as few steps as possible and without violating any safety constraints. However, the per-step computation time increases significantly with the number of parameters and the generality of the approach can lead to slow convergence on functions that are easier to optimize. To overcome these limitations, we divide the global problem into sequential subproblems that can be solved efficiently using safe Bayesian optimization. This allows us to trade off local and global convergence and to adapt to additional structure in the objective function. Further, we provide slice-plots of the function as user feedback during the optimization. We showcase how we use our algorithm to tune up the FEL output of SwissFEL with up to 40 parameters simultaneously, and reach convergence within reasonable tuning times in the order of 30 minutes (< 2000 steps)., FEL2019, Proceedings of the 39th International Free-Electron Laser Conference, ISBN:978-3-95450-210-3

The Accelerator on a Chip International Program (ACHIP) is an international collaboration, funded by the Gordon and Betty Moore Foundation, whose goal is to demonstrate that a laser-driven accelerator on a chip can be integrated to fully build an accelerator based on dielectric structures. PSI will provide access to the high brightness electron beam of SwissFEL to test structures, approaches and methods towards achieving the final goal of the project. In this contribution, we will describe the two interaction chambers installed on SwissFEL to perform the proof-of-principle experiments. In particular, we will present the positioning system for the samples, the magnets needed to focus the beam to sub-micrometer dimensions and the diagnostics to measure beam properties at the interaction point., Proceedings of the 38th Int. Free Electron Laser Conf., FEL2017, Santa Fe, NM, USA

High repetition rate diagnostics are required when detecting single-shot electro-optical (EO) bunch profiles. The KIT storage ring KARA (KArlsruhe Research Accelerator) is the first storage ring in the world that has a near-field EO bunch-profile monitor in operation. By imprinting longitudinal electron bunch profiles onto chirped laser pulses, single-shot detection is feasible. However, limitations of available detection systems are challenging: The constraints are either given by the repetition rate or the duration of the consecutive acquisitions. Two strategies can overcome these limitations: Based on the photonic time-stretch method, the ps laser pulses can be stretched to the ns range using km long fibers. The readout with a high-bandwidth oscilloscope then enables a single-shot detection at high repetition rates. The other strategy is the development of dedicated ultra-fast photodetector arrays allowing direct detection of the ps pulses at MHz repetition rates. We developed KALYPSO, a linear detector array with a DAQ allowing to record high data-rates over long time scales. Here, we present recent results of studies of the longitudinal electron bunch dynamics using KALYPSO., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

SwissFEL is a free electron laser user facility at the Paul Scherrer Institute in Villigen, Switzerland designed to provide FEL radiation at photon energies ranging from 0.2 to 12 keV. Beam commissioning of the hard x-ray line ARAMIS has started in October 2016 and lasing at 300 eV was achieved in May 2017. First pilot user experiments at photon energies ≥ 2 keV are foreseen for the end of 2017. This contribution comprehends commissioning results and first operational experience of various diagnostics systems, such as beam position monitors, charge and loss monitors as well as transverse profile measurements with screens, wire scanners and synchrotron radiation monitors. It also provides information about sliced beam parameters using a transverse deflector and shows first results from the BC-1 compression monitor and measurements with the electron bunch arrival time monitors., Proceedings of the 6th Int. Beam Instrumentation Conf., IBIC2017, Grand Rapids, MI, USA

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

Dual-grating Dielectric Laser-driven Accelerators (DLAs) are considered to be one of the most promising technologies to miniaturize future particle accelerators. Accelerating gradients in the GV/m range seem accessible and 690 MV/m has been demonstrated in fused silica structures. However, the increase in beam energy is limited by the short interaction length between the laser pulses and the electron bunch. In this contribution, a pulse-front-tilt operation for a laser beam is studied to extend the interaction length, resulting in a greater energy gain for a dual-grating DLA. The VSIM code is used to compare this new scheme with the commonly used approach of a normally incident laser beam and advantages are summarized., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

The acquisition rate of commercially available line array detectors is a bottleneck for beam diagnostics at high-repetition rate machines like synchrotron lightsources or FELs with a quasi-continuous or macro-pulse operation. In order to remove this bottleneck we have developed KALYPSO, an ultra-fast linear array detector operating at a frame-rate of up to 2.7 Mfps. The KALYPSO detector mounts InGaAs or Si linear array sensors to measure radiation in the near-infrared or visible spectrum. The FPGA-based read-out card can be connected to an external data acquisition system through a high-performance PCI-Express 3.0 data-link, allowing continuous data taking and real-time data analysis. The detector is fully synchronized with the timing system of the accelerator and other diagnostic instruments. The detector is currently installed at several accelerators: ANKA, the European XFEL and TELBE. We present the detector and the results obtained with Electro-Optical Spectral Decoding (EOSD) setups., Proceedings of the 5th Int. Beam Instrumentation Conf., IBIC2016, Barcelona, Spain

The ANKA storage ring offers different operation modes including the short-bunch mode with bunch lengths tuned down to a few picoseconds. This can lead to the occurrence of micro-bunching instabilities coupled to the emission of coherent synchrotron radiation (CSR) in so-called 'bursts'. To study this CSR instability we use several turn-by-turn enabled detector systems to synchronously measure both the THz signal as well as bunch profiles. The different detectors are placed at different locations around the storage ring. Here we discuss the experimental setup and calibration of the various systems' synchronisation., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

An electron energy measurement setup based on the detection of Compton backscattered photons, generated by laser light scattered off the relativistic electron beam, has been proposed and developed for operation at the ANKA storage ring of the Karlsruhe Institute of Technology (KIT). In contrast to conventional methods based on head-on collisions, the setup at ANKA is, for the first time, realized in a transverse configuration where the laser beam hits the electron beam at an angle of ~90°. This makes it possible to achieve a relatively low-cost and very compact setup since it only requires a small side-port instead of a straight section. This development could benefit storage rings with restricted space or where no straight sections are available, for example due to interferences with existing beamlines. The setup and the first measurement results are presented in the paper., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

ANKA, the synchrotron light source at Karlsruhe Institute of Technology (KIT), can be operated in different modes including the short bunch operation with bunch lengths compressed to a few picoseconds. In this mode, coherent synchrotron radiation (CSR) is emitted leading to beam instabilities. For gaining further insight into those processes, a setup based on a fast gated intensified camera was installed recently at the visible light diagnostics beamline of the ANKA storage ring. The experimental layout consists of an optical setup, which magnifies the image of the beam in the horizontal and demagnifies it in the vertical plane to obtain a projection of the horizontal beam shape, the camera itself and a fast scanning galvanometric mirror that sweeps this image across the sensor. This allows the tracking of the horizontal bunch size and position over many turns. In this paper we present the setup and show first measurement results., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

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

FLUTE, a new linac-based test facility and THz source is currently being built at the Karlsruhe Institute of Technology (KIT) in collaboration with DESY and PSI. It consists of an RF photo gun and a traveling wave linac accelerating electrons to beam energies of ~41 MeV in the charge range from a few pC up to 3 nC. The electron bunch will then be compressed in a magnetic chicane in the range of 1 - 300 fs, depending on the charge, in order to generate coherent THz radiation with high peak power. An overview of the simulation and hardware status is given in this contribution., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

The ANKA electron storage ring of the Karlsruher Institute of Technology (KIT, Germany) is regularly operated in low-alpha mode to produce short bunches for the generation of coherent synchrotron radiation (CSR). This paper evaluates systematic bunch length measurements taken in low-alpha operation of the ANKA storage ring. Above the bursting threshold not only the emission of CSR occurs in bursts, but also a continuous fluctuation of the bunch's length is observed. The measurements were carried out using concurrent multi turn (using a streak camera) as well as single shot (using electro-optical spectral decoding) methods. Furthermore, we compare information obtained on the fluctuation to simulations., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

A new compact linear accelerator FLUTE is currently under construction at Karlsruhe Institute of Technology (KIT) in collaboration with DESY and PSI. It aims at obtaining femtosecond electron bunches (~1fs - 300 fs) with a wide charge range (1 pC - 3 nC) and requires a precise bunch length diagnostic system. Here we present the layout of a bunch length monitor based on the electro-optic technique of spectral decoding using an Yb-doped fiber laser system (central wavelength 1030 nm) and a GaP crystal. Simulations of the electro-optic signal for different operation modes of FLUTE were performed and main challenges are discussed in this talk. This work is funded by the European Union under contract PITN-GA-2011-289191, Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

A new digital three dimensional fast bunch by bunch feedback system has been installed and commissioned at ANKA. Immediate improvements to stored current and lifetime were achieved for normal user operation. For this, the feedback has to be running during the injection and the energy ramp to 2.5 GeV. Additionally, the feedback system was also incorporated into the diagnostic tool-set at ANKA and opened up new possibilities of automated and continuous measurements of certain beam parameters. The system can operate in different modes such as the low alpha operation mode, which has different requirements on the feedback system compared to normal user operation. Results on the various aspects will be presented as well as future improvements., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

In the framework of this thesis, a setup for single-shot bunch profile measurements was designed, successfully installed into the vacuum chamber of ANKA and commissioned. It allows single-shot bunch profile measurements with a sub-ps resolution.

The ANKA light source is regularly operated with a low momentum compaction factor lattice where short bunches are created for the generation of coherent synchrotron radiation (CSR). Short bunches with high electron density can generate strong self fields which act back on the bunch. This can lead to bunch shape deformation and a microbunching instability which were studied theoretically for the ANKA low alpha parameters (Klein et al. PAC 09). We extended these studies to a comparison of calculated electron distributions and bunch profiles measured with a streak camera. The Haissinski equation was solved for the CSR impedance to obtain a prediction for the distortion of the bunches for different bunch lengths and bunch currents. The comparison shows that the theory predicts a much stronger deformation caused by CSR than the streak camera observes. However, high frequency components of measured FTIR spectra show a clear indication for strong deformation or small, Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

Since a few years CSR-Radiation created in low alpha mode is provided by the ANKA light source of the KIT*. Depending on the bunch current, the radiation is emitted in bursts of high intensity. These bursts display a time evolution which can be observed only on long time scales with respect to the revolution period. The intensity of the emitted radiation during a burst is significantly increased w.r.t. steady state emission. Some users of the THz radiation don’t require particularly constant emission characteristics and could profit from the higher intensity. A better understanding of the long term behaviour of those bursts could help to improve the conditions for those users. We have investigated THz radiation in multiturn mode with a hot electron bolometer. Its time response of 165ps allowed us to resolve the signals of individual bunches. Using a 6GHz LeCroy oscilloscope for data acquisition, we were able to save up to 1.6ms long signal sequences at a sampling rate of 20GS/s. This amount of data corresponds to over 4000 bunch revolutions and allows turn-by-turn signal tracking of desired bunches. In single bunch mode we are able to take segmented data to avoid a huge overhead., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

A new 90 kV e-gun had been installed at the 50 MeV microtron at ANKA. The emittance of the gun has been measured in long pulse mode (1 us, 200 mA) with a pepper-pot, resulting in 5 u.rad RMS normalised emittance. The single pulse width is less than 1 ns, resulting in a bunch purity in the storage ring of better 0.5 %. The old timing system for gun and injection elements based on 4 Stanford delay generator has now been replaced by an event driven system from Micro-Research Finland (MRF). This consists of one event generator and one event receiver. Visualisation and programming is achieved with PVSS from ETM Austria. The e-gun trigger can be adjusted in 10 ps steps. The entire system is phase locked to the 499.69 MHz RF signal., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

The Karlsruhe Institute of Technology (KIT) proposes to build a new light source called TBONE (THz Beam Optics for New Experiments), which aims at a spectral range from 0.1 to 150 THz with a peak power of several MW and a pulse length of only 5 fs. In order to achieve this, a beam transport system with minimal losses and a high bunch compression is required. In this paper we present first beam dynamic simulations of the superconducting linac as well as the bunch compressor and give a short status report of the TBONE project., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

In synchrotron radiation sources coherent radiation is emitted when the bunch length is comparable to or shorter than the wavelength of the emitted radiation. At the ANKA storage ring this radiation is observed as so-called edge radiation (emitted in the fringe field of a bending magnet). This radiation exhibits a radial polarisation pattern. The observed pattern, however, is influenced by the radiation transport in the beam line. A detector system based on a superconducting NbN ultra-fast bolometer with an intrinsic response time of about 100 ps as well as conventional Si bolometers were used to study the beam polarisaion. This paper reports the observations made during measurements., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

We present results of a series of measurements aimed at characterizing the beam coupling impedances in the ANKA electron storage ring. The measurements include transverse coherent tune shifts, bunch lengthening and synchronous phase shift as a function of single bunch current. These were performed under a variety of conditions in the ANKA ring, including injection energy (500 MeV), nominal operating energy (2.5 GeV) as well as at 1.3 GeV and in the low alpha mode and are part of a longer term effort to understand the ANKA impedance over a wide frequency range., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan