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A new generation of high-gradient normal conducting 1.3 GHz RF gun with 1% duty factor was developed to provide a high-quality electron source for superconducting linac driven free-electron lasers like FLASH and European XFEL. Compared to the Gun4 series, Gun5 aims for a ~50% longer RF pulse length (RF pulse duration of up to 1 ms at 10 Hz repetition rate) combined with high gradients (up to ~60 MV/m at the cathode). In addition to the improved cell geometry and cooling concept, the new cavity is equipped with an RF probe to measure and control the amplitude and phase of the RF field inside the gun. The first characterization of Gun5.1 included measurements of RF amplitude and phase stability (pulse-to-pulse and along 1 ms RF pulse). The dark current was measured at various peak power levels. The results of this characterization will be reported.

Frontiers in physics 10, 903559 (2022). doi:10.3389/fphy.2022.903559, Longitudinal properties of electron bunches are critical for the performance of a wide range of scientific facilities. In a free-electron laser, for example, the existing diagnostics only provide very limited longitudinal information of the electron bunch during online tuning and optimization. We leverage the power of artificial intelligence to build a neural network model using experimental data, in order to bring the destructive longitudinal phase space (LPS) diagnostics online virtually and improve the existing current profile online diagnostics which uses a coherent transition radiation (CTR) spectrometer. The model can also serve as a digital twin of the real machine on which algorithms can be tested efficiently and effectively. We demonstrate at the FLASH facility that the encoder-decoder model with more than one decoder can make highly accurate predictions of megapixel LPS images and coherent transition radiation spectra concurrently for electron bunches in a bunch train with broad ranges of LPS shapes and peak currents, which are obtained by scanning all the major control knobs for LPS manipulation. Furthermore, we propose a way to significantly improve the CTR spectrometer online measurement by combining the predicted and measured spectra. Our work showcases how to combine virtual and real diagnostics in order to provide heterogeneous and reliable mixed diagnostics for scientific facilities., Published by Frontiers Media, Lausanne

[Ebook] IBIC 2022, International Beam Instrumentation Conference : 11-15 September 2022, Krakow, Poland : IBIC2022 - proceedings / Organizers: GSI [Helmholtzzentrum für Schwerionenforschung]; SOLARIS, National Synchrotron Radiation Centre, Jagiellonian University in Krakow , [Geneva, Switzerland] : JACoW Publishing, [2022], 11th International Beam Instrumentation Conference, IBIC2022, Krakow, Poland, 11 Sep 2022 - 15 Sep 2022; [Geneva, Switzerland] : JACoW Publishing, Geneva, Switzerland 447-450 (2022). doi:10.18429/JACoW-IBIC2022-WEP24, X-ray Free-Electron Laser (XFEL) facilities, such as the 3.4-km European XFEL, use all-optical links with electro-optic bunch arrival-time monitors (BAM) for a long-range synchronization. The current BAM systems achieve a resolution of 3.5 fs for 250 pC bunches. Precise bunch arrival timing is essential for experiments, which study ultra-fast dynamical phenomena with highest temporal resolution. These experiments will crucially rely on femtosecond pulses from bunch charges well below 20 pC. The state-of-the-art BAMs are not allowing accurate timing for operation with such low bunch charges. Here we report on the progress in development of an advanced BAM (system) based on rod-shaped pickups mounted on a printed circuit board and ultra-wideband travelling-wave electro-optic modulators with low operating voltages. We perform modeling and experimental evaluation for the fabricated pickups and electro-optic modulators and analytically estimate timing jitter for the advanced BAM system. We discuss an experimental setup to demonstrate joint operation of new pickups and wideband EO modulators for low bunch charges less than 5 pC., Published by JACoW Publishing, Geneva, Switzerland, [Geneva, Switzerland]

Superconducting radio frequency (SRF) cavities are used in modern particle accelerators to take advantage of their very high quality factor (Q). A higher Q means that a higher RF field can be sustained, and a higher acceleration can be produced in the cavity for length unity. However, in certain situations, e.g., too high RF field, the SRF cavities can experience quenches that risk creating damage due to the rapid increase in the heat load. This is especially negative in continuous wave (CW) operation due to the impossibility of the system to recover during the off-load period. The design goal of a quench-detection system is to protect the system without being a limiting factor during the operation. In this paper, we compare two different classification approaches for improving a quench detection system. We perform tests using traces recorded from LCLS-II and show that the ARSENAL classifier outperforms a CNN classifier in terms of accuracy., Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK

Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand 13th International Particle Accelerator Conference, IPAC'22, Bangkok, Thailand, 12 Jun 2022 - 17 Jun 2022; JACoW Publishing, Geneva, Switzerland 4 pp. (2022). doi:10.18429/JACOW-IPAC2022-MOPOPT019, The European XFEL (EuXFEL) and other notable X-ray Free-Electron Laser facilities rely on an all-optical synchronization system with electro-optical bunch arrival-time monitors (BAM). The current BAMs were benchmarked with a resolution of 3.5 fs for nominal 250 pC bunches at the EuXFEL, including jitter of the optical reference system. The arrival-time jitter could be reduced to about 10 fs with a beam-based feedback system. For future experiments at the EuXFEL the bunch charge will be decreased to a level where the existing system’s accuracy will no longer be sufficient. In simulations a concept based on rod-shaped pickups mounted on a printed circuit board indicated its potential for such low charge applications. For the feasibility of the proposed design, its contribution to the total impedance is essential. In this work the design and an intermediate version are compared to state-of-the-art BAM regarding their wake potential. Furthermore, measures to mitigate wakefields are discussed., Published by JACoW Publishing, Geneva, Switzerland

[Ebook] IBIC 2022, International Beam Instrumentation Conference : 11-15 September 2022, Krakow, Poland : IBIC2022 - proceedings / Organizers: GSI [Helmholtzzentrum für Schwerionenforschung]; SOLARIS, National Synchrotron Radiation Centre, Jagiellonian University in Krakow , [Geneva, Switzerland] : JACoW Publishing, [2022], 11th International Beam Instrumentation Conference, IBIC 2022, Cracow, Poland, 11 Sep 2022 - 15 Sep 2022; Geneva, Switzerland : JACoW Publishing 488-491 (2022). doi:10.18429/JACoW-IBIC2022-WEP36, PETRA IV will be a new, fourth-generation, high-brilliance synchrotron radiation source in the hard X-ray range. To keep the emittance low at high beam current an active feedback system to damp transverse multi-bunch instabilities is required. The particular challenge to the system is the very low-noise, while maintaining high bandwidth, which is defined by the 2 ns bunch spacing. In this paper, we present the conceptual design of the transverse multi-bunch feedback (T-MBFB) system and technical challenges to fulfill the performance require-ments. An overview is given on the hardware and the method for detecting and damping the coupled-bunch oscillations. Using modern high-speed ADCs enables direct sampling of pulses from beam pick-ups, which removes the necessity for down-converters. Powerful digital signal processing allows not only for the effective feedback implementation, but also for developing versa-tile tools for the machine diagnostics., Published by JACoW Publishing, Geneva, Switzerland

[Ebook] IBIC 2022, International Beam Instrumentation Conference : 11-15 September 2022, Krakow, Poland : IBIC2022 - proceedings / Organizers: GSI [Helmholtzzentrum für Schwerionenforschung]; SOLARIS, National Synchrotron Radiation Centre, Jagiellonian University in Krakow , [Geneva, Switzerland] : JACoW Publishing, [2022], 11th International Beam Instrumentation Conference, IBIC2022, Krakow, Poland, 11 Sep 2022 - 15 Sep 2022; Geneva, Switzerland : JACoW Publishing 343-347 (2022). doi:10.18429/JACOW-IBIC2022-TUP43, PETRA IV is the upcoming low-emittance, 6 GeV, fourthgenerationlight source at DESY Hamburg. It is based upona six-bend achromat lattice with additional beamlines ascompared to PETRA III. A stringent stability of the electronbeam orbit in the ring will be required to achieve adiffraction-limited photon beam quality. In this regard, therequirements and the proposed topology of the global orbitfeedback system are discussed for expected perturbations.An initial analysis based upon system requirements, designand modeling of the subsystems of the orbit feedback systemis also presented., Published by JACoW Publishing, Geneva, Switzerland

[Ebook] 13th International Particle Accelerator Conference : June 12-17, 2022, Impact Forum, Muangthong Thani, Bangkok, Thailand : conference proceedings / Chanwattana, Thakonwat , [Geneva] : JACoW Publishing, July 2022, 13th International Particle Accelerator Conference, IPAC'22, Bangkok, Thailand, 17 Jun 2022 - 22 Jun 2022; [Geneva] : JACoW Publishing, Geneva, Switzerland 1475-1478 (2022). doi:10.18429/JACoW-IPAC2022-TUPOMS029, DESY is planning the upgrade of PETRA III to a fourth generation light source, providing high brightness, quasi diffraction limited hard X-ray photons. The project is underpinned by the construction of a new storage ring PETRA IV, based on a 20 pm accelerator lattice using a hybrid 6-bend achromat concept. We review here the status of the machine project, the latest development in the different technical subsystems, the status of the engineering integration and the plans for the implementation of the new ring in the existing PETRA III tunnel., Published by JACoW Publishing, Geneva, Switzerland, [Geneva]

Proceedings of the 10th International Beam Instrumentation Conference, IBIC2021, Pohang, Rep. of Korea 10th International Beam Instrumentation Conference, IBIC 2021, Pohang, Korea, 13 Sep 2021 - 17 Sep 2021; JACoW Publishing, Geneva, Switzerland 5 pp. (2021). doi:10.18429/JACOW-IBIC2021-WEPP19, The all-optical synchronization system implemented in the European X-ray free-electron laser (EuXFEL) is to receive an upgrade. The modifications are intended to allow operation with consistently high accuracy in a 1 pC mode, which is required for various user experiments. The lower charges, e.g. a factor of 20, lead to a reduced signal strength at the pickups and thus to a decreased resolution. A significant potential for improvement has been identified in a modified pickup structure and transmission network, which provide the transient voltage signal to subsequent parts of the synchronization system. One solution for a broadband pickup structure with short signal paths, large active surfaces and minimum aperture diameter could be achieved by connecting rod-shaped pickups to a combination network on a printed circuit board, which will be mounted in the beamline. In this contribution the proposed design is introduced and analyzed by electromagnetic field simulations., Published by JACoW Publishing, Geneva, Switzerland

Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil 12th International Particle Accelerator Conference, IPAC'21, Campinas, Brazil, 24 May 2021 - 28 May 2021; JACoW Publishing, Geneva, Switzerland 6 pp. (2021). doi:10.18429/JACOW-IPAC2021-THXB02, Free electron laser facilities, such as the European XFEL, make increasingly high demands on the longterm temporal stability and uniformity of the electron bunches, as pump-probe experiments meanwhile aim for timing stabilities of few femtoseconds residual jitter only. For a beam-based feedback control of the linear accelerator, electro-optical bunch arrival-time monitors are deployed, achieving a time resolution better than 3 fs. In a first attempt, we recently demonstrated a beam-based feedback system, reducing the arrival time jitter of the electron bunches to the 10 fs level with stable operation over hours. For pump-probe experiments it is crucial to equally verify this new level of precision in the FEL pulse arrival time with independent methods. In this work, we are discussing first results from examining the facility-wide temporal stability at the European XFEL, with attention to the contributions of various sub-systems and on the different time scales., Published by JACoW Publishing, Geneva, Switzerland

Proceedings of the 18th International Conference on Accelerator and Large Experimental Physics Control Systems, ICALEPCS2021, Shanghai, China 18th International Conference on Accelerator and Large Experimental Physics Control Systems, ICALEPCS 2021, Shanghai, DESY, Peoples R China, 14 Oct 2021 - 22 Oct 2021; JACoW Publishing, Geneva, Switzerland 916-918 (2021). doi:10.18429/JACOW-ICALEPCS2021-THPV025, The currently ongoing PETRA IV project at DESY proposes an upgrade of the PETRA III synchrotron light source towards a fourth-generation, low emittance machine. The goal is to provide X-ray energies in the regime of 10 keV bringing the electron beam production to its physical limits with respect to the smallest achievable source size, and thus approaching the diffraction limit.The realization of this new, challenging machine im-plies a new design of the timing and synchronization system because requirements on beam quality and controls will become significantly more demanding with respect to the existing implementation at PETRA III. Furthermore, the PETRA IV baseline for the fast front-end electronics read-out will be based on the MTCA.4 standard. Given the success of the at DESY developed MicroTCA.4-based timing system for the European XFEL accelerator, it has been chosen to utilize the MTCA.4 technology for the PETRA IV timing system as well. We present in this paper general concepts of the timing and synchronization system, its integration into the con-trol system as well as first design ideas and evaluations of the major timing system hardware component, a MicroTCA.4-based AMC., Published by JACoW Publishing, Geneva, Switzerland

Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil 12th International Particle Accelerator Conference, IPAC'21, Campinas, SP, Brazil, 24 May 2021 - 28 May 2021; 3347 - 3350 (2021). doi:10.18429/JACOW-IPAC2021-WEPAB294, The linear accelerator ARES (Accelerator Research Experiment at SINBAD) is a new research facility at DESY. Electron bunches with a maximum repetition rate of 50 Hz are accelerated up to 155 MeV. The facility aims for ultra-stable sub-femtosecond arrival-times and high peak-currents at the experiment, placing high demands on the reference distribution and field regulation of the S-band RF structures. In this paper, we report on the current status of the RF reference generation, facility-wide distribution, and the LLRF systems of the RF structures.

12th International Particle Accelerator Conference, IPAC'21, Campinas, Brazil, 24 May 2021 - 28 May 2021; JACoW Publishing, Geneva, Switzerland 3 pp. (2021). doi:10.18429/JACOW-IPAC2021-MOPAB192, In the frame of the NICA (Nuclotron-based Ion Collider fAcility) ion collider upgrade a new light ion LINAC for protons and ions will be built in collaboration between JINR and BEVATECH GmbH. While ions with a mass-to-charge ratio up to 3 will be fed into the NUCLOTRON ring with an energy of 7 MeV/u, protons are supposed to be accelerated up to an energy of 13 MeV using a third IH structure. This energy upgrade comprises a third IH structure, a dual-use Debuncher cavity as well as an extension of the LLRF control system built on MicroTCA technology., Published by JACoW Publishing, Geneva, Switzerland

Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil 12th International Particle Accelerator Conference, IPAC21, Campinas, Brazil, 24 May 2021 - 28 May 2021; Geneva : JACoW Publishing, Switzerland 3 pp. (2021). doi:10.18429/JACoW-IPAC2021-WEPAB293, The low-level RF (LLRF) system at the European XFEL, DESY, is of major importance for a high-performant and reliable operation. Faults here can jeopardize the overall operation. Therefore, the trip event logger is currently developped, - a fault diagnosis tool to detect errors online, inform the operators and trigger automatic supervisory actions. Further goals are to provide information for a fault tree and event tree analysis as well as a database of labeled faulty data sets for offline analysis. The tool is based on the C++ framework ChimeraTK Application Core. With this close interconnection to the control system it is possible not only to monitor but also to intervene as it is of great importance for supervisory tasks. The core of the tool consists of fault analysis modules ranging from simple ones (e.g., limit checking) to advanced ones (model-based, machine learning, etc.). Within this paper the architecture and the implementation of the trip event logger are presented., Published by JACoW Publishing, Switzerland, Geneva

The linear accelerator ARES (Accelerator Research Experiment at SINBAD) is a new research facility at DESY. Electron bunches with a maximum repetition rate of 50 Hz are accelerated to a target energy of 155 MeV. The facility aims for ultra-stable sub-femtosecond arrival-times and high peak-currents at the experiment, placing high demands on the reference distribution and field regulation of the RF structure. In this contribution, we present the physical parameter estimation of key RF properties such as cavity detuning not directly measurable on the RF field decay. The method can be used as a fast monitor of inner cell temperature. The estimated properties are finally compared with the measured ones., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil 12th International Particle Accelerator Conference, IPAC'21, Campinas, Brazil, 24 May 2021 - 28 May 2021; JACoW Publishing, Geneva, Switzerland 3 pp. (2021). doi:10.18429/JACOW-IPAC2021-TUPAB302, For pump-probe and seeding experiments at free electron lasers, a femtosecond precise bunch arrival time stability is mandatory. To stabilize the arrival times a fast longitudinal intra bunch-train feedback (L-IBFB) using bunch arrival time monitors is applied. The electron bunch energy prior to a bunch compression chicane is modulated by superconducting radio frequency (SRF) cavities to compensate fast arrival time fluctuations of the subsequent bunches. A broadband normal conducting RF cavity was installed in front of the first bunch compression chicane at FLASH. The L-IBFB uses the normal conducting cavity for small but fast energy corrections together with the SRF cavities for larger and slower corrections. Current measurements show arrival time stabilities of the electron bunches towards 5 fs (rms) at the end of the linac, if the normal conducting cavity acts together with the SRF cavities in the L-IBFB system., Published by JACoW Publishing, Geneva, Switzerland

Proceedings of the 12th International Particle Accelerator Conference, IPAC2021 Campinas, SP, Brazil 12th International Particle Accelerator Conference, IPAC���21, Campinas, Brazil, 24 May 2021 - 28 May 2021; 3 pp. (2021). doi:10.18429/JACOW-IPAC2021-THPAB287, It is possible to connect the PCIe bus of a high performance computer to a MicroTCA crate. This allows the software on the computer to communicate with the modules in the crate, as if they were peripherals of the computer. This article will discuss the use of this feature in respect to accelerator control with a focus on High Level Controllers.

Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil 12th International Particle Accelerator Conference, IPAC���21, Campinas, Brazil, 24 May 2021 - 28 May 2021; 3 pp. (2021). doi:10.18429/JACOW-IPAC2021-TUPAB291, The optical synchronization system for the European X-Ray Free-Electron Laser provides sub-10 femtosecond timing precision * for the accelerator subsystems and experiments. This is achieved by phase locking a mode-locked laser oscillator to the main RF reference and distributing the optical pulse train carrying the time information via actively propagation-time stabilized optical fibers to multiple end-stations. Making up roughly one percent of the entire European XFEL, it is the first subsystem to receive a large-scale data acquisition system [2] for storing not just hand-selected information, but in fact all diagnostic, monitoring, and configuration data relevant to the optical synchronization available from the distributed control system infrastructure. A minimum of 100 TB per year may be stored in a persistent archive for long-term health monitoring and data mining whereas excess data is stored in a short-term ring buffer for high-resolution fault analysis and feature extraction algorithm development. This paper describes scale, challenges and first experiences from the optical synchronization data acquisition system.

9th International Beam Instrumentation Conference, IBIC2020, Santos, Brazil, 14 Sep 2020 - 18 Sep 2020; JACoW Publishing, Geneva, Switzerland 145-149 (2020). doi:10.18429/JACOW-IBIC2020-WEPP21, The all-optical synchronization systems used in various Xray free-electron lasers (XFEL) such as the European XFEL depend on transient fields of passing electron bunches coupled into one or more pickups in the Bunch Arrival Time Monitors (BAM). The extracted signal is then amplitude modulated on reference laser pulses in a Mach-Zehnder type electro-optical modulator. With the emerging demand of the experimenters for future experiments with ultra-short FEL shots, fs precision is required for the synchronization systems even with 1 pC bunches. Since the sensitivity of the BAM depends in particular on the slope of the bipolar signal at the zero crossing and thus, also on the bunch charge, a redesign with the aim of a significant increase by optimized geometry and bandwidth is inevitable. In this contribution a possible new pickup concept is simulated and its performance is compared to the previous concept. A significant improvement of slope and voltage is found. The improvement is mainly achieved by the reduced distance to the beam and a higher bandwidth., Published by JACoW Publishing, Geneva, Switzerland