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13th International Particle Accelerator Conference, (IPAC'22), Bangkok, Thailand, 12 Jun 2022 - 17 Jun 2022; Journal of physics / Conference Series 2420(1), 012028 (2023). doi:10.1088/1742-6596/2420/1/012028, The magnetic bunch compressor was designed as part of a THz accelerator source being developed at the Photo Injector Test facility at DESY in Zeuthen (PITZ) as a prototype for pump-probe experiments at the European XFEL. As an electron bunch is compressed to achieve higher bunch currents for the THz source, the beam dynamics in the bunch compressor was studied by numerical simulations. A start-to-end simulation optimizer including coherent synchrotron radiation (CSR) effects has been developed by combining the use of ASTRA, OCELOT, and GENESIS to support the design of the THz source prototype. In this paper, we present simulation results to explore the possibility of improving the performance of the THz FEL at PITZ by using the developed bunch compressor., Published by IOP Publ., Bristol

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 1033-1036 (2022). doi:10.18429/JACOW-IPAC2022-TUPOPT016, In order to allow THz pump/X-ray probe experiments at full bunch repetition rate for users at the European XFEL, the Photo Injector Test Facility at DESYin Zeuthen (PITZ) is building a prototype of an accelerator-based THz source. The goal is to generate THz SASE FEL radiation with a mJ energy level per bunch using an undulator driven by the electron beam from PITZ. Therefore, the existing PITZ beam line is extended into a tunnel annex downstream of the existing accelerator tunnel. The final design of the beam line extension consists of a bunch compressor, a collimation system and a beam dump in the PITZ tunnel. In the tunnel annex one LCLS-I undulator is installed for the production of the THz radiation with a quadrupole triplet in front of it for matching the beam parameters for the FEL process. Behind the undulator two screen stations couple out the THz radiation, for measurements of bunch compression, pulse energy or spatial distribution. A dipole separates the electron from the THz beam and a quadrupole doublet transports the electron beam to the beam dump. The installation progress will be presented., Published by JACoW Publishing, Geneva, Switzerland

Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK 31st Linear Accelerator Conference, LINAC22, Liverpool, United Kingdom, 28 Aug 2022 - 2 Sep 2022; JACoW Publishing, Geneva, Switzerland 699-702 (2022). doi:10.18429/JACoW-LINAC2022-THPOJO03, A new generation of normal conducting 1.3GHz RF gun 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% increase of the duration of the RF pulse (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 impedance, 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 prototype of the new RF gun was manufactured at DESY and installed at the Photo Injector Test facility at DESY in Zeuthen (PITZ) in October 2021. In mid-October 2021 the RF conditioning began, aiming for achieving the aforementioned RF parameters. The conditioning procedure involves a slow gradual increase in repetition rate, RF pulse duration and peak power while carefully monitoring vacuum conditions and signals from interlock sensors. The results of RF conditioning will be reported., Published by JACoW Publishing, Geneva, Switzerland

Proceedings of the 11th International Beam Instrumentation Conference, IBIC2022, Kraków, Poland 11th International Beam Instrumentation Conference, IBIC2022, Krakow, Poland, 12 Sep 2022 - 15 Sep 2022; [Geneva, Switzerland] : JACoW Publishing 273-276 (2022). doi:10.18429/JACoW-IBIC2022-TUP20, The Photo Injector Test Facility at DESY in Zeuthen (PITZ) characterizes and optimizes electron sources for use at FLASH and European XFEL. AT PITZ, the transverse phase space is measured using a single slit scan and scintillator screen method. With the trend in photoinjectors towards lower current and emittance, these measurements become increasingly influenced by systematic errors including camera resolution and scintillator response due to smaller spot sizes. This study investigates the effects and corrections of the systematic errors for phase space measurements at PITZ., Published by JACoW Publishing, [Geneva, Switzerland]

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 1063-1066 (2022). doi:10.18429/JACOW-IPAC2022-TUPOPT027, An accelerator-based THz source is under development at the Photo Injector Test Facility at DESY in Zeuthen (PITZ). The facility can produce high brightness electron beams with high charge and small emittance. Currently, a study on development of a tunable high-power THz SASE FEL for supporting THz-pump, X-ray-probe experiments at the European XFEL is underway. An LCLS-I undulator, a magnetic chicane bunch compressor, and THz pulse diagnostics have been installed downstream the previously existing setup of the PITZ beamline. Additional to the SASE FEL, a possibility to generate superradiant THz undulator radiation from short electron bunches is under investigation, which is the focus in this study. Numerical simulations of the superradiant THz radiation by using sub-picosecond electron bunches with energy of 6 - 22 MeV and bunch charge up to 2 nC produced from the PITZ accelerator are performed. The results show that the radiation with a spectral range of 0.5 to 9 THz and a pulse energy in the order of sub-uJ can be obtained. The results from this study can be used as a benchmark for the future development., Published by JACoW Publishing, Geneva, Switzerland

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 310-312 (2022). doi:10.18429/JACOW-IPAC2022-MOPOPT029, The longitudinal phase space characteristics of space-charge dominated electron beams are keys to achieving bunch compression for the accelerator-based THz source at the Photo Injector Test facility at DESY in Zeuthen (PITZ). Such a THz source is proposed as a prototype for an accelerator-based THz source for pump-probe experiments at the European XFEL. A start-to-end simulation has suggested the settings of the phase of booster linear accelerator manipulating longitudinal beam characteristics to optimize the performance of the THz FEL. Although beam diagnostics after compression at PITZ are limited, the longitudinal beam characteristics as a function of the booster phase have been measured and compared with the corresponding simulations. The benchmark involves measurements of longitudinal phase space distribution for bunch charges up to 2 nC. The measurement technique assigned uses 50-um slits to achieve higher momentum and time resolution (1.8 keV/c and 0.5 ps, respectively)., Published by JACoW Publishing, Geneva, Switzerland

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 3 pp. (2022). doi:10.18429/JACoW-IPAC2022-THPOST009, The European XFEL has planned to perform pump-probe experiments using its X-ray pulses and THz pulses. A promising concept to provide the THz pulses with a pulse repetition rate identical to that of the X-ray pulses is to generate them using an accelerator-based THz source. The THz source requires a bunch compressor in order to manipulate the longitudinal phase space of the electron bunch to match with various options of THz radiation generation. This paper presents and discusses simulation study of the bunch compressor for the THz source., 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 105-108 (2022). doi:10.18429/JACoW-IBIC2022-MOP28, Methodical studies to improve the longitudinal phase space (LPS) tomography of space-charge dominated electron beams were carried out at the Photo Injector Test facility at DESY in Zeuthen (PITZ). An analytical model was developed to quantify mean momentum, RMS energy spread, bunch length and phase advance. Phase advance analysis determined the booster phase scan range and step size to be used for obtaining momentum projections. A slit was introduced before the booster to truncate the beam in transverse plane to strongly reduce the space charge effects. The signal resolution of this truncated beam was improved by careful beta function control at the reference screen of the momentum measurements. The reconstruction algorithm was changed from Algebraic Reconstruction Technique (ART) to Image Space Reconstruction Algorithm (ISRA) owing to its assurance of non-negative solutions. In addition, the initial physically justified assumption of LPS, based on low-energy section measurements, was established to clear out noise-like artefacts. This paper will highlight the improvements made in the LPS tomography and compare the simulated and experimental results., Published by JACoW Publishing, Geneva, Switzerland

Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK 31st International Linear Accelerator Conference, LINAC2022, Liverpool, United Kingdom, 28 Aug 2022 - 2 Sep 2022; [Geneva] : JACoW Publishing, Geneva, Switzerland 83-86 (2022). doi:10.18429/JACoW-LINAC2022-MOPOPA04, The European XFEL considers to perform THz-pump and X-ray-probe experiments. A promising concept to provide the THz pulses with satisfactory properties for the experiments is to generate them using a linear accelerator-based free-electron laser (FEL). A simulation study of a THz FEL facility capable of generating powerful tunable coherent THz radiation that covers the wavelength range of 25 ’m to 100 ’m was performed. An accelerator beamline layout based on the Photo Injector Test Facility at DESY in Zeuthen (PITZ) and an APPLE-II undulator with a period length of 40 mm were used in the simulation study. Results of the study are presented and discussed in this paper., Published by JACoW Publishing, Geneva, Switzerland, [Geneva]

[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], International Beam Instrumentation Conference, IBIC 2022, Krakow, Poland, 11 Sep 2022 - 15 Sep 2022; Geneva, Switzerland : JACoW Publishing 277-280 (2022). doi:10.18429/JACoW-IBIC2022-TUP21, A standard technique to measure beam profiles in linear accelerators are screen monitors using scintillating screens. This technique is used e.g. at the European XFEL in order to overcome coherence effects in case of OTR usage [*]. During the XFEL commissioning it was found out that screens based on LYSO:Ce as scintillating material revealed a nonproportional light output [**]. Reason for it is the high particle beam density. As consequence it was decided to exchange LYSO:Ce by GAGG:Ce scintillators because the excitation carriers can rapidly transfer their energy to excited states of gadolinium, and a rapid migration of this energy among the Gd sub-lattice is expected. Driven by the observations at XFEL a series of measurements was started to investigate the properties of various scintillator materials (LYSO:Ce, YAP:Ce, YAG:Ce, LuAG:Ce and GAGG:Ce). The last measurement campaign was carried out at PITZ which allows to operate at higher beam charge and lower electron energy compared to the XFEL. The present work summarizes the results of these measurements., Published by JACoW Publishing, Geneva, Switzerland

12th International Particle Accelerator Conference, IPAC'21, Campinas, Brazil, 24 May 2021 - 28 May 2021; doi:10.18429/JACOW-IPAC2021-WEPAB115, The need for carrier-envelope-phase (CEP) stable THz pump pulses is recognized at many pump-probe experiments at the European XFEL. At the Photo Injector Test Facility at DESY in Zeuthen (PITZ), a proof-of-principle experiment of an accelerator-based THz FEL source is in preparation. Since the CEP stability of FEL pulses is not guaranteed in the SASE regime, a seeding scheme is needed. A common scheme for seeding is to drive the microbunching process with external laser pulses, which are power-limited in the THz range. Alternatively, a pre-bunched beam, generated for example by applying a temporally modulated photocathode laser pulse, can be used to drive the FEL. The beam dynamics with such a seeding method are studied with ASTRA tracking code simulations with space-charge forces as well as experimentally. The results of these studies are shown and discussed.

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; 4 pp. (2021). doi:10.18429/JACoW-IPAC2021-WEPAB274, A magnetic bunch compressor has been recently designed for an accelerator-based THz source which is under development at the Photo Injector Test facility at DESY in Zeuthen (PITZ). The THz source is assumed to be a prototype for an accelerator-based THz source for pump-probe experiments at the European XFEL. As an electron bunch is compressed to achieve higher bunch currents for the THz source, we investigate the beam dynamics in the bunch compressor by numerical simulations. A start-to-end simulation optimizer has been developed by combining the use of ASTRA, IMPACT-T, and OCELOT to support the design of the THz source prototype. Coherent synchrotron radiation effects degrade the compression performance for our study cases with bunch charges up to 4 nC and beam energy of 17 MeV at a bending angle of 19 degrees. Simulation and preliminary beam characteristic results will be presented in this paper.

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; 3244-3247 (2021). doi:10.18429/JACOW-IPAC2021-WEPAB257, The Photo Injector Test facility at DESY in Zeuthen (PITZ) is developing a THz SASE FEL as a prototype high repetition rate accelerator-based source for the THz-pumped, X-ray-probed experiments at the European XFEL. For the generation of THz pulses of mJ-level energy from SASE, an electron beam with a high charge (up to 4 nC) and high peak current (~200 A) will be injected into an LCLS-I undulator, which is currently being installed at the end of the photo-injector. The narrow vacuum chamber (11x5 mm) between the magnetic poles and the strong vertical focusing from the undulator, as well as the lack of beam diagnostics, have made it a challenge to match the space-charge dominated beam into the undulator without beam loss during the following transport. In this paper, boundary conditions of a matched electron beam will be discussed and the simulation and experimental study on our matching strategy will be presented.

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 4 pp. (2021). doi:10.18429/JACOW-IPAC2021-TUPAB071, In order to allow THz pump-X-ray probe experiments at full bunch repetition rate for users at the European XFEL, the Photo Injector Test Facility at DESY in Zeuthen (PITZ) is building a prototype of an accelerator-based THz source. The goal is to generate THz SASE FEL radiation with a mJ energy level per bunch using an LCLS-I undulator driven by the electron beam from PITZ. Therefore, the existing PITZ beam line is extended into a tunnel annex downstream of the existing accelerator tunnel. The beam line extension in the PITZ tunnel consists of three quadrupole magnets, a bunch compressor, a collimation system and a beam dump. In the second tunnel a dipole magnet allows to serve two beam lines, one of them the THz@PITZ beam line. It consists of one LCLS-I undulator for the production of the THz radiation, a quadrupole triplet in front of it and a quadrupole doublet behind it. For the electron beam diagnostic six new screen stations are built, three of them also allow for the observation of the THz radiation for measurements. In addition six BPMs and a new BLM system for machine protection and FEL gain curve measurement will be installed. The progress of this work will be presented., Published by JACoW Publishing, Geneva, Switzerland

Linac based X-ray free electron laser demand a high beam quality from the electron source, therefore RF photoinjectors are used to generate the electron bunches for state of the art beam brightness. One important figure of merit for these injectors is the transverse emittance of the generated electron beam, which can be minimized by shaping the photocathode laser pulses. Best performance can be achieved with ellipsoidal laser pulses, but 3D shaping is technically challenging. Typically, a quasi-uniform transverse laser profile is truncated from the Gaussian profile generated by the laser with an aperture to reduce the transverse nonlinear space charge forces. This is investigated in detail by optimizing the laser transverse profile at the Photoinjector Test facility at DESY in Zeuthen (PITZ), where photoinjector R is conducted for the E-XFEL and FLASH free electron lasers at DESY in Hamburg. In this contribution we present experimental results at high acceleration gradients (up to 60 MV/m) for both 250 pC and 500 pC. For a bunch charge of 500 pC an emittance reduction of about 30% compared to the commonly used transverse flat-top laser distribution was achieved., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

Dissertation, Universität Hamburg, 2020; 145 pp. (2020). = Dissertation, Universität Hamburg, 2020, The European XFEL has planned to perform pump-probe experiments by using its x-ray pulses and THz pulses. A promising concept to provide the THz pulses is to generate them using a tunable high-power accelerator-based THz source. The Photo Injector Test Facility at DESY in Zeuthen (PITZ) can serve as a prototype for the development of the THz source. This thesis investigates the capabilities to generate THz pulses using electron bunches from the PITZ accelerator and three methods of THz radiation generation including Self-Amplification of Spontaneous Emission Free-Electron Lasers (SASE FELs), Coherent Transition Radiation (CTR), and Coherent Diffraction Radiation (CDR).Studies of the THz SASE FEL using 4 nC electron beams and an APPLE-II type undulator with a period length of 40 mm in the helical mode were performed. Start-to-End (S2E) simulations show that FEL pulse energies at 100 $\mu$m and 20 $\mu$m wavelengths (corresponding to 3 THz and 15 THz frequencies) of up to 2.5 mJ are achievable. Experimental optimization and characterization of 4 nC electron beams for the SASE FEL option were performed at PITZ. Parameters of the beam, including slice emittance, slice energy spread, and current distribution, were measured. FEL simulations based on measured beam parameters show that the FEL pulse energies are in the sub-mJ level. S2E simulations of the THz radiation generated by CTR and CDR were performed. By using a short Gaussian photocathode laser pulse and an electron bunch compressed by velocity bunching with bunch charge up to 1 nC, CTR and CDR pulse energies up to 4 $\mu$J and frequencies covering up to 0.4 THz are achievable. Corresponding experimental generations of CTR and CDR were performed successfully. Average pulse energies of up to 1.85 $\mu$J and coherent frequencies of up to 1.5 THz were measured. Furthermore, S2E simulations and corresponding experiments of the THz radiation generated by using a comb beam were performed. Several narrow-band peaks at higher-order harmonics were observed in the spectral distributions.

39th International Free-Electron Laser Conference, FEL19, Hamburg, Germany, 26 Aug 2019 - 30 Aug 2019; JACoW Publishing, Geneva, Switzerland 45-47 (2019). doi:10.18429/JACOW-FEL2019-TUP003, For pump-probe experiments at the European XFEL, a THz source is required to produce intense THz pulses at the same repetition rate as the X-ray pulses from XFEL. Therefore, an accelerator-based THz source with identical electron source as European XFEL was suggested and proof-of-principle experiments utilizing an LCLS I undulator will be performed at the Photo Injector Test Facility at DESY in Zeuthen (PITZ). The main idea is to use a 4nC beam for maximum SASE radiation but to allow different radiation regimes a magnetic bunch compressor can be used. This helps e.g. to reduce the saturation length inside the undulator and also to study super-radiant THz radiation. In this paper a design of a chicane type magnetic bunch compressor using HERA corrector magnets is presented., Published by JACoW Publishing, Geneva, Switzerland

The 13th International Computational Accelerator Physics Conference, ICAP2018, Key West, USA, 20 Oct 2018 - 24 Oct 2018; Geneva, Switzerland : JACoW 7 pp. (2018)., The Photo Injector Test facility at DESY in Zeuthen (PITZ) develops high brightness electron sources for modern linac-based Free Electron Lasers (FELs). The PITZ accelerator has been proposed as a prototype for a tunable, high power THz source for pump and probe experiments at the European XFEL. A Self-Amplified Spontaneous Emission (SASE) FEL is considered to generate the THz pulses. High radiation power can be achieved by utilizing high charge (4 nC) shaped electron bunches from the PITZ photo injector. THz pulse energy of up to several mJ is expected from preliminary simulations for 100 um radiation wavelength. For the proof-of-principle experiments a re-usage of LCLS-I undulators at the end of the PITZ beamline is under studies. One of the challenges for this setup is transport and matching of the space charge dominated electron beam through the narrow vacuum chamber. Start-to-end simulations for the entire experimental setup - from the photocathode to the SASE THz generation in the undulator section - have been performed by combination of several codes: ASTRA, SC and GENESIS-1.3. The space charge effect and its impact onto the output THz radiation have been studied. The results of these simulations will be presented and discussed., Published by JACoW, Geneva, Switzerland

39th International Free-Electron Laser Conference, FEL19, Hamburg, Germany, 26 Aug 2019 - 30 Aug 2019; JACoW Publishing, Geneva, Switzerland 41-44 (2019). doi:10.18429/JACOW-FEL2019-TUP002, A proof-of-princle experiment for a THz SASE FEL is undergoing preparation at the Photo Injector Test facility at DESY in Zeuthen (PITZ), as a prototype THz source for pump-probe experiments at the European XFEL, which could potentially provide up to mJ/pulse THz radiation while maintaining the identical pulse train structure as the XFEL pulses. In the proof-of-principle experiment, LCLS-I undulators will be installed to generate SASE radiation in the THz range of 3-5 THz from electron bunches of 16-22 MeV/c. One key design is to obtain the peak current of nearly 200 A from the heavily charged bunches of a few nC. In this paper, we report our simulation results on the optimization of the space charge dominated beam in the photo injector and the following transport line with two cathode laser setups. Experimental results based on a short Gaussian laser will also be discussed., Published by JACoW Publishing, Geneva, Switzerland

The Photo Injector Test Facility at DESY in Zeuthen (PITZ) was built to test and to optimize sources of high brightness electron beams for Free-Electron Lasers (FELs). In order to achieve high accelerating gradients and long RF pulse lengths in the RF gun cavities an extensive and safe RF conditioning is required. A State Machine based Automatic Conditioning application (SMAC) was developed to automate the RF conditioning processes, allowing for greater efficiency and performance optimization. SMAC is written in Java and uses State Chart XML (SCXML) as the finite-state machine execution environment based on Harel statecharts. It employs the Distributed Object-Oriented Control System (DOOCS) and Three-fold Integrated Networking Environment (TINE) for the communication with the control system of PITZ. The graphical user interface (GUI) is created by using the Java Swing toolkit. Communication between GUI and SXML processing layer is performed via Document Object Model (DOM) events. The SMAC application has been successfully applied to RF conditioning of several gun cavities at PITZ., Proceedings of the 12th Int. Workshop on Emerging Technologies and Scientific Facilities Controls, PCaPAC2018, Hsinchu, Taiwan

8th International Beam Instrumentation Conference, IBIC2019, Malmö, Sweden, 8 Sep 2019 - 12 Sep 2019; 4 pp. (2019)., At the Photo Injector Test Facility at DESY in Zeuthen (PITZ) high-brightness electron sources are optimized for use at the X-ray free-electron lasers FLASH and European XFEL. Transverse projected emittance measurements are carried out by a single-slit scan technique in order to suppress space charge effects at an energy of ~20 MeV. Previous slice emittance measurements, which employed the emittance measurement in conjunction with a transverse deflecting structure, suffer from limited time resolution and low signal-to-noise ratio (SNR) due to a long drift space from the mask to the observation screen. Recent experimental studies at PITZ show improvement of the temporal resolution and SNR by utilizing quadrupole magnets between the mask and the screen. The measurement setup is described and first results are shown.

10th International Particle Accelerator Conference, IPAC’19, Melbourne, Australia, 19 May 2019 - 24 May 2019; Geneva, Switzerland : JACoW Publishing 2286-2290 (2019). doi:10.18429/JACOW-IPAC2019-WEZPLS2, Beam driven wakefield acceleration (PWFA) schemes in plasmas are among the most promising candidates for novel, compact accelerators. Several aspects of PWFA are under investigation at the Photoinjector Test facility at DESY in Zeuthen (PITZ). One of the main characteristics of these accelerators is the ratio between field strength usable for acceleration and decelerating field strength in the driver bunch, the so called transformer ratio. To reach high transformer ratios usually shaped bunches, e.g. with ramped current profiles are employed as drivers. The so-called self-modulation instability, which causes transverse modulation of a bunch longer than the plasma wavelength, is proposed as a means of supplying short driver bunches for proton-driven PWFA. This talk will give an overview on experimental results in these two aspects of PWFA at PITZ with a focus on the production of electron bunches enabling high transformer ratio acceleration by shaping the photocathode laser pulses of a photoinjector and the demonstration of high transformer ratio PWFA. Simulations and further developments on the shaping techniques, allowing highly flexible electron bunches for future plasma wakefield accelerators are also presented., Published by JACoW Publishing, Geneva, Switzerland

39th International Free-Electron Laser Conference, FEL19, Hamburg, Germany, 26 Aug 2019 - 30 Aug 2019; JACoW Publishing, Geneva, Switzerland 38-40 (2019). doi:10.18429/JACOW-FEL2019-TUP001, The Photo Injector Test Facility at DESY in Zeuthen (PITZ) has been proposed as a suitable facility for research and development of an accelerator-based THz source prototype for pump-probe experiments at the European XFEL. A proof-of-principle experiment to generate THz SASE FEL radiation by using an LCLS-I undulator driven by an electron bunch from the PITZ accelerator has been planned and studied. The undulator is foreseen to be installed downstream from the current PITZ accelerator, and an extension of the accelerator tunnel is necessary. Radiation shielding for the extended tunnel was designed, and construction works are finished. Design of the extended beamline is ongoing, not only for this experiment but also for other possible experiments. Components for the extended beamline, including magnets for beam transport, a chicane bunch compressor, electron beam diagnostics devices, and THz radiation diagnostics devices have been studied. An overview of these works will be presented in this paper., Published by JACoW Publishing, Geneva, Switzerland

39th International Free-Electron Laser Conference, FEL19, Hamburg, Germany, 26 Aug 2019 - 30 Aug 2019; JACoW Publishing, Geneva, Switzerland 440-443 (2019). doi:10.18429/JACOW-FEL2019-WEP051, A continuous wave (CW) mode operation of the European X-ray Free-Electron Laser (XFEL) is under considerations for a future upgrade. Therefore, a superconducting radio frequency (SRF) CW gun is under experimental development at DESY in Hamburg. Beam dynamics simulations for this setup have been done assuming 100 pC bunch charge and a maximum electric field at the photocathode of 40 MV/m. Experimental studies for these parameters using a normal conducting RF photogun have been performed at the Photo Injector Test facility at DESY in Zeuthen (PITZ). The beam transverse emittance was minimized by optimizing the main photo injector parameters in order to demonstrate the feasibility of generating electron beams with a beam quality required for successful CW operation of the European XFEL for conditions similar to the SRF gun setup., Published by JACoW Publishing, Geneva, Switzerland

4. Annual MT Meeting, Berlin, Germany, 12 Jun 2018 - 14 Jun 2018

Transverse slice emittance is one of the most important properties of high-brightness electron beams for freeelectron lasers (FELs). The photo injector test facility at DESY in Zeuthen (PITZ) develops high-brightness electron sources for modern FELs. With a 23 MeV, 1 nC beam at PITZ the experimental slice emittance characterization with the quadrupole scan technique is complicated by strong space charge effects. Combining the slit scan technique with a transverse deflecting cavity (TDS) allows for timeresolved emittance measurements of such a space-chargedominated beam. The first proof-of-principle results of slice emittance measurements at PITZ based on the 'TDS + slit scan'-technique are presented in this paper., Proceedings of the 29\textsuperscript{th} Linear Accelerator Conf., LINAC2018, Beijing, China

Hamburg Alliance New Beams and Accelerators, Hamburg, Germany, 5 Sep 2018 - 7 Sep 2018

DPG Frühjahrstagung 2018, Würzburg, Germany, 19 Mar 2018 - 23 Mar 2018, The photo injector test facility at DESY, Zeuthen site (PITZ), was built to test, develop and experimentally optimize high brightness photoelectron sources for superconducting linac driven SASE FELs, such as the Free electron LASer in Hamburg (FLASH) and the European X-ray Free Electron Laser (European XFEL). Extremely low beam emittance beyond the original European XFEL requirements has been demonstrated at PITZ in 2011. Further improvements of the transverse projected beam emittance are in good progress by generating 3D ellipsoidal electron beams on the basis of photocathode laser pulse shaping. In this talk, an overview of the PITZ facility is given. New progress on emittance optimization will be presented.

38th International Free-Electron Laser Conference, Santa Fe, USA, 20 Aug 2017 - 25 Aug 2017; WEP007 (2017)., The electron beam asymmetry observed at the Photo Injector Test Facility at DESY in Zeuthen (PITZ) was traced back to multipole kicks in the gun section, namely around the location of the coaxial power coupler and the main solenoid. Several dedicated studies have been performed to quantify the kick location and strength. Based on these studies, two designs of correction quadrupole coils were proposed. The coils were fabricated and tested with an electron beam. The second updated design implies a two-quadrupole setup on a frame installed around the gun coaxial coupler close to the main solenoid centre location. Skew and normal quadrupole magnets are powered independently, enabling flexibility in electron beam manipulations. By means of this setup, a more symmetric beam was obtained at several screens. This led also to more equal measured horizontal and vertical phase spaces and to even smaller overall emittance values. Some details of the gun quadrupole designs, magnetic measurements, and results of electron beam measurements including emittance optimization will be reported.

2018 Joint FLASH/TELBE THz user meeting, Hamburg, Germany, 20 Jul 2018 - 20 Jul 2018

29th Linear Accelerator Conference, LINAC2018, Beijing, China, 16 Sep 2018 - 21 Sep 2018; Geneva, Switzerland : JACoW Publishing 4 pp. (2018)., The cathode emission physics plays a crucial role in the overall beam dynamics in an RF gun. Interplays between intricate emission mechanisms in the cathode vicinity strongly influence the cathode quantum efficiency (QE) and the intrinsic emittance. The presence of strong space-charge effects in high gradient RF guns further complicates the emission process. A proper modeling of photoemission and a careful treatment of the space-charge contribution is thus of great necessity to understanding the formation of the beam slice emittance. In this article, emission measurements are carried out using the L-band cesium-telluride photocathode RF gun at the Photo Injector Test Facility at DESY in Zeuthen (PITZ)and the S-band copper photocathode RF gun at Tsinghua University. Following the Dowell model a simple so-called space-charge iteration approach is developed and used to determine the QE through temporal- and spatial-dependent electromagnetic fields. An impact of the space-charge cooling on the intrinsic emittance is presented. Measurementdata are shown and discussed in comparisons to preliminary simulation results, Published by JACoW Publishing, Geneva, Switzerland

9th International Particle Accelerator Conference, IPAC'18, Vancouver, Canada, 29 Apr 2018 - 4 May 2018; Geneva, Switzerland : JACoW Publishing 1648-1650 (2018). doi:10.18429/JACoW-IPAC2018-TUPML047, The transformer ratio, the ratio between maximum accelerating field and maximum decelerating field in the driving bunch of a plasma wakefield accelerator (PWFA), is one of the key aspects of this acceleration scheme. It not only defines the maximum possible energy gain of the PWFA but it is also connected to the maximum percentage of energy that can be extracted from the driver, which is a limiting factor for the efficiency of the accelerator. Since in linear wakefield theory a transformer ratio of 2 cannot be exceeded with symmetrical drive bunches, any ratio above 2 is considered high. After the first demonstration of high transformer ratio acceleration in a plasma wakefield at PITZ, the photoinjector test facility at DESY, Zeuthen site, limiting aspects of the transformer ratio are under investigation. This includes e.g. the occurrence of bunch instabilities, like the transverse two stream instability, or deviations of the experimentally achieved bunch shapes from the ideal., Published by JACoW Publishing, Geneva, Switzerland

DPG - Frühjahrstagung 2018, Würzburg, Germany, 19 Mar 2018 - 23 Mar 2018, The photo injector test facility at DESY, Zeuthen site (PITZ), was built to test, develop and experimentally optimize high brightness photoelectron sources for coherent light sources. The produced high quality electron beam and a large variety of advanced beam diagnostics at PITZ also provide excellent oppotunities for a wide field of research activities. This includes experiments of particle beam driven plasma wakefield acceleration, experiments towards a prototype IR/THz source for pump-probe experiments at the European XFEL, experimental demonstration of ballistic bunching with dielectric-lined waveguides, electron diffraction experiments and many others. In this talk, an overview of recent research activities at PITZ is given. Corresponding results will be presented.

8th International Particle Accelerator Conference, IPAC2017, Copenhagen, Denmark, 14 May 2017 - 19 May 2017; Geneva : JACoW, TUPIK051 (2017). doi:10.18429/JACoW-IPAC2017-TUPIK051, The Photo Injector Test Facility at DESY in Zeuthen (PITZ) develops, tests and characterizes high brightness electron sources for FLASH and European XFEL. Since these FELs work with superconducting accelerators in pulsed mode, also the corresponding normal-conducting RF gun has to operate with long RF pulses. Generating high beam quality from the photo-cathode RF gun in addition requires a high accelerating gradient at the cathode. Therefore, the RF gun has to ensure stable and reliable operation at high average RF power, e.g. 6.5 MW peak power in the gun for 650 μs RF pulse length and 10 Hz repetition rate for the European XFEL. Several RF gun setups have been operated towards these goals over the last years. The latest gun setup is in operation since March 2016 and includes RF Gun 4.6 with an improved contact spring design. The RF input distribution consists of a coaxial coupler, a T-combiner and 2 RF windows from DESY production. In this contribution we will present statistics on the high average power operation and results from the characterization of the produced electron beam., Published by JACoW, Geneva

38th International Free-Electron Laser Conference, Santa Fe, USA, 20 Aug 2017 - 25 Aug 2017; 4 pp. (2017)., The Photo Injector Test Facility at DESY, Zeuthen site (PITZ) was built to test and optimize high brightness electron sources for Free Electron Lasers (FELs) like FLASH and the European XFEL. Although the beam emittance has been optimized and experimentally demon-strated to meet the requirements of FLASH and XFEL, transverse beam asymmetries, such as wing structures and beam tilts were observed during many years of operation with different generations of guns. These cannot be ex-plained by simulations with the rotationally symmetric gun cavities and symmetric solenoid fields. Based on previous coupler kick, solenoid field imperfection studies and coupling beam dynamics, the beam asymmetries most probably stem from anomalous quadrupole field error in the gun section. A thin lens static quadrupole model is applied in the RF gun section simulations to fit the position and intensity of quadrupole field errors by comparing the beam asymmetry directions in experiments and ASTRA simulations. Furthermore, by measuring the laser position movement at the photocathode and the corre-sponding beam movement at downstream screens, the integrated quadrupole field strength can also be extracted.

8th International Particle Accelerator Conference, Copenhagen, Denmark, 14 May 2017 - 19 May 2017; JACoW, Geneva, Switzerland 2857-2860 (2017). doi:10.18429/JACoW-IPAC2017-WEPAB122, We report on the experimental demonstration of ballistic bunching of photoinjected, nC-scale electron bunches at the PITZ facility. In the experiment, electron bunches emanating from the photocathode were directly focused into a mm-scale dielectric-lined waveguide. The wakefield excited by the bunch acts back onto itself, leading to an energy modulation, which at a relatively low energy of 6~MeV, is converted into a density modulation before entering the linac ∼ 1~m downstream. We discuss the basic theory, experimental layout and results., Published by JACoW, Geneva, Switzerland

8th International Particle Accelerator Conference, Copenhagen, Denmark, 14 May 2017 - 19 May 2017; JACoW, Geneva, Switzerland 1718-1720 (2017). doi:10.18429/JACoW-IPAC2017-TUPIK018, Plasma wakefield acceleration (PWFA), the acceleration of particles in a plasma wakefield driven by high current-density particle bunches, is one of the most promising candidates for a future compact accelerator technology. A key aspect of this type of acceleration is the ratio between the accelerating fields experienced by a witness beam and the decelerating fields experienced by the drive beam, called the transformer ratio. As for longitudinally symmetrical bunches this ratio is limited by the fundamental theorem of beamloading to 2 in the linear regime*, a transformer ratio above this limit is considered high. This can be reached by using a modulated drive bunch or a shaped train of drive bunches. So far, only the latter case has been shown for wakefields in a RF-structure**. We show the experimental setup, simulations and first, preliminary results of high transformer ratio acceleration experiments at the Photoinjector Test Facility at DESY in Zeuthen (PITZ)., Published by JACoW, Geneva, Switzerland

LUSIA project meeting, Pecs, Hungary, 27 Nov 2017 - 27 Nov 2017

28th Linear Accelerator Conference, LINAC2016, East Lansing, USA, 25 Sep 2016 - 30 Sep 2016; JACoW, Geneva, Switzerland 3 pp. (2017). doi:10.18429/JACoW-LINAC2016-MOPLR013, Since more than a decade, the photo injector test facility at DESY, Zeuthen site (PITZ), has developed and optimized high brightness electron sources for modern Free Electros Lasers like FLASH and the European XFEL. Despite a very high performance of the photo injector was experimentally demonstrated, several discrepancies between measurements and beam dynamics simulations have been revealed. Although the optimized measured values of the projected transverse emittance are close to those obtained from the beam dynamics simulations, the corresponding experimental machine parameters show certain systematic deviations from the simulated optimized setup. As a source for these deviations, electron beam imperfections were experimentally investigated. This includes studies on bunch charge production, electron beam imaging using the RF gun with its solenoid, and investigations on the transverse asymmetry of the electron beam generated in a rotationally symmetric gun cavity. Experimental studies were supplied with corresponding beam dynamics simulations. The paper reports on results of these studies., Published by JACoW, Geneva, Switzerland

28th International Linear Accelerator Conference, LINAC16, East Lansing, USA, 25 Sep 2016 - 30 Sep 2016; JACoW, Geneva, Switzerland 3 pp. (2017). doi:10.18429/JACoW-LINAC2016-MOOP08, The Photo Injector Test Facility at DESY in Zeuthen (PITZ) develops, tests and characterizes high brightness electron sources for FLASH and European XFEL. Since these FELs work with superconducting accelerators in pulsed mode, also the corresponding normal-conducting RF gun has to operate with long RF pulses. Generating high beam quality from the photocathode RF gun in addition requires a high accelerating gradient at the cathode. Therefore, the RF gun has to ensure stable and reliable operation at high average RF power, e.g. 6.5 MW peak power in the gun for 650 μs RF pulse length at 10 Hz repetition rate for the European XFEL. Several RF gun setups have been operated towards these goals over the last years. The latest gun setup was brought into the PITZ tunnel on February 10th 2016 and its RF operation started on March 7th. This setup includes RF gun prototype 4.6 with a new cathode contact spring design and an RF input distribution which consists of an in-vacuum coaxial coupler, an in-vacuum T-combiner and 2 RF windows from DESY production. In this contribution we will summarize the experience from the RF conditioning of this setup towards high average RF power and first experience from the operation with photoelectrons., Published by JACoW, Geneva, Switzerland

8th International Particle Accelerator Conference, Copenhagen, Denmark, 14 May 2017 - 19 May 2017; Geneva : JACoW, 2650 pp. (2017). doi:10.18429/JACoW-IPAC2017-WEPAB033, The Photo Injector Test facility at DESY, Zeuthen site (PITZ), develops high brightness electron sources for modern linac-based Free Electron Lasers (FELs). The PITZ accelerator can also be considered as a suitable machine for the development of an IR/THz source prototype for pump-probe experiments at the European XFEL. One of the interesting options for the IR/THz generation with PITZ is to generate the radiation by means of a SASE FEL using an uncompressed electron beam with bunch length of a few 10 ps and a peak current of ~200 A. In this paper, results of experimental optimizations and characterizations, including transverse phase space, slice transverse emittance and longitudinal phase space, of electron beams with bunch charges of 4 nC are presented and discussed. The measurements were done with beam momenta of 15 MeV/c and 22 MeV/c. Results of IR/THz SASE FEL calculations by using the GENESIS1.3 code based on the measured beam parameters are also presented and discussed., Published by JACoW, Geneva

The Photo Injector Test facility at DESY, Zeuthen site (PITZ), develops high brightness electron sources for modern linac-based Free Electron Lasers (FELs). The PITZ accelerator can also be considered as a suitable machine for the development of an IR/THz source prototype for pump-probe experiments at the European XFEL. Calculations of THz radiation by means of a SASE FEL based on the simulated and the measured beam profiles at PITZ for the radiation wavelength of 100 microns were performed by using the GENESIS1.3 code. The results of these simulations are presented and discussed in this paper., Proceedings of the 38th Int. Free Electron Laser Conf., FEL2017, Santa Fe, NM, USA

DPG-Frühjahrstagung, Darmstadt, Germany, 14 Mar 2016 - 18 Mar 2016 ; 1-11(2016).

7th International Particle Accelerator Conference, Busan, Korea, 8 May 2016 - 13 May 2016 ; (2016)., The Photo Injector Test facility at DESY, Zeuthen site (PITZ), was built with the aim to develop and characterize electron sources for future usage at FLASH and at the European XFEL. Recently, the main focus at PITZ has been the study of gun reliability and photoinjector performance at high average power. The goal is to get stable and reliable operation with 6.4 MW peak power in the gun at 650 μs RF pulse length and 10 Hzrepetition rate. To achieve this, a new RF feed system with two RF windows was installed at PITZ in 2014. During this test, the old gun 4.2 with a modified back-plane design for better cathode contact has been used. In this contribution the results of the RF conditioning of gun 4.2 with a detailed interlock analysis will be reported as well as results from recent electron beam characterization.

5th International Beam Instrumentation Conference, IBIC 2016, Barcelona, Spain, 11 Sep 2016 - 15 Sep 2016; JACoW, Geneva, Switzerland 1-4 (2016). doi:10.18429/JACoW-IBIC2016-WEPG47, A transverse deflecting system (TDS) is under commissioning at the Photo Injector Test Facility at DESY, Zeuthen site (PITZ). The structure was designed and manufactured by the Institute for Nuclear Research (INR RAS, Moscow, Russia) as prototype for the TDS in the injector part of the European XFEL. Last year the deflection voltage was limited for safety reasons, but after thorough investigations of the waveguide system we are now able to operate the cavity close to design specifications. The PITZ TDS streaks the electron beam vertically, allowing measurements of the longitudinal bunch profile, and, in combination with a subsequent horizontal bending magnet, also of the longitudinal phase space and slice energy spread. Furthermore, several quadrupole magnets and screen stations can be employed for slice emittance measurements using the TDS. This paper describes the progress in commissioning of the hardware, measurement techniques and simulations, and outlines the prospects of reliable slice emittance measurements at 20 MeV/c, where space charge forces complicate the determination of transfer matrices., Published by JACoW, Geneva, Switzerland