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Since end of the year 2020 the energy recovery linac (ERL) project bERLinPro of Helmholtz-Zentrum Berlin has been officially completed. But what is the status of this facility, the next scientific goals in the framework of accelerator physics at HZB, what are the perspectives? To reflect the continuation of this endeavor and the broadening of applications of this machine from high current SRF based energy recovery concept up to an ultrafast electron diffraction (UED) facility producing shortest electron pulses, the facility is now named Sealab, Superconducting RF Electron Accelerator Laboratory. In this contribution, an overview of lessons learned so far, the status of the machine, the coming set up and commissioning steps with an outlook to midterm and future applications will be given. In summary, Sealab will expand, including the ERL application, and become a general accelerator physics and technology test machine to employ UED as a first study case and will also be an ideal testbed to investigate new control schemes based on digital twins or machine learning methods., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

The first radiation from the cryogenic permanent magnet undulator (CPMU17) has been observed in December 2018 at the BESSY II storage ring at HZB, and since then this device has served as a light source for beamline commissioning. It is the first in-vacuum undulator installed at BESSY II, and a new in-vacuum APPLE undulator (IVUE32) is planned to be installed in near future. Thus, a detailed study of the interactions between such an in-vacuum device and the electron beam is required. Beam-based measurements using orbit-bump and tune-shift methods have been applied to estimate the vertical impedance of CPMU17. For CPMU17 the first results of broad-band impedance studies are presented., Proceedings of the 9th International Beam Instrumentation Conference, IBIC2020, Santos, Brazil

The Helmholtz-Zentrum Berlin is constructing the Energy Recovery Linac Prototype BERLinPro, a SRF based demonstration facility for the science and technology of ERLs for future high power, high brilliance electron beam applications. BERLinPro was designed to accelerate a high current (100 mA, 50 MeV), high brilliance (norm. emittance below 1 mm mrad) cw electron beam. Given the recent prioritization of the BESSY II upgrade to the BESSY VSR variable pulse length storage ring, HZB is forced to reduce the project goals of BERLinPro. As a result, the project had to be rescoped with the goal to maximize its scientific impact within the present boundary conditions. We report on the last year’s progress of the building, the warm and cold infrastructure and on the time line, goals nd opportunities for the remaining project run time., Proceedings of the 63th ICFA Advanced Beam Dynamics Workshop on Energy Recovery Linacs, ERL2019, Berlin, Germany

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

Journal of applied physics 125(6), 063301 (2019). doi:10.1063/1.5068753, In the field of beam driven acceleration of particles in plasma wakefields (PWFA), the source of the plasma medium is a crucial part of the accelerator setup. Gas discharges have proven to be a reliable and simple type of a plasma source in past experiments. Nevertheless, especially in plasma cells that aim for peak density in the range of 10^{15}1/cm^3, physical apertures around10 mm, and lengths of up to several meters, the stability of the discharge ignition and the pulse current waveform is limiting theapplicability. We show successful mitigation of these jitters in a 0.1 m argon gas discharge cell, operating at maximum densitiesof10^{16}1/cm^3by optimisation of the cell design and the discharge current pulse circuit., Published by American Inst. of Physics, Melville, NY

We investigate a transverse RF kick induced by the transition between rectangular waveguide and coaxial line of the RF coupler in the 1.6-cell L-band normal conducting (NC) RF gun at the Photo Injector Test Facility at DESY, Zeuthen site (PITZ). A three-dimensional electromagnetic simulation shows the disturbed RF field distributions in the fundamental accelerating mode. Based on the 3D RF field map, an electron beam based characterization and quantification of the coaxial coupler RF kick in the PITZ gun is simulated. Preliminary results of the investigations are presented., Proceedings of the 38th Int. Free Electron Laser Conf., FEL2017, Santa Fe, NM, USA

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

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.

The optimization of photoinjectors is crucial for the successful operation of linac-based free electron lasers, and beam dynamics simulations have shown that ellipsoidal photocathode laser pulses result in significantly lower electron beam emittance than that of conventional cylindrical pulses. Therefore, in collaboration with the Institute of Applied Physics (Nizhny Novgorod, Russia) and the Joint Institute of Nuclear Research (Dubna, Russia), a laser system capable of generating quasi-ellipsoidal laser pulses has been developed and installed at the Photo Injector Test facility at DESY, Zeuthen site (PITZ). The pulse shaping has been realized using the spatial light modulator technique, characterized by cross-correlation and spectrographic measurements, and is demonstrated with electron beam measurements. In this contribution the overall setup, operating principles, and results of first regular electron beam measurements will be presented together with corresponding beam dynamics simulations. Furthermore, the numerous improvements of the simplified re-design currently under construction shall be detailed., Proceedings of the 38th Int. Free Electron Laser Conf., FEL2017, Santa Fe, NM, USA

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.

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 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

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

PITZ collaboration meeting, Zeuthen, DESY Zeuthen, Germany, 31 May 2016 - 1 Jun 2016 ; (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

At DELTA, a 1.5-GeV synchrotron light source operated by the TU Dortmund University, a source for coherent and ultrashort vacuum-ultraviolet (VUV) and terahertz (THz) pulses is now in operation. The VUV source is based on a laser-induced energy modulation and coherent harmonic generation (CHG). A subsequently developing dip in the longitudinal electron distribution gives rise to coherent THz radiation. Recent results regarding the optimization of the laser-electron interaction and characterization of the CHG pulses are presented., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

For the operation of free electron lasers (FELs) like the European X-FEL and FLASH located at DESY, Hamburg Site, high quality electron beams are required already from the source. The Photo Injector Test facility at DESY, Zeuthen Site (PITZ) was established to develop, characterize and optimize electron sources for such FELs. Last year the work at PITZ focused on the optimization of a photo injector operated with the startup parameters of the European X-FEL. This implies photocathode laser pulses with a Gaussian temporal profile of about 11-12 ps FWHM to drive the photo gun operated at a gradient of 53 MV/m. Significant effort was spent on the electron beam characterization and optimization for various bunch charges. Emittance measurements were performed as a function of major accelerator parameters such as main solenoid current, laser spot size on the cathode and the gun launching phase. The requirement on the beam emittance for bunch charge of 500 pC for the European XFEL commissioning phase has been demonstrated. Results of these studies accompanied with the corresponding simulations are presented in this paper., Proceedings of the 37th International Free Electron Laser Conference, FEL2015, Daejeon, Republic of Korea

High brightness electron sources for free electron lasers like FLASH and the European XFEL are developed, optimized and characterized at the Photo Injector Test facility at DESY in Zeuthen (PITZ). Last year the facility was significantly upgraded with a new prototype photocathode laser capable of producing homogeneous ellipsoidal pulses. Previous simulations have shown that the corresponding pulses produce high brightness electron bunches with minimized emittance. Furthermore, a new normal conducting RF gun cavity was installed with a modified two-window waveguide RF feed layout for stability and reliability tests, as required for the European XFEL. Other relevant additions to the facility include beamline modifications for improved electron beam transport through the PITZ accelerator, refinement of both the cooling and RF systems for improved parameter stability, and preparations for the installation of a plasma cell. This paper describes the facility upgrades and reports on the operational experience with the new components., Proceedings of the 37th International Free Electron Laser Conference, FEL2015, Daejeon, Republic of Korea

DELTA is a 1.5-GeV synchrotron light source operated by the TU Dortmund University. The beam lifetime, which is a critical issue for user operation of a light source, was studied experimentally and by simulation for different operation modes, i.e. single-bunch and multibunch fill patterns and for different beam currents. The electron loss rate is dominated by residual-gas scattering (Coulomb scattering and Bremsstrahlung) and by electron-electron scattering (Touschek effect). Since these processes depend in different ways on the momentum acceptance of the storage ring, a variation of the RF cavity voltage allows to disentangle their respective contributions to the total loss rate. The experimental results lead to a consistent picture for different operation modes with a characteristic dependence of the residual-gas pressure on the beam current., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

At the 1.5-GeV electron storage ring DELTA operated by the TU Dortmund University as a synchrotron radiation user facility, bunch-by-bunch feedback systems are in use for electron beam diagnostics and for the suppression of multibunch instabilities. An automatic readout of bunch position data allows a real-time modal analysis during machine operation. An excitation of particular multibunch modes enables the determination of growth and damping times for all modes independently. Further investigations of beam stability and natural damping times of all modes even below the instability threshold have been performed. In addition, first bunch-by-bunch data taken from the booster synchrotron are shown., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

A light source facility employing the coherent harmonic generation (CHG) principle is being commissioned and operated since 2011 at DELTA, a 1.5-GeV electron storage ring at the TU Dortmund University, with the purpose of providing ultrashort coherent VUV radiation for time-resolved experiments. CHG is based on the interaction of ultrashort laser pulses with electrons in an undulator to generate coherent harmonics of the laser wavelength. Different methods have been used to optimize, detect and characterize the CHG radiation. One example is the study of transverse and longitudinal coherence properties in double-slit and Michelson experiments. Moreover, final steps towards performing pump-probe experiments to study ultrafast magnetic phenomena have been taken., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

Free Electron Laser erzeugen hochbrillante, ultrakurze Laserpulse variabler Wellenlänge und kombinieren somit die Vorteile von Synchrotronstrahlung und Laser. Im Rahmen dieser Arbeit wurde der FEL-Oszillator am Speicherring DELTA hinsichtlich Geschwindigkeit und Reproduzierbarkeit der gesamten Justageprozedur optimiert, um einen stabilen FEL-Betrieb für beschleunigerphysikalische Experimente zu etablieren. Damit war erstmalig die Messung und Untersuchung der Zusammenhänge zwischen Gain, Ausgangsleistung und Pulsstruktur des Lasers, und des Strahlstroms, der Energiebreite und der longitudinalen Dynamik des Elektronenstrahls bei DELTA möglich. Zu diesem Zweck wurden neue Spiegelkammern und Spiegelsteuerungen für den optischen Resonator konstruiert. Der FEL konnte erfolgreich wieder in Betrieb genommen werden, so dass im zweiten Teil dieser Arbeit eine weitreichende Charakterisierung der erzeugten Laserstrahlung im sichtbaren Bereich erfolgte. Lasing wurde mit unterschiedlichen Füllstrukturen im Speicherring und unterschiedlichen Laserpulsstrukturen erzielt. Mithilfe des optischen Klystrons wurde die Energiebreite des Elektronenstrahls direkt, unabhängig von der Bunchlänge gemessen. Der Gain und die Leistung des FELs wurden gemessen und mit den theoretischen Modellen, insbesondere dem Low-Gain-Modell und dem Renieri-Limit, verglichen. Hierdurch konnte gezeigt werden, dass das Einsetzen des FEL-Prozesses eine dämpfende Wirkung auf die Energiebreite des Elektronenstrahls hat; die turbulente Bunchverlängerung wird ganz oder zum Teil außer Kraft gesetzt.

The Photo Injector Test facility at DESY, Zeuthen site (PITZ), develops, optimizes and characterizes high brightness electron sources for free electron lasers like FLASH and the European XFEL. In the last year, the facility was significantly upgraded by the installation of a new normal conducting radio- frequency (RF) gun cavity with its new waveguide system for the RF feed, which should allow stable and reliable gun operation, as required for the European XFEL. Other relevant additions include beamline modifications for improving the electron beam transport through the PITZ accelerator, extending the beam-based measurement capabilities, and preparing the installation of a plasma cell. Furthermore, the laser hutch was re-arranged in order to be able to house an additional, new photo cathode drive laser system which should be able to produce 3D ellipsoidal laser pulses to further improve the electron beam quality. This paper describes in detail the aforementioned facility upgrades and reports on the first operation experience with the new gun setup., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

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

In the field of plasma wakefield acceleration (PWFA) significant progress has been made throughout the recent years. However, an important issue in building plasma based accelerators that provide particle bunches suitable for user applications will be a high transformer ratio, i.e. the ratio between maximum accelerating field in the witness and maximum decelerating fields in the driver bunch. The transformer ratio for symmetrical bunches in an overdense plasma is naturally limited to 2*. Theory and simulations show that this can be exceeded using asymmetrical bunches. Experimentally this was proven in RF-structures**, but not in PWFA. To study transformer ratios above this limit in the linear regime of a plasma wake, an experimental scheme tailored to the unique capabilities of the Photoinjector Test Facility Zeuthen PITZ, a 20-MeV electron accelerator at DESY, is being investigated. This includes analytical plasma wakefield calculations, numerical simulations of beam transport and plasma wakefields, as well as preparatory studies on the photocathode laser system and the plasma sources., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

Physical review letters 120(14), 144802 (2018). doi:10.1103/PhysRevLett.120.144802, Self-modulation of an electron beam in a plasma has been observed. The propagation of a long (several plasma wavelengths) electron bunch in an overdense plasma resulted in the production of multiple bunches via the self-modulation instability. Using a combination of a radio-frequency deflector and a dipole spectrometer, the time and energy structure of the self-modulated beam was measured. The longitudinal phase space measurement showed the modulation of a long electron bunch into three bunches with an approximately 200 keV=c amplitude momentum modulation. Demonstrating this effect is a breakthrough for proton-driven plasma accelerator schemes aiming to utilize the same physical effect., Published by APS, College Park, Md.

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., Proceedings of the 8th International Beam Instrumentation Conference, IBIC2019, Malmö, Sweden

For successful operation of X-ray Free Electron Lasers, one crucial parameter is the ultrashort electron bunch length yielding a high peak current and a short saturation length. In order to effectively compress the bunches during the acceleration process, a detailed understanding of the full longitudinal phase space distribution already in the injector is required. Transverse deflecting RF structures (TDS) can shear the bunch transversely, mapping the longitudinal coordinate to a transverse axis on an observation screen downstream. In addition to the bunch length, the slice emittance along the bunch as well as the full longitudinal phase space can be obtained. At the Photo Injector Test Facility at DESY, Zeuthen site (PITZ), an S-band traveling wave TDS is under commissioning since 2015. This cavity is a prototype for the TDS in the injector part of the European XFEL and has been designed and manufactured by the Institute for Nuclear Research (INR, Moscow, Russia). In this paper, first commissioning results of the system at PITZ are presented and discussed., Proceedings of the 37th International Free Electron Laser Conference, FEL2015, Daejeon, Republic of Korea

DPG - Frühjahrstagung 2018, Würzburg, Germany, 19 Mar 2018 - 23 Mar 2018, Transverse emittance is one of the most important properties for high-brightness electron beams used for X-Ray free-electron lasers. The photo injector test facility at DESY in Zeuthen (PITZ) focuses on the development of high-brightness electron sources. The two main methods to measure the emittance are the quadrupole scan and the slit scan. Combining either of these methods with a transverse deflecting cavity allows the measurement of the slice emittance. At PITZ, space-charge effects at the low beam momentum of 24 MeV/c complicate in particular the quadrupole scan. This has to be considered in the emittance measurements. First slit-scan based slice emittance results will be shown next to studies on the beam transport for quadrupole scans.

7th International Beam Instrumentation Conference, IBIC 2018, Shanghai, China, 9 Sep 2018 - 13 Sep 2018; Geneva, Switzerland : JACoW 3 pp. (2018)., The Photo Injector Test facility at DESY in Zeuthen (PITZ) is dedicated to the development of high-brightness electron sources for free-electron lasers. At PITZ, to measure the emittance of space-charge-dominated beams, the slit scan technique is used. For slice emittance measurements a transverse deflecting structure (TDS) is employed. Theelectron beam distribution is measured by means of scintillator screens. Both the TDS and the slit mask reduce the signal strength, giving stringent requirements on the sensi-tivity of the screens. At PITZ, high-sensitivity Ce:LYSO screens have been installed at the same screen stations as the standard Ce:YAG screens to solve low-intensity issues. Acomparison of both screens is presented., Published by JACoW, Geneva, Switzerland

At DELTA, a 1.5-GeV electron storage ring operated as a light source by the Center for Synchrotron Radiation at the TU Dortmund University, coherent ultrashort THz pulses are routinely generated by density-modulated electron bunches. Tracking simulations as well as experimental studies using ultrafast THz detectors and an FT-IR spectrometer aim at understanding the turn-by-turn evolution of the density modulation after an initial laser-electron interaction. Furthermore, intensity-modulated laser pulses are applied to create narrow-band THz radiation. This setup is part of the new short-pulse facility based on coherent harmonic generation., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany