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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.

The photoinjectors of FLASH at DESY (Hamburg, Germany) and the European XFEL are operated by laser driven RF-guns. In both facilities cesium telluride photocathodes are successfully used since several years. We present recent data on the lifetime, quantum efficiency (QE), and dark current of the photocathodes currently in operation. In addition we present recent design changes in the photocathode transfer systems in order to further improve the cathode handling.

Superconducting Undulators (SCUs) can produce higher photon flux and cover a wider photon energy range compared to permanent magnet undulators (PMUs) with the same vacuum gap and period length. To build the know-how to implement superconducting undulators for future upgrades of the European XFEL facility, two magnetic measurement test stands named SUNDAE 1 and 2 (Superconducting UNDulAtor Experiment) are being developed. SUNDAE1 will facilitate research and development on magnet design thanks to the possibility of training new SCU coils and characterizing their magnetic field. The experimental setup will allow the characterization of magnets up to 2m in length. These magnets will be immersed in a Helium bath at 2K or 4K temperature. In this article, we describe the experimental setup and highlight its expected performances., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

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

European XFEL foresees a superconducting undulator (SCU) afterburner in the SASE2 hard X-ray beamline. It consists of six 5m-long undulator modules with a 5mm vacuum gap, where each module contains two 2m-long coils and one phase shifter. Prior to installation, the magnetic field must be mapped appropriately. Two magnetic measurement test stands named SUNDAE 1 and 2 (Superconducting UNDulAtor Experiment) are being developed at European XFEL. While SUNDAE1 will be a vertical test stand to measure SCU coils up to two meters with Hall probes in a liquid or superfluid helium bath, SUNDAE2 will measure the SCU coils assembled in the final cryostat. This contribution presents the development status of SUNDAE2 and its main requirements., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

Caesium Telluride (Cs₂Te) photocathodes, are the elec-tron source of choice, by many global accelerators such as European XFEL, FLASH and AWA. It offers high quantum efficiency and reasonable operational lifetime with lower vacuum requirements than multi-alkali photocathodes. In this paper, we report on the first synthesised CsxTe photocathodes at ASTeC, using both sequential and co-deposition of Te and Cs on Mo substrate. Te deposition is carried out using ion beam deposition whilst the Cs is deposited using a SAES getter alkali. The ion beam deposition of Te provides a high degree of control to give a dense, smooth layer with a reproducible film thickness. The chemical state with respect to film composition of the deposited CsxTe is determined with in-situ XPS anal-yses. The films exhibit a quantum efficiency between 7.5 to 9 % at 266 nm wavelength., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

P3Workshop@SLAC, DESY, 10 Nov 2021

Photocathode Physics for Photoinjectors Workshop, California, DESY, USA, 10 Nov 2021 - 12 Nov 2021

39th International Free-Electron Laser Conference, FEL19, Hamburg, Germany, 26 Aug 2019 - 30 Aug 2019; 0-3 (2019).

The photoinjectors of FLASH and the European XFEL at DESY (Hamburg, Germany) are operated by laser driven RF-guns. In both facilities Cs2Te photocathodes are successfully used. In this paper we give an update on the lifetime, quantum efficiency (QE) and dark current of the photocathodes used over the last years. At FLASH cathode #73.3 was operated for a record lifetime of 1413 days and was replaced December 2018 by cathode #10⁵.2. At the European XFEL cathode #680.1 is in operation since December 2015, for 1356 days up to now., Proceedings of the 39th Free Electron Laser Conference, FEL2019, Hamburg, Germany

39th International Free-Electron Laser Conference, FEL19, Hamburg, Germany, 26 Aug 2019 - 30 Aug 2019; JACoW Publishing, Geneva, Switzerland 473-476 (2019). doi:10.18429/JACOW-FEL2019-WEP062, Cesium telluride is a widely used cathode in photo injectors, and its performance is one of the keys for not only emittance but also reliable operation. Over the years lots of experiences with Cs2Te photocathodes produced with the same recipe and thickness were gained at the DESY photo injectors, but cathode performance dependence on the cathode layer thickness were not investigated. In this paper, we test fresh Cs2Te cathodes with different thickness at the Photo Injector Test Facility at DESY in Zeuthen (PITZ). The QE and thermal emittance of these cathodes inside the high gradient RF gun will be compared. Besides, the injector emittance under the operation conditions of the XFEL will also be measured with these cathodes., 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 396-399 (2019). doi:10.18429/JACOW-FEL2019-WEP036, A collaboration between DESY, PSI and CERN has been established to develop and build an advanced modular X- band transverse deflection structure (TDS) system with the new feature of providing variable polarization of the deflecting force. The prototype of the novel X-band TDS, the Polarizable X-band (PolariX) TDS, was fabricated at PSI following the high-precision tuning-free production process developed for the C-band Linac of the SwissFEL project. Bead-pull RF measurements were also performed at PSI to verify, in particular, that the polarization of the dipole fields does not have any rotation along the structure. The high-power test was performed at CERN and now the TDS is at DESY and has been installed in FLASHForward, where the first streaking experience with beam will be accomplished. We summarize in this paper the status of the project, the results of the bead-pull measurements and the high power test., Published by JACoW Publishing, Geneva, Switzerland

The ARES (Accelerator Research Experiment at SINBAD) linac at the accelerator R facility SINBAD (Short innovative bunches and accelerators at DESY) will drive multiple independent experiments including the acceleration of ultrashort electron bunches. In addition the linac will host an experimental area, open for transnational access, to study advanced high gradient, laser driven, acceleration concepts, like the ones studied within the ACHIP (accelerator on a chip) project. The area will be operational mid-2019. This paper will report on the current status of the experimental area, including hardware parameters, beam optics, achievable beam parameters, design of the experimental chamber and commissioning plans. The modification plans for a micro-bunching experiment in the frame of the ACHIP experiment and future upgrade plans will be shown and discussed in detail., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

Bunch compressors are essential for the generation of short bunches with applications in e.g. colliders, free electron lasers, and advanced accelerator concepts. The up-and-coming ARES accelerator located at SINBAD, DESY will support the formation of ~100~MeV, pC, sub-fs electron bunches for LWFA research and development. We give an overview on the ARES bunch compressor, providing start-to-end simulations of the machine and an update on its technical design., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The SINBAD facility (Short and INnovative Bunches and Accelerators at DESY) is foreseen to host multiple experiments relating to the production of ultra-short electron bunches and novel high gradient acceleration techniques. The SINBAD-ARES linac will be a conventional S-band linear RF accelerator allowing the production of low charge (0.5 pC - tens pC) ultra-short electron bunches (FWHM length =< 1 fs - few fs) with 100 MeV energy. The installation of the linac will proceed in stages. In this paper we report on the status of the characterization of the ARES RF gun and the installations of the related infrastructure., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

9th International Particle Accelerator Conference, IPAC’18, Vancouver, Canada, 29 Apr 2018 - 4 May 2018; JACoW Publishing 3865-3868 (2018). doi:10.18429/JACoW-IPAC2018-THPAL095, The photoinjector of the CLARA FEL test facility Front End at Daresbury Laboratory is based on a S-band 10 Hz photocathode RF-gun operating with a copper photocath-ode which is driven by the third harmonic of a Ti:Sapphire laser (266 nm). The main aim of this study was to establish a procedure to prepare the Cu surface prior to installation so a Quantum Efficiency (QE) of 10⁻⁵ or higher can be achieved at laser power density below the ablation threshold of copper. The best results have been obtained by ex-situ chemical cleaning. This removed the surface oxide layer whilst at the same time producing a surface buffer layer. This inhibited the regrowth of native oxide for up to a week when exposed to normal ambient atmospheric conditions. With either chemical cleaning or Ar plasma cleaning after heating the sample in-situ to 150 °C for 90 minutes or 250 °C for 40 hours, almost all of the surface oxide was removed. For these surfaces a QE of 4.10-5 or better was measured. Oxygen plasma cleaning at 100% and 20% power produced CuO layer with surface carbon contaminant to 3 atomic %, however in-situ thermal cycling resulted in at best a QE of 3·10-6., Published by JACoW Publishing

6th ARD ST3 workshop, Dresden, HZDR, Germany, 26 Sep 2018 - 28 Sep 2018

9th International Particle Accelerator Conference, IPAC'18, Vancouver, Canada, 29 Apr 2018 - 4 May 2018; Geneva, Switzerland : JACoW Publishing 3808-3811 (2018). doi:10.18429/JACOW-IPAC2018-THPAL068, A collaboration between DESY, PSI and CERN has been established to develop and build an advanced modular X-band transverse deflection structure (TDS) system with the new feature of providing variable polarization of the deflecting force. This innovative CERN design requires very high manufacturing precision to guarantee highest azimuthal symmetry of the structure to avoid the deterioration of the polarization of the streaking field. Therefore, the high-precision tuning-free production process developed at PSI for the C-band and X-band accelerating structures will be used for the manufacturing. We summarize in this paper the status of the production of the prototype and the waveguide networks foreseen in the different facilities., Published by JACoW Publishing, Geneva, Switzerland

Cockcroft Institute Seminar, Daresbury, STFC Daresbury, UK, United Kingdom, 21 Nov 2018

[Ebook] FEL 2017 : 38th International Free Electron Laser Conference : 20th-25th August, 2017, Santa Fe Convention Center, Santa Fe, NM, USA / editors: Kip Bishofberger (LANL), Bruce Carlsten (LANL), Volker RW Schaa (GSI , [Genf] : [CERN], [2018], 38th International Free Electron Laser Conference, Santa Fe, USA, 20 Aug 2017 - 25 Aug 2017; Geneva, Switzerland : JACoW 42-45 (2018). doi:10.18429/JACoW-FEL2017-MOP008, A Hard X-ray Self-Seeding setup is currently under realization at the European XFEL, and will be ready for installation in 2018. The setup consists of two single-crystal monochromators that will be installed at the SASE2 undulator line. In this contribution, after a short summary of the physical principles and of the design, we will discuss the present status of the project including both electron beam and X-ray optics hardware. We will also briefly discuss the expected performance of the setup, which is expected to produce nearly Fourier-limited pulses of X-ray radiation with increased brightness compared to the baseline of the European XFEL, as well as possible complementary uses of the two electron chicanes., Published by JACoW, Geneva, Switzerland

9th International Particle Accelerator Conference, IPAC'18, Vancouver, Canada, 29 Apr 2018 - 4 May 2018; JACoW Publishing 2493-2495 (2018). doi:doi:10.18429/JACoW-IPAC2018-WEPMF055, Since 2011 the Relativistic Electron Gun for Atomic Exploration (REGAE) is operated at DESY in Hamburg. The accelerator consists mainly of a high gradient S-band RF-gun, which generates ultra-low emittance electron bunches, and an S-band RF-buncher cavity for bunch compression. In this contribution we describe the vacuum system of the REGAE accelerator. We will cover design aspects, applied cleaning and installation procedures as well as operation experience over the last years., Published by JACoW Publishing

The photoinjector of the free-electron laser facility FLASH at DESY (Hamburg, Germany) uses Cs2Te photocathodes. We report on an update of the lifetime and quantum efficiency of cathodes operated at FLASH during the last years., Proceedings of the 38th Int. Free Electron Laser Conf., FEL2017, Santa Fe, NM, USA

The 9th International Particle Accelerator Conference, IPAC'18, Vancouver, Canada, 29 Apr 2018 - 4 May 2018, The photoinjectors of FLASH and the European XFEL at DESY (Hamburg, Germany) use Cs$_2$ Te photocathodes. In this contribution we give an update on the lifetime and quantum efficiency of the cathodes operated in both facilities. Cathode #680.1 was operated at the European XFEL from the injector commissioning to the first user run for over 700 days. At FLASH cathode #73.3 has been operated with a record of more than 1000 days.

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

8th International Particle Accelerator Conference, IPAC17, Copenhagen, Denmark, 15 May 2017 - 19 May 2017 ; Geneva : JACoW, 3 pp. (2017). doi:10.18429/JACoW-IPAC2017-TUPAB040, ARES (Accelerator Research Experiment at Sinbad) is a linear accelerator for the production of low charge (from few pC to sub-pC) electron bunches with 100 MeV energy, fs and sub-fs duration and excellent arrival time stability. This experiment is currently under construction at DESY Hamburg and it is foreseen to start operation by the beginning of 2018 with the commissioning of the RF-gun. After an initial beam characterization phase, ARES will provide high temporal resolution probes for testing novel acceleration techniques, such as Laser driven plasma Wake-Field Acceleration (LWFA), Dielectric Laser Acceleration (DLA) and THz driven acceleration. In this work we present an overview of the present design of the linac with a special focus on 3D integration and planned installation phases of the beamline., Published by JACoW, Geneva

8th International Particle Accelerator Conference, IPAC17, Copenhagen, Denmark, 15 May 2017 - 19 May 2017 ; Geneva : JACoW, 3 pp. (2017). doi:10.18429/JACoW-IPAC2017-WEPVA048, Non Evaporable Getter pumps have been used since four decades in various scientific and industrial Ultra High and Extremely Ultra High Vacuum applications. For the majority of applications properties like high pumping speed vs. small size, powerless operation and hydrocarbon cleanliness are main aspects for the usage. In addition to this a growing number of applications nowadays also require particle free systems. In this paper we report on investigations on in-vacuum particle creation during the conditioning and activation process of CapaciTorr pumps., Published by JACoW, Geneva

38th International Free Electron Laser Conference, FEL2017, Santa Fe, United States, 20 Aug 2017 - 25 Aug 2017; 4 pp. (2017)., The photoinjector of the free-electron laser facility FLASH at DESY (Hamburg, Germany) uses Cs2Te photocathodes.We give an update on lifetime and quantumefficiency of cathodes operated at FLASH during the lastyears. At the time of the conference, cathode 73.3 has been operated with a record of 933 days with a stable quantum efficiency of in average 8.8 %.

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

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.

The injector of the free-electron laser facility FLASH at DESY (Hamburg, Germany) uses Cs2Te photocathodes. We report on the lifetime, quantum efficiency (QE), and darkcurrent of photocathodes operated at FLASH during the last year. Cathode 618.3 has been operated for a record of 439 days with a stable QE in the order of 3%. The fresh cathode 73.3 shows an enhancement of emitted electrons for a few microseconds of a 1 MHz pulse train., Proceedings of the 37th International Free Electron Laser Conference, FEL2015, Daejeon, Republic of Korea

At DESY, caesium telluride photocathodes are successfully used for the RF Guns at DESY,namely FLASH, PITZ, and REGAE. Their high quantum efficiency and long lifetime allow toproduce routinely thousands of bunches per second with a single bunch charge in the nCrange. We report on the status of the preparation system and updates on lifetime, quantumefficiency, darkcurrent, and operating experience.

At the Photo Injector Test facility at DESY, Zeuthen site (PITZ), high brightness electron sources for linac based Free Electron Lasers (FELs), like FLASH and the European XFEL are developed and characterized. The electrons are generated via the photoeffect at a cesium telluride (Cs₂Te) cathode and are accelerated by a 1.6-cell L-band RF-gun cavity with an accelerating gradient at the cathode of about 60 MV/m. The profile of the cathode laser pulse has been optimized yielding small emittances using laser pulse shaping methods. The transverse projected emittance is measured by a single slit scan technique. The measurement program in the last run period at PITZ concentrated on emittance measurements for the nominal 1 nC beam and emittance optimization for lower bunch charges. The recent results show that normalized projected emittances of about 1 mm-mrad for 1 nC charge and below 0.5 mm-mrad for 250 pC bunch charges can be realized at PITZ. The facility setup and measurement results including the uncertainty of the measured values will be reported and discussed in this contribution., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

In dieser Arbeit wird mit Hilfe der koinzidenten Messung des Energieverlusts gestreuter Projektile zusammen mit der Anzahl emittierter Elektronen pro Streuprozess die Wechselwirkung schneller Atome mit Metalloberflächen untersucht. Dabei wird insbesondere die streifende Streuung der Edelgasatome Helium, Neon und Argon an Al(110)-, Al(111)- und Cu(111)-Oberflächen betrachtet. In den ersten Kapiteln wird die Messmethode der streifenden Streuung, der verwendete experimentelle Aufbau sowie der Charakterisierung der untersuchten Metalloberflächen anhand ihrer geometrischen und elektronischen Eigenschaften erläutert. Nach einführenden Betrachtungen zu Energieverlust und Elektronenemission bei der streifenden Streuung von Heliumatomen erfolgt eine detaillierte Diskussion zum Schwellenverhalten der kinetischen Elektronenemission (KE). Dabei wird gezeigt, dass das Schwellenverhalten durch ein Modell basierend auf dem zentralen Stoss zwischen Projektil und Valenzelektronen beschrieben werden kann. Aus den Schwellengeschwindigkeiten werden Informationen über Elektronenimpulse und Elektronenpotentiale vor Metalloberflächen abgeleitet. Ferner wird die Streuung von Neon- und Argonatomen untersucht. Für das System Ne-Al(111) wird ab Senkrechtenergien von ca. 25 eV Elektronenpromotion beobachtet. KE unterhalb der klassischen Schwelle für die Streuung von Neon- und Argonatomen wird im Rahmen von zwei alternativen Modellen interpretiert: der Effekt der Impulsdichteverteilung der Elektronen vor der Oberfläche oder die gleichzeitige Anregung zweier benachbarter Elektronen mit anschließenden Auger-Zerfall. Abschließend die unterschiedlichen KE für axiales und planares Oberflächen-Channeling untersucht und interpretiert., The kinetic electron emission (KE) in coincidence with the energy loss of noble gas atoms impinging on metal surfaces under grazing angles of incidence is studied. Results for scattering of helium, neon, and argon atoms from Al(111), Al(110), and Cu(111) are presented and discussed. In the first chapters the experimental technique of grazing scattering, the experimental setup, and a geometric and electronic characterization of the surfaces is described. General aspects of projectile energy loss and KE for grazing scattering of helium atoms are discussed. It is shown that the threshold behavior of the KE can be interpreted in terms of a simple model of binary-encounter between projectiles and valence electrons. From threshold velocities for KE electron momenta and potentials in front of the studied metal surfaces are derived. Then special features for the grazing scattering of neon and argon are discussed. For neon impinging on Al(111) with energies normal to the surface above 25 eV electron promotion was found to dominate the electron emission process. Sub-threshold KE for scattering of neon and argon atoms is interpreted by two models. The first one is based on the local electron momentum distribution in front of the surface. The second one involves correlated excitation of two conduction electrons well above the Fermi level with subsequent emission of an electron via Auger deexcitation. Furthermore an explanation for the different KE yields under axial and planar surface channeling conditions is provided.

8th International Particle Accelerator Conference, IPAC17, Copenhagen, Denmark, 15 May 2017 - 19 May 2017 ; Geneva : JACoW, 184-187(2017). doi:10.18429/JACoW-IPAC2017-MOPAB044, Based on the success of the X-Band Transverse Deflecting Structure (TDS) diagnostic at LCLS*, a collaboration between DESY, PSI and CERN has formed with the aim of developing and building an advanced modular X-Band TDS system. The designed TDS has the new feature of providing variable polarization of the deflecting field**. The possibility of changing the orientation of the streaking field of the TDS to an arbitrary azimuthal angle allows for 3D characterization of the phase space using tomographic methods***. Moreover the complete 6D characterization of the beam phase space is possible by combining this technique with quadrupole scans and a dipole spectrometer. As this new cavity design requires very high manufacturing precision to guarantee highest azimuthal symmetry of the structure to avoid the deterioration of the polarization of the streaking field, the high precision tuning-free assembly procedures developed at PSI for the SwissFEL C-band accelerating structures will be used for the manufacturing****. The high-power rf system is based on the CERN-based X-band test stands. We summarize in this work the status of the projects and its main technical parameters., Published by JACoW, Geneva

Recently three RF guns were prepared at the Photo Injector Test Facility at DESY, location Zeuthen (PITZ) for their subsequent operation at FLASH and the European XFEL. The gun 3.1 is a previous cavity design and is currently installed and operated at FLASH, the other two guns 4.3 and 4.4 were of the current cavity design and are dedicated to serve for the start-up of the European XFEL photo-injector. All three cavities had been dry-ice-cleaned prior their conditioning and hence showed low dark current levels. The lowest dark current level – as low as 60μA at 65MV/m field amplitude – has been observed for the gun 3.1. This paper reports in details about the conditioning process of the most recent gun 4.4. It informs about experience gained at PITZ during establishing of the RF conditioning procedure and provides a comparison with the other gun cavities in terms of the dark currents. It also summarizes the major setup upgrades, which have affected the conditioning processes of the cavities., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

Caesium telluride photocathodes are used as laser driven electron sources at the Free-Electron-Laser Hamburg, FLASH, and will be used at the European XFEL. One concern of the operation of photocathodes in these user facilities is the degradation of the quantum efficiency during operation. After improving vacuum conditions and removing contaminants, the cathode life time increased from a couple of weeks to several months. In this contribution we report on long time operation of Cs₂Te cathodes in terms of QE measurements and investigations on the homogeneity of the electron emission. Another concern of electron guns operated with long RF-pulses (0.8 ms at FLASH) is the generation of dark current either from the cathode or from the gun body. During the last years a constant high amount of dark current, emitted from the gun body itself, was observed at FLASH. Caused by that during the shut-down 2009/2010 the RF-gun at FLASH, operated more than five years, was replaced. The improved dark current situation with the new RF-gun is presented in terms of dark current measurements under different operational conditions., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan