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Multi-alkali antimonide photocathodes can have high quantum efficiency similar as UV sensitive (Cs2Te) photocathodes, but with the advantages of photoemission sensitivity in the visible region of the light spectrum and a significant reduction in the mean transverse energy of photoelectrons. A batch of three KCs2Sb photocathodes was grown on molybdenum substrates via a sequential deposition method in a new preparation system at INFN LASA. Afterwards, the cathodes were successfully tested in the high gradient RF gun at PITZ. This contribution summarizes the experimental results obtained in both the preparation chamber and the RF gun. Based on those findings, we are now optimizing the recipe of KCs2Sb and NaKSb(Cs) photocathodes for lower field emission and longer lifetime, and the measurements for the latest photocathodes with the improved recipe are also presented.

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 Photo Injector Test Facility at DESY in Zeuthen (PITZ) develops a prototype of an accelerator-based high-power tunable THz source for pump-probe experiments at the European XFEL. The PITZ injector is also the site for the development and preparation of the high-brightness electron source for the main linac of the European XFEL and has the same pulse train structure as the X-ray photon source of the XFEL. For the proof-of-principle experiments on high-power THz generation an LCLS- I undulator (on loan from SLAC) is installed in the tunnel annex downstream of the existing accelerator. The extension of the beam line consists of a bunch compressor and a collimation system in the main PITZ tunnel, as well as a matching section, the undulator and the THz diagnostic setup in the tunnel annex. A Self-Amplified Spontaneous Emission (SASE) FEL is used to generate the THz pulses. High radiation power can be achieved by utilizing high charge (up to several nC) electron bunches from the PITZ photo injector. A beam energy of ~17 MeV is used to generate THz radiation with a centre wavelength of 100 μm. The transport of this space charge dominated electron beam and its thorough matching into the planar LCLS-I undulator with a strong vertical focusing is one of the project challenges. The installation of the first THz beamline setup was finished in summer 2022 and com-missioning with electron beam started. A specially developed procedure for a high charge beam matching into the undulator was successfully tested resulting in a first THz pulse generation. The start-up THz diagnostics is based on pyrodetectors. First measurements of the THz generation from 1,2 and 3 nC bunches have been taken, the statistics properties analysis corresponds to the expected SASE performance. The gain curve for the 3 nC case reflects the onset of saturation regime.

Research and development of an accelerator-based THz source prototype for pump-probe experiments at the European XFEL are ongoing at the Photo Injector Test Facility at DESY in Zeuthen (PITZ). A proof-of-principle experiment to generate THz SASE FEL radiation using an LCLS-I undulator driven by an electron bunch from the PITZ accelerator has been prepared. After four years of designs and construction, the first commissioning with an electron beam was started in July 2022. This paper presents and discusses the experience and results of the first commissioning.

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; [Geneva] : JACoW Publishing, Geneva, Switzerland 2954-2957 (2022). doi:10.18429/JACoW-IPAC2022-THPOMS008, The Photo Injector Test facility at DESY in Zeuthen (PITZ) is preparing an R\&D platform for electron FLASH radiotherapy, very high energy electron (VHEE) radiotherapy and radiation biology based on its unique beam parameters: ps scale bunches with up to 5 nC bunch charge at MHz bunch repetition rate in bunch trains of up to 1 ms in length repeating at 10 Hz. This platform is called FLASHlab@PITZ. The PITZ beam is routinely accelerated to 22 MeV, with a possible upgrade to 250 MeV for VHEE radiotherapy in the future. The 22 MeV beam will be used for dosimetry experiments and studying biological effects in thin samples in the next years. A new beamline to extract and match the beam to the experimental station is under physics design. The main features include: an achromatic dogleg to extract the beam from the PITZ beamline; a sweeper to scan the beam across the sample within 1 ms for tumor painting studies. In this paper, the beam dynamics with bunch charges from 10 pC to 5 nC in and the preparation of the new beamline will be presented., Published by JACoW Publishing, Geneva, Switzerland, [Geneva]

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

[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

[Ebook] 13th International Particle Accelerator Conference : June 12-17, 2022, Impact Forum, Muangthong Thani, Bangkok, Thailand : conference proceedings / Chanwattana, Thakonwat , [Geneva] : JACoW Publishing, July 2022, 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand, 12 Jun 2022 - 17 Jun 2022; [Geneva] : JACoW Publishing, Geneva, Switzerland 2958-2961 (2022). doi:10.18429/JACOW-IPAC2022-THPOMS010, The high-brightness electron beam at the Photo Injector Test facility at DESY in Zeuthen (PITZ) is being prepared for use in dosimetry experiments and for the study of biological effects in thin samples. This is part of the preparations for FLASHlab@PITZ which is going to be an R platform for FLASH and VHEE radiation therapy and radiation biology. These studies require precise information on the electron beam parameters downstream of the exit window, such as the scattering angle and the energy spectrum of the particles as well as the thermal load on the exit window. A Titanium window is compared with a DESY Graphite window design. Heat deposition in the window by a single 22MeV / 1nC electron bunch of various size, its scattering and energy spectrum due to passage through the window are calculated by means of the Monte Carlo program FLUKA. Time resolved temperature profiles, as generated by the passage of 1ms long electron pulse trains with up to 4500 single pulses, each of them between 0.1 and 60ps long, are calculated with a self-written FEM code., Published by JACoW Publishing, Geneva, Switzerland, [Geneva]

Physica medica 104, 174 - 187 (2022). doi:10.1016/j.ejmp.2022.10.026, At the Photo Injector Test facility at DESY in Zeuthen (PITZ), an R&D platform for electron FLASH and very high energy electron radiation therapy and radiation biology is being prepared FLASH$\mathrm{{\ell}ab@}$PITZ). The beam parameters available at PITZ are worldwide unique. They are based on experiences from 20 + years of developing high brightness beam sources and an ultra-intensive THz light source demonstrator for ps scale electron bunches with up to 5 nC bunch charge at MHz repetition rate in bunch trains of up to 1 ms length, currently 22 MeV (upgrade to 250 MeV planned). Individual bunches can provide peak dose rates up to 10$^{14}$ Gy/s, and 10 Gy can be delivered within picoseconds. Upon demand, each bunch of the bunch train can be guided to a different transverse location, so that either a “painting” with micro beams (comparable to pencil beam scanning in proton therapy) or a cumulative increase of absorbed dose, using a wide beam distribution, can be realized at the tumor. Full tumor treatment can hence be completed within 1 ms, mitigating organ movement issues. With extremely flexible beam manipulation capabilities, FLASHlab@PITZ will cover the current parameter range of successfully demonstrated FLASH effects and extend the parameter range towards yet unexploited short treatment times and high dose rates. A summary of the plans for FLASH$\mathrm{{\ell}ab@}$PITZ and the status of its realization will be presented., Published by Elsevier, Amsterdam

[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

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

FRPT 2021, Wien, DESY, Austria, 1 Dec 2021 - 3 Dec 2021

FRPT 2021, Wien, DESY, Austria, 1 Dec 2021 - 3 Dec 2021

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.

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

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.