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.

In this paper, a cathode laser pulse shaper at 515 nm is presented that will be used for emittance optimizations. In case alkali antimonide photocathodes are used, the shaped green pulses can be applied directly for photoemission while Cs₂Te photocathodes requires second harmonic generation to provide UV laser pulses. Recent tests of CsK₂Sb photocathodes in the high gradient RF gun at PITZ are first steps for the future usage of green laser pulses, which would simplify the requirements for the photocathode laser system, especially for CW operation cases envisioned in future. As long the alkali antimonide photocathodes are not in regular use yet, the laser pulses need to be converted into the UV. The green pulse shaper still simplifies the laser system since two conversion stages from IR to green to UV were needed in the past, which dilutes the quality of the shaped laser pulses. In this paper, a pulse shaper for direct generation of 515nm 3D ellipsoidal pulses is presented that is expected to further improve the beam emittance generated by ellipsoidal laser shaping.

The slice energy spread of the electron beam is one of the key parameters for high performance of linac-driven free electron lasers (FELs). The simulated uncorrelated energy spread in modern XFEL photoinjectors with beam energies of many tens of MeV is on the order of a few keV or even less. Thus, accurate measurement of the slice energy spread is not trivial. Two recent studies on high energy (>100 MeV) photoinjectors at SwissFEL and European XFEL have reported much higher slice energy spread than expected at their XFEL working points (200 – 250 pC). A new method for measuring slice energy spread at a lower beam energy (∼20 MeV) is proposed and demonstrated at the Photo Injector Test facility at DESY Zeuthen (PITZ). The contribution will summarize previous results obtained on high energy injectors and then review the details of the technique used at PITZ as well as the experimental results for 250 pC, which are considerably lower than the results measured at high energy injectors.

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.

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.

Photoemission laser shaping is essential for both beam brightness and advanced accelerator concepts, therefore is an important R&D at the Photo Injector Test Facility at DESY in Zeuthen (PITZ). The laser pulse shaper presented here is based on spectral amplitude modulation of chirped laser pulses. In this approach one can do temporal-spatial coupled laser shaping, i.e. 3D shaping. The laser shaping is done at 1030 nm with spatial light modulators, and then converted to 257.5 nm through harmonic generation for photoemission. Experimental results of laser pulse shaping and shape preservation through harmonic generation are presented for different cases: spatial shaping, temporal shaping and full 3D shaping. Electron beam testing results will also be presented.

At the Photo Injector Test facility at DESY in Zeuthen (PITZ) photo electron guns for the use at the X-ray free-electron laser (FEL) facilities FLASH and European XFEL are conditioned. An electron beam with high current and low transverse emittance is required for high performance in an X-ray FEL. As the lasing process occurs on the part of the electron bunch with the highest charge density the emittance of this part is of interest. A scheme to measure the slice emittance which uses a transversely deflecting structure and a single-slit scan has been developed at PITZ. This allows the beam characterisation at low beam energies and high charge densities. The contribution shows that using laser pulses with temporal flattop shape (and temporal Gaussian shape) or temporal and transverse flattop shape lead to a reduced center slice emittance compared to an electron beam emitted using a laser pulse with temporal Gaussian and transverse flattop shape.