Delivering and tailoring high brightness electron beams for a wide range of novel applications is a challenging task in single pass accelerator test facilities. This paper will review beam dynamics challenges at single pass accelerator test facilities in Europe to generate, transport and tailor low- to medium-energy high brightness electron beams for a range of novel applications.

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). Proof-of-principle experiments have been performed to generate a high-gain THz Free-electron Laser (FEL) based on the Self-Amplified Spontaneous Emission scheme. The FEL radiation pulses with a central wavelength of about \SI{100}{\micro\metre} (\SI{3}{\tera\hertz}) and single pulse energy of several tens~\SI{}{\micro\metre} can be generated. In this paper, we present and discuss the photon diagnostic setup for the THz FEL together with examples of diagnostic results, including pulse energy and an FEL gain curve. The upgraded photon diagnostic setup, capable of measuring pulse energy, transverse distribution, and spectral distribution, is expected to be operational in the spring of 2023.

INFN LASA photocathode lab develops and produces films that are used in high brightness photoinjectors. Besides the long-time and still on-going experience on Cs2Te, recently we have restarted an activity on alkali-antimonide films, sensitive to visible light, exploring the possibility of their stable operation in CW machine. We report in this paper the recent results obtained both on the advancements on cesium telluride and on the characterization of alkali antimonide.

A THz SASE FEL is currently under operation at the Photo Injector Test facility at DESY in Zeuthen (PITZ) as a prototype THz source for pump-probe experiments at the European XFEL.This prototype should provide tunable (3-5 THz) narrowband THz radiation with THz pulse energies up to several hundred μJ from 17-20MeV electron beams with a beam charge of several nC and a peak current up to 200 A to demonstrate the THz SASE FEL concept. In experiments it has been learned that strong space charge effects, steering effects from quadrupoles and possibly geometrical and conductive wall wakefields should be carefully treated during the beam transport from the photocathode to the undulator. These effects have been reduced by applying a smooth beam transport and improving the beam trajectory in the booster accelerator and the quadrupole magnets. Furthermore, the beam trajectory and matching into the undulator is critical for the THz output energy. This has been optimized by the Bayesian optimization algorithm. In this paper, experimental findings regarding the optimization of electron beams and THz radiations will be reported.

A THz free electron laser (FEL) prototype has been developed at the Photo Injector Test Facility at DESY in Zeuthen (PITZ) for obtaining high intensity radiation for THz-pump-X-ray-probe experiments at the European XFEL. In this development, a magnetic chicane was recently installed to optimize the THz FEL performance. The aim of this study was to investigate the beam dynamics in the chicane for a trajectory commissioning by tracking the electron beam via ASTRA using a 3-dimensional magnetic field of the chicane simulated with CST-EM Studio. The simulated results indicate the possibility of obtaining on-axis trajectory and zero-momentum dispersion of the compressed beam.

Development of an accelerator-based tunable THz source prototype for pump-probe experiments at the European XFEL is ongoing at the Photo Injector Test facility at DESY in Zeuthen (PITZ). The proof-of-principle experiments on the THz SASE FEL are performed utilizing the LCLS-I undulator installed in the PITZ beamline. The first lasing at a center wavelength of 100 µm was observed in the summer of 2022. The lasing of the narrowband THz source was achieved using an electron beam with an energy of ~17 MeV and a bunch charge up to several nC. Optimization of beam transport and matching resulted in the measurement of THz radiation with a pulse energy of tens of µJ, measured with pyroelectric detectors. The THz FEL gain curves were measured by means of specially designed short coils along the undulator. The results of the first characterization of the THz source at PITZ will be presented.

Methodical studies to improve the existing e-beam Longitudinal Phase Space (LPS) tomography were performed at the Photo Injector Test facility at DESY in Zeuthen. Proof-of-principle simulations were done to address some core concerns e.g. booster phase range, space charge effects and noisy artefacts in results. Phase advance analysis was done with the help of an analytical model that determined the booster phase range and step size. A slit was introduced before the booster to truncate the beam and reduce space charge forces. The reconstruction method adopted was image space reconstruction algorithm owing to its assurance of non-negative solution. An initial scientific presumption of LPS from low energy momentum measurements was established to reduce artefacts in the phase space. This paper will explain the proof-of-principle simulations highlighting the key aspects to obtain accurate results. Reconstructed LPS for different experimental cases will be presented to demonstrate the diagnostic capability.

The Photo Injector Test facility at DESY in Zeuthen (PITZ) utilizes slit scan technique as a standard tool for reconstruction of horizontal and vertical phase spaces of its space charge dominated electron beams. A novel method for 4-dimensional transverse phase space characterization, known as Virtual Pepper Pot, is proposed at PITZ, that can give insight to transverse beam phase space coupling. It utilizes the horizontal and vertical single slit scans to form pepper pot-like beamlets by careful crossing and post-processing of the slit scan data. All the elements of the 4D transverse beam matrix are calculated and used to obtain the 4D transverse emittance and coupling factor. The proposed technique has been applied to the experimental data with coupled beam phase space in order to demonstrate the diagnostic capability. The loss of signal at tails of the beamlets due to low signal-to- noise (SNR) ratio is considered in the algorithm and the systematic error resulting from crossing of the beamlets is also explored.

The high-brightness electron beam at the Photo Injector Test facility at DESY in Zeuthen (PITZ) is now also used for FLASHlab@PITZ: an R&D platform for studying radiation biology and the FLASH effect in radiation therapy. The available parameter space of the electron beam with a momentum of 22 MeV/c allows bunch charges from 10 pC up to 5nC, bunch durations of 0.1–60ps, and bunch train lengths up to 1 ms. The number of bunches in the single train can currently be varied between 1 and 1000 bunches, with an upgrade to 4500 foreseen in 2023. Radiation biology studies require accurate dose prediction, therefore Monte Carlo simulations based on the FLUKA code were performed. According to estimations, dose delivery of 0.002 Gy (low charge case 0.1pC) and 10Gy (high charge case 5nC) is possible, if the beam is confined to a circular area with a radius of 5 mm with a lead collimator. For the Monte Carlo simulations, the experimental setup was accurately modeled, including the exit window, lead collimator, etc. Dose measurements were used to compare simulations with experiments. Dose profiles were experimentally measured with Gafchromic films and then compared with Monte Carlo simulations. The first experiments at FLASHlab@PITZ in 2023 have demonstrated flexible dose options for studying the FLASH effect and radiation biology studies

The aim of this work is to demonstrate the principal possibility to enhance the electron beam dose deposition in the depth of the sample for radiation therapy purposes. Trains of electron bunches of 22 MeV generated at PITZ are focused inside the sample using a dedicated fast deflector and a solenoid magnet. To explore the capabilities of the proposed setup, dose distributions are calculated for multiple electron bunches focused in a single point inside a water phantom. Electron beam focusing produces dose peaks with a tunable maximal dose depth which is interesting for healthy tissue sparing at the surface and enhancing treatment quality. The duration of the full bunch train is 1 ms. During this time interval, the FLASH effect could be efficiently triggered inside the irradiated target volume. Monte Carlo simulations based on the FLUKA code were performed to evaluate the depth dose curves distributions in a water phantom. Using the PITZ electron beam parameters, simulations have shown the possibility to produce a peak dose in water seven times higher than compared to the dose at the surface. Moreover, the RMS size homogeneous area around the maximal dose is approximately 25 mm.

An R&D platform for electron FLASH radiation therapy and radiation biology is being prepared at the Photo Injector Test facility at DESY in Zeuthen (FLASHlab@PITZ). This platform is based on the unique beam parameters available at PITZ: ps scale electron bunches of up to 22 MeV with up to 5 nC bunch charge at MHz bunch repetition rate in bunch trains of up to 1 ms in length repeating at 1 to 10 Hz. These beams allow to study an uniquely wide parameter range for radiation biology and FLASH radiation therapy, which is a new treatment modality against cancer. A startup beamline has been installed to allow dosimetry studies and irradiation experiments on chemical, biochemical and biological samples and cell cultures after a 60-degree dispersive arm. The measured dose and dose rates under different beam conditions and first experimental results will be reported in this paper. In addition, a dedicated beamline for FLASHlab@PITZ has been designed for better control of the electron beams. This includes a dogleg to translate the beam and a 2D kicker system to scan the tiny beam focused by quadrupoles across the samples within less than 1 ms. Simulation studies will be presented to demonstrate the extremely flexible dose parameters with various irradiation options for FLASH radiation therapy and radiation biology studies.