Studies concerning the FLASH effect for radiation therapy are currently performed at ELSA. The booster synchrotron is used in a preliminary mode of operation to deliver electron beam pulses of 1.2 GeV energy with fixed length of 250 ns to irradiate cell samples. To enable different spill durations ranging from nanoseconds up to several ms in an energy range of 0.8 to 3.2 GeV a fast extraction from the stretcher ring is developed. Therefore a repurposing of the existing injection kickers for extraction is under study to achieve single turn extraction, up to extraction within a few turns. While the effect on the beam dynamics is observed with a streak camera, the measurement of the extracted beam is performed via current and chromox monitors. For longer spill durations, reaching up to ms, the feasibility of multiple concepts for a quicker resonant extraction at ELSA is investigated.

The ELSA facility at the University of Bonn uses a storage ring to accelerate polarized electrons up to 3.2 GeV. The photoinjector source is driven by a Ti:Sa laser beam to obtain a high polarization degree (~86%) from a GaAsP strained-layer superlattice crystal photocathode. After a prolonged shutdown of the source we restored its status to fully operational and fine-tuned the laser system, the crystal storage and cleaning apparatus as well as the Linac transfer beamline. The in-house developed diagnostic software FGrabbit has been employed for the analysis of laser and electron beam camera images, providing increased precision and dynamic range in the optimization process. The impact of the crystal cleaning process was studied with spatially resolved quantum efficiency mapping of the photocathode surface.

To support both routine operation and accelerator research at ELSA, a dual-mode dispenser-cathode based electron gun capable of thermionic emission and thermally assisted photoemission (TAPE) is being developed. A dedicated gun test stand is being designed to measure beam properties and quality, as well as quantum efficiency in the TAPE mode under operational conditions. Instrumentation will include a pepper pot emittance stage, quadrupole scan capabilities, profile measurements using screens and wire-scans or SEM grids, and bunch charge and energy spread determination. In a basic test environment, experiments were carried out at low accelerating voltages using a setup consisting of the dispenser cathode, a pickup anode, and a simple laser system with an optical shutter. The shutter enables alternating measurements of photocurrent and dark current at the anode, allowing first estimations of quantum efficiency. The influence of different cathode heating cycles on both the absolute quantum efficiency and its temporal stability was investigated with this setup. Quantum efficiency measurements under different conditions and simulations of the test beamline are presented.

The ELSA facility at the University of Bonn uses a storage ring to accelerate polarized electrons up to 3.2 GeV. To monitor the polarization degree of the stored beam a Compton polarimeter is used to analyze the profile of the backscattered beam of gamma rays. In addition to a silicon microstrip detector with vertical resolution, a Timepix3 pixel detector is tested as alternative detector for the usage in beam polarimetry and beam position monitoring. The current status of the alternative detector setup is presented.