FLUTE (Ferninfrarot Linac- Und Test-Experiment) is a new compact versatile linear accelerator at KIT. Its main goal is to serve as a platform for a variety of accelerator studies as well as a generation of strong ultra-short THz pulses for photon science. Also it will be used as an injector for a Very Large Acceptance compact Storage Ring (VLA-cSR) which will be realized at KIT in the framework of the compact STorage Ring for Accelerator Research and Technology (cSTART) project. To achieve acceleration of electrons in the RF photo-injector and linac with high stability, it is necessary to provide stable RF power. For this goal, an upgrade of the existing RF system design has been proposed and is currently being implemented. In this contribution an updated RF system design and the status of the RF photo-injector, linac and bunch compressor commissioning will be reported.

FLUTE is a compact and flexible linac-based accelerator test facility at the Karlsruhe Institute of Technology (KIT) in Germany. It serves as a platform for a variety of accelerator studies and to generate intense short THz pulses for various photon science experiments. Later, FLUTE will be also used as an injector of sub-100 fs bunches into the VLA-cSR (Very Large Acceptance compact Storage Ring), which is part of the cSTART (compact STorage Ring for Accelerator Research and Technology) project currently in the technical design phase at KIT. Recently, FLUTE's high energy section has been installed and commissioned. This includes the linac, bringing FLUTE beyond 5 MeV to full energy, the bunch compressor, and two corresponding diagnostics sections. A metal foil in the last diagnostics section has been used to generate a first THz signal with high energy electron bunches.

The Karlsruhe Institute of Technology is currently exploring a compact method of longitudinal electron bunch diagnostics with femtosecond resolution that has recently been demonstrated for other parameter ranges. The experimental setup utilizes a THz-based streaking approach with resonator structures, achieving both high compactness and efficiency. In this paper, we report on the experimental observation of streaking signals with our Compact Transverse Deflecting System, which has been successfully tested using two different resonators, an Inverse Split-Ring Resonator and a Tilted-Slit-Resonator.

The KIT cSTART project (compact storage ring for accelerator research and technology) aims to demonstrate injection and storage of a high intensity ultra-short bunch using the FLUTE LINAC, as well as a laser-plasma accelerator (LPA). cSTART is planned to operate with a wide range of demanding parameters, such as bunch charge, bunch length and energy spread (from the LPA), making it extremely challenging for the choice of beam diagnostics with large dynamic ranges that are capable of operating within specifications. Moreover, turn by turn measurements are necessary in the cSTART storage ring as bunch characteristics are expected to dramatically change within a single turn. In this paper, we will describe the planned beam diagnostics system of the cSTART storage ring focusing on the turn-by-turn signal processing and reporting on characterization tests which were performed.