The superconducting radio-frequency photoelectron injector (SRF photoinjector), now under commissioning at the SEALab accelerator test facility, has the potential to cover a fast area of beam parameters. Electron bunches from fs to ps length, with fC to nC charge can be accelerated to a couple of MeV beam energy. The legacy from the energy-recovery linac (ERL) test facility bERLinPro, the foundation of SEALab, allows us to operate the SRF photoinjector at very high repetition rate, with energy recovery (ERL), in a sustainable way for fundamental accelerator research into novel, energy-efficient electron accelerators. In this paper preparatory work for two applications is detailed. One is the use of the SRF photoinjector as a direct beam source for ultrafast scattering experiments with high 6D coherence, the other are experiments towards an ERL application for high-energy physics at high average current.

In this article, the results obtained with a new designing approach for the active disturbance rejection control (ADRC) algorithm are presented, where loop shaping techniques are used in order to stabilize the controller and make it more resilient to delay. The objective of this work is to describe the experiment performed to test the microphonic reduction capability of the modified ADRC (MADRC), as well as to present and discuss the results obtained on the test system, which is a 9-cell super conducting radio frequency (SRF) cavity. This is in respond to the need of a precise microphonics control in SRF cavities that are operated with high quality factors. Due to the stochastic nature of microphonics and the relatively large delay of piezoelectric actuators, feedback controllers tend to destabilize the system before an acceptable control bandwidth is obtained and, therefore, are quite limited. The objective of this new approach is to modify the basic structure of the ADRC in order to enable the study of its frequency response and then make it more robust via loop shaping techniques.

The Superconducting RF photo-injector with the prototype 1.4 lambda/2-cell Niobium cavity of the bERLinPro Energy Recovery Linac (ERL), recently renamed to SEALab*, was tested and characterized in a dedicated beam test facility called Gunlab to analyze its performance for the ERL**. After dismantling and refurbishing of the cavity, a small surface defect was found close to the cathode opening and by simulated reconstruction of the set-up it was demonstrated to be the main source of the dark current measured at Gunlab. Later, a method was found to remove that defect***, but still the question remains, what amount of dark current is acceptable for an ERL injector, especially for the SRF systems? In this contribution, we show a fully 3D simulation based emulation of the dark current measurements in Gunlab and extrapolate the impact on the complete injector at bERLinPro (SEALab). Here, it can be shown, that besides a small meshed beam loss diagnostics, methods need to be found to determine the amount of field emitted current dumped into the SRF systems.

The synchrotron light source BESSY-II has been in operation for almost 25 years and modernization measures are needed to maintain competitiveness until its successor BESSY-III comes online. One measure is to replace the old analogue LLRF control units with new, state of the art mTCA.4-based digital ones. The so-called “single cavity” firmware developed by DESY is being used together with the ChimeraTK adapter to connect the mTCA to the EPICS control system. A pair of SIS8300KU and a DWC8VM is used, while the tuner is driven by a PhyMotion chassis connected to the EPICS system. We discuss the implementation of the system.

For SRF cavity systems operated in continous wave (CW) at low effective beam loading as in Energy Recovery Linacs or Free Electron Lasers with rather low beam current, control of the tuning and counteracting any detuning caused by microphonics or Lorentz force driven coupled ponderomotive instability is mandatory to deliver and preserve a stable beam in longitudinal phase space regime. To develop beyond the currently employed mTCA based LLRF systems, a compact RF on a chip system was developed, which features several potential applications. Those range from a digital PLL to test and characterize the RF performance of cavities to a selection of detuning control algorithms, we have worked on in recent years, as e.g. a Kalman filter based state estimator controller [1] or an adaptive feedforward algorithm [2]. Here, we will show our first experimental findings with a TESLA style nine-cell SRF cavity operated in CW at our horizontal test facility HoBiCaT.