Low energy electron bunches experience emittance growth due to space charge. This effect can lead to large emittances which are unacceptable for a facility like PERLE at IJCLab. PERLE will be an ERL test facility circulating a high current electron beam. The traditional method to reduce emittance due to this effect is already planned for the PERLE injector, this has a limit of how small the emittance can be reduced to. This limit is defined by the quality of the bunch as it is upon production at the cathode. The transverse and longitudinal properties of the laser pulse incident on the cathode defines some characteristics of the bunch, to which the space charge effect is related. In addition, the complex evolution of the bunch along the injector could result in optimal laser parameters which are different from the simple flattop distribution currently simulated. Presented here are simulation-based studies of the bunch charge distribution at the cathode and its subsequent evolution along the injector. An optimization of the laser parameters which create the bunch is also performed. We find that there is an optimal bunch charge shape which corresponds to minimal emittance growth.

The compact ERL (cERL) is operated at mid-energy region around 17 MeV for beam studies on industrial applications since 2017. Toward the future high power FEL source for EUV lithography, high current beam operation was demonstrated at low bunch charge after install of undulators as a first step. It is critical to reduce beam loss not to exceed 20 uSv/h outside the shield wall of the cERL acceleration room, however, it can increase especially at the arc sections, the undulators, and superconducting cavities for decelerating. Therefore, 16 high-speed loss monitors are located along the whole beam line as the machine protection system. Recently, machine learning is applied for beam tuning to reduce all loss monitor signal. In addition, we tried the energy recovery operation while undulator light is amplified at a high bunch charge around 60 pC.

Johannes Gutenberg University Mainz is currently constructing a new electron accelerator that employs an energy recovery scheme. The Mainz Energy Recovery Superconducting Accelerator (MESA) will provide two modes of operation: the Energy Recovery (ER) mode, which will supply an internal gas target experiment, and the Extraction Beam (EB) mode, primarily used in the P2 experiment where MESA's spin-polarized electrons will be directed towards a target. As an Energy Recovery Linac (ERL), MESA shows potential as an accelerator for an Inverse Compton Scattering (ICS)-based gamma source. To anticipate the impact of the scattering on electron beam parameters, significant for energy recovery, a novel quasi-analytical simulation code, "COMPARSE", has been developed and used for the feasibility studies. The investigations examine various applications of ICS sources at MESA. This paper gives an overview of the results as well as the limitations and possibilities of the underlying mathematical approach.

Low energy electron bunches experience emittance growth due to space charge. This effect can lead to large emittances which are unacceptable for a facility like PERLE at IJCLab. PERLE will be an ERL test facility circulating a high current electron beam. The traditional method to reduce emittance due to this effect is already planned for the PERLE injector, this has a limit of how small the emittance can be reduced to. This limit is defined by the quality of the bunch as it is upon production at the cathode. The transverse and longitudinal properties of the laser pulse incident on the cathode defines some characteristics of the bunch, to which the space charge effect is related. In addition, the complex evolution of the bunch along the injector could result in optimal laser parameters which are different from the simple flattop distribution currently simulated. Presented here are simulation-based studies of the bunch charge distribution at the cathode and its subsequent evolution along the injector. An optimization of the laser parameters which create the bunch is also performed. We find that there is an optimal bunch charge shape which corresponds to minimal emittance growth.

The PERLE (Powerful Energy Recovery Linac for Experiments) project requires an injector capable of delivering a beam current of 20 mA at a total beam energy of 7 MeV with 500 pC bunches. These requirements present challenges for achieving the high quality beam required for the main ERL loop. At low energy and high bunch charge, the electron bunches will predominantly experience emittance growth due to the space charge effects. The compensation of this emittance growth will be performed with the traditional method of two solenoids a single bunching cavity and a linac to reach the intended injection energy. Additionally, the control of longitudinal and transverse bunch size must be performed to meet the requirements at the end of the injector. For stable operation of PERLE a rms bunch length of < 3 mm is required, with transverse emittances < 6 mm·mrad and acceptable transverse size. Presented here is the re-optimization of the injector settings used during commissioning for two alternative DC photoguns. It is found that the former cathode does not perform to the standard of previous optimizations. However, a newly procured cathode when optimized can meet the requirements for PERLE.