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Energy Recovery Linacs such as PERLE require high average current high brightness beams. This sets particular requirements on the kind of injectors that they can use as the injectors must be capable of producing bunches at MHz repetition rates, compressing the bunches to the specified value and transporting those bunches while they are still in the space charge dominated regime into the main ERL all while keeping the emittance low. In particular, PERLE will require a 20 mA beam consisting of 500 pC bunches with a repetition rate of 40 MHz. These bunches will be required to have rms lengths of 3mm, a total beam energy of 7 MeV, appropriate Twiss parameters to match them to the main loop and transverse emittances of 6 mm mrad. In this paper, a DC gun based injector capable of meeting this specification will be presented with beam dynamics simulation showing the behaviour of the beam from the photocathode to the exit of the first main linac pass. The beam dynamics challenges will be discussed in terms of both the transverse emittance growth and the sources of non-linearity in the longitudinal phase space., Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK

The regenerative Beam Break Up (BBU) excited by the dipole Higher Order Modes (HOMs) in superconducting RF (SRF) cavities is a crucial issue for continuous-wave high-current energy recovery linacs. Beam-induced monopole HOMs can increase the cryogenic losses of the linac also. One of the ways to limit these effects is to use HOM couplers on the beam tubes of cavities to absorb and untrap cavity eigenmodes. These couplers feature antennas designed to damp dangerous HOMs and adequately reject the fundamental mode. This study illustrates an investigation of the HOMs of a 5-cell 801.58 MHz elliptical SRF cavity designed for PERLE (Powerful Energy Recovery Linac for Experiments), a multi-turn energy recovery linac (ERL) currently under study and later to be hosted at IJCLab in Orsay. Time-domain wakefield and frequency-domain eigenmode simulations have been used to calculate the cavity broadband HOM impedance spectra and identify the dangerous BBU HOMs. The transmission characteristics of several coaxial HOM couplers have been studied. The efficiencies of several HOM-damping schemes have been compared to propose a HOM endgroup to be fabricated and added to the existing bare SRF cavity., Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK