This paper presents a systematic study on an optimized design of a high-performance energy recovery linac injector characterized by a low injection energy, carried out within the framework of the BriXSinO INFN project. Key design elements include the use of two sub-harmonic bunchers to mitigate chromatism and space-charge effects. A first-of-its-kind quantitative comparative analysis of buncher frequencies, conducted using modern multi-objective AI optimization, reveals a systematic correlation between buncher operating frequency and emittance preservation, with the 650 MHz case outperforming 1.3 GHz by almost a factor of 4 in bunch brightness. Furthermore, beyond the BriXSinO injector objectives, we explore the behavior of additional lower-frequency bunchers, showing a strong correlation between buncher frequency and beam emittance. This correlation paves the way for a new class of high-performance injectors that can achieve optimal performance even with non cutting-edge guns. The innovative design also incorporates a fine tuning, described in detail, of established high-brightness beam generation concepts such as cigar-like shaping at the cathode, velocity bunching, ballistic bunching, and emittance compensation. Overall, this study highlights how innovative design strategies can be essential for developing high-performance, low-energy injectors and mA-class machines that meet the needs of many modern accelerator facilities. Additionally, we introduce an experimental scheme for Full Inverse Compton Scattering (FICS) that makes full use of the injector object of this study.
Bacci et al. (Mon,) studied this question.