High-brightness megahertz-rate electron beams are highly desired for cutting-edge applications in many areas of science. Photocathode electron guns capable of generating such beams with low dark current remain to be a challenging field. In this paper, we report breakthroughs with a hybrid gun combining a direct-current gap and a superconducting radio-frequency (SRF) cavity. The gun, employing K 2 CsSb photocathodes driven by a green laser, delivers a few MeV electron beam at 1 and 81.25 MHz rates with an average current up to 3 mA and a dark current several orders lower than current normal conducting continuous-wave guns. Emittance compensation and multipole field corrections have been applied to achieve a high-quality beam. The achievement will inspire the development of high-brightness SRF guns and promote megahertz-rate beam applications including coherent linac light sources and ultrafast electron diffraction/microscopy. Published by the American Physical Society 2024

The performance of ultrafast scintillators under ultrahigh dose rate is highly important for applications utilizing brilliant radiation sources. In this work, the scintillation properties of β-Ga₂O₃, a high-performance ultrafast wide-bandgap semiconductor scintillator, are systematically investigated under dose rates of 10⁷ to 10⁹ Gy/s for the first time by employing ultrashort high-charge electron bunches (bunch charge from 500 fC to 50 pC) generated from a superconducting radio-frequency accelerator. Our results show that in spite of the ultrahigh dose rate, the scintillation intensity was still linearly proportional to the electron bunch charge. Lifetime analysis reveals a fast decay component ranging from 3 to 4 ns, along with an average lifetime of 20 ns. These findings establish a solid foundation for the application of β-Ga₂O₃ as the scintillation material for high-charge electron sources such as laser-wakefield accelerated electrons.

Continuous-wave photocathode guns are capable of delivering electron beams with high repetition rates and high average currents. However, they are limited by relatively low accelerating gradients and cathode fields. This limitation leads to a larger beam size at the gun exit due to space-charge forces, making the beam more sensitive to optical aberrations and posing challenges for low-emittance electron beam transmission. This paper focuses on the aberrations induced by multipole fields. We analyze the effects of quadrupole, sextupole, and higher-order fields on beam profile and transverse emittance and propose a beam-based method for the rapid characterization and correction of these multipole fields. Furthermore, we present an experimental study conducted on the DC-SRF-II photocathode gun equipped with dedicated correctors. Both simulation and experimental results demonstrate that our approach effectively mitigates beam aberrations caused by multipole fields, resulting in improved beam symmetry and reduced emittance. Published by the American Physical Society 2025

Continuous-wave photocathode guns are capable of delivering electron beams with high repetition rates and high average currents. However, they are limited by relatively low accelerating gradients and cathode fields. This limitation leads to a larger beam size at the gun exit due to space charge forces, making the beam more sensitive to optical aberrations and posing challenges for low-emittance electron beam transmission. This paper focuses on the aberrations induced by multipole fields. We analyze the effects of quadrupole, sextupole, and higher-order fields on beam profile and transverse emittance and propose a beam-based method for the rapid characterization and correction of these multipole fields. Furthermore, we present an experimental study conducted on the DC-SRF-II photocathode gun equipped with dedicated correctors. Both simulation and experimental results demonstrate that our approach effectively mitigates beam aberrations caused by multipole fields, resulting in improved beam symmetry and reduced emittance.