Bunch length evaluation for typical low-energy beam injectors based on RF-phasing techniques

Abstract

As a challenging task in the development of picosecond beam injectors, effective evaluation for bunch length is of utmost importance in precisely characterizing high brightness bunches, but conventional diagnostics usually involve dedicated devices and techniques, which result in complicated peripheral sub-systems and high costs. Techniques based RF-phasing, however, present the potential to be more convenient and efficient by maximizing online components commonly contained in typical injectors, such as RF sections and energy spectrometers. By adjusting the standard RF-phasing techniques to adapt the space-charge-dominated beams, we propose cost-efficient methods and derive analytical formulas to directly calculate the bunch length. Furthermore, to validate the feasibility and reliability for such methods, both dynamic simulations and verification experiments were carried with use of the HUST THz-FEL injector, which was similar to the typical injectors. Elaborate comparisons and analyses for the measurements from different formulas demonstrate that the direct calculation methods based on the RF-phasing techniques present as economically supplements to involved injectors.