Compensation and improvement for bunch length diagnostics based on RF-phasing techniques

Abstract

Reliable bunch length measurement for electron beams is critical for the successful development of high-brightness beam injectors. Compared with commonly used schemes involving complicated techniques and dedicated devices, RF-phasing techniques have advantages in low-energy injectors owing to their convenience and low cost. Although previous direct calculation formulas originating from RF-phasing techniques are feasible and efficient in low-energy injectors, non-negligible errors are inevitable in practical operations, which limits application. By recalling the analytical derivation procedure and reconsidering the approximate conditions, compensation methods were explored through theoretical analysis and numerical simulations. Virtual measurements using beam dynamics calculations were used to evaluate reliability, and experimental validations were conducted at the HUST (Huazhong University of Science and Technology) injector to verify the compensation. Both of these efforts demonstrate that the improvements in the RF-phasing-based diagnostics for bunch length are feasible and reliable in typical low-energy injectors in common operating conditions. With compensation, these diagnostic methods are a promising alternative to conventional methods. For beam injectors, there may be a tradeoff among a compact layout, low cost, and complete characterization functions.