Speaker
Description
Laser heaters are commonly used in free-electron laser (FEL) injectors to suppress microbunching instabilities by increasing uncorrelated slice energy spread. We investigate using a third-harmonic laser–undulator interaction in the LCLS-I injector for this purpose. Measurements of the central slice energy spread as a function of laser power are performed for both fundamental and third-harmonic interactions, enabling a direct comparison of heating efficiency and scaling behavior. While the fundamental interaction exhibits the expected dependence on laser power, the third-harmonic configuration shows distinct deviations from expected scaling, suggesting increased higher-order and three-dimensional effects. The experimental results are compared with GENESIS simulations of realistic beam distributions, showing qualitative agreement and highlighting the limitations of simplified models for higher harmonic couplings. These results demonstrate the feasibility of third-harmonic laser heating in an operational injector, potentially allowing for heater functionality at lower than design beam energies or constrained machine configurations.
Funding Agency
Work supported in part by US Department of Energy contract number
DE-AC02-76SF00515.
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