ELECTRON-MAGNETIC-PHASE MIXING IN A LINAC-DRIVEN FEL TO SUPPRESS MICROBUNCHING IN THE OPTICAL REGIME AND BELOW

Abstract

Control of microbunching instability is a fundamental requirement in modern high brightness electron linacs, in order to prevent malfunction of beam optical diagnostics and contamination in the generation of coherent radiation, such as free electron lasers. We present experimental control and suppression of microbunching instabilityinduced optical transition radiation by means of particles’ longitudinal phase mixing in a magnetic chicane. In presence of phase mixing, the intensity of the beamemitted coherent optical transition radiation is reduced by one order of magnitude and brought to the same level provided, alternatively, by beam heating. The experimental results are in agreement with particle tracking and analytical evaluations of the instability gain. A discussion of applications of magnetic phase mixing to the generation of quasi-cold high-brightness ultrarelativistic electron beams is finally given. BACKGROUND The strength of the microbunching instability is usually quantified by its spectral gain, which is the ratio of the final to the initial bunching. When only longitudinal space charge (LSC) force is considered, the gain can be evaluated by [1]: