Compensating slice emittance growth in high brightness photoinjectors using sacrificial charge

Autor: W. H. Li, A. C. Bartnik, A. Fukasawa, M. Kaemingk, G. Lawler, N. Majernik, J. B. Rosenzweig, J. M. Maxson
Jazyk: angličtina
Rok vydání: 2024
Předmět:
Zdroj: Physical Review Accelerators and Beams, Vol 27, Iss 8, p 084401 (2024)
Druh dokumentu: article
ISSN: 2469-9888
DOI: 10.1103/PhysRevAccelBeams.27.084401
Popis: Achieving maximum electron beam brightness in photoinjectors requires detailed control of the 3D bunch shape and precise tuning of the beam focusing. Even in state-of-the-art designs, slice emittance growth due to nonlinear space charge forces and partial nonlaminarity often remains non-negligible. In this work, we introduce a new means to linearize the transverse slice phase space: a sacrificial portion of the bunch’s own charge distribution, formed into a wavebroken shock front by highly nonlinear space charge forces within the gun, whose downstream purpose is to dynamically linearize the desired bunch core. We show that linearization of an appropriately prepared bunch can be achieved via strongly nonlaminar focusing of the sacrificial shock front, while the inner core focuses laminarly. This leads to a natural spatial separation of the two distributions: a dense core surrounded by a diffuse halo of sacrificial charge that can be collimated. Multiobjective genetic algorithm optimizations of the ultracompact x-ray free electron laser injector employ this concept, and we interpret it with an analytic model that agrees well with the simulations. In simulation, we demonstrate a final bunch charge of 100 pC, peak current ∼30 A, and a sacrificial charge of 150 pC (250 pC total emitted from cathode) with normalized emittance growth of
Databáze: Directory of Open Access Journals