Abstract
Collective effects such as wakefields affect the dynamics of high brightness electron beams in linear accelerators (linacs) and can degrade the performance of short wavelength free-electron lasers (FELs). If a reliable model of wakefields is made available, the accelerator can be designed and configured with parameters that minimize their disrupting effect. In this paper, the simulated effect of geometric (diffractive) wakefields and of coherent synchrotron radiation on the electron beam energy distribution at the FERMI FEL is benchmarked with measurements, so quantifying the accuracy of the model. Wakefield modeling is then extended to the undulator line, where particle tracking confirms the limited impact of the resistive wall wakefield on the lasing process. The study reveals an overall good understanding of collective effects in the facility.
Highlights
The advent of subpicosecond-long electron bunches with hundreds of ampere peak current and submicron-level energy-normalized transverse emittances, such as those driving linac-based extreme ultraviolet and x-ray free electron lasers (FELs) [1,2,3,4,5,6,7], has raised the awareness of the accelerator community to the dilution of the electron beam brightness by the interaction with wakefields in the accelerator and with coherent synchrotron radiation (CSR) in magnetic compressors [8]
(Received 7 November 2018; published 4 January 2019). Collective effects such as wakefields affect the dynamics of high brightness electron beams in linear accelerators and can degrade the performance of short wavelength free-electron lasers (FELs)
Projected emittance [9,17], and to compare one- vs threedimensional CSR effects on the beam emittance [18,19,20]. They all confirm, on top of the routine operation of the facility, that the electron beam dynamics is strongly affected by geometric wakefields in the linac sections (L0–L4 in Fig. 1) and by CSR emission in the magnetic chicane devoted to bunch length compression (BC1)
Summary
The advent of subpicosecond-long electron bunches with hundreds of ampere peak current and submicron-level energy-normalized transverse emittances, such as those driving linac-based extreme ultraviolet and x-ray free electron lasers (FELs) [1,2,3,4,5,6,7], has raised the awareness of the accelerator community to the dilution of the electron beam brightness (i.e., six-dimensional charge density) by the interaction with wakefields in the accelerator and with coherent synchrotron radiation (CSR) in magnetic compressors [8]. Projected emittance [9,17], and to compare one- vs threedimensional CSR effects on the beam emittance [18,19,20] They all confirm, on top of the routine operation of the facility, that the electron beam dynamics is strongly affected by geometric (diffractive) wakefields in the linac sections (L0–L4 in Fig. 1) and by CSR emission in the magnetic chicane devoted to bunch length compression (BC1). The study is extended (Sec. III B) to the computation and simulation of resistive wall wakefields in the FERMI FEL-2 undulator vacuum chamber. III B) to the computation and simulation of resistive wall wakefields in the FERMI FEL-2 undulator vacuum chamber This is the second and longer undulator line of the two currently installed at FERMI.
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