Abstract
Nonlinear simulations are devoted to the comparative study of the equilibrium electrons' motion and stability in the combination of a three-dimensional helical wiggler and a positive or reversed guide magnetic field, where effects of the self-field, off-axis guiding center and adiabatic magnetic field are included. It is shown that a reversed guide magnetic field configuration brings the electron motion much smaller Larmor radius and transverse displacement span than a positive guide magnetic field does, and consequently, provides better transportation quality of the electron beam. Although the electron motion far from the resonance and antiresonance is stable in both the positive and the reversed guide magnetic field configurations, fluctuation induced by a reversed guide magnetic field is smaller than that by a positive guide magnetic field, especially in the adiabatic region of the wiggler. In a certain parameters domain, the self-field of the electron beam is advantageous to confine the electrons' motion at antiresonance.
Highlights
INTRODUCTIONFree-electron lasers (FELs) with the combination of a wiggler and a positive or a reversed guide magnetic field have been recognized as a kind of high-power coherent radiation sources in the infrared, terahertz, and millimeter wave ranges, and have continuously drawn wide attention [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25]
It is shown that a reversed guide magnetic field configuration brings the electron motion much smaller Larmor radius and transverse displacement span than a positive guide magnetic field does, and provides better transportation quality of the electron beam
The electron motion far from the resonance and antiresonance is stable in both the positive and the reversed guide magnetic field configurations, fluctuation induced by a reversed guide magnetic field is smaller than that by a positive guide magnetic field, especially in the adiabatic region of the wiggler
Summary
Free-electron lasers (FELs) with the combination of a wiggler and a positive or a reversed guide magnetic field have been recognized as a kind of high-power coherent radiation sources in the infrared, terahertz, and millimeter wave ranges, and have continuously drawn wide attention [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25]. By means of nonlinear simulations, this paper presents a comparative investigation for the functions of a positive guide magnetic field and a reversed guide magnetic field on the equilibrium electrons’ motion, trajectory stability, and the electron-beam transmission. Treated to be on axis [5,6,7,10], and the adiabatic field over the initial region of the wiggler was mostly neglected These factors may substantially affect the equilibrium electrons’ motion, stability, and transmission.
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