Experimental study of a 33.3-GHz free-electron-laser amplifier with a reversed axial guide magnetic field

Abstract

We report on a new regime of free electron laser operation with reversed axial guide magnetic field, in which the cyclotron rotation of the electrons in the uniform axial field opposes the rotation in the helical wiggler field. The 33.3 GHz free electron laser amplifier is driven by a mildly relativistic electron beam (750 kV, 300 A, 30 ns) and generates 61 MW of radiation with a 27% conversion efficiency. The results are compared with those obtained when the axial guide field is in its conventional orientation where considerable loss of power and efficiency is observed.

Equilibrium electrons in free-electron lasers with a 3D helical wiggler and a guide magnetic field: Nonlinear simulations

“…We compare the functions of the positive guide magnetic field and the reversed guide magnetic field by employing the parameters in the experiments conducted at the Massachusetts Institute of Technology (MIT) [13]. In the MIT experiment the setup had the basic parameters of a wiggler period w ¼ 3:18 cm, a wiggler length L w ¼ 200 cm, an average beam energy factor 0 ¼ 2:4677, a beam radius R b ¼ 0:25 cm, and a waveguide radius R w ¼ 0:52 cm.…”

“…By solving the velocity and configuration equations (10)- (15), two nearby equilibrium electrons' phase-space trajectories and the Kolmogorov entropylike quantity k can be easily traced, no matter how complex the magnetic or electric field that is applied to the electrons. Figure 3(a) plots the comparison of the Kolmogorov entropylike quantity for the positive guide magnetic field and the reversed guide magnetic field by use of the MIT experiment parameters [13]. To ensure the reliability of the simulation results, we choose the iteration step to be 2 Â 10 À7 cm, which corresponds to a total iteration number of 10 9 .…”

“…II, beam current transmission as a function of the positive guide magnetic field is plotted in Fig. 4(a) by using the parameters of the MIT experiment [13], where the beam current transmission is defined as the ratio of the current at the exit to that at the entrance: …”

“…Then, in Sec. III, in terms of the experimental parameters reported by Conde and Bekefi [13], comparative simulations are carried out for the functions of a positive guide magnetic field and a reversed guide magnetic field. In Sec.…”

RF sources for linear colliders

“…and 18% efficiency (~ 1 ps pulse) at NRL [40]. FEL Experiments with field emission diodes have generated 61 MW at 33.3 GHz with 27% efficiency (30 ns pulse) at MIT [41]. FEL experiments at KEK have produced 30 MW with 30 dB gain for a 60 ns pulse at 9.6 GHz with 6% efficiency [42].…”