Beam dynamic study of a Ka-band microwave undulator and its potential drive sources

Abstract

Microwave undulators (MUs) have great potential to be an alternative solution to permanent magnet undulators in a free electron laser (FEL) when shorter undulator periods are required. In this paper, the factors that affect the choice of the high-power drive sources were studied via a Ka-band cavity-type MU with a corrugated waveguide proposed for the CompactLight X-ray FEL. They include the technology of the high-power vacuum electronic devices, the quality factor of the MU cavity that was demonstrated by prototyping a short section of the MU structure, and the beam dynamic study of the electrons' trajectories inside the MU. It showed that at high beam energy, a high-power oscillator is feasible to be used as the drive source. At low beam energy, the maximum transverse drift distance becomes larger therefore an amplifier has to be used to minimize the drift distance of the electrons by controlling the injection phase.

Figure 1

Experimental setup of the microwave undulator.

Figure 2

The electric field pattern of the MU cavity with 72 periods of regular corrugation sections (a), and the magnetic and electric fields on-axis (b).

Figure 3

Machined structures of the Ka-band MU by (a) electroforming, (b) direct machining, and (c) the measurement results.

Figure 4

Trajectories of the electrons with 5.5 GeV energy at different phase shifts $\phi$ inside the MU.

Figure 5

The maximum drift distance as a function of phase shift $\phi$ at different beam energies.

Figure 6

Radiation flux density as the function of radiation energy at different electron beam energies.

Figure 7

The trajectory of the electron calculated by SPECTRA.