Configurations for short period rf undulators

Abstract

Several configurations for rf undulators energized at millimeter wavelengths and designed to produce coherent nanometer radiation from sub-GeV electron beams are analyzed and compared with one another. These configurations include a traveling-wave resonant ring, a standing wave resonator, and a resonator operating close to cutoff.

Microwave Undulator Using a Helically Corrugated Waveguide

“…The principle of the MU can be found in [3,[11][12][13]. The highfrequency FEL radiation is generated from the stimulated Compton counter scattering of the backward traveling wave by the relativistic electron bunch, which has a high Doppler upshift frequency [14].…”

“…The transverse motion of the electron bunch in the backward traveling wave was analytically studied in reference [13], under the assumption of a paraxial wave condition. The ratio between the transverse and axial velocities was found to be on the order of K/γ, which is also a small value.…”

“…2, its impact can be minimized if the impedance of the MU is close to the impedance of free space. Recent study on the electron motion in reference [13] showed the effect of the co-propagating wave could not be ignored and it could cause spectrum degradation at larger K values. In this paper, only the electromagnetic properties were considered when designing the microwave undulator.…”

Radiation emission processes and properties: synchrotron, undulator and betatron radiation

“…Millimeter-wave undulators using micro pulsed undulators or RF undulators are also reported [43,44]. A different approach has been proposed that exploits the field periodicity of the lattice structure inside a crystal.…”

A traveling-wave ring resonator with Bragg deflectors in a two-stage terahertz free-electron laser

“…In addition to the compatibility with a system transporting two REBs, the advantage of a ring resonator based on Bragg deflectors is its rather high selectivity with respect to the longitudinal mode index, which is caused by the limited band of Bragg reflections. Moreover, the proposed resonator scheme ensures the absence of a copropagating component of the pumping field, which could introduce additional low frequency oscillations into the beam and lead to its transverse drift, thus significantly impairing conditions for the generation of scattered terahertz radiation [10].…”