Cyclotron radiation cooling of a short electron bunch kicked in an undulator with guiding magnetic field

Abstract

We propose to use of an undulator with the guiding axial magnetic field as a "kicker" forming a bunch of electron gyro-oscillators with a small spread in the axial velocity. The cyclotron emission from the bunch leads to losing oscillatory velocity of electron gyrorotation, but it does not perturb the axial electron velocity. This effect can be used for transformation of minimization of the spread in electron axial velocity in the undulator section into minimization of the spread in electron energy in the cyclotron radiation section.

Energy enhancement and spectrum narrowing in terahertz electron sources due to negative mass instability

“…These limitations can partially be mitigated by means of using preliminarily energy-chirped [5,6] or spatially modulated [7,8] bunches. However, significantly higher energy enhancement and spectrum narrowing can be expected [9] if a helical undulator with a very strong (over-resonance) guiding field is used and, thus, the conditions for nonisochronous longitudinal electron oscillations [10][11][12][13][14][15][16][17] are fulfilled. In this case, development of the negative mass instability can lead to formation of a long-living electron "core" with a sufficiently small longitudinal size.…”

Spontaneous superradiant sub-THz coherent cyclotron emission from a short dense electron bunch

“…In order to describe the spatiotemporal evolution of the slow rf wave amplitude aðz; tÞ, we follow the way described in detail in Ref. [27]. We consider the wave equation for the vector potential:…”

Undulator radiation of premodulated and nonmodulated electron bunches in the negative mass instability regime

“…The NMI in undulators is possible in the presence of a strong uniform guiding field [17][18][19][20][21][22][23]. For example, it can be developed in the combined helical undulator and uniform guiding fields.…”

“…Another character of the evolution of relatively long modulated bunches and their radiation should be expected when the particles are not repulsed from areas with increased density, but are attracted to them. This "anomalous" situation occurs, in particular, in undulators with a strong (over-resonance) guiding magnetic field due to the development of the so-called undulator negative mass instability (NMI) [17][18][19] in bunches [20][21][22][23]. Due to NMI, an increase/decrease in electron energy under the action of the space charge of a dense bunch can cause approaching to/moving away from the resonance between the cyclotron and undulator oscillations.…”