Single pass, THz spectral range free-electron laser driven by a photocathode hybrid rf linear accelerator

Abstract

A single pass, THz spectral range free-electron laser (FEL) driven by a photocathode hybrid rf-LINAC is considered, taking the Israeli THz FEL project developed in Ariel University as an example. Two possible configurations of such FEL are discussed: an enhanced coherent spontaneous emission FEL, and a prebunched FEL utilizing periodically modulated short electron beam pulses. A general study of the FEL configurations is carried out in the framework of a space-frequency approach, realized in WB3D numerical code. The configurations are studied and compared based on preliminary parameters of a drive hybrid rf-LINAC gun under development in

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

“…A precise description of the space-charge field term which includes mutual electromagnetic interactions between relativistic charges moving arbitrarily in a waveguide appears to be a hard problem to solve. We use the "free-space" Lorenztransformed Coulomb field and neglect the effect of the waveguide walls on the space-charge field affecting the particles moving close to the waveguide axis [6,25]. The equations are integrated in the space-frequency domain along the beam line axis z, when each simulation particle j arrives to a point z at its own time t j ðzÞ.…”

“…This method meets, however, strict limitations because of very strong Coulomb repulsion and fast longitudinal spreading of dense bunches consisting of "too light" electrons. 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.…”

“…The interaction between the field and the particles is described by a set of coupled equations for wave excitation and particle dynamics in the selfconsistent field, expressing the evolution of mode amplitudes along the interaction region. The method was realized in the numerical code WB3D and has been successfully applied to the analysis of various effects in FELs (see [6] and references therein).…”

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

“…Modern sources of dense electron beams (including laser-driven photoinjectors) allow the formation of compact and accessible sources of dense electron bunches with a moderate energy of 3-6 MeV, picosecond pulse durations, and charges of up to 1 nC and even greater [1][2][3][4][5][6]. These bunches can be used for the realization of relatively simple and compact terahertz (THz) sources operating in the regime of spontaneous coherent radiation [7][8][9][10][11][12][13][14]. This type of radiation is realized when the effective phase size of the electron bunch with respect to the wave is small enough so that the wave packets emitted by each of the electrons add up basically in phase ( Fig.…”

Compression of a photoinjector electron bunch in the negative-mass undulator

“…Laser-driven photoinjectors allow formation of fairly compact and accessible sources of dense electron bunches with a moderate energy of 3-6 MeV, picosecond pulse durations, and charges of up to 1 nC and even greater [1][2][3][4][5]. These bunches can be directly exploited for radiation in the THz frequency range [6][7][8][9][10][11][12][13]. They can be used, in particular, for realization of comparatively simple and compact sources operating in the regime of spontaneous coherent undulator radiation.…”