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

Abstract

The use of the "negative mass" regime provides stabilization of longitudinal size of dense photoinjector electron bunches moving through a long undulator. This allows one to increase significantly the power capabilities of a terahertz source based on coherent spontaneous emission from a short bunch. However, such type of emission is produced if the bunch length is comparable with the radiation wavelength. This work discusses the use of the negative mass regime to provide effective compression of dense bunches down to "terahertz" lengths.

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

“…In this approximation, the axial Coulomb electric field inside the bunch can be easily calculated by using the bunch model described in detail in Ref. [18].…”

“…This results in the saturation of the process of spontaneous emission. Thus, in the case of undulator and Cherenkov masers, special methods providing control of the axial length of the bunch [13,14] (and, possibly, the compression of the bunch [16][17][18]) are required. This paper is devoted to studying possibilities for organizing spontaneous coherent emission from a short electron bunch in cyclotron masers.…”

Capabilities of Terahertz Cyclotron and Undulator Radiation from Short Ultrarelativistic Electron Bunches

“…In the study of the dynamics of bunches and radiation in this paper, two computational approaches are used. In the approximate method [13,18], the bunch is represented by a set of solid uniformly charged disks whose centers are initially placed on the waveguide axis; the disks interact with the radiation field and between each other, and the radiation field is represented by the lowest TE 11 wave with a smoothly varying amplitude. In a more general and precise spatial-frequency approach WB3D [19], macroparticles are used, which are thrown at the initial moment into the waveguide and interact with each other and with the radiation field represented by a set of waveguide modes excited at any cyclotron harmonic.…”

“…, where the coefficient 0.4 is equal to the norm of the wave. It should be mentioned that according to simulations, the model of a solid disk set [13,18] is a fairly accurate approximation for the description of Coulomb interaction inside a bunch and its radiation in a relatively narrow waveguide.…”

Development of photoinjector in IAP RAS

“…Photoinjector accelerators [1,2] make it possible to obtain dense cold electron bunches of picosecond duration with an average particle energy of several MeV and a characteristic charge from fractions of a nanocoulomb to tens of nanocoulombs. Such bunches can be used, for example, to generate high-power short terahertz pulses of undulator or cyclotron radiation [3][4][5][6][7][8], in experiments on Compton scattering of laser pulses [9], and also for injection into more energetic accelerators. A photoinjection complex [10] is being created at the IAP RAS, in which stepwise acceleration of electrons up to energies of the order of 20 MeV should be implemented while maintaining the normalized transverse bunch emittance at a level of 1 mm×mrad.…”