Effective compression of photo-injector electron bunches in the negative-mass undulators

The use of the “negative mass” regime provides stabilization of longitudinal size of dense photo-injector electron bunches at long distances. This allows one to increase significantly the power capabilities of a terahertz source based on coherent spontaneous undulator 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.