Quasi-Optical THz Accelerating Structures

Abstract

We consider three types of THz accelerating structures. The structures of the first type operate with relatively long THz pulses having narrow bandwidth. These structures are assumed to be fed by THz radiation produced by high-power rf sources like gyrotrons or by the drive electron beam. The mentioned structures exploit Bragg principles, in order to provide high shunt impedance as well as necessary mode selection. The dielectric structures of this type could be produced by a femtosecond laser ablation system developed at Euclid Techlabs. This technology had already been tested for production of a 270 GHz Photonic Band Gap (PBG) structure made out of high resistivity silicon. Recently, gradients on the order of ~1 GV/m were be obtained in a form of single cycle (~1 ps) THz pulses produced by conversion of a high peak power laser radiation in nonlinear crystals (~ mJ, 1 ps, up to 3 % conversion efficiency). These pulses however are broadband (0.1-5 THz) and therefore a new accelerating structure type is required. For electron beam acceleration with such pulses we consider conventional dielectric capillaries as well as arrays of parabolic micro-mirrors with common central.