Long range terahertz driven electron acceleration using phase shifters

Abstract

Terahertz radiation (THz)-based electron acceleration has the potential as a technology for driving the next-generation, compact ultrafast and ultrabright electron and x-ray sources. Dephasing is one of the key problems that prevent long THz–electron interaction lengths in the sub- to few-MeV range, where electron velocities vary significantly during high-field acceleration. Here, we present a phase-shifter design with double vacuum channels to alternate the phase velocity that effectively extends the THz–electron interaction length in THz-powered dielectrically loaded waveguides. The electrons are swept multiple-times back and forth through the accelerating phase of the THz wave to undergo continuous acceleration along the entire interaction. In addition, the double vacuum channel design enables increases in both the phase and group velocities of the THz wave, which leads to an adaptive synchronous acceleration with extended interaction length. This method paves the way for the practical implementation of THz-powered devices for high-energy ultrafast electron sources.