Design of Tapered Extended Interaction Structures for Particle Acceleration and Terahertz Generation

We present design methodologies and Figures of Merit (FoM) for developing extended interaction structures intended for particle acceleration and/or terahertz generation. The proposed Physics-Based (PB) approach enables the design of structures with a continuous matching of sub relativistic electrons with electromagnetic guided waves and works by gradually adjusting the wave phase velocity along the interaction structure to match with the electron speed. Our focus is on geometries where the guided mode of the electromagnetic field and the particle beam propagate co-linearly, since this configuration offers superior scalability and performance compared to transverse illumination configurations. Moreover, only such interaction structures can work also in reverse mode for electromagnetic wave generation.