Design of a cylindrical corrugated waveguide for a collinear wakefield accelerator

Abstract

We present the design of a cylindrical corrugated waveguide for use in the A-STAR accelerator under development at Argonne National Laboratory. A-STAR is a high gradient, high bunch repetition rate collinear wakefield accelerator that uses a 1-mm inner radius corrugated waveguide to produce a $90\text{ }\text{ }\mathrm{MV}\text{ }{\mathrm{m}}^{\ensuremath{-}1}$, 180-GHz accelerating field when driven by a 10-nC drive bunch. To select a corrugation geometry for A-STAR, we analyze three types of corrugation profiles in the overmoded regime with $a/\ensuremath{\lambda}$ ranging from 0.53 to 0.67, where $a$ is the minor radius of the corrugated waveguide and $\ensuremath{\lambda}$ is the free-space wavelength. We find that the corrugation geometry that optimizes the accelerator performance is a rounded profile with vertical sidewalls and a corrugation period $p\ensuremath{\ll}a$. Trade-offs between the peak surface fields and thermal loading are presented along with calculations of pulse heating and steady-state power dissipation. In addition to the ${\mathrm{TM}}_{01}$ accelerating mode, properties of the ${\mathrm{HEM}}_{11}$ mode and contributions from higher order modes are discussed.