Twisted waveguides for particle accelerator applications

A novel microwave device for accelerating charged particles based on twisted waveguide is presented. Twisted guides support slow-wave TM modes whose phase velocity could reach the speed of light c. The axial electric field in these structures can travel synchronously with the particles to achieve nearly uniform acceleration in a traveling-wave topology. The advantages of using twisted guides over conventional RF accelerating cavities are discussed. We present two types of twisted accelerating structures, one analogous to the well-known disk-loaded accelerating structure, and the other analogous to the popular elliptical (or TESLA-type) accelerating geometry. The propagation characteristics of these two structures are considered, and prototypes are made to experimentally validate our theoretical results.

I. Introduction

RF cavities have long been used to accelerate charged particles to achieve high electric field strengths and because of the wide availability of high power RF sources. However, special care must always be taken to match the phase velocity of the wave in the RF structure (whether it be traveling or standing) to the velocity of the particle to be accelerated. This constraint prohibits empty straight waveguides and cavities from being used, because the phase velocity in such structures is always greater than . Dielectrics can sometimes be used to circumvent this problem, but dielectrics introduce difficulties of their own, such as outgassing and dielectric breakdown. In practice, corrugated structures are almost always used to achieve slow wave operation, since these structures tend to have high accelerating electric field and can also be used in a superconducting regime.