The RF Travelling Wave Particle Deflector

As a result of interest in mass separators stimulated by Blewett, Panofsky and others, the writer suggested use of a travelling wave interaction as an improvement on existing cavity deflectors then under study at Stanford by Philips. The specific structure proposed was the use of the TMll-like mode in disc-loaded waveguide. This configuration was subsequently adopted by CERN, BNL, ENS and SLAC, where projects to demonstrate particle deflection are in progress. The principle on which the separator functions is the production of a deflecting force, resulting from field components of a wave travelling synchronously with the particle beam. A beam transport system, appropriate to the experimental arrangement, permits observation of the differentiated particles. It can be shown that the motion of a particle interacting with a propagating wave at the velocity of light is characterized by uniform, aberrationless deflection over the beam aperture. The experimentally determined properties of such a waveguide (transverse shunt impedance, group velocity and solutions of the determinantal equation) are presented for the π/2-mode of propagation. A measurement technique for determining the shunt impedance, based on a perturbation method, is also discussed.