A spiral loaded low-β accelerating structure

Abstract

This letter describes a new accelerating structure for a heavy‐particle linear accelerator: a quarter‐wavelength spiral loaded radio‐frequency resonator. Experiments and preliminary analysis of this structure indicate that its performance as an accelerating structure is considerably superior to the helically loaded resonator in such important areas as surface electric field level, mechanical stability, and shunt impedance. As a superconducting device, a superconductiong lead‐plated copper spiral resonator of phase velocity β = 0.045 has been run continuously at an accelerating field level of 1.46 MV/m with little degradation in Q below the low‐field level. Measured properties of superconducting niobium imply that a niobium resonator of this type could reach accelerating fields in excess of 4 MV/m before reaching breakdown conditions.