Design of a Standing-Wave Multi-Cavity Beam-Monitor for Simultaneous Beam Position and Emittance Measurements

Abstract

A high precision emittance measurement requires precise beam position at the measurement location. At present there is no existing technique, commercial or otherwise, for non‐destructive pulse‐to‐pulse simultaneous beam position and emittance measurement. FAR‐TECH, Inc. is currently developing a high precision cavity‐based beam monitor for simultaneous beam position and emittance measurements pulse‐to‐pulse, without beam interception and without moving parts. The design and anlysis of a multi‐cavity standing wave structure for a pulse‐to‐pulse emittance measurement system in which the quadrupole and the dipole standing wave modes resonate at harmonics of the beam operating frequency is presented. Considering the Next Linear Collider beams, an optimized 9‐cavity standing wave system is designed for simultaneous high precision beam position and emittance measurements. It operates with the π ‐ quadrupole mode resonating at 16th harmonic of the NLC bunch frequency, and the 3 π /4 dipole mode at 12th harmonic (8.568 GHz). The 9‐cavity system design indicates that the two dipoles resonate almost at the same frequency 8.583 GHz and the quadrupole at 11.427 GHz according to the scattering parameter calculations. The design can be trivially scaled so that the dipole frequency is at 8.568 GHz, and the quadrupole frequency can then be tuned during fabrication to achieve the desired 11.424 GHz. The output powers from these modes are estimated for the NLC beams. An estimated rms‐beam size resolution is sub micro‐meters and beam positions in sub nano‐meters.