A Non-interceptive Method to Measure Longitudinal Twiss Parameters of a Beam in a Hadron Linear Accelerator using Beam Position Monitors

Abstract

A new method of measuring of the RMS longitudinal Twiss parameters of a beam in linear accelerators is presented. It is based on using signals from beam position monitors (BPM) sensitive to the second order moment of the longitudinal charge distribution in the bunch. The applicability of the method is demonstrated on the superconducting section of the Oak Ridge Spallation Neutron Source (SNS) linear accelerator. The results are compared to a direct measurement of the bunch longitudinal profiles using an interceptive bunch shape monitor (BSM) in the linac warm section of the same accelerator. Limitations of the method are discussed. The method is fast and simple, and can be used to obtain the initial parameters for the longitudinal matching in linear accelerators where interceptive diagnostics are not desirable.