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 sum signals from beam position monitors sensitive to 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 linear accelerator. The results are compared to a direct measurement of the bunch longitudinal profiles using an interceptive bunch shape monitor 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.
Highlights
It is important to know the longitudinal Twiss parameters of the bunch for beam dynamics optimization and loss reduction in linear accelerators
In this paper we suggest a new method to measure the longitudinal Twiss parameters at the entrance of a
Where J! is an amplitude of the beam current harmonic with the frequency !, zð!Þ is a factor describing transfer function of the beam position monitor (BPM) including the pickup geometry, amplifier gain, etc., R is the radius of the pickup aperture, c is the speed of light, and are relativistic factors, and I0 is Published by the American Physical Society
Summary
It is important to know the longitudinal Twiss parameters of the bunch for beam dynamics optimization and loss reduction in linear accelerators. That method is based on an amplitude scan of the first SCL cavity combined with a phase scan of the rest of the SCL linac, measurements of beam loss, and assumptions about sharpness of the edges of the longitudinal acceptance. Superconducting linac based on the analysis of the beam position monitor (BPM) sum signals during a phase scan of the first accelerating cavity. These signals are proportional to the amplitude of the frequency spectrum of the longitudinal bunch distribution at the BPM’s frequency. We will show that by combining information on the bunch length at multiple BPM locations and using a simple model of a cavity and a drift one can determine the longitudinal Twiss parameters at the linac entrance with good accuracy.
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