[SLAC] [SLAC Pubs and Reports]
SLAC-PUB-7891
Characterizing Transverse Beam Jitter in the SLC Linac
Abstract
Transverse pulse-to-pulse trajectory instability, 'jitter', in the
linac of the SLAC Linear Collider (SLC) can be caused by various
sources, including mechanical vibration, poor power supply regulation,
and malfunctioning of trajectory feedbacks systems. Additionally, the
linac can amplify pulse to pulse centroid motion that originates in
the damping ring or the transport line that connects the ring to the
linac. The purpose of this study is to identify and characterize these
sources and to apply corrections and fixes. Transverse jitter has been
reduced in the last year from 0.5 to 0.2 in x and 1 to 0.3 in
y, measured in units of beam size. Jitter is estimated using
position monitor data from a large sample of successive pulses. The
FFT power spectrum of the data often indicate roughly equal
contributions from motion at 59 Hz due to the accelerator cooling
water pumps, 10 Hz motion due to mechanical vibration or power
supplies, and <0.4 Hz due to the feedback loops. Some of the
broadband, or random, pulse to pulse motion can be correlated with the
microwave instability in the damping ring. In this paper we describe
the data analysis and interpretation that can be used to help locate
the subsystem component which is causing the instability.
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