[SLAC] [SLAC Pubs and Reports]
SLAC-PUB-7939
New Apparatus for Precise Synchronous Phase Shift Measurements in Storage Rings
Abstract
Measuring a synchronous phase shift as a function of beam current is
commonly done in accelerator physics to estimate the longitudinal
impedance of a storage ring vacuum chamber. This measurement is
normally done with RF techniques that don't have enough accuracy to
detect small phase shifts typical to the newer storage rings. In this
paper we report results from a new method for precise measurement of a
synchronous phase shift. Our method involves downmixing from the RF
frequency to a kHz range and then using an audio DSP lock-in amplifier
for the actual phase detection. This paper describes the idea and the
advantages of a new method as well as its practical implementation in
the apparatus we build for precise synchronous phase measurements in
the Stanford Linear Collider damping rings. The results of those
measurements are also presented.
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