Abstract
We present a new technique to measure the synchronous phase shift in an electron storage ring. A digital sampling oscilloscope is used to observe the cavity and beam signals simultaneously, and the amplitude and relative phase are obtained from a Fourier transform of the time-domain data. This procedure gives 6 mdeg resolution and is largely insensitive to input signal amplitude variations. The measurement system was used to study the dependence of the synchronous phase shift on beam current, gap voltage, and beam energy in the Brazilian Synchrotron Light Source electron storage ring.
Highlights
The measurement of the shift in the phase of the stored electron beam with respect to the cavity voltage is a well-known procedure to determine various important beam parameters in an electron storage ring
The variation of the synchronous phase shift as a function of gap voltage has been used to determine the energy loss to synchrotron radiation [2], and its variation as a function of beam current has been used in several machines [2,3,4,5] to determine parasitic mode losses
A novel method was proposed by Podobedov and Siemann [6] to mix the cavity and beam signals down to audio frequencies, allowing the use of a fully digitized lock-in amplifier for the phase detection
Summary
The measurement of the shift in the phase of the stored electron beam with respect to the cavity voltage (the synchronous phase shift [1]) is a well-known procedure to determine various important beam parameters in an electron storage ring. Electronic noise is reduced by averaging many readings of the scope, and harmonic contamination effects are kept under control by the digital filtering provided by the fast-Fourier transform (FFT) analysis, avoiding the use of high Q analog filters for the beam signal. This phase measurement technique reached 6 mdeg resolution and is quite insensitive to signal amplitude variations: test bench measurements have shown less than 610 mdeg phase variation over a 10 dB input signal range.
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