Abstract
In accelerators, the electron beam longitudinal dynamics critically depend on the energy distribution of the beam. Noninvasive, highly accurate measurement of the energy spread of the electron beam in the storage ring remains a challenge. Conventional techniques are limited to measuring a relatively large energy spread using the energy spread induced broadening effect of radiation source size or radiation spectrum. In this work, we report a versatile method to accurately measure the electron beam relative energy spread from ${10}^{\ensuremath{-}4}$ to ${10}^{\ensuremath{-}2}$ using the optical klystron radiation. A novel numerical method based on the Gauss-Hermite expansion has been developed to treat both spectral broadening and modulation on an equal footing. A large dynamic range of the measurement is realized by properly configuring the optical klystron. In addition, a model-based scheme has been developed for the first time to compensate the beam-emittance-induced inhomogeneous spectral broadening effect to improve the accuracy of the energy spread measurement. Using this technique, we have successfully measured the relative energy spread of the electron beam in the Duke storage ring from $6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ to $6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ with an overall uncertainty of less than 5%. The optical klystron is a powerful diagnostic for highly accurate energy spread measurement for storage rings and other advanced electron accelerators.
Highlights
In electron accelerators, the energy distribution of the electron beam is an essential parameter for the study of the longitudinal beam dynamics and beam instabilities
III and IV, we have demonstrated that optical klystron radiation can be used to accurately determine a wide range of values of the electron beam energy spread by applying the G-H method
Using various configurations of the electron beams at the Duke storage ring, we have demonstrated the measurement of the energy spread from 6 Â 10À4 to 6 Â 10À3 using the optical klystron radiation with an overall uncertainty of less than 5%
Summary
The energy distribution of the electron beam is an essential parameter for the study of the longitudinal beam dynamics and beam instabilities. At ESRF, the energy spread was determined using the broadening of the undulator high harmonic radiation to take advantage of a narrowed undulator spectrum at a higher harmonic [6] In this scheme, the reduced opening angle of the harmonic radiation beam increased the sensitivity of the spectrum to the angular spread of the electron beam, leading to the necessity of performing emittance correction. The conventional techniques described above, based upon the broadening of either the source size or spectrum of the synchrotron radiation beam, are useful for a relatively large energy spread, but not for a small energy spread. The emittance effect is compensated for the measured spectra using a simulation model to improve the accuracy of the energy spread measurement This new technique has been used to measure the energy spread of the electron beam in the Duke storage ring. VI, we present our experimental results on energy spread measurements using the optical klystron radiation with the electron beam energy spread manipulated in a wide range by tuning the FEL interaction
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