Abstract
Generally, turn-to-turn fluctuations of synchrotron radiation power in a storage ring depend on the 6D phase-space distribution of the electron bunch. This effect is related to the interference of fields radiated by different electrons. Changes in the relative electron positions and velocities inside the bunch result in fluctuations in the total emitted energy per pass in a synchrotron radiation source. This effect has been previously described assuming constant and equal electron velocities before entering the synchrotron radiation source. In this paper, we present a generalized formula for the fluctuations with a non-negligible beam divergence. Further, we corroborate this formula in a dedicated experiment with undulator radiation in the Integrable Optics Test Accelerator (IOTA) storage ring at Fermilab. Lastly, possible applications in beam instrumentation are discussed.
Highlights
Full understanding of the radiation generated by accelerating charged particles is crucial for accelerator physics and electrodynamics in general
We describe our observation of turn-to-turn power fluctuations of incoherent spontaneous undulator radiation in the Integrable Optics Test Accelerator (IOTA) storage ring at Fermilab [18]
We employed a dedicated test light source with known fluctuations to verify this method of measurement of hN i and varðN Þ [Eqs. (20) and (25)]. This verification is described in Appendix C, where we estimated the statistical error of the measurement of varðN Þ by our apparatus, namely, Æ2.7 × 106—it is approximately constant in the range of varðN Þ observed with the undulator radiation in IOTA
Summary
Full understanding of the radiation generated by accelerating charged particles is crucial for accelerator physics and electrodynamics in general. Some examples are the pioneering determination of the elementary charge e by the shot noise [19], and the determination of the Boltzmann constant kB by the Johnson-Nyquist noise [20] Another example, relevant to the field of accelerator physics, is the use of Schottky noise pick-ups in storage rings [21,22,23] to measure transverse rms emittances, momentum spread, number of particles, etc. We present one example of a measurement of an unknown small vertical emittance of a flat beam in IOTA, given a known horizontal emittance, a longitudinal bunch shape, and ring focusing functions, using our new formula for the fluctuations. For more results regarding beam diagnostics via fluctuations in IOTA, we refer the reader to our separate publication [24]
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