Study of Fluctuations in Undulator Radiation in the IOTA Ring at Fermilab [Slides]

Abstract

We study turn-by-turn fluctuations in the number of emitted photons in an undulator, installed in the IOTA electron storage ring at Fermilab with an InGaAs PIN photodiode and an integrating circuit. Our study was motivated by the previous experiment [1]. We propose a theoretical model for the experimental data from [1] and in our own experiment we attempted to verify the model in an independent and more systematic way. Moreover, these fluctuations are an interesting subject for a study by itself, since they act as a seed for SASE in FELs. We improve the precision of the measurements from [1] by subtracting the average signal amplitude using a comb filter with a one-turn IOTA delay, and by using a special algorithm for noise subtraction. We obtain a reasonable agreement between our theoretical model and experiment. Along with repeating the experiment from [1], which was performed at a constant beam current, we also collect data for fluctuations in undulator light at different beam current values. Lastly, in our experiment we were able to see the transition from Poisson statistics to Super-Poisson statistics for undulator light, whereas in [1] only the latter statistics was observed.

Statistical properties of spontaneous synchrotron radiation with arbitrary degree of coherence

“…[2], which was derived for a relative fluctuation of classical radiation intensity. Also, it agrees with a simple order-of-magnitude estimate of M, provided in Appendix F. Equation 37is satisfied in the Brookhaven experiment [1] and in the proposed experiment in IOTA [17,18], which will be discussed in Secs. V and VI, respectively.…”

“…We calculate the expectation values in Eqs. (16) and (17) for the vacuum state of the second input port in the Appendix A. The results are as follows,…”

“…In the numerical examples in this paper (the Brookhaven experiment [1], and in the proposed experiment in IOTA [17,18]) we use the full version of Eq. (49) and perform numerical integration, because the values of the parameters in these experiments do not allow to use any approximations or simplifications in the integrals.…”

“…Therefore, in Sec. VI, we propose a new experiment in the IOTA storage ring [16][17][18], where all relevant parameters will be measured with good accuracy.…”

Statistical properties of undulator radiation in the IOTA storage ring

“…Then, the theoretical predictions are compared with the empirical data from [1]. Finally, we describe our experiment in IOTA [17], and how the empirical data from this experiment compare with our model.…”