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Statistical Properties of Undulator Radiation

Two experiments were carried out to study the statistical properties of undulator radiation in the Integrable Optics Test Accelerator (IOTA) storage ring at Fermilab. The first experiment studied the turn-to-turn fluctuations in the power of the radiation generated by an electron bunch. The magnitude of these fluctuations depends on the 6D phase-space distribution of the electron bunch. In IOTA, we demonstrated that this effect can be used to measure some electron bunch parameters, small transverse emittances in particular. In the second experiment, a single electron was stored in the ring, emitting a photon only once per several hundred turns. In this regime, any classical interference-related collective effects were eliminated, and the quantum fluctuations could be studied in detail to search for possible deviations from the expected Poissonian photon statistics. In addition, the photocount arrival times were used to track the longitudinal motion of a single electron and to compare it with simulations. This allowed us to determine several dynamical parameters of the storage ring such as the rf cavity phase jitter and the dependence of the synchrotron motion period on amplitude.

43 PARTICLE ACCELERATORS↗

Observation of Undulator Radiation Generated by a Single Electron Circulating in a Storage Ring and Possible Applications

An experimental study into the undulator radiation, generated by a single electron was carried out at the Integrable Optics Test Accelerator (IOTA) storage ring at Fermilab. The individual photons were detected by a Single Photon Avalanche Diode (SPAD) at an average rate of 1 detection per 300 revolutions in the ring. The detection events were continuously recorded by a picosecond event timer for as long as 1 minute at a time. The collected data were used to test if there is any deviation from the classically predicted Poissonian photostatistics. It was motivated by the observation * of sub-Poissonian statistics in a similar experiment. The observation * could be an instrumentation effect related to low detection efficiency and long detector dead time. In our experiment, the detector (SPAD) has a much higher efficiency (65%) and a much lower dead time. In addition, we show that the collected data (recorded detection times) can be used to study the synchrotron motion of a single electron and infer some parameters of the ring. For example, by comparing the results of simulation and measurement for the synchrotron motion we were able to estimate the magnitude of the RF phase jitter.

43 PARTICLE ACCELERATORS↗

Experiments with Undulator Radiation, Emitted by a Single Electron

We study a single electron, circulating in the Fermilab IOTA storage ring and interacting with an undulator through single and multi-photon emissions. The focus of this research is on single-photon and two-photon undulator emissions. We begin by using one Single Photon Avalanche Diode (SPAD) detector to detect the undulator radiation photons and search for possible deviations from the expected Poissonian photon statistics. Then, we go on to use a two-photon interferometer consisting of two SPAD detectors separated by a beam splitter. This allows to test if there is any correlation in the detected photon pairs. In addition, the photocount arrival times can be used to track the longitudinal motion of a single electron and to compare it with simulations. This allowed us to determine several dynamical parameters of the storage ring such as the rf cavity phase jitter and the dependence of the synchrotron motion period on amplitude.

43 PARTICLE ACCELERATORS↗

Optical Diagnostics with Undulator Radiation for EIC Hadron Ring

Optical diagnostics is widely used for measurement of the electron beam parameters such as bunch length, beam size, and emittance. Using undulator radiation extends these measurements to the beam energy and energy spread. In this paper, we will study the applicability of synchrotron radiation for protons.

43 PARTICLE ACCELERATORS↗

Undulator radiation of single electrons: coherence length and quantum-optical properties

The aims of the CLARA experiment at the Fermilab Integrable Optics Test Accelerator (IOTA) were to directly measure the coherence length of undulator radiation emitted by a single electron and to test whether the radiation is in a pure classical Glauber coherent state or in a quantum mixture of coherent and Fock states. We used a Mach-Zehnder interferometer (MZI) to study visible radiation generated by 150-MeV electrons circulating in the ring. The relative delay between the two arms of the MZI was adjusted by varying the length of one of them with a resolution of 10 nm. The intensity of the circulating beam spanned several orders of magnitude, down to single electrons. A pair of single-photon avalanche diodes (SPADs) was placed at the output of the MZI arms to detect photocounts with high efficiency and timing resolution. We describe the observed interference patterns and photocount rates as a function of interferometer delay and discuss their implications.

43 PARTICLE ACCELERATORS↗

Undulator Radiation of Single Electrons: Coherence Length and Quantum-Optical Properties

The aims of the CLARA experiment at the Fermilab Integrable Optics Test Accelerator (IOTA) were to directly measure the coherence length of undulator radiation emitted by a single electron and to test whether the radiation is in a pure classical Glauber coherent state or in a quantum mixture of coherent and Fock states. We used a Mach-Zehnder interferometer (MZI) to study visible radiation generated by 150-MeV electrons circulating in the ring. The relative delay between the two arms of the MZI was adjusted by varying the length of one of them with a resolution of 10 nm. The intensity of the circulating beam spanned several orders of magnitude, down to single electrons. A pair of single-photon avalanche diodes (SPADs) was placed at the output of the MZI arms to detect photocounts with high efficiency and timing resolution. We describe the observed interference patterns and photocount rates as a function of interferometer delay and discuss their implications.

43 PARTICLE ACCELERATORS↗

Measurement of Coherence Length in UndulAtor RAdiation (CLARA): Run 4 Proposal

The goal of the proposed experimental research is to investigate the quantum nature of “a particle in a ring” by studying a single 135-MeV electron, circulating in the IOTA storage ring and interacting with an undulator through single- and multi-photon emissions. The focus of this proposal will be two-photon undulator emissions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Transverse Beam Emittance Measurement by Undulator Radiation Power Noise

Generally, turn-to-turn power fluctuations of incoherent spontaneous synchrotron radiation in a storage ring depend on the 6D phase-space distribution of the electron bunch. In some cases, if only one parameter of the distribution is unknown, this parameter can be determined from the measured magnitude of these power fluctuations. In this contribution, we report the results of our experiment at the Integrable Optics Test Accelerator (IOTA) storage ring, where we carried out an absolute measurement (no free parameters or calibration) of a small vertical emittance (5–15 nm rms) of a flat beam by this new method, under conditions, when the small vertical emittance is unresolvable by a conventional synchrotron light beam size monitor.

43 PARTICLE ACCELERATORS↗

Reconstructions from randomly generated longitudinal electron bunch profiles with Gaussian envelopes using the Gerchberg–Saxton algorithm

Knowledge of longitudinal electron bunch profiles is vital to optimize the performance of plasma wakefield accelerators and x-ray free electron laser linacs. Because of their importance to these novel applications, noninvasive frequency domain techniques are often employed to reconstruct longitudinal bunch profiles from coherent synchrotron, transition, or undulator radiation measurements. In this paper, we detail several common reconstruction techniques involving the Kramers–Kronig phase relationship and Gerchberg–Saxton algorithm. Additionally, through statistical analysis, we draw general conclusions about the accuracy of these reconstruction techniques and the most suitable candidate for reconstructing well-isolated longitudinal bunch profiles from spectroscopic data.

47 OTHER INSTRUMENTATION↗

Ultracold Storage Ring

The modern ring upgrades aim at reaching beam low emittance while paying little attention to the beam energy spread. The purpose of this note is to conjecture on a possibility of designing a storage ring with ultimately small energy spread. This might be of interest with respect to the following two applications: increasing brightness and coherence of radiation at higher harmonics of undulator radiation and a potential of building a soft X-ray FEL on a storage ring. Throughout the tech note we are taking a 3 GeV storage ring of the NSLS-II size as an example.

43 PARTICLE ACCELERATORS↗