Carsten Mai | Search arXiv

arXiv2026

Experimental Verification of Circumferential Bunch Length Variation and Head-Tail Exchange Affecting Microwave Instability in a Storage Ring

Classical analyses of microwave instability are built upon the longitudinal adiabatic approximation, which assumes that the bunch length remains constant around the storage ring. However, in a storage ring with small global phase slippage, the bunch length can vary around the ring and some particles can experience head-tail exchange due to the partial phase slippage and transverse-longitudinal coupling. Our theoretical study reveals that these effects can be beneficial for suppressing microwave instability. A new microwave instability threshold evaluation method has been correspondingly proposed to account for these effects. Here we present the first experimental evidence supporting our theoretical analysis. The measurements confirm that the microwave instability threshold can be increased by a factor of up to six compared to the classical prediction in our cases. Our results can also provide practical guidance for the design of extremely short bunch storage rings.

physics.acc-ph↗

arXiv2026

Undulator Radiation from a Single Electron: A Temporal Double-Slit Experiment

Double-slit diffraction studies with photons or massive particles rank among the most beautiful experiments in physics. In particular, measurements at very low intensities demonstrate the particle-wave duality and the coherent superposition of states very clearly. In this paper, low-intensity double-slit experiments in the time domain are presented measuring the spectral distribution of synchrotron light from a single relativistic electron in a storage ring. In two consecutive radiation sources (so-called undulators) with a magnetic detour between them, electrons emit two temporally separated light pulses leading to a spectrum with interference fringes, very much like the angular distribution of light behind two spatially separated slits. Independent experiments at two synchrotron light sources (DELTA in Germany and UVSOR-III in Japan) directly demonstrate that the spectral distribution of accumulated synchrotron light from a single electron is essentially the same as the spectrum from a beam of many electrons. While the latter is usually explained as interference between electromagnetic waves from the two undulators, the single-electron experiments demonstrate that coherent photon emission is delocalized over several meters and the accumulated spectral distribution exhibits a deterministic interference pattern at small wavelengths. The experiments presented here were conducted with near-ultraviolet light to avoid an elaborate in-vacuum setup, but the very wide spectral range of synchrotron radiation, from infrared light to X-rays, enables access to regimes not available in laser-based quantum optics experiments.

physics.acc-ph↗