First measurement of energy diffusion in an electron beam due to quantum fluctuations in the undulator radiation.

Plasma and beam physics are usually considered as classical physics disciplines with quantum effects featuring only rarely. In particular, free electron lasers (FELs) even in the Angstrom regime (developed recently and being upgraded towards even shorter wavelengths) are well described by classical mechanics and electrodynamics. There is, however, a quantum effect that can influence the operation of these devices and limit the shortest achievable wavelength, namely energy diffusion in an electron beam due to quantum fluctuations in undulator radiation.

Measuring and optimizing the momentum aperture in a particle accelerator.

Particle motion in storage rings is confined by various aperture limits, the size of which restricts the performance of the ring in terms of injection efficiency, lifetime, etc. Intrabeam scattering makes particles sweep a large portion of the phase space, where their motion may eventually be resonantly or chaotically excited to large amplitudes leading to collision with the vacuum chamber. We report here the studies performed at the Advanced Light Source (ALS) on the on- and off-momentum particle motion that provides a good understanding of these limitations.