Transverse beam emittance measurement by undulator radiation power noise

TL;DR

This paper introduces a novel method to measure very small vertical beam emittance in a storage ring using power noise fluctuations of undulator radiation, achieving absolute measurements without calibration.

Contribution

It demonstrates an absolute measurement technique for small vertical emittance using radiation power noise, effective when conventional methods cannot resolve the beam size.

Findings

Measured vertical emittance of 5-15 nm rms.

Method is calibration-free and absolute.

Effective for unresolvable beam sizes.

Abstract

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 Letter, we report an absolute measurement (no free parameters or calibration) of a small vertical emittance (5--15 nm rms) of a flat beam by this method, under conditions, when it is unresolvable by a conventional synchrotron light beam size monitor.