Non-invasive characterization of transverse beam emittance of electrons from a laser-plasma wakefield accelerator in the bubble regime using betatron x-ray radiation

TL;DR

This paper introduces a non-invasive method to measure the transverse emittance of electron beams from laser-plasma wakefield accelerators using betatron x-ray radiation, providing accurate results consistent with models.

Contribution

The study presents a novel non-invasive technique combining x-ray source size measurements and electron beam divergence to determine transverse emittance in the bubble regime.

Findings

Measured normalized RMS transverse emittance <0.5 π mm·mrad.

Results agree with numerical modeling and analytic theory.

Technique applicable to relativistic electron beams at 230 MeV.

Abstract

We propose and use a technique to measure the transverse emittance of a laser-wakefield accelerated beam of relativistic electrons. The technique is based on the simultaneous measurements of the electron beam divergence given by $v_{\perp}/v_{\parallel}$, the measured longitudinal spectrum $\gamma_\parallel$ and the transverse electron bunch size in the bubble $r_{\perp}$. The latter is obtained via the measurement of the source size of the x-rays emitted by the accelerating electron bunch in the bubble. We measure a \textit{normalised} RMS beam transverse emittance $<0.5$ $\pi$ mm$\:$mrad as an upper limit for a spatially gaussian, spectrally quasi-monoenergetic electron beam with 230 MeV energy in agreement with numerical modeling and analytic theory in the bubble regime.