Abstract

The application of phase-retrieval algorithms to the reconstruction of the longitudinal bunch profile of an electron bunch from the spectrum of the coherent transition radiation (CTR) it produces is considered. The development of a new algorithm for this application, the Bubblewrap algorithm, is described. Tests with synthetic data show successful reconstruction of the longitudinal profile of single and double electron bunches, provided that the CTR spectrum is known over a sufficiently wide range. The application of the Bubblewrap algorithm to the reconstruction of laser-accelerated electron bunch profiles from experimental data is demonstrated. The results are shown to be consistent with estimates of the bunch length obtained by other methods.

Highlights

  • When a charged particle crosses a boundary between media of different dielectric indices it causes emission of very broadband transition radiation [1]

  • III we present a new algorithm—which we call the Bubblewrap algorithm—that is targeted at longitudinal bunch profile reconstruction

  • VI we present the reconstruction of longitudinal electron bunch profiles through application of the Bubblewrap algorithm to coherent transition radiation (CTR) spectra obtained in this experiment, and compare the results with fits to an assumed bunch profile

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Summary

INTRODUCTION

When a charged particle crosses a boundary between media of different dielectric indices it causes emission of very broadband transition radiation [1]. This may be insufficient, as in some (realistic) circumstances additional phase contributions, known as the Blaschke phase, can change the deduced longitudinal profile significantly Given these limitations it is interesting to explore alternative methods for reconstructing the longitudinal profile from full or partial measurements of the radiation spectrum. In this paper we consider, for the first time, the application of phase-retrieval algorithms to deducing the longitudinal bunch profile of a charged particle beam from measurements of part of the CTR spectrum.

PHASE-RETRIEVAL ALGORITHMS
Gerchberg-Saxton algorithm
Hybrid input-output algorithm
Difference map algorithms
Choice of function support and initial estimate
Adaptive support selection
AN ALGORITHM FOR RECONSTRUCTION OF BUNCH PROFILES FROM CTR DATA
Selection of algorithm
The Bubblewrap algorithm
RECONSTRUCTION OF PROFILES FROM SYNTHETIC SPECTRAL DATA
MEASUREMENT OF CTR SPECTRA FROM LASER-ACCELERATED ELECTRON BUNCHES
RECONSTRUCTION OF LONGITUDINAL BUNCH PROFILES FROM MEASURED CTR SPECTRA
Findings
CONCLUSIONS

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