Compact Spectroscopy of keV to MeV X-rays from a Laser Wakefield Accelerator

TL;DR

This paper presents a compact, modular calorimeter system for reconstructing broad X-ray spectra from laser wakefield accelerators, enabling rapid, single-shot spectral analysis of diverse X-ray sources.

Contribution

It introduces a novel, compact calorimeter and an iterative reconstruction algorithm for detailed spectral analysis of X-rays from laser wakefield accelerators.

Findings

Successful reconstruction of X-ray spectra from keV to >100 MeV.

Single-shot spectral measurements within approximately one minute.

Effective separation and characterization of mixed X-ray sources.

Abstract

We reconstruct spectra of secondary X-rays from a tunable 250-350 MeV laser wakefield electron accelerator from single-shot X-ray depth-energy measurements in a compact (7.5 $\times$ 7.5 $\times$ 15 cm), modular X-ray calorimeter made of alternating layers of absorbing materials and imaging plates. X-rays range from few-keV betatron to few-MeV inverse Compton to >100 MeV bremsstrahlung emission, and are characterized both individually and in mixtures. Geant4 simulations of energy deposition of single-energy X-rays in the stack generate an energy-vs-depth response matrix for a given stack configuration. An iterative reconstruction algorithm based on analytic models of betatron, inverse Compton and bremsstrahlung photon energy distributions then unfolds X-ray spectra, typically within a minute. We discuss uncertainties, limitations and extensions of both measurement and reconstruction methods.