Abstract
A new methodology able to model and reconstruct the transverse trace space of low-emittance electron beams accelerated in the bubble regime of laser-plasma interaction is presented. The single-shot measurement of both the electron energy spectrum and the betatron radiation spectrum is shown to allow a complete measurement of the transverse emittance, including the correlation term. A novel technique to directly measure the betatron oscillation amplitude distribution is described and tested at the SPARC-LAB test facility through the interaction of the ultrashort ultraintense Ti:Sa laser FLAME with a He gas-jet target. Via the exposed technique the beam transverse profile is also retrieved. From the study of the electron transverse dynamics inside the plasma bubble, the nonlinear correlation between the betatron amplitude and the divergence, i.e. the angle with respect the acceleration axis, is found. The angular distribution of the electron beam inside the bubble is retrieved. The knowledge of the trace-space density allows a more accurate measurement of the transverse emittance with respect to previous paradigms.
Highlights
The betatron radiation [1,2] from laser-plasma accelerated electrons [3,4,5] has been largely studied both theoretically and experimentally
A new methodology able to model and reconstruct the transverse trace space of low-emittance electron beams accelerated in the bubble regime of laser-plasma interaction is presented
In the present work we do not consider the cases of Direct Laser Acceleration (DLA) [25], i.e. we focus on the cases when the laser pulse does not significantly extend inside the plasma accelerating structure and it does not directly interact with the accelerated electrons
Summary
The betatron radiation [1,2] from laser-plasma accelerated electrons [3,4,5] has been largely studied both theoretically and experimentally. Electron bunch accelerated in the bubble regime [17,18] In this way the transverse profile of the electron beam, related to the betatron oscillation amplitude distribution, is retrieved. An expression is given for the correlation function between the betatron oscillation amplitude and the divergence of the single accelerated electrons, i.e. the angle with respect the acceleration axis, in order to obtain the distribution of the electron divergences. This distribution is compared to the one measured outside the plasma on the scintillator screen of a magnetic spectrometer. The final normalized emittance, measured with this novel and accurate technique, turns out to be a fraction of the upper limit evaluated by the product of the beam average energy times the beam radius times the beam divergence [10,11], since the correlation term can be taken into account
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