Abstract
We report on an indirect and non-invasive method to simultaneously characterise the energy-dependent emittance and source size of ultra-relativistic positron beams generated during the propagation of a laser-wakefield accelerated electron beam through a high-Z converter target. The strong correlation of the geometrical emittance of the positrons with that of the scattered electrons allows the former to be inferred, with high accuracy, from monitoring the latter. The technique has been tested in a proof-of-principle experiment where, for 100 MeV positrons, we infer geometrical emittances and source sizes of the order of 3 µm and 150 µm, respectively. This is consistent with the numerically predicted possibility of achieving sub-µm geometrical emittances and micron-scale source sizes at the GeV level.
Highlights
In the past decade, significant experimental effort has been put in generating relativistic positron beams using high-power lasers in an all-optical configuration [1]
We report on an indirect and non-invasive method to simultaneously characterise the energy-dependent emittance and source size of ultra-relativistic positron beams generated during the propagation of a laser-wakefield accelerated electron beam through a high-Z converter target
Significant experimental effort has been put in generating relativistic positron beams using high-power lasers in an all-optical configuration [1]
Summary
Significant experimental effort has been put in generating relativistic positron beams using high-power lasers in an all-optical configuration [1]. Generating GeV-scale, μm-size positron beams with sufficiently good emittance would provide experimentalists with an ideal platform to study plasma-based acceleration of positrons; for example, a dedicated experimental area for this kind of work has been included in the Conceptual Design Report for the European plasma-based accelerator facility EuPRAXIA [33]. For these studies, it would be highly beneficial to have an online monitoring system for the laser-driven positron beam, where energy, emittance, and source size can be measured on a shot-to-shot basis without interfering with the positron beam.
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