Abstract
The effective scaling of positron-electron pair production by direct, ultraintense laser-matter interaction is investigated for a range of target materials and thicknesses. An axial magnetic field, acting as a focusing lens, was employed to measure positron signals for targets with atomic numbers as low as copper (Z = 29). The pair production yield was found to be consistent with the Bethe-Heitler mechanism, where the number of positrons emitted into a 1 steradian cone angle from the target rear was found to be proportional to Z2. The unexpectedly low scaling results from Coulomb collisions that act to stop or scatter positrons into high angles. Monte Carlo simulations support the experimental results, providing a comprehensive power-law scaling relationship for all elemental materials and densities.
Highlights
Laboratory created relativistic positron jets1,2 have recently been shown to have wide ranging potential applications such as in the injector stages of linear accelerators,3 in creating magnetically confined charge-neutral pair plasmas,4 and as a platform for astrophysically relevant collisionless shock experiments.5–7 The feasibility of these applications is heavily dependent on the total number of positrons emitted from the pair-production target, as well as their energy and angular properties
The effective scaling of positron-electron pair production by direct, ultraintense laser-matter interaction is investigated for a range of target materials and thicknesses
The pair production yield was found to be consistent with the BetheHeitler mechanism, where the number of positrons emitted into a 1 steradian cone angle from the target rear was found to be proportional to Z2
Summary
Laboratory created relativistic positron jets have recently been shown to have wide ranging potential applications such as in the injector stages of linear accelerators, in creating magnetically confined charge-neutral pair plasmas, and as a platform for astrophysically relevant collisionless shock experiments. The feasibility of these applications is heavily dependent on the total number of positrons emitted from the pair-production target, as well as their energy and angular properties. Laboratory created relativistic positron jets have recently been shown to have wide ranging potential applications such as in the injector stages of linear accelerators, in creating magnetically confined charge-neutral pair plasmas, and as a platform for astrophysically relevant collisionless shock experiments.. Laboratory created relativistic positron jets have recently been shown to have wide ranging potential applications such as in the injector stages of linear accelerators, in creating magnetically confined charge-neutral pair plasmas, and as a platform for astrophysically relevant collisionless shock experiments.5–7 The feasibility of these applications is heavily dependent on the total number of positrons emitted from the pair-production target, as well as their energy and angular properties. An extrapolation from the data creates a predictive model for arbitrary target materials and laser intensities, consistent with other recent measurements of positron production.
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