Identifying Signature of the QED Plasma Regime

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This award will enable a study of interactions between light, matter, and antimatter. A matter-antimatter plasma, comprising electrons and positrons, is thought to be found in the atmosphere of pulsars and other exotic astrophysical settings. When electrons encounter positrons, there is mutual annihilation of the electron-positron pair, releasing a large amount of light; conversely, pairs of electrons and positrons may be produced by sources of very high intensity light. To date, only small amounts of electron-positron pairs have been produced in the laboratory. However, it would be of great interest to produce many electron-positron pairs to observe the collective interactions in a matter-antimatter plasma. This regime is called the Quantum ElectroDynamics (QED) plasma regime, comprising an electron-positron plasma and featuring both strong field quantum and collective plasma effects. There exists a theoretical model of the QED plasma regime, but until it is demonstrated in the laboratory we cannot be sure there will be no surprises. The goal of this effort is to show how the QED plasma regime may be demonstrated in the laboratory with existing technology.Producing electron-positron pairs in sufficient numbers to observe collective effects will require large facilities to collide ultra-intense laser beams with each other, with intense beams of particles, or with a solid target. But even if the pairs are created in large numbers, collective effects are notoriously hard to observe for several reasons: the plasma is small; it is ephemeral; it is moving at relativistic speeds; and, because of the high speeds, collective plasma effects are diminished due to the relativistic mass enhancement. However, the requirements on the facilities might be considerably relaxed by identifying very distinct signatures of the collective effects. For a relativistic electron beam counter-propagating to an intense laser, there are induced frequency shifts in the laser light as it traverses through the developing electron-positron plasma. Those signatures inform importantly on plasma collective effects, suggesting a joint production-observation solution to observing the QED plasma regime with existing technology. Optimizing this joint solution, this project will identify theoretically and evaluate numerically how the radiation reaction reduces the pair energy, thereby enhancing the collective effects. This project will also investigate how spatially and temporally structured laser pulses might increase the pair plasma density, reduce the pair energy, and thereby enhance signatures of the collective effects.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.