Laboratory studies of neutral and collimated electron-positron beams

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Electron-positron pair plasmas (EPPs) represent a unique state of matter, whereby an intrinsic and complete symmetry exists between the negatively charged (matter) and positively charged (anti-matter) particles. EPPs are emitted, in the form of ultra-relativistic winds or collimated jets, by some of the most energetic or powerful objects in the Universe, such as black-holes, pulsars, and quasars. They are frequently associated with violent emission of gamma-rays in the form of short-lived (milliseconds up to a few minutes) bursts, which are amongst the most luminous events ever observed in the Universe. These systems represent a unique astrophysical laboratory, since their immense distance from Earth (some exceeding a billion light years) provides invaluable insight into the Universe at its early stage and allow testing physical models at their very limits. However, the dynamics of EPPs in the intergalactic medium and, crucially, their radiative properties, are still subject of fervent debate in the community, chiefly due to the fact that our knowledge of them is intrinsically restricted to astrophysical observation and numerical modelling. Precious help would naturally arise from dedicated laboratory experiments, in which the microphysics can be accessed in a reproducible and controllable manner. However, despite dedicated efforts at several leading research institutes worldwide, the generation of a neutral EPP in the laboratory has until recently remained elusive. Recently, our research group has succeeded in generating a neutral EPP in a fully optical experimental setup, placing our group at the forefront of this research branch. This is an absolute first in the area, despite continued dedicated efforts from other research institutes worldwide. Besides the academic interest, this work has proven to attract significant media attention, as demonstrated by dedicated articles in the New Scientist, CERN Courier, Physics World, and The Conversation, among others. Our proposed research project is then focused on consolidating our world-leading role in this emerging branch of experimental physics by expanding our experimental investigations of this fascinating state of matter. In particular, we aim at generating, for the first time, a collimated and neutral EPP and study its interaction with a background ionised medium over cm scales. We aim at spatially and temporally characterising instabilities arising during the EPP propagation, from its early stages up to saturation. The extraction of detailed experimental data on the plasma dynamics and subsequent field generation will provide the first laboratory platform for the small-scale study of astrophysical jets and GRB emission, against which numerical models used to interpret astrophysical observations can be compared and refined.