Laboratory studies of neutral and collimated electron-positron beams

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.

Our proposed research project is focused on consolidating our world-leading role in an emerging branch of experimental physics: the study of electron-positron pair plasmas in the laboratory. The Principal Investigator has carried out the first pioneering experiments in this area, and seeks to expand these exciting preliminary results into regimes of direct relevance to astrophysics.

The successful completion of this research projects will have ample repercussions for the already high level of scientific research in the UK, since it will highlight our group as world-leaders in the field of plasma physics and laser-based laboratory astrophysics.

The first study of the dynamics of electron-positron plasmas will provide an invaluable set of experimental data that will dramatically advance our understanding of plasma physics and, more in general, of collective systems. Besides, we aim at creating and studying phenomena that are of direct relevance to astrophysics, since they are thought to be at the core of the dynamics of astrophysical jets and the subsequent generation of gamma-ray bursts and acceleration of cosmic particles. Providing a set of experimental data in this area will allow, for the first time, benchmarking and refining numerical and analytical models currently used to interpret astrophysical observations. The proposed research project will then open up a new field of experimental research, namely the study of electron-positron pair plasmas in the laboratory, and it will benefit a wide range of research and academic communities, including plasma physics, astrophysics, and theoretical physics.

Moreover, we envisage that the successful completion of the proposed research project will fascinate also the general audience, improving the general conception of scientific research within the UK and abroad. The interest of the general audience for this subject and, in particular, for the work carried out by the Principal Investigator in this area, is already demonstrated by the significant amount of media coverage that the Principal Investigator has obtained. This includes dedicated articles in the New Scientist, Physics World, and the CERN Courier, together with 3 dedicated articles in the popular science website "The Conversation", which have already been read by more than half a million readers around the world in only five months since their release.