Experimental Observation of a Current-Driven Instability in a Neutral Electron-Positron Beam

Abstract

We report on the first experimental observation of a current-driven instability developing in a quasineutral matter-antimatter beam. Strong magnetic fields (amp;gt;= 1 T) are measured, via means of a proton radiography technique, after the propagation of a neutral electron-positron beam through a background electron-ion plasma. The experimentally determined equipartition parameter of epsilon(B) approximate to 10(-3) is typical of values inferred from models of astrophysical gamma-ray bursts, in which the relativistic flows are also expected to be pair dominated. The data, supported by particle-in-cell simulations and simple analytical estimates, indicate that these magnetic fields persist in the background plasma for thousands of inverse plasma frequencies. The existence of such long-lived magnetic fields can be related to analog astrophysical systems, such as those prevalent in lepton-dominated jets.<p>Funding Agencies|EPSRC [EP/N022696/1, EP/N027175/1, EP/L013975/1, EP/N002644/1, EP/P010059/1]; DOE [DE-NA0002372]; ARO [W911NF-16-1-0044]</p

General features of experiments on the dynamics of laser-driven electron–positron beams

“…An alternative method for the generation of neutral electron-positron plasmas has been identified in exploiting the quantum cascade initiated by a laser-driven electron beam propagating through a solid target. Even though this method suffers from the difficulty of generating cold populations and confining them, promising results have been obtained in different configurations [11,12,13,14,15,16,17], with, to-date, the first experimental demonstration of a neutral electron-positron beam able to show collective behaviour [14,17]. The details of the laser-driven generation of neutral electron-positron beams (EPBs) can be found elsewhere [13,14,15,16]; in this paper, we will instead focus our attention on some of the main experimental issues involved in detecting the dynamics of these objects, when they propagate through a background electron-ion plasma.…”

“…Typical optimum parameters of the EPB at the source thus far include a source size of D 0 200 − 300 µm, a duration in the range of τ 10s to 100s of fs, a number of leptons of the order of N 10 9 -10 10 , and an average divergence of θ 30 − 50 mrad. The broad spectrum of the EPB, virtually insensitive to the initial shape of the electron spectrum but mainly determined by the cascade itself, is well approximated by a Juttner-Synge distribution, with a typical average Lorentz factor of γ 10 − 20 [14,15,17]. At the source, one can easily achieve a number density of the EPB of the order of 10 16 cm −3 .…”

Thermalization of electron–positron plasma with quantum degeneracy

“…Attempts to create such a plasma in laboratory [2] are linked with the development of ultra-intense lasers [3,4,5,6,7] within large projects, such as ELI 1 and XCELS 2 . A number of interesting phenomena such as relativistic transparency [8], ultrafast thermalization in magnetized plasma [9] and current-driven instability [10] are predicted and observed in such a plasma. The presence of the pairs greatly enhances plasma opacity, in many cases making it optically thick to photons.…”

Collimated GeV attosecond electron–positron bunches from a plasma channel driven by 10 PW lasers

“…Compared with the conventional positron sources, laser-driven positron sources have many potential advantages, such as having a high energy, yield and density, ultrashort beam size, etc. Currently, by use of high power intense lasers, multi-MeV positrons can be easily produced in laboratories [4][5][6][7]. However, giant highly-energetic (i.e., GeV and TeV energies) positron jets with extremely high-density are still out of reach, which occur only in energetic astrophysical environments [2,8,9], such as γ-ray bursts, pulsars and black holes.…”