ELEMENTARY PARTICLE PHYSICS

Relativistic electron-positron pair plasmas are tightly related to extreme astrophysical objects such as pulsar magnetospheres or gamma-ray bursts. Due to the inherent difficulties of studying these remote objects it is extremely desirable to study dense pair plasmas in the laboratory, both for fundamental purposes and astrophysical applications. The recent spectacular rise in laser intensities accompanied by the ongoing construction of new laser facilities such as ELI [1] or the Vulcan 20 PW will place intensities above 10²³W/cm² within reach. The magnitude of these lasers electromagnetic fields overlaps with the estimated fields of milliseconds pulsars.

Producing pair plasmas in ultra strong fields may demonstrate that we can mimic the conditions appropriate to these astrophysical environments in terrestrial laboratories. The pair creation in such energy density environments is caused by the decay of gamma rays in intense fields. This process usually leads to quantum electrodynamics (QED) cascades, as the pairs created re-emit hard photons that decay anew in pairs, eventually resulting in electron-positron-photon plasmas.

A configuration was recently proposed, comprising two counter propagating laser pulses with some seed electrons in the interaction region to initiate the cascade. The development of a cascade is shown in Fig.1 for two colliding lasers. The conditions to achieve substantial laser absorption were investigated and the ratio between the absorption time and the pulse duration is the relevant parameter for the laser depletion [2,3,4]. A significant laser energy conversion to hard photons can be achieved at lower intensities when using four colliding lasers instead of two. Fig. 2 shows the electric field structure of a standing wave formed by 4 lasers as well as the shape of the density distribution of the created plasma.