Description
The Schwinger field sets the critical field for quantum electrodynamics, (QED). The Schwinger field is the electric field required to do work on an electron (or positron) equal to its rest mass energy over the reduced Compton wavelength. This field is therefore strong enough to move the virtual electron-positron pairs comprising the quantum vacuum onto the mass shell such that they become real (colloquially known as ‘boiling’ the vacuum). There is an equivalent QED-critical magnetic field (given by the Schwinger field over the speed of light) where novel QED effects not before seen in the laboratory become crucially important to the behaviour of the system. Pulsars, active black hole and magnetar magnetospheres are examples of environments where magnetic fields approaching (and even exceeding) the QED-critical magnetic field can be found. Here it is believed that these fields lead to the cascade of electron-positron pair production which populates the magnetosphere with the electron-positron plasma required by the most widely accepted models of these systems. The high multiplicity of the QED processes in the strong background fields renders calculation of the hard photon and pair production rates impractical from first-principles. Furthermore, the behaviour of strong-field QED processes in a plasma, critical to the astrophysical environments just described, is not well understood.
We will discuss the various methodologies for including strong-field QED in plasma modelling codes, in particular in the particle-in-cell (PIC) code EPOCH. These methodologies result in an equation of motion for electron and positrons including strong-field QED. We will use EPOCH simulations to show that this single-particle dynamics can be tested in the laboratory and discuss several previous experiments which did this using high-intensity lasers as well as the outstanding questions still to resolve. We will also show (again using EPOCH) that we shall soon be able to realise experiments where these QED effects are important in a plasma environment, enabling us to study the physics underpinning the extreme astrophysical scenarios mentioned previously in the laboratory for the first time.
