A novel perturbation theory describes electromagnetic field components in a bubble regime of plasma wakefield

The plasma wakefield behind a laser pulse or a relativistic particle bunch can accelerate charged particles in short distance to high energies. When the forces created by the laser pulse or particle bunch are sufficiently large, electrons in the wakefield are expelled from a small spherical region, a “bubble”, which moves quickly just behind the laser or particle bunch and about which several physicists have offered theoretical descriptions. In Physics of Plasmas, theoretical physicists from Russia and Germany present their perturbation theory for the bubble that focuses on electromagnetic field components, both inside and outside a bubble in non-uniform plasma, and the electron sheath at the bubble’s boundary.

To determine spatial distributions of electromagnetic fields in the bubble regime of a wakefield, the authors described electromagnetic fields using the cylindrical coordinates. They then considered a bubble model like that of earlier models with bubble regime properties observed in the particle-in-cell (PIC) simulations, that had an underlying assumption that plasma electrons are absent inside the bubble and that a thin electron sheath is present on the bubble boundary.

The authors compared the shape of their bubble and the analytical distributions of the electromagnetic field components to PIC simulations and found consistency with their findings. Lead author Anton Golovanov says these results validate their approximate theory for the field descriptions both inside and outside the bubble.

The authors note their perturbation theory assumes a small ratio between the thickness of the electron sheath at the bubble’s boundary and the size of the bubble. They add that their theory requires simulation work to identify the “profile and the width of the electron sheath and the size of the bubble.”

Source: “Analytic model for electromagnetic fields in the bubble regime of plasma wakefield in non-uniform plasmas,” by A. A. Golovanov, I. Yu. Kostyukov, J. Thomas, and A. Pukhov, Physics of Plasmas (2017). The article can be accessed at https://doi.org/10.1063/1.4996856 .