Travelling waves and light-front approach in relativistic electrodynamics.

We briefly report on a recent proposal (Fiore in J Phys A Math Theor 51:085203, 2018) for simplifying the equations of motion of charged particles in an electromagnetic (EM) field $F^{\mu\nu}$ that is the sum of a plane travelling wave $F_t^{\mu\nu}(ct\!-\!z)$ and a static part $F_s^{\mu\nu}(x,y,z)$; it adopts the light-like coordinate $\xi=ct\!-\!z$ instead of time $t$ as an independent variable. We illustrate it in a few cases of extreme acceleration, first of an isolated particle, then of electrons in a plasma in plane hydrodynamic conditions: the Lorentz-Maxwell \& continuity PDEs can be simplified or sometimes even completely reduced to a family of decoupled systems of ordinary ones; this occurs e.g. with the impact of the travelling wave on a vacuum-plasma interface (what may produce plasma waves or the slingshot effect).