Acceleration of relativistic particles and gamma-ray emission in standing Alfvén waves

In a strong magnetic field where the cyclotron frequency exceeds the frequency of electromagnetic waves, the scattering rate of the relativistic intensity wave will be high, and it is not evident that transmission is possible. Such considerations can constrain the theoretical modeling of the magnetosphere of planets and neutron stars. Therefore, we have been analyzing wave-particle interactions under such extreme plasma conditions using PIC simulations. In this presentation, we will primarily focus on the collision process of Alfvén waves. We theoretically show that all electrons with non-relativistic speeds are accelerated to relativistic speeds in standing waves created by counter-propagating circularly polarized Alfvén waves. The condition to realize such acceleration is when the amplitude of the electromagnetic wave is larger than the background magnetic field. Furthermore, most of the energy of the original electromagnetic wave can transfer to the radiation energy of gamma rays, which may lead to pair production. We will also discuss the possibility of future proof-of-principle laser experiments of this mechanism.