Neutron stars produce ultra-relativistic particles efficiently accelerated by their ultra strong elec-
tromagnetic fields, copiously radiation very high energy photons in the GeV/TeV range. However,
no numerical code is able to handle such very high Lorentz factors and magnetic field strengths
around the quantum critical limit of 4,4 · $10^{9}$ T. In this work, we study particle acceleration and
radiation reaction damping in a magnetic dipole with magnetic field strengths as high as $10^{10}$ T,
typical for magnetars. We investigated particle acceleration and the impact of radiation reaction for
electrons, protons and iron nuclei. The maximum Lorentz factor depends on the particle species
but only weakly on the magnetic field strength. Electrons reach energies up to 𝛾𝑒 ≈ $10^{8}$ − $10^{9}$
whereas protons energies up to 𝛾 𝑝 ≈ $10^{5}$ − $10^{6}$ and iron up to 𝛾 ≈ $10^{4}$ − $10^{5}$ . While protons and
irons are not affected by radiation reaction, electrons are drastically decelerated, reducing their
maximum Lorentz factor by 2 orders of magnitude [10].