Electrons have an electric field. By the influence of an external electric field, the electron is attracted or repelled. Electrons also possess a magnetic dipole moment. This moment is coupled to the rotation of the electron (the magnetic dipole moments of an electron and a positron are opposed with the same direction of rotation). When electrons moving through a magnetic field the magnetic dipoles and therefore also the axes of rotation of the electrons are aligned. Now arises a gyroscopic effect and the electron goes under emission of a photon out of alignment again. Detailed see [here](http://physics.stackexchange.com/questions/146990/how-does-the-lorentz-force-work/147036#147036).

The acceleration of electrons can be done not only by electric fields. Under the influence of electromagnetic fields, electrons are also accelerated. With a positive acceleration the energy of photons is transmitted parcial to the electron. In case of negative acceleration more energy is emitted as received. As described above, a magnetic field through which electron moves - not parallel to the magnetic field lines! - influential on the electron too. The electron emit photons and its kinetic energy get lost.