Synchrotron radiation from relativistic electrons in intense magnetic fields

The synchrotron radiation spectrum is calculated for relativistic electrons in the case where no restriction is placed on the strength of the magnetic field. It is shown that in intense fields H? H₀ = m²c³/e₀? =4.41 · 10¹³ G a major contribution to the total radiation intensity comes from transitions to the ground state and also to weakly excited levels. In particular, the contribution from transitions to the ground state (final electron energy E' =mc²) for electrons of initial energy E = 10 MeV in a field H = 2H₀ is 14% of the contribution from transitions to highly excited states (E'?mc²).