[en] Here, the interaction of an electron oscillating in an ion channel and irradiated by a plane electromagnetic wave is considered. It is shown that the interaction qualitatively changes with the increase of electron energy, as the oscillations across the channel become relativistic. The “square-wave-like” profile of the transverse velocity in the relativistic case enables breaking of the adiabaticity that precludes electron energy retention in the non-relativistic case. For an electron with a relativistic factor $\mathrm{\gamma <!--\; ??\; -->}$₀, the adiabaticity breaks if ω_L/ω_p0$\ll <!--\; ???\; -->$$\sqrt{\mathrm{\gamma <!--\; ??\; -->}0}$. Under these conditions, the kinetic energy acquired by the electron is retained once the interaction with the laser field ceases. This mechanism notably enables electron heating in regimes that do not require a resonant interaction between the initially oscillating electron and the laser electric field.