de Acceleration of Charged Particles by an Electrostatic Wave Propagating Obliquely to a Magnetic Field

A charged particle trapped in an electrostatic wave is accelerated in the plane perpendicular to the wave vector $\overrightarrow{\mathrm{k}}$. It is found that there is an optimum angle $\theta ={\theta }_m$ at which the particle gains a maximum energy which is about four times larger than that at $\theta =\frac{\pi }{2}$, $\theta$ being the angle between $\overrightarrow{\mathrm{k}}$ and the magnetic field.