Mechanism of resonant electron acceleration at half gyrofrequency in non-neutral plasmas

The experiments studying the electron heating in a magnetic trap by an incident wave at half gyrofrequency showed that there is an essential increase in electron energy and the intensity of the produced x-rays compared to the acceleration at gyrofrequency. The estimates of the influence of various non-linearities do not allow for a satisfactory explanation of this phenomenon. Proposed in this paper is the interpretation of the experimental results in the framework of a non-neutral plasma model. We show the existence of a strong resonance of an incident wave at half gyrofrequency in non-neutral plasma created by an excess of electron density. The analysis of confinement of a cylindrical electron layer is carried out both in radial and in axial directions; we have taken into account several factors such as mirror geometry, pulse mode and relativistic influence. We made separate estimates for each mechanism independently. They show that the proposed mechanisms are quite adequate for the explanation of the increase in x-ray energy and intensity.