We study the operation regime of a hybrid planar free-electron maser (FEM) amplifier near the magnetoresonant value of the uniform longitudinal (guide) magnetic field. Using analytical expressions for individual test electron trajectories and normal frequencies of their three-dimensional oscillations in the magnetostatic field of the hybrid planar FEM, an analytical condition of chaotization of motion is established and shown to be given by the Chirikov resonance-overlap criterion applied to the normal undulator and cyclotron frequencies with respect to the coupling induced by the undulator magnetic field. It is also shown analytically that, in spite of the well-known drop for the exact magnetoresonance, the gain attains its maximal value in the zone of regular dynamics slightly above the magnetoresonant value of the guide magnetic field. Under the condition of undulator resonance, it is practically independent of the amplitude of the undulator magnetic field and the wavelength of amplified signal. To account for spacecharge effects, we propose a theoretical model of a weakly relativistic FEM, which accommodates not only potential but also rotational parts of the nonradiated electromagnetic field of a moving charged particle. It turns out that the rotational part of nonradiated field diminishes the defocusing influence of the potential part on the beam bunching. Numeric simulation of the nonlinear stage of amplification is fulfilled, taking into consideration adiabatic entrance of the electron beam to the interaction region and initial electron velocity spread. We find that nonradiated field and initial electron velocity spread do not influence essentially the efficiency of hybrid planar FEM amplification if parameters of the beammicrowave interaction correspond to the operational regime in the zone of regular dynamics near the magnetoresonance.

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We propose a novel gridless continuous-wave radiofrequency (rf) thermionic gun capable of generating nC ns electron bunches with a rms normalized slice emittance close to the thermal level of 0.3 mm mrad. In order to gate the electron emission, an externally heated thermionic cathode is installed into a stripline-loop conductor. Two high-voltage pulses propagating towards each other in the stripline-loop overlap in the cathode region and create a quasielectrostatic field gating the electron emission. The repetition rate of pulses is variable and can reach up to one MHz with modern solid-state pulsers. The stripline attached to a rf gun cavity wall has with the wall a common aperture that allows the electrons to be injected into the rf cavity for further acceleration. Thanks to this innovative gridless design, simulations suggest that the bunch emittance is approximately at the thermal level after the bunch injection into the cavity provided that the geometry of the cathode and aperture are properly designed. Specifically, a concave cathode is adopted to imprint an Ƨ-shaped distribution onto the beam transverse phase-space to compensate for an S-shaped beam distribution created by the spherical aberration of the aperture-cavity region. In order to compensate for the energy spread caused by rf fields of the rf gun cavity, a 3rd harmonic cavity is used. A detailed study of the electrodynamics of the stripline and rf gun cavity as well as the beam optics and bunch dynamics are presented.

The experimental research results for operation of the cold cathode magnetron injection gun in the linear traveling wave accelerator are described. The mechanism of the gun operation is connected with the current secondary electronic increase and the establishment of a self-supported secondary emission. The comparison of the beam passage conditions for a thermionic gun points on the fact, that the characteristics of the magnetron gun are acceptable for the purposes of injection in the rf accelerator.

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