Electron beam-plasma discharge in GDT mirror trap: Particle-in-cell simulations

The paper presents the results of numerical simulations of the collective relaxation of an electron beam in a magnetized plasma at the parameters typical to experiments on the ignition of a beam-plasma discharge in the Gas Dynamic Trap. The goal of these simulations is to confirm the ideas about the mechanism of the discharge development, which are used to interpret the results of recent laboratory experiments [Soldatkina et al 2021 {\it Nucl. Fusion}]. In particular, a characteristic feature of these experiments is the localization of the beam relaxation region in the vicinity of the entrance mirror. A strong mirror magnetic field compresses the beam so that its transverse size becomes less than the wavelength it excites. In addition, near the mirror, the electron cyclotron frequency is much higher than the plasma one, which can significantly affect the possibility of propagation of the most unstable waves outside the beam. Particle-in-cell simulations make it possible not only to find how efficiently intense plasma oscillations penetrate the rarefied periphery, but also to prove that the turbulent zone in a realistic nonuniform plasma has regions dominated by transverse electric fields. This creates the necessary conditions for efficient acceleration of the trapped particles to energies much higher than the initial beam energy.