Emission Features and Structure of an Electron Beam versus Gas Pressure and Magnetic Field in a Cold-Cathode Coaxial Diode

The structure of the emission surface of a cold tubular cathode and electron beam was investigated as a function of the magnetic field in the coaxial diode of the high-current accelerator. The runaway mode of magnetized electrons in atmospheric air enabled registering the instantaneous structure of activated field-emission centers at the cathode edge. The region of air pressure (about 3 Torr) was determined experimentally and via analysis, where the explosive emission mechanism of the appearance of fast electrons with energies above 100 keV is replaced by the runaway electrons in a gas.

Increasing the energy of the initiating spark discharge in order to reduce and stabilize the delay time in a compact vacuum breaker

The similarity of the switching mechanisms of compact vacuum spark breakers and spark breakers with laser ignition is established at a comparable level of energy flux density in the ignition node–ionization of the residual gas by a stream of short-wave radiation and fast electrons from the cathode spot plasma or laser plasma. This mechanism allows you to effectively reduce the delay in triggering the spark gap by increasing the ignition energy. An experimental study of the advantages of using an ignition circuit with increased energy for controlling small-sized vacuum spark breakers is carried out. There is a steady decrease in the delay time of the spark gap and an increase in the level of delay stability. From the point of view of minimization and stability of the delay time of the spark gap, the energy investment in the formation of the initiating plasma occurs most effectively at the spark stage of the auxiliary discharge along the surface of the dielectric in the ignition node.

Electron Energization Dynamics in Interaction of Self-Generated Magnetic Vortices in Upstream of Collisionless Electron/Ion Shocks

Relativistic collisionless shocks are considered responsible for particle energization mechanisms leading to particle acceleration. While electron energization in shock front region of electron/ion collisionless shocks are the most commonly studied, the mechanism of electron energization in interaction with self-generated magnetic vortices (MVs) in upstream region is still unclear. We investigate electron energization mechanism in upstream region of electron/ion relativistic collisionless shocks, using two dimensional particle-in-cell (PIC) simulations. We discuss mechanism of electron energization which takes place in upstream region of the shock, where the counter stream particles interact with incoming flow. The energy gain of electrons happens during their interaction with evolving fields of self-generated magnetic vortices in this region. Three Fermi-like electron energization scenarios are discussed. Stochastic acceleration of electrons in interaction with fields of MV leads to anisotropic heating of fast electrons due to diffusion in the momentum space of electrons and, finally, synergetic effect of evolving fields of MVs leads to the formation of a power-law tail of supra-thermal particles.

Angular distributions in the double ionization of argon by fast electron impact

A model describing the two electrons ejected by distorted waves is applied to the study of the double ionization of argon by fast electrons (~ 5500 eV). The correlation is also partially taken into account both in the final state and in the initial state. The results obtained by our model as well as by other models also based on the first Born approximation are compared with the available experimental data.

Subnanosecond breakdown of air-insulated coaxial line initiated by runaway electrons in the presence of a strong axial magnetic field

Flow of runaway electrons (RAEs) propagating in a radial, air-filled gap of coaxial line (CL) changes the dynamics of breakdown in the field of traveling voltage pulse. However, despite the effect of RAEs, breakdown does not occur if subnanosecond pulse is less in duration and amplitude than some values. In this work, we study the influence of an external axial magnetic field (B z) on the breakdown development. We demonstrate the transformation of the voltage pulse reflection from the ionized (breakdown) zone with changing B z. Due to gyration of fast electrons in an applied magnetic field, the gas region ionized by RAEs does not reach the anode. The ionized bridge between the cathode and anode is gradually replaced by a near-cathode plasma layer representing a discrete, reflecting/absorbing inhomogeneity in the CL.

Minimization of the delay time and its spread in a compact vacuum breaker

The similarity of the switching mechanisms of compact vacuum spark breakers and spark breakers with laser ignition is established at a comparable level of energy flux density in the ignition node–ionization of the residual gas by a stream of short-wave radiation and fast electrons from the cathode spot plasma or laser plasma. This mechanism allows you to effectively reduce the delay in triggering the spark gap by increasing the ignition energy. An experimental study of the advantages of using an ignition circuit with increased energy for controlling small-sized vacuum spark breakers is carried out. There is a steady decrease in the delay time of the spark gap and an increase in the level of delay stability. From the point of view of minimization and stability of the delay time of the spark gap, the energy investment in the formation of the initiating plasma occurs most effectively at the spark stage of the auxiliary discharge along the surface of the dielectric in the ignition node.