Initial kinetics of electrons, ions and electric field in planar vacuum diode with plasma cathode

Abstract

The paper presents the results of a 1D1V theoretical study of the initial stage of plasma expansion into a planar vacuum gap 1 cm long with an applied voltage of 500–5000 V. Based on the collisionless kinetic and Maxwell equations, the motion of a two-component electron–ion plasma in a self-consistent electric field is described. The fundamental mechanism of ‘superthermal’ velocities of the emission edge of the plasma and anode-directed velocities of positive ions is demonstrated in detail. The general regularities of this process are established for variations in the number density of the initial plasma and the applied voltage.

The kinetic theory of cathode plasma expansion in a spatially non-uniform geometric configuration of a vacuum diode

“…This outcome constitutes the pivotal point of our calculations, presenting a fundamentally new mechanism for the generation of highenergy ions directed toward the anode in vacuum discharges. The computational results indicate that this effect is observed not only in planar vacuum diodes where the gap geometry does not make sense and where the electric field is uniform [14]. In an axisymmetric configuration, where the electric field without particles near the cathode is significantly stronger than near the anode due to geometric factors, we obtain similar plasma dynamics.…”

“…The energy distribution of ions expands to energies exceeding ε i ∼ 250 eV, even though the depth of the potential well never surpasses ∆φ = −50 V in magnitude. As it was previously mentioned in [14], this may appear implausible, but this situation indeed occurs due to the collective motion of ions with a range of velocities in tandem with the advancement of a region featuring a significant potential gradient. The nearly synchronous movement of the ion ensemble and the electric field strength region responsible for ion acceleration can give rise to ions with 'anomalously high energies.'…”

“…Given the diversity of hypotheses concerning this phenomenon, preference is given to models that rely on the minimum number of initial assumptions. One such theory of cathode plasma expansion is the previously proposed 'minimal' kinetic model, based on the Vlasov-Poisson system of equations for a planar (one-dimensional) vacuum gap, where the cathode plasma emission under the application of the anode potential is simulated by specifying simple boundary conditions [13,14]. This model has provided answers to the fundamental question of why anomalous ion acceleration occurs.…”

“…Despite the comprehensive and internally consistent kinetic theory of the 'anomalous ions acceleration' that has been given in [14], some theoretical inquiries have persisted beyond the scope of the proposed theory. The issue lies in the fact that explosive electron emission and the corresponding vacuum breakdown always occur in strongly non-uniform spatial conditions.…”

“…This paper presents further development of the kinetic theory of cathode plasma expansion previously given in [13,14]. The main improvement here lies in the use of a 1.5dimensional kinetic description, where the Vlasov equations, formulated in cylindrical coordinates, include one spatial coordinate r and two components of momentum p r and p φ , corresponding to the radial and azimuthal directions, respectively.…”