Drastic changes in the plasma potential inside a hollow anode during an applied accelerating pulse

Abstract

We present results which show drastic changes in the parameters of a hollow anode (HA) which serves as a cathode in an electron diode. The HA has a ferroelectric plasma source (FPS) incorporated in it. The applied accelerating pulse causes increase of the potential of the plasma inside the HA up to 7 kV and switches the direction of the current of plasma electrons from the HA and its output grid towards the accelerating gap. It is shown that, in spite of the large positive plasma potential, electron emission occurs due to the dynamics of ion motion in the sheath near the HA grid.

High-current diode with ferroelectric plasma source-assisted hollow anode

“…17 Also, one can see I d Ϸ 3 kA with acc Ϸ 180 kV ͑"low-impedance" mode of the diode operation͒ and I d Ϸ 1.2 kA with acc Ϸ 240 kV ͑"highimpedance" mode of the diode operation͒ for the same d Ϸ 18 s. One can suppose that this difference occurs because of the change in plasma parameters at the HA output grid as a result of the HA nonreproducible operation. However, earlier research 10,11,14,15 of the HA does not show such nonreproducibility. Taking into account that the application of the accelerating pulse leads to the switching ͑except ion current͒ of the HA discharge current with amplitude I HA Յ 1 kA from the HA walls to the diode anode, 15 one has to consider the appearance of additional electron sources not related to FPS-assisted HA discharge.…”

“…However, earlier research 10,11,14,15 of the HA does not show such nonreproducibility. Taking into account that the application of the accelerating pulse leads to the switching ͑except ion current͒ of the HA discharge current with amplitude I HA Յ 1 kA from the HA walls to the diode anode, 15 one has to consider the appearance of additional electron sources not related to FPS-assisted HA discharge.…”

“…Also, it was found that, during the accelerating pulse, the HA bulk plasma potential drastically increases and the plasma-grid potential difference reaches up to a few kilovolts. 15 The latter should form an almost opaque potential barrier for the HA bulk plasma electrons moving toward the anode, which contradicts the experimentally obtained high-current electron beam with a current density in the range 5 -15 A / cm 2 and total electron current amplitude up to 1.5 kA. To explain this apparent contradiction, a model of the ion's screening of the grid potential was suggested.…”

“…The nonuniformity of the electric field in the vicinity of the grid wires leads to randomization of the ions velocities in both value and direction. These trapped ions, whose "effective temperature" can reach several hundreds of electron volt, 14,15 screen the grid negative potential, thus allowing electrons to be extracted from the boundary of the HA plasma located in the vicinity of the HA grid. Also, the LIF signal that was obtained from this plasma volume and showed increased Ar II ion temperature has a significantly smaller amplitude than the LIF signal from the HA bulk plasma.…”

Passive and Active Plasma Emission Sources for High-current Electron Beam Generation

“…The disk was placed at different distances (20-60mm) from the anode. The electron diode was powered by a high-voltage (HV) generator producing a HV pulse up to 300kV in amplitude, 350ns in duration and variable rise time in the range of dE/dt ≈ (0.5-2.5)×10 12…”